Proguanil

Origins of Biguanide Antimalarial Research

The history of biguanides in medicine predates their use as antimalarials, with early research in the 1920s exploring guanidine compounds found in Galega officinalis for their glucose-lowering properties. wikipedia.orgwikidoc.orgchemeurope.comnih.govaston.ac.uk While some guanidine derivatives were used for diabetes treatment, their toxicity led to their decline in favor of insulin. wikipedia.orgwikidoc.orgnih.govaston.ac.uk

The focus shifted to biguanides for antimalarial purposes during World War II. wikipedia.orgnih.govmmv.orgwikipedia.org A joint US-UK research program was established to find new, non-toxic, and easily produced antimalial drugs. wikipedia.org A British team at Imperial Chemical Industries (ICI), led by Frank Rose, played a key role in this effort. wikipedia.orgwikipedia.org Their research initially focused on pyrimidines, but they also investigated biguanides (then referred to as diguanides), a class of compounds with which Rose was familiar from his earlier sulfonamide research. wikipedia.org This line of investigation ultimately led to the discovery of proguanil. wikipedia.orgwikipedia.org

Initial Synthesis and Early In Vitro/Animal Model Investigations

This compound was synthesized in the 1940s as part of the intensive pharmaceutical research during World War II aimed at finding new antimalarial agents. justdial.com These compounds were initially prepared as acyclic analogs of certain anilino pyrimidines being studied at ICI. nih.gov Scientists were particularly interested in compounds that could inhibit the growth of Plasmodium species. justdial.com

Early investigations involved testing this compound in animal models and in vitro studies. nih.gov A published study in 1945 reported that this compound demonstrated greater activity than quinine against avian malaria and possessed a better therapeutic index in animal models. nih.gov These promising results in experimental settings provided the impetus for its evaluation in humans. nih.gov

This compound functions as a prodrug, being metabolized in the body to its active form, cycloguanil. justdial.comwikipedia.orgdovepress.com Cycloguanil is known to inhibit the enzyme dihydrofolate reductase (DHFR) in the malaria parasite, which is crucial for the synthesis of nucleic acids. justdial.comwikipedia.orgdovepress.comfda.gov This inhibition disrupts the parasite's folate metabolism and DNA synthesis. nih.govfda.govpatsnap.com Studies have shown that cycloguanil inhibits Plasmodium DHFR at concentrations significantly lower than those required to inhibit mammalian DHFR. fda.gov

Early research findings indicated that this compound was a causal prophylactic agent for Plasmodium falciparum, acting on the primary tissue stages of the parasite, although it was slow-acting against the blood-stage parasite. nih.govwikipedia.org It was also noted to have limited usefulness in treating Plasmodium vivax malaria. nih.gov

Evolution of this compound's Role in Antimalarial Drug Development

Following promising early investigations, this compound was introduced by ICI in 1945. wikipedia.org It was subsequently approved for human use as an antimalarial agent. nih.gov this compound's success in treating humans spurred further research into its chemical class, contributing to the development of other antimalarials like pyrimethamine, another inhibitor of dihydrofolate reductase. mmv.orgnih.gov

Despite its initial promise, resistance to this compound when used as monotherapy emerged relatively quickly in Plasmodium parasites, reportedly within one year in some cases. nih.govmmv.org Resistance to P. falciparum was noted in Tanzania by 1953. mmv.org This led to a decline in its use as a single agent, and in the United States, marketing of this compound as a single drug ceased in the 1970s. nih.gov

However, this compound continued to be utilized in combination with other antimalarial agents in various countries, such as with chloroquine, for malaria prophylaxis. nih.gov The emergence of resistance to various antimalarials highlighted the need for combination therapies to enhance efficacy and potentially delay the development of resistance. mmv.orgjustdial.comfda.gov

In later years, this compound found a renewed role in combination with atovaquone, forming a fixed-dose combination known by the trade name Malarone. nih.govoup.comrunwayhealth.comresearchgate.net This combination was approved by the FDA for the prophylaxis and treatment of malaria caused by P. falciparum in 2000. nih.govoup.com The combination of atovaquone and this compound demonstrated synergistic activity against P. falciparum. nih.govoup.comrunwayhealth.comresearchgate.netresearchgate.net While this compound's role in this combination was initially thought to primarily involve DHFR inhibition, studies suggest it may also enhance atovaquone's activity by reducing resistance and increasing its ability to trigger mitochondrial apoptosis in the parasite. wikipedia.orgrunwayhealth.comresearchgate.net Pre-clinical and clinical studies conducted by institutions like the Walter Reed Army Institute of Research and the Armed Forces Research Institute of Medical Sciences were instrumental in the development and evaluation of the atovaquone-proguanil combination, demonstrating high efficacy against multidrug-resistant P. falciparum. oup.comsociete-mtsi.fr

The evolution of this compound's role reflects the ongoing challenges posed by drug-resistant malaria and the strategies employed in antimalarial drug development, including the use of combination therapies to improve outcomes and combat resistance. mmv.orgjustdial.comfda.govnih.gov

Biotransformation to the Active Metabolite, Cycloguanil

Proguanil is converted in the liver to its principal active metabolite, cycloguanil drugbank.comoup.com. Cycloguanil is a dihydrotriazine compound that inhibits parasitic dihydrofolate reductase (DHFR), an enzyme essential for the biosynthesis of purines and pyrimidines required for DNA synthesis and cell multiplication in Plasmodium parasites drugbank.comfda.gov. This inhibition disrupts the parasite's folate cycle, preventing the recycling of dihydrofolate to tetrahydrofolate wikipedia.org. While both mammals and parasites possess DHFR, cycloguanil exhibits selective inhibitory activity towards the parasitic enzyme wikipedia.org. Early research indicated that this compound itself was not active against malaria and that its antimalarial activity was solely due to its metabolites, with cycloguanil identified as the principal active metabolite researchgate.net. However, some findings have since questioned the complete inactivity of the parent compound researchgate.net.

