naphthoquinones and cycloguanil

To investigate the pharmacokinetics, safety and efficacy of the recommended 3-day treatment regimen of Malarone in third-trimester pregnant women with acute uncomplicated falciparum malaria.. Twenty-six pregnant women in their third trimester (gestational age: 24-34 weeks) with acute uncomplicated Plasmodium falciparum malaria who fulfilled the enrollment criteria were recruited from the antenatal clinics of Mae Sot Hospital, Tak Province, Thailand, (n = 8) and the Tropical Diseases Research Centre, Ndola, Zambia (n = 18). Patients were treated with four Malarone tablets (GlaxoSmithKline: each tablet contains 250 mg atovaquone and 100 mg proguanil) once daily for 3 consecutive days. Blood samples were taken for pharmacokinetic investigations of atovaquone, proguanil, and cycloguanil up to 288 h (day 14) after the last dose. Urine samples were collected for the evaluation of proguanil and cycloguanil 0-8, 8-16, 16-24 and 24-48 h after the last dose. Efficacy assessments included the clinical and parasitological evaluation of mothers and newborns. Adverse events were evaluated at each visit to the antenatal clinics.. Malarone appeared to be effective and well tolerated when used for the treatment of falciparum malaria in pregnant women. All patients showed prompt clinical improvement and the disappearance of parasitaemia after treatment. There were no serious adverse effects or unexpected adverse effects and no stillbirths or spontaneous abortions. The plasma concentration-time profiles of atovaquone and proguanil in most cases were best characterised by the two-compartment open model with zero-order input with/without absorption lag time and first-order elimination. There were no significant differences in any of the pharmacokinetic parameters of atovaquone, proguanil or cycloguanil between patients from Thailand and Zambia. For atovaquone, a Cmax of 1.33-8.33 microg/ml was reached at 2.0-9.3 h after the last dose on day 2. V/F, CL/F and t(1/2beta) were 6.9-39.5 l/kg, 83-384 ml/h/kg, and 57.8-130.8 h, respectively. The Cmax and t(max) values for proguanil versus cycloguanil were 383-918 versus 0-129 ng/ml and 3.3-8.6 versus 3-12 h, respectively. V/F, CL/F, and t(1/2beta) values for proguanil were 10.7-34.0 l/kg, 431-1,662 ml/h/kg and 11.2-30.3 h. The CL(R-CG), t(1/2z), (CG), proguanil/cycloguanil metabolic ratios, AUC ratios for proguanil to cycloguanil (AUC(PG/CG)) were 107.2-1,001 ml/h/kg, 5-95 ml/h/kg, 7.8-20.7 h, 5-57, and 4.7-20.2, respectively.. The pharmacokinetics of atovaquone and cycloguanil appeared to be influenced by the pregnancy status, resulting in an decrease in the Cmax and AUC of approximately twofold.

Topics: Adolescent; Adult; Antimalarials; Atovaquone; Drug Combinations; Female; Humans; Malaria, Falciparum; Naphthoquinones; Pregnancy; Proguanil; Thailand; Triazines; Zambia

To determine the pharmacokinetic profiles of atovaquone (ATO), proguanil (PROG) and its active metabolite cycloguanil (CYCLO) with respect to possible accumulation and kinetic interaction upon repeated dosing with Malarone.. Thirteen healthy volunteers first received a single dose and then after 1 week, repetitive daily doses of Malarone (one tablet) for 13 days. For analysis of plasma drug concentrations, blood samples were collected at regular intervals over 8 days after a single dose and over 12 days after the last day of multiple dosing. Single-dose and steady-state pharmacokinetic parameters were determined for each individual. Genotyping of the gene coding for CYP2C19, a major enzyme catalyzing PROG metabolism, was performed using polymerase chain reaction, and in vitro enzyme kinetic experiments were carried out to study the possible effect of ATO on the catalytic activities of CYP2C19 and 3A4 using fluorometric assays.. For ATO, the ratio of the area under the concentration-time curve (AUC) during the last dose interval to the AUC after the single dose (AUC(0- tau)/AUC(0- infinity)) was found to be 0.90 [95% confidence interval (CI) 0.56, 1.24] indicating absence of undue accumulation. AUC(0- tau), and peak plasma concentration at steady state (C(max,ss)) values were, however, threefold lower than those reported in human immunodeficiency virus-infected subjects after 12 multiple daily doses of 250 mg ATO alone. Four volunteers, with mean CYCLO/PROG AUC(0-tau) of 0.03 (-0.23, 0.09) were classified as poor metaboliser (PM) phenotypes. There was a significant increase in the AUC of PROG at steady state with a PROG AUC(0-tau)/AUC(0-infinity) ratio of 1.38 (1.07, 1.69) in extensive metaboliser (EM) phenotypes. CYCLO/PROG AUC ratios were significantly lower 0.67 (0.54, 0.81) at steady state than that after the first single dose in EM phenotypes. The in vitro kinetic experiments on recombinant enzymes (CYP2C19 and CYP3A4) suggested a possible inhibition of catalytic activity of CYP3A4 by ATO.. There was no unexpected accumulation of ATO following repeated administrations of the combination. In EM phenotypes, PROG elimination was reduced at steady state. Also, at steady state, either the elimination of CYCLO was increased or its formation clearance decreased the latter possibly by inhibition of CYP3A4 by ATO.

