Effects of a MATE protein inhibitor, pyrimethamine, on the renal elimination of metformin at oral microdose and at therapeutic dose in healthy subjects.

A microdose study of metformin was conducted to investigate the predictability of drug-drug interactions at the therapeutic dose (ThD). Healthy subjects received a microdose (100 µg) or ThD (250 mg) of metformin orally, with or without a potent and competitive multidrug and toxin extrusion (MATE) inhibitor, pyrimethamine (50 mg, p.o.), in a crossover fashion. Pyrimethamine significantly reduced the renal clearance of metformin by 23 and 35% at the microdose and ThD, respectively. At ThD, but not at microdose, it caused significant increases in the maximum concentration (C(max)) and area under the plasma concentration-time curve (AUC) of metformin (142 and 139% of control values, respectively). Human canalicular membrane vesicles showed pyrimethamine-inhibitable metformin uptake. Pyrimethamine did not affect plasma lactate/pyruvate after ThD of metformin but significantly reduced the renal clearance of creatinine, thereby causing elevation of plasma creatinine level. This microdose study quantitatively predicted a drug-drug interaction involving the renal clearance of metformin at ThD by pyrimethamine. Pyrimethamine is a useful in vivo inhibitor of MATE proteins.

Urinary elimination kinetics of pyrimethamine.

In this study, the kinetics of pyrimethamine elimination via the urine was investigated. The experiments were carried out on six healthy male volunteers aged 23-32 years. The drug was administered orally (p.o.) in a single dose at three different concentrations i.e.: 50, 75 and 100 mg. The concentration of the drug in the urine was determined via the modified method of Bonini et al. and Garber et al. It was found that 13.4 +/- 1.3% of the dose eliminated via the urine was in unchanged form. The process of pyrimethamine elimination may be described according to an open kinetic two-compartmental model: the formula showing the course of pyrimethamine elimination over time has been given. Several examples of the quantitative exposure test have been proposed, which allow the calculation of the drug dose absorbed and thus the degree of toxicity to be determined. This test can also be useful in a controlled clinical setting.

A simple technique for the detection of anti-malarial drug formulations and their presence in human urine.

A simple, sensitive, specific assay technique for the detection and semi-quantification of chloroquine, amodiaquine, quinine, primaquine, sulfadoxine and pyrimethamine in formulations and in human urine by using thin layer chromatography (TLC) was developed and tested in the laboratory. The method involved developing test samples spotted on TLC chromatogram by diethylamine-toluene-isopropanol (1:4:5 v/v/v) as the eluting solvent. The solvent system diethylamine-toluene-isopropanol (1:4:5 v/v/v) enabled the elution and detection of all the tested antimalarial drugs in solution and those spiked in human urine. Detection limits for chloroquine, amodiaquine, quinine and primaquine were the lowest at 0.00025 mg/ml. Sulfadoxine exhibited a detection limit of 0.0005 mg/ml whereas that of pyrimethamine was 0.001 mg/ml. The results indicate the suitability of this technique in antimalarial drug quality and bioavailability studies. It is envisaged that this technique will adequately address the role of drug absorption and excretion in the chemotherapy of malaria as well as to detect types of antimalarial drugs commonly used in the community.

Effect of sulfadiazine and pyrimethamine on selected physiologic and performance parameters in athletically conditioned thoroughbred horses during an incremental exercise stress test.

Following the regimen used to treat equine protozoal myeloencephalitis, sulfadiazine (20 mg/kg) and pyrimethamine (1mg/kg) were administered orally once daily to 12 physically conditioned Thoroughbred horses for 4 consecutive days. The horses were randomly assigned to two test groups in a crossover design, with each horse serving as its own control. A stepwise exercise stress test was conducted to exhaustion. No effect on athletic performance was observed, and only marginal effects were noted in some hematologic and serochemical measurements, including decreased total white blood cell counts, red blood cell distribution width, total hemoglobin, serum sodium, and serum chloride. Serum folic acid concentration decreased significantly following sulfadiazine/pyrimethamine treatment.

Plasmodium falciparum pfcrt and pfmdr1 polymorphisms are associated with the pfdhfr N108 pyrimethamine-resistance mutation in isolates from Ghana.

The Plasmodium falciparum chloroquine resistance transporter gene (pfcrt) T76 and multidrug resistance gene analogue (pfmdr1) Y86 mutations are associated with chloroquine(CQ)-resistance. In isolates from 172 pregnant women living in the area of Agogo, Ghana, pfcrt T76 was detected in 69% and pfmdr1 Y86 in 66%. Pfcrt T76 but not pfmdr1 Y86 was more prevalent in samples from women with residual CQ in urine or serum. Parasite densities and multiplicity of infection of pfmdr wild type but not of resistant isolates were reduced by CQ. Adjusted for CQ and pyrimethamine (PYR) in urine, the P. falciparum dihydrofolate reductase (pfdhfr) N108 mutation which confers PYR-resistance was 3.1 and 3 times, respectively, more likely to be detected in isolates containing pfcrt and pfmdr1 mutations than in those comprising wild type alleles. Pfcrt, pfmdr, and pfdhfr mutations are frequent in P. falciparum from this part of Ghana which may limit the choice of drugs for the prevention of malaria in pregnancy. The association of CQ- and PYR-resistance mutations independent of recent drug use could indicate accelerated development of resistance to structurally unrelated drugs. Alternatively, it may reflect selection of resistance in persisting infections due to no longer detectable drug pressure.