Enzymatic Basis of this compound Metabolism

The metabolic conversion of this compound to cycloguanil and other metabolites is primarily mediated by hepatic cytochrome P450 (CYP) enzymes.

Identification and Characterization of Other Metabolites (e.g., 4-Chlorophenylbiguanide)

In addition to cycloguanil, this compound is also metabolized to other compounds. A notable minor metabolite is 4-chlorophenylbiguanide drugbank.comoup.comresearchgate.netnih.gov. The formation of 4-chlorophenylbiguanide from this compound is also diminished in individuals who are poor metabolizers of S-mephenytoin, indicating that this metabolic pathway is also catalyzed by CYP2C19 nih.gov.

Research has also explored the potential metabolism of this compound into chlorazanil, a diuretic agent. While no direct metabolic relation was initially reported, this compound is metabolized in humans to N-(4-chlorophenyl)-biguanide (4-chlorophenylbiguanide), which is a chemical precursor in the synthesis of chlorazanil wada-ama.org. In vitro simulations have shown that in the presence of certain reactants like formic acid or formaldehyde, 4-chlorophenylbiguanide can convert to chlorazanil in human urine, suggesting that detected chlorazanil in this compound users might be an artifact formation wada-ama.org.

Genetic Polymorphism of Metabolizing Enzymes and its Impact on Prodrug Activation Efficiency

Genetic polymorphisms in the enzymes and transporters involved in this compound metabolism significantly impact its prodrug activation efficiency. The variable metabolism of this compound by cytochrome P450 isoenzymes, particularly CYP2C19, can have significant clinical implications drugbank.com.

CYP2C19 exhibits genetic polymorphism, leading to different metabolizer phenotypes, including extensive metabolizers (EM) and poor metabolizers (PM) ki.se. The impaired metabolism in PMs is often due to defects in the CYP2C19 gene, such as the m1 and m2 genetic defects oup.com. The frequency of these poor metabolizer phenotypes varies among different populations, being lower in Caucasians, Ethiopians, and Zimbabweans compared to Oriental populations oup.com.

Studies have demonstrated a relationship between the CYP2C19 genotype and the metabolic ratio of this compound to cycloguanil nih.govdrugbank.com. Individuals who are poor metabolizers of CYP2C19 show diminished formation of both cycloguanil and 4-chlorophenylbiguanide nih.gov. This variability in metabolic capacity means that some individuals are less efficient at converting this compound into its active metabolite, cycloguanil africaresearchconnects.com.

Research in various populations has highlighted this variability. For instance, a study involving British troops and Kenyan schoolchildren observed large inter-subject variability in this compound and cycloguanil concentrations, attributed to differences in the ability to metabolize this compound to cycloguanil africaresearchconnects.com. In some populations, a comparatively high proportion of individuals may metabolize this compound poorly nih.gov.

Furthermore, genetic polymorphisms in SLC22A1, the gene encoding OCT1, can also affect the hepatic uptake of this compound and consequently its metabolism nih.govresearchgate.netescholarship.org. Common variants of OCT1, such as OCT13 and OCT14, can cause a substantial decrease in this compound uptake researchgate.netnih.gov. Studies have shown that certain SLC22A1 genotypes are associated with altered systemic exposure to this compound and cycloguanil, with decreased OCT1 activity leading to reduced hepatic uptake of this compound and subsequently decreased formation of cycloguanil nih.govescholarship.org.

The combined effect of polymorphisms in CYP2C19, CYP3A5, and OCT1, along with other factors, can account for a significant portion of the variation observed in the cycloguanil-to-proguanil ratio researchgate.netnih.gov. This genetic variability underscores the importance of considering individual metabolic profiles in relation to this compound's effectiveness.

Below is a summary of research findings on the impact of CYP2C19 genotype on this compound metabolism:

Note: The table above presents data from a specific study and illustrates the relationship between CYP2C19 genotype and the this compound/cycloguanil metabolic ratio. The metabolic ratio is calculated from urine samples collected after this compound administration. drugbank.com

While a CYP2C19 gene-dose effect on this compound oxidation to cycloguanil has been observed, there can be overlap in metabolic ratios between different genotypes, potentially due to the influence of other enzymes involved in cycloguanil formation nih.govdrugbank.com.