Topics: Adult; Antimalarials; Atovaquone; Biological Availability; Dose-Response Relationship, Drug; Drug Combinations; Female; Genotype; Humans; In Vitro Techniques; Male; Middle Aged; Naphthoquinones; Phenotype; Proguanil; Time Factors; Triazines

To assess the magnitude of the putative effect of atovaquone on the pharmacokinetics of proguanil and to determine whether the pharmacokinetics of atovaquone are affected by concomitant administration of proguanil, with both drugs administered for 3 days to healthy adult volunteers.. This was an open-label, randomized, three-way cross-over study, in which 18 healthy volunteers received 400 mg proguanil, 1000 mg atovaquone and 1000 mg atovaquone + 400 mg proguanil. Each treatment was given once daily for 3 days with a 3-week wash-out period between each occasion. For the assay of proguanil, cycloguanil and atovaquone, blood was sampled before dosing and at regular intervals over 8 days when proguanil was given, and over 17 days when atovaquone was given.. The geometric mean of the area under the atovaquone plasma concentration-time curve calculated from 0 to 24 h after the last dose (AUC0->24h) was 180 microg x ml(-1) h following administration of atovaquone alone and 193 microg x ml(-1) h following atovaquone with proguanil. The geometric mean AUC0->24h for proguanil was 6296 ng x ml(-1) x h after proguanil alone and 5819 ng x ml(-1) x h following proguanil with atovaquone. The corresponding values for the metabolite cycloguanil were 1297 ng x ml(-1) x h and 1187 ng x ml(-1) x h, respectively. The geometric mean elimination half-life (t1/2) of atovaquone was 57.1 h when given alone and 59.0 h when administered together with proguanil. The corresponding geometric mean values of t1/2 for proguanil were 13.7 h and 14.5 h. Exploratory statistical analysis showed no important gender effects on the pharmacokinetics of atovaquone, proguanil, or cycloguanil.. The pharmacokinetics of atovaquone and proguanil and its metabolite, cycloguanil, were not different when atovaquone and proguanil were given alone or in combination.

Topics: Adult; Antimalarials; Atovaquone; Cross-Over Studies; Drug Interactions; Female; Humans; Male; Naphthoquinones; Proguanil; Sex Factors; Triazines

The use of synergistic drug combinations for the treatment of drug-resistant malaria is a major strategy to slow the selection and spread of Plasmodium falciparum resistant strains. In order to investigate synergistic compounds, with different modes of action, as alternative candidates for combination therapy, we used standard in vitro P. falciparum cultures and an established synergy testing method to define interactions among dapsone (DDS), atovaquone (ATQ), chlorproguanil (CPG) and its triazine metabolite chlorcycloguanil (CCG). Strong synergy was observed in the combinations DDS/CCG and ATQ/CPG. Multiple combination of these drugs, DDS/CCG/CPG/ATQ also exhibited high synergy although not higher than that of either of the two drug combinations separately. The use of this triple combination DDS/CPG/ATQ, even without an increase in synergy over their double combinations, ATQ/CPG and DDS/CCG, would contribute towards slowing the selection pressure since these drugs act against different targets and would delay the selection of parasites resistant to the three drugs, extending the useful therapeutic life of these valuable compounds.