Dihydrofolate Reductase (DHFR) Inhibition by Cycloguanil

Cycloguanil, the major active metabolite of proguanil, is a potent inhibitor of dihydrofolate reductase (DHFR) in malaria parasites. drugbank.compatsnap.com This enzyme is a crucial component of the folate synthesis pathway, essential for the parasite's survival and replication. drugbank.compatsnap.com

Independent Antimalarial Activities of Proguanil (Beyond DHFR Inhibition)

Emerging research indicates that this compound possesses antimalarial activities that are independent of its metabolism to cycloguanil and subsequent DHFR inhibition. researchgate.netgeneesmiddeleninformatiebank.nlasm.orgncats.iohres.ca This is particularly evident in its synergistic interaction with atovaquone. geneesmiddeleninformatiebank.nlasm.orgnih.gov

Mechanistic Basis of Synergism in Combination Therapies (e.g., Atovaquone-Proguanil)

The combination of atovaquone and this compound (commonly known by the brand name Malarone) exhibits significant synergistic antimalarial activity gsk.comasm.orgresearchgate.netnih.govnih.govresearchgate.netreliasmedia.comrunwayhealth.comnih.govresearchgate.net. This synergy is crucial for the effectiveness of the combination, particularly considering that resistance to this compound monotherapy is widespread in some regions asm.orgnih.govebi.ac.uk. The synergistic effect is suspected to involve mechanisms beyond the well-established inhibition of parasite DHFR by cycloguanil asm.orgnih.gov.

The combination interferes with two distinct pathways involved in the biosynthesis of pyrimidines required for nucleic acid replication gsk.com. Atovaquone inhibits mitochondrial electron transport at the cytochrome bc1 complex, disrupting parasite respiration and inhibiting de novo pyrimidine biosynthesis oup.comgsk.comreliasmedia.comresearchgate.netnih.gov. Cycloguanil, the metabolite of this compound, inhibits DHFR, which is essential for deoxythymidylate synthesis drugbank.compatsnap.comoup.comgsk.comreliasmedia.com.

Efficacy Against Plasmodium Species and Life Stages

This compound and its metabolite cycloguanil exhibit activity against different developmental stages of the Plasmodium parasite, contributing to both causal prophylaxis (acting on hepatic stages) and suppressive prophylaxis (acting on erythrocytic stages). nih.govresearchgate.net

This compound per se demonstrates weak activity against the asexual erythrocytic stages of Plasmodium falciparum in vitro. medchemexpress.comnih.gov Its effectiveness against this stage is primarily attributed to its active metabolite, cycloguanil, which potently inhibits parasite dihydrofolate reductase, thereby blocking essential DNA synthesis and cell multiplication. medchemexpress.comdrugbank.com Published in vitro studies report variable activity for this compound against asexual intraerythrocytic-stage P. falciparum parasites, with IC50 values ranging from 2 to 71 µM in 42–72 hour assays. nih.gov Some data also indicate that this compound and a related compound show potent slow-action in vitro activity against P. falciparum parasites, with activity improving significantly in 72-hour and 96-hour assays compared to 48-hour assays. nih.govresearchgate.net For instance, IC50 values for this compound against the Pf3D7 line were reported as 46.23 µM at 48 hours, decreasing to 0.49 µM at 72 hours and 0.11 µM at 96 hours. researchgate.net

Both this compound and its active metabolite cycloguanil have demonstrated activity against the pre-erythrocytic (hepatic) stages of malaria parasites. nih.govoup.com This activity is crucial for causal prophylaxis, preventing the development of the parasite in the liver before it can invade the bloodstream. researchgate.net Studies, particularly those involving the combination of atovaquone and this compound, have shown efficacy against hepatic stages of P. falciparum. researchgate.netasm.org Research using Plasmodium yoelii parasites in human hepatocytes with impaired cytochrome P450 activity (to minimize this compound metabolism to cycloguanil) has shown that the atovaquone-proguanil combination synergistically inhibits the growth of liver stage parasites. asm.org

This compound and its active metabolite cycloguanil also exhibit activity against malaria parasite gametocytes, the sexual stages responsible for transmission to mosquitoes. medchemexpress.comnih.govoup.com While some antimalarials may not clear mature gametocytes, the combination of atovaquone and this compound has been shown to reduce infectivity of gametocytes to mosquitoes. nih.gov However, one study using an ATP bioluminescence assay reported that atovaquone had no activity against mature gametocytes of P. falciparum in that specific assay, despite the combination being transmission-blocking. plos.org This suggests complex interactions or activity of this compound/cycloguanil on gametocyte viability or development within the mosquito vector.

Concentration-Response Characterization in Parasite Assays (e.g., IC50, EC50 values)

In vitro studies provide crucial data on the potency of antimalarial compounds, typically expressed as the 50% inhibitory concentration (IC50) or 50% effective concentration (EC50). For this compound, these values highlight the significant difference in activity between the parent compound and its metabolite. This compound per se has weak activity in vitro with reported IC50 values ranging from 2.4 to 19 µM. medchemexpress.comnih.gov In contrast, its active metabolite, cycloguanil, is significantly more potent, with IC50 values ranging from 0.5 to 2.5 nM. medchemexpress.comnih.gov

The duration of the in vitro assay can influence the observed IC50 values for this compound, with longer exposure times (72 and 96 hours) showing considerably lower IC50s compared to 48-hour assays. nih.govresearchgate.net This suggests a slow-acting component to this compound's activity, independent of immediate DHFR inhibition by cycloguanil. nih.gov