Topics: Animals; Antimalarials; Atovaquone; Dapsone; Drug Synergism; Drug Therapy, Combination; Folic Acid Antagonists; Naphthoquinones; Plasmodium falciparum; Proguanil; Triazines

We studied the viability of Plasmodium falciparum parasites reappearing in long-term cultures after repetitive exposure to atovaquone and proguanil. Parasites (F32 and FCR3) exposed to 100-5000 nM atovaquone for 96 hours were reduced to <5% of initial parasitaemia but recrudesced after 9-15 days. Also, parasites exposed to 1000 nM atovaquone for 48, 72, 96 and 144 hours recrudesced after 9, 14, 21 and 23 days respectively. Immediately after removal of the drug, only 1-3 schizonts per 10000 red blood cells were found consistently, apparently unable to produce trophozoites and thus, possibly, adopting a "dormant state". Parasites (F32 and FCR3) exposed to 500 nM atovaquone for 72 hours reappeared after 14 days. These recrudescing parasites were then re-exposed and suppressed by atovaquone in three consecutive follow-up experiments. They reappeared after 12, 11 and 9 days respectively. No known point mutations in cytochrome b gene (cytb), associated with atovaquone resistance, were detected in any recrudescing parasites. Finally, parasites (F32) exposed to various concentrations of atovaquone and proguanil in combination for 72 hours reappeared after 9-17 days. The baseline susceptibilities of the parasites to individual drugs were similar before and after recrudescence in all experiments.

Topics: Animals; Antimalarials; Atovaquone; Culture Media; Cytochrome b Group; Dose-Response Relationship, Drug; Drug Resistance; Drug Therapy, Combination; Humans; Malaria, Falciparum; Naphthoquinones; Parasitic Sensitivity Tests; Plasmodium falciparum; Proguanil; Recurrence; Triazines

The shikimate pathway for aromatic biosynthesis presents a target for antimalarial drug development as this pathway is absent from animals. This study extends previous work on inhibitors of the shikimate pathway, by examining their interaction with the antimalarial drugs pyrimethamine and atovaquone. Combinations of atovaquone with several shikimate analogues exhibited synergistic effects. These findings highlight potential use of shikimate pathway inhibitors in combination therapy.

Topics: Animals; Antimalarials; Atovaquone; Drug Interactions; Naphthoquinones; Plasmodium falciparum; Proguanil; Pyrimethamine; Shikimic Acid; Triazines

Atovaquone-proguanil has recently been introduced for the treatment and prophylaxis of malaria. However, resistance of Plasmodium falciparum is increasingly reported. We assessed P. falciparum polymorphisms associated with resistance to atovaquone (cytochrome b, cytb) and to cycloguanil, the active compound of proguanil (dihydrofolate reductase, dhfr) in 100 isolates from northern Ghana. None of these exhibited cytb codon 268 mutations. Moreover, no dhfr V16A, S108T or I164L mutations linked with cycloguanil resistance were detected. However, dhfr triple mutants (S108N-I51L-C59R) conferring resistance to proguanil and sulphadoxine-pyrimethamine were seen in 51% of the isolates. In northern Ghana, P. falciparum cytb codon 268 mutations associated with atovaquone resistance are absent. Although proguanil appears to act synergistically with atovaquone in a way different from its antifolate property, the abundance of dhfr polymorphisms will likely compromise the prevention of dissemination of atovaquone-resistant parasites once emerged.

Topics: Animals; Antimalarials; Atovaquone; Child, Preschool; Cytochromes b; Drug Combinations; Drug Resistance; Drug Synergism; Drug Therapy, Combination; Female; Folic Acid Antagonists; Ghana; Humans; Infant; Malaria, Falciparum; Male; Mutation; Naphthoquinones; Plasmodium falciparum; Polymorphism, Restriction Fragment Length; Proguanil; Pyrimethamine; Sulfadoxine; Tetrahydrofolate Dehydrogenase; Triazines

Resistance of Plasmodium falciparum to atovaquone in vitro and in vivo has been associated to mutations in the parasite cytochrome b gene.. Cultures were sequentially subjected to increasing doses of atovaquone alone or in combination with cycloguanil and the cytochrome b gene was sequenced. Additionally, we investigated the parasite cytochrome b gene of a patient returning from Mali with Malarone treatment failure in vivo.. All strains that survived atovaquone concentrations in vitro of 2 x 10(-8) to 2 x 10(7) M showed the M133I mutation and one strain with the highest atovaquone concentration the additional mutation L171F. Sequencing of the in vivo treatment failure revealed a point mutation at codon 268 resulting in an amino acid change from tyrosine to serine. Based on the repeated emergence of mutations at codon 268, but no detection of alterations at codon 133 in vivo, we developed a detection method for the diagnostic of codon 268 polymorphisms as a potential atovaquone/proguanil resistance marker. A nested PCR with 3 different pairs of primers for the second round was designed. Each product was digested with restriction enzymes, capable to distinguish the wild type from the two reported mutations at codon 268.. Mutations at codon 268 of the parasite cytochrome bc1 gene are associated with atovaquone/proguanil treatment failure in vivo and can be used as potential resistance marker This method provides a novel and robust tool to investigate the relevance of codon 268 polymorphisms as resistance marker and to monitor the further emergence of atovaquone/proguanil resistance.