Evaluation of Synergistic Interactions with Co-Administered Agents In Vitro

This compound is notably used in combination with atovaquone, and numerous in vitro studies have demonstrated a synergistic interaction between these two compounds against Plasmodium falciparum. nih.govasm.orgscielo.brcapes.gov.br This synergy is observed against replicating blood stage parasites and is also conserved against liver stage parasites. asm.org The synergistic effect of this compound with atovaquone is independent of cycloguanil's activity and DHFR inhibition. this compound appears to enhance the activity of atovaquone by sensitizing the parasite to atovaquone's effect on mitochondrial membrane potential. nih.gov This synergistic interaction contributes significantly to the enhanced efficacy of the atovaquone-proguanil combination compared to either drug alone. scielo.br However, studies have also indicated a loss of synergy against atovaquone-resistant strains of P. falciparum. capes.gov.br

Efficacy Assessment in Rodent Malaria Models (e.g., Plasmodium berghei infection)

Rodent malaria models, particularly those using Plasmodium berghei, are valuable tools for assessing the in vivo efficacy of antimalarial compounds, including this compound. mdpi.com These models can be used to evaluate causal prophylactic activity, suppressive activity, and the ability to prevent transmission. who.intmmv.org Studies in mice infected with P. berghei have shown that this compound, often in combination with atovaquone, can prevent blood stage infection, indicating causal prophylactic efficacy. biorxiv.org The P. berghei yoelii model has been used to assess the causal prophylactic activity of various compounds, demonstrating that pre-erythrocytic stages of this parasite are susceptible to this compound and cycloguanil. who.int While the search results primarily highlight the efficacy of the atovaquone-proguanil combination in these models, the use of P. berghei infection in mice is a standard approach for evaluating the in vivo antimalarial activity of compounds like this compound. mdpi.commmv.org

Molecular Basis of Resistance to Cycloguanil

The molecular basis of resistance to cycloguanil is intricately linked to specific genetic mutations within the parasite's pfdhfr gene. These mutations lead to amino acid changes in the DHFR enzyme, affecting its interaction with the inhibitor.

Cross-Resistance Patterns with Other Antifolate Drugs

Cross-resistance between cycloguanil and other antifolate drugs, particularly pyrimethamine, is a significant concern in malaria treatment and prophylaxis. Both cycloguanil and pyrimethamine target the same enzyme, Plasmodium falciparum DHFR, and mutations conferring resistance to one drug can often affect susceptibility to the other plos.orgnih.govnih.govnih.gov.

The degree of cross-resistance depends on the specific DHFR mutations present. While some mutations, like A16V combined with S108T, confer resistance primarily to cycloguanil, other mutations or combinations of mutations can lead to broader cross-resistance plos.orgnih.govnih.gov. For example, mutations involving residues 51, 59, 108, or 164 can confer cross-resistance to both pyrimethamine and cycloguanil nih.gov. Significant cross-resistance to both drugs is observed in parasites with mutations including S108N and I164L nih.govnih.gov.

Studies evaluating the in vitro activity of pyrimethamine and cycloguanil against P. falciparum isolates have shown a significant positive correlation between resistance to these two antifolates, indicating widespread cross-resistance nih.gov. The spread of resistance to one DHFR inhibitor in a region can therefore compromise the effectiveness of other drugs targeting the same enzyme nih.gov.

The evolutionary pathways of resistance mutations can also influence cross-resistance patterns. The accumulation of mutations often leads to increasing levels of resistance and broader cross-resistance to antifolate drugs plos.orgcabidigitallibrary.orgnih.gov.

Novel or Uncharacterized Resistance Mechanisms to Proguanil

While point mutations in the pfdhfr gene are the primary and most well-characterized mechanism of resistance to this compound (cycloguanil), there is ongoing research into the possibility of novel or uncharacterized mechanisms that might contribute to reduced susceptibility.

Some studies suggest that genetic factors outside the dhfr gene may play a role in modulating this compound or other antifolate susceptibility thaiscience.info. However, these mechanisms are less understood compared to the well-established role of DHFR mutations.

Research into novel antimalarial drug targets and resistance mechanisms often involves high-throughput screening and genomic analysis of resistant parasite lines nih.govasm.org. These approaches can potentially identify new genes or pathways involved in resistance that are independent of the classical DHFR-mediated mechanism. For instance, studies aimed at finding new antimalarials have identified compounds with novel mechanisms of action that remain potent against parasites resistant to existing drugs like atovaquone and chloroquine nih.govasm.org. While these studies don't directly address this compound resistance, the methodologies used could potentially uncover novel mechanisms relevant to cycloguanil if applied to cycloguanil-resistant parasite lines.

Furthermore, metabolic network reconstructions and systems biology approaches are being used to understand the metabolic changes that occur in resistant parasites researchgate.net. These studies can reveal altered metabolic pathways that might contribute to drug resistance, potentially including mechanisms relevant to antifolate drugs beyond the direct inhibition of DHFR.

Despite these avenues of research, the current understanding of this compound resistance predominantly centers on mutations in the pfdhfr gene. Novel or uncharacterized mechanisms are still areas of active investigation.

Strategies for Overcoming Resistance in Preclinical Models

Strategies for overcoming this compound resistance in preclinical models primarily focus on developing new inhibitors that are effective against mutant PfDHFR enzymes and exploring combination therapies.

One approach involves designing and synthesizing new antifolate inhibitors that can bind effectively to the altered active site of mutant DHFR enzymes cambridge.orgresearchgate.net. Guided by the structural information of mutant enzymes, researchers are developing compounds with high affinity against both wild-type and resistant PfDHFRs cambridge.orgresearchgate.net. Some of these novel inhibitors have shown potent antimalarial activity against drug-resistant P. falciparum strains in culture and in vivo preclinical models cambridge.org.

Another strategy is the use of drug combinations. Combining inhibitors that target the same enzyme but have different binding interactions can potentially overcome resistance conferred by specific mutations nih.gov. For example, combining inhibitors from different antifolate classes has been proposed to impede the emergence of resistance by requiring conflicting mutations for resistance to each component nih.gov. Studies using combinations of pyrimethamine and cycloguanil analogs have shown reduced generation of resistant mutants in preclinical settings nih.gov.

Preclinical models, including in vitro parasite cultures and in vivo mouse models, are crucial for evaluating the efficacy of new drug candidates and combination therapies against resistant P. falciparum strains cambridge.orgcrownbio.com. Advanced techniques like CRISPR engineering are also being used in preclinical studies to generate parasite lines with specific resistance mutations, allowing for a better understanding of resistance mechanisms and the testing of new interventions crownbio.comhappylungsproject.org.

Furthermore, high-throughput screening of diverse compound libraries is employed to identify novel chemical scaffolds with antimalarial activity, including those effective against resistant parasites nih.govasm.org. Compounds with novel mechanisms of action identified through such screenings could potentially be used in combination with existing drugs like this compound to overcome resistance.

Metabolic network models are also being utilized to predict candidate drug targets that might be effective against resistant parasites researchgate.net. This systems biology approach can help identify vulnerabilities in the metabolism of resistant strains that could be exploited therapeutically.

Absorption and Systemic Exposure of Proguanil and its Metabolites

The absorption of this compound varies among animal species. In rats, oral absorption is limited, with only about 10-15% of an oral dose being excreted in the urine. geneesmiddeleninformatiebank.nl In contrast, dogs show a higher oral absorption, with 50-60% of a radiolabeled oral dose recovered in urine. geneesmiddeleninformatiebank.nl Studies in rats using radiolabeled this compound demonstrated rapid disappearance of the parent drug from plasma. fda.gov In pregnant female rats, this compound was quantifiable in plasma only at a dose of 20 mg/kg. fda.gov

This compound is metabolized to its major active metabolite, cycloguanil, and an inactive metabolite, 4-chlorophenylbiguanide, in all species examined, including rats, rabbits, and dogs. fda.gov The relative amounts of these metabolites can differ between species. In rat, rabbit, and dog hepatocytes, greater amounts of 4-chlorophenylbiguanide were produced relative to cycloguanil. fda.gov

Systemic exposure to this compound and its metabolites can be influenced by various factors, including the presence of other drugs. In rats, the tissue distribution of radiolabeled this compound and its metabolites appeared more restricted when administered in combination with atovaquone. geneesmiddeleninformatiebank.nl

Distribution Profile in Animal Tissues

Following oral administration, this compound is extensively distributed in tissues. nih.gov In male rats, whole-body radiography studies using radiolabeled this compound showed that radioactivity distributed mainly to the liver within 24 hours of administration. fda.gov A similar study in pregnant female rats indicated that radiolabeled this compound was primarily found in the maternal liver, with no apparent penetration of the placental barrier and limited distribution to the fetuses. fda.govdrugs.com

This compound, but not its metabolite cycloguanil, is concentrated in erythrocytes, leading to a notable difference between whole blood and plasma concentrations. nih.gov this compound is approximately 75% protein bound in plasma. nih.govhres.canih.govgsk.comhres.camedicines.org.ukhres.ca

Elimination Pathways and Excretion Rates in Various Animal Species

The main routes of elimination for this compound and its metabolites are hepatic biotransformation and renal excretion. drugs.comgskpro.com this compound is partially metabolized, primarily by the cytochrome P450 isoenzyme CYP2C19. nih.govhres.cagsk.comhres.camedicines.iehpra.iepdr.net Less than 40% of the administered dose is excreted unchanged in the urine. nih.govhres.cagsk.comhres.cadrugs.commedicines.iehpra.ie The metabolites, cycloguanil and 4-chlorophenylbiguanide, are also excreted in the urine. hres.cagsk.comhres.camedicines.iehpra.ie Fecal excretion accounts for about 10% of an administered dose. pdr.net

Species differences exist in the extent of urinary excretion. In rats, only 10-15% of an oral dose is excreted in urine, while in dogs, urinary excretion accounts for 50-60% of a radiolabeled oral dose. geneesmiddeleninformatiebank.nl

The elimination half-life of this compound and cycloguanil is approximately 12-15 hours in both adults and children. geneesmiddeleninformatiebank.nlhres.cagsk.comhres.cahpra.ie

Comparative Pharmacokinetic Analysis Across Animal Models (e.g., rat, dog, rabbit)

Comparative pharmacokinetic studies in different animal models reveal species-specific differences in this compound disposition. After oral administration, this compound exposure is limited in rats but extensive in dogs. oup.comnih.gov Conversely, the exposure to the active metabolite cycloguanil is extensive in dogs but limited in rats. oup.comnih.gov