Topics: Animals; Antimalarials; Antiprotozoal Agents; Atovaquone; Codon; Drug Resistance; Electron Transport Complex III; Genetic Markers; Humans; Malaria, Falciparum; Mutation; Naphthoquinones; Plasmodium falciparum; Polymerase Chain Reaction; Polymorphism, Genetic; Polymorphism, Restriction Fragment Length; Proguanil; Triazines

The in-vitro effects of folinic acid on the antimalarial activities of the triazine antifolates, cycloguanil and WR99210, were compared with those of their parent biguanides, proguanil and PS-15, a dihydrofolate-reductase inhibitor, pyrimethamine, and a pyrimidine antagonist, atovaquone. It was found that the minimum inhibitory concentrations of cycloguanil and WR99210 were not affected by physiological concentrations of folic or folinic acids in human serum. Experiments with Plasmodium falciparum growing in erythrocytic culture showed that the antimalarial effect of cycloguanil is readily antagonised by folinic acid, whereas WR99210 is much more refractory. Plasmodium falciparum exposed to cycloguanil (2.5 microM, 6 h) and WR99210 (1 microM, 6 h), showed depressed levels of thymidine 5'-triphosphate (dTTP) in the absence and presence of folinic acid (25 microM and 10 microM, respectively). The decrease in dTTP may be attributed to inhibition of dihydrofolate reductase. However, as the addition of folinic acid did not restore dTTP levels in the parasites, the drugs may have an additional or different mechanism of toxicity.

Topics: Animals; Antimalarials; Atovaquone; Drug Interactions; Folic Acid; Humans; Leucovorin; Naphthoquinones; Plasmodium falciparum; Proguanil; Purine Nucleotides; Pyrimethamine; Pyrimidine Nucleotides; Triazines

A new, orally-active inhibitor of dihydrofolic acid reductase (DHFR), PS-15 (N-(3-(2,4,5-trichlorophenoxy)propyloxy)-N'-(1-methylethyl)- imidocarbonimidic diamide hydrochloride), has significant activity against drug-resistant Plasmodium falciparum. It is not cross-resistant with other inhibitors of DHFR (e.g., pyrimethamine and cycloguanil). Although it bears similarities to proguanil, PS-15 represents a new antifolate class of drugs that we have named oxyguanils or hydroxylamine-derived biguanides. This compound displays intrinsic antimalarial activity and also is metabolized in vivo to WR99210, an extremely active triazine inhibitor of DHFR. When tested in vitro against drug-resistant clones of P. falciparum, PS-15 was more active than proguanil, and the putative metabolite, WR99210, was more active than the proguanil metabolite cycloguanil. The drug is also more active as well as less toxic than proguanil when administered orally to mice infected with P. berghei. When administered orally to Aotus monkeys infected with multidrug-resistant P. falciparum, PS-15 was more active than either proguanil or WR99210. In 1973, WR99210 underwent clinical trials for safety and tolerance in volunteers. The trials showed gastrointestinal intolerance and limited bioavailability; further development of the drug was abandoned. Because PS-15 has intrinsic antimalarial activity, is not cross-resistant with other DHFR inhibitors, and can be metabolized to WR99210 in vivo, oral administration of this new drug should circumvent the shortcomings and retain the advantages found with both proguanil and WR99210.

Topics: Administration, Oral; Animals; Antimalarials; Aotus trivirgatus; Atovaquone; Drug Synergism; Folic Acid Antagonists; Imides; Injections, Subcutaneous; Malaria, Falciparum; Mice; Naphthoquinones; Phenyl Ethers; Plasmodium falciparum; Proguanil; Sulfamethoxazole; Triazines

Topics: Animals; Antiprotozoal Agents; Drug Interactions; Folic Acid Antagonists; Hypoxanthines; Naphthoquinones; Plasmodium falciparum; Proguanil; Pyrimethamine; Triazines

Topics: Animals; Antimalarials; Chloroquine; Dimethylpolysiloxanes; Drug Implants; Malaria; Male; Mefloquine; Mice; Mice, Inbred Strains; Naphthoquinones; Piperidines; Plasmodium berghei; Primaquine; Proguanil; Pyrimethamine; Quinolines; Silicone Elastomers; Sulfadiazine; Triazines