In vitro studies using hepatic microsomes and hepatocytes from various species, including rat, rabbit, dog, and monkey, have shown species differences in the metabolism of this compound. fda.gov Rabbit hepatic preparations displayed significantly greater metabolic activity compared to other species tested. fda.gov All examined species produced the metabolites cycloguanil and 4-chlorophenylbiguanide, with a higher proportion of the latter in animal species compared to humans. fda.gov

Studies in pregnant rabbits showed limited exposure to this compound. fda.gov At a dose of 100:40 mg/kg (atovaquone:this compound), the AUC for this compound in pregnant rabbits was approximately 45% of the estimated human exposure. fda.gov Cycloguanil exposure in pregnant rabbits at this dose was slightly greater than expected human exposure. fda.gov

The oral clearance of this compound has been shown to be a function of body weight in both adults and children. hres.cagsk.comhres.ca

Here is a summary table of some pharmacokinetic parameters across species:

Interactions Involving Cytochrome P450 Enzymes and Proguanil Metabolism

This compound undergoes metabolic activation in the liver to its active metabolite, cycloguanil. This biotransformation is significantly mediated by cytochrome P450 enzymes, particularly CYP2C19. drugbank.comnih.gov The involvement of CYP enzymes in this compound metabolism makes it susceptible to pharmacokinetic interactions with compounds that inhibit or induce these enzymes.

Interactions with Transport Proteins (e.g., OCT2, MATE2-K)

This compound and its active metabolite, cycloguanil, have been identified as substrates for several transport proteins. In vitro studies using HEK293 cells expressing human transporters have shown that this compound is a substrate of Organic Cation Transporter 1 (OCT1) and Organic Cation Transporter 2 (OCT2) with specific affinities. nih.govresearchgate.net Additionally, Multidrug and Toxin Extrusion 1 (MATE1) and Multidrug and Toxin Extrusion 2-K (MATE2-K) were identified as putative transport proteins for this compound. nih.govresearchgate.net

Cycloguanil was also found to be a substrate of OCT1, OCT2, MATE1, and MATE2-K. nih.govresearchgate.net These findings highlight the potential importance of these transporters in the distribution and excretion of both this compound and cycloguanil. nih.gov Studies using double-transfected cell models (e.g., HEK-OCT1-MATE2-K) have indicated an interplay between OCT1-mediated uptake and MATE2-K-mediated export of this compound, suggesting that these transporters can influence the intracellular accumulation of the drug. frontiersin.org

The interaction of antimalarials, including this compound, with OCT1 and OCT2 can reduce the transport activity of these proteins in vitro. nih.govresearchgate.net This substrate overlap with transporters involved in the disposition of other drugs, such as metformin, suggests that DDIs mediated by transport proteins can be anticipated during concurrent treatment. nih.gov

Pharmacodynamic Interactions with Other Antimalarials (e.g., Atovaquone, Chloroquine)

This compound is frequently used in combination with other antimalarials, most notably atovaquone, due to a synergistic effect. nih.govwikipedia.org While cycloguanil, the metabolite of this compound, inhibits parasite dihydrofolate reductase, this compound itself contributes to the synergy with atovaquone through a distinct mechanism. nih.govasm.org

In vitro studies have shown that this compound, acting as a biguanide rather than through its metabolite cycloguanil, significantly enhances the ability of atovaquone to collapse the mitochondrial membrane potential (ΔΨm) in malaria parasites. nih.govasm.org This enhancement occurs at pharmacologically achievable concentrations of this compound and is specific to atovaquone, not affecting the activity of other mitochondrial electron transport inhibitors like myxothiazole and antimycin. nih.govasm.org This mechanism, where this compound in its prodrug form lowers the effective concentration of atovaquone required to collapse ΔΨm, is believed to contribute to the increased efficacy and reduced resistance emergence observed with the atovaquone-proguanil combination. nih.govasm.org

The search results did not provide specific nonclinical mechanistic details regarding pharmacodynamic interactions between this compound and chloroquine.

Interactions Affecting Anticoagulant Activities (e.g., Warfarin)

This compound may potentiate the anticoagulant effect of warfarin and other coumarin-based anticoagulants. fda.govmedicines.org.ukmedicines.iefda.govmedsafe.govt.nzhpra.ierxlist.com While this interaction has been observed, the precise mechanism underlying this potential drug interaction has not been definitively established in the provided search results. fda.govmedicines.org.ukmedicines.iefda.govmedsafe.govt.nzhpra.ierxlist.com Caution is advised when co-administering this compound with coumarin-based anticoagulants, and close monitoring of coagulation tests is recommended. fda.govmedicines.org.ukmedicines.iefda.govmedsafe.govt.nzhpra.ierxlist.com

Based on the search results, one potential contributing factor could involve CYP interactions, as warfarin is metabolized by several CYP enzymes, including CYP2C9, CYP1A2, and CYP3A4 nih.gov, and this compound is metabolized by CYP2C19 and CYP3A nih.govtandfonline.com. However, a direct mechanistic link explaining how this compound potentiates warfarin's effect through CYP modulation or other mechanisms was not clearly elucidated in the provided information.

Data Table: Summary of Nonclinical Interaction Mechanisms

Synthetic Routes and Methodologies for Proguanil

The synthesis of this compound typically involves the reaction of a 4-chloroaniline derivative with an isopropylcyano guanidine or related precursors google.comresearchgate.netresearchgate.net. Several synthetic routes have been explored and reported. One common method involves the reaction of p-chlorophenyl dicyandiamide with isopropylamine google.comgoogle.com. This reaction can be carried out in various solvent systems, including aqueous ethanol or a mixture of methanol and water, often in the presence of a catalyst like copper sulfate pentahydrate google.comgoogle.com. The reaction mixture is typically heated to reflux for several hours to ensure completion google.comgoogle.com.

Another approach involves the reaction of isopropylcyano guanidine with p-chloroaniline hydrochloride google.com. However, this method has been noted to use p-chloroaniline, which can pose safety concerns on a commercial scale google.com.

A process for preparing this compound hydrochloride involves reacting p-chlorophenylcyanoguanidine with a molar excess of isopropylamine google.comgoogle.com. This reaction can utilize a solvent system such as THF-water to achieve high purity and yield google.com. The process may involve heating the reaction mixture, followed by cooling, addition of acid, and subsequent addition of an ammoniacal solution containing a chelating agent like EDTA to remove copper impurities google.comgoogle.com. Filtration and drying of the precipitated product yield this compound hydrochloride google.comgoogle.com.

Research has also explored the synthesis of this compound derivatives by reacting 4-(trifluoromethoxy)aniline with sodium dicyandiamide, followed by reaction with corresponding alkylamines mdpi.com. This method has been used to obtain novel this compound derivatives with varied carbon chain lengths mdpi.com.

Design and Synthesis of Novel Biguanide Analogues

The biguanide scaffold has served as a basis for the design and synthesis of numerous analogues with potential antimalarial and other therapeutic activities researchgate.netthieme-connect.com. The design of novel biguanide analogues often involves modifications to the core biguanide structure or the attached substituents to explore their impact on biological activity and pharmacokinetic properties researchgate.net.

Studies have focused on synthesizing biguanide derivatives with different aryl or alkyl substituents. For instance, the reaction of aryl biguanides with γ-pyridones has been explored to yield new compounds, although some of these derivatives did not show appreciable antimalarial activity in experimental models acs.org.

The synthesis of 1-substituted-biguanide derivatives has been reported through the reaction of substituted anilines or hydrazines with dicyandiamide in the presence of acid thieme-connect.com. These synthesized biguanide salts have been characterized and evaluated for biological activities, such as anti-diabetic effects thieme-connect.com.

In the context of antimalarial research, novel biguanide analogues have been synthesized as potential prodrugs that can be metabolized to active dihydrotriazine compounds researchgate.net. These synthetic efforts aim to develop compounds with improved in vivo activity and favorable ADME properties researchgate.net.

Structure-Activity Relationship (SAR) Studies for Antimalarial Potency

SAR studies for biguanides and their active metabolites, dihydrotriazines, have revealed key structural features essential for antimalarial activity firsthope.co.in. The presence of the biguanide functional group is crucial for the activity of the parent compounds firsthope.co.in. These guanidine moieties provide basic centers that can interact with the active site of dihydrofolate reductase (DHFR), the primary target of the active metabolite, cycloguanil firsthope.co.in.

This compound itself acts as a prodrug, undergoing metabolic cyclization in the host to form cycloguanil, a dihydrotriazine firsthope.co.indrugbank.comnih.gov. This cyclization reaction is critical for the potent inhibition of parasitic DHFR firsthope.co.in. The lipophilicity of biguanides and dihydrotriazines can influence their cellular uptake and potency firsthope.co.in. Introducing a lipophilic side chain can potentially improve cell permeability and antimalarial activity firsthope.co.in. The basic amine groups in these compounds can be protonated, affecting their membrane permeability and intracellular distribution firsthope.co.in.

SAR studies on cycloguanil derivatives have explored the relationship between various physicochemical properties and binding affinity to wild-type and mutant Plasmodium falciparum DHFR nih.gov. Hydrophobicity of substituents on the N1-phenyl ring has been found to have a parabolic relationship with wild-type binding affinity nih.gov. Steric factors are considered crucial for resistance against the A16V+S108T mutant of PfDHFR-TS nih.gov.

Research on fluorine-containing this compound derivatives has shown that the incorporation of fluorine can lead to compounds with enhanced biological activities, including potentially improved binding interactions and metabolic stability nih.gov.

Development of Cyclization-Blocked this compound Analogues and their Activity

While this compound's antimalarial action is largely attributed to its metabolic conversion to cycloguanil, studies have also investigated the intrinsic activity of this compound and the potential of cyclization-blocked analogues researchgate.netmmv.orgnih.govdntb.gov.ua. Evidence suggests that this compound possesses limited intrinsic activity, which is associated with mitochondrial function researchgate.netmmv.orgnih.gov.

Cyclization-blocked this compound analogues are designed to prevent the metabolic formation of the dihydrotriazine ring, allowing for the study of the biguanide structure's inherent activity. One such analogue is tBuPG, a cyclization-blocked derivative of this compound researchgate.netmmv.orgnih.govresearchgate.net. Studies with tBuPG have demonstrated that both this compound and this cyclization-blocked analogue exhibit potent, albeit slow-acting, in vitro anti-plasmodial activity researchgate.netmmv.orgnih.gov. This activity has been found to be independent of folate metabolism and isoprenoid biosynthesis researchgate.netmmv.orgnih.gov.

Furthermore, cyclization-blocked analogues like tBuPG have shown activity against liver-stage parasites, similar to this compound researchgate.netmmv.orgnih.gov. Interestingly, these analogues can act synergistically with cytochrome bc1 inhibitors, such as atovaquone, against blood-stage parasites in vitro researchgate.netmmv.orgnih.gov. This contrasts with cycloguanil, which has been shown to antagonize the activity of atovaquone researchgate.netmmv.orgnih.gov. These findings suggest that a cyclization-blocked this compound analogue could potentially be a superior combination partner for bc1 inhibitors in vivo researchgate.netmmv.orgnih.gov.

The synthesis of cyclization-blocked this compound analogues allows for the deconvolution of the pharmacological effects of the parent drug and its active metabolite, providing insights into alternative mechanisms of action for the biguanide scaffold researchgate.net.

Photolysis and Abiotic Degradation Pathways in Aquatic and Terrestrial Environments

Photolysis is considered a major abiotic degradation process for some organic pollutants in surface waters. researchgate.net While direct data on the photolysis of proguanil in aquatic and terrestrial environments is limited in the provided search results, one source indicates a photolysis half-life of 2.63 hours for atovaquone, a compound often co-formulated with this compound. fass.sefass.se Abiotic degradation mechanisms in polymers, such as thermal, photo-oxidative, and hydrolytic degradation, can be influenced by environmental factors like heat, humidity, and radiation. encyclopedia.pub Hydrolytic degradation, for instance, involves the scission of chemical bonds in the presence of water. encyclopedia.pub

Microbial Degradation and Biotransformation in Soil and Water Systems

Microbial activity plays a significant role in the fate of pesticides and other organic compounds in the environment. researchgate.netacademicjournals.org Microorganisms, including bacteria and fungi, possess enzymatic pathways that can degrade or biotransform these substances. academicjournals.orgresearchgate.netagriscigroup.us The efficiency of microbial degradation is influenced by various environmental parameters such as pH, temperature, moisture content, and the presence of nutrients. researchgate.netagriscigroup.us While specific details on the microbial degradation of this compound in soil and water are not extensively detailed in the provided snippets, studies on other compounds like the herbicide propanil and its degradation product 3,4-dichloroaniline highlight the role of microbial consortia in their biodegradation in bioreactors and soil. nih.govnih.gov Certain bacterial genera, including Pseudomonas, Acinetobacter, and Rhodococcus, have been implicated in the degradation of chlorinated anilines. nih.gov Research also suggests that biotransformation potential in activated sludge can be indicative of degradation pathways in soil and water-sediment systems. acs.orgnih.gov

Identification and Characterization of Environmental Degradation Products

One significant degradation product associated with this compound is 4-chloroaniline (PCA). researchgate.netresearchgate.net Studies investigating the degradation of this compound tablets have identified the formation of 4-chloroaniline, which is known to be genotoxic. researchgate.net The synthesis of this compound itself involves 4-chloroaniline as an intermediate product. researchgate.net Another related compound, 3,4-dichloroaniline (3,4-DCA), is a known degradation product of the herbicide propanil and is considered slowly biodegradable with potential adverse health and ecotoxicity effects. nih.govnih.govresearchgate.net While 3,4-dichloroaniline is a degradation product of propanil, its direct formation from this compound in the environment is not explicitly detailed in the provided texts. However, the presence of chlorinated aniline structures in both this compound and related compounds suggests potential pathways leading to such products upon degradation.

Research on the degradation of diuron, another phenylurea herbicide, shows its transformation to 3,4-dichloroaniline, which is subsequently metabolized through dehalogenation and hydroxylation pathways. researchgate.net

Persistence and Half-Life Assessments in Environmental Compartments

This compound is considered potentially persistent in the environment. fass.sefass.se This classification is based on assessments indicating it is not readily or inherently degradable. fass.sefass.se While specific half-life data for this compound in various environmental compartments like soil, water, and sediment are not comprehensively provided, information on its co-formulated drug, atovaquone, suggests a rapid degradation in soil with 50% degradation in less than 1 day. fass.sefass.se However, for the aquatic compartment, the potential for atovaquone's persistence could not be excluded due to a lack of data. fass.sejanusinfo.se this compound's elimination half-life in humans is approximately 12-21 hours, which is significantly shorter than that of atovaquone (2-3 days in adults). medscape.commdpi.comnih.gov This primarily relates to its metabolism and excretion from the body rather than environmental degradation.

Methodologies for Environmental Monitoring of this compound and its Metabolites

High-performance liquid chromatography (HPLC) is a commonly used analytical method for the determination of this compound and its metabolites in various matrices, including biological fluids like urine and plasma. researchgate.netnih.govajtmh.orgajol.infonih.gov Improved and validated HPLC methods utilizing solid-phase extraction (SPE) have been developed for the determination of this compound, cycloguanil, and 4-chlorophenylbiguanide in plasma, whole blood, and urine, offering good precision and sensitivity. ajol.infonih.gov These methods often employ reversed-phase C-18 columns and UV detection. researchgate.netajol.info While these methods are primarily described for biological samples, similar chromatographic techniques are widely applicable for environmental monitoring of pharmaceuticals and their degradation products in water and soil. The identification of degradation products can also involve techniques such as HPLC coupled with mass spectrometry (HPLC-MS) and gas chromatography coupled with flame ionisation detection (GC-FID). researchgate.net