Nonfatal prolonged overdosage of pyrimethamine in an infant: measurement of plasma and urine levels using HPLC with diode-array detection.

A nonfatal case of accidental prolonged overdosage of pyrimethamine (10 times the usual dose for 10 days) in a seven-week-old infant treated for congenital toxoplasmosis is presented. The drug was identified and quantitated in plasma and urine using an HPLC technique with diode-array detection. Initial plasma concentration of pyrimethamine was 6.22 micrograms/mL. Results are discussed in light of the existing literature.

Compliance with malaria chemoprophylaxis over a five-year period among children in a rural area of The Gambia.

We have reviewed a malaria chemoprophylaxis programme in which Maloprim (pyrimethamine and dapsone) has been administered fortnightly by village health workers (VHWs) to approximately 1500 children each year aged 6-59 months resident in 15 primary health care villages in a rural area of The Gambia over 5 years. Reasonable levels of compliance with chemoprophylaxis have been maintained by many children over this period. this has occurred despite minimal outside supervision and support of the programme. Factors which may have affected the level of compliance in individual villages are identified. Large villages and those where social or political factionalism were evident tended to have low levels of compliance. The attitudes of VHWs and mothers to the programme were determined. Most VHWs cooperated enthusiastically and kept accurate records of compliance, despite receiving no compensation from the villagers for administering chemoprophylaxis. The administration of a drug to prevent illness in children was complementary to the curative service provided by VHWs. The chemoprophylactic was widely acceptable and nearly all mothers stated that the tablets were good for their children's health. However, knowledge of the specific purpose of chemoprophylaxis in the prevention of malaria was limited. Improvements in the programme which may result in higher levels of compliance are discussed.

Lack of efficacy of pyrimethamine prophylaxis in pregnant Nigerian women.

To evaluate the efficacy of pyrimethamine on the blood stage (suppressive prophylaxis) and liver stage (causal prophylaxis) of Plasmodium falciparum in pregnant women, in vivo and in vitro field studies were conducted in Ilorin, Nigeria, from Jan 1 to June 30, 1988. For pregnant women with P falciparum infections who received 25 mg of pyrimethamine weekly for suppressive prophylaxis, 67% (59/88) of in vivo and 60% (6/10) of in vitro tests showed pyrimethamine resistance. A second group of parasitaemic and parasite-free pregnant women was enrolled to evaluate the efficacy of pyrimethamine as a primary tissue schizonticide; after receiving a curative dose of chloroquine (25 mg/kg), half the women were given 25 mg of pyrimethamine weekly and half received no prophylaxis. Parasitologic failure rates did not differ between the pyrimethamine-treated (8/34) and the control (11/37) groups during the 16-week follow-up. Thus, pyrimethamine is not effective for suppressive or causal prophylaxis in pregnant women in Ilorin.

PIP: New studies on the suppressive and curative effects of the anti-malarial drug pyrimethamine in pregnant women from Ilorin, Nigeria showed both ineffective prophylaxis and suppression, and parasite resistance. The drug has been used in pregnant women because of its effectiveness in suppression of asexual forms of malaria infections due to Plasmodium falciparum, its long half life and its safety. 1st a group of 88 pregnant women infected with only P falciparum received 25 mg pyrimethamine weekly for 4 weeks and parasites were counted on blood smears. 67% retained parasites by Day 7, and 60% by Day 14. All were treated with curative doses of chloroquine. A 2nd group of 71 pregnant women were first treated for malaria parasites with 2 doses of chloroquine, 25 mg/kg, in 300 mg tablets, followed by weekly pyrimethamine 25 mg for 10 weeks. All subjects and controls were given iron and folic acid supplements to take daily. 24% developed parasitemia during the 10 weeks of the study, compared to 30% of the controls. The mean intervals to development of parasitemia, and the geometric mean parasite density in blood did not differ significantly. In 6 of 10 in vitro tests of parasite resistance to pyrimethamine, parasite growth was uninhibited, compared to 22 of 23 tests for resistance to chloroquine. In vivo and in vitro tests correlated well for pyrimethamine resistance. The results also indicated that primigravidae, who are more likely to harbor malaria parasites, were also more likely to fail in parasite suppression with pyrimethamine treatment. Thus pyrimethamine is not expected to reduce incidence of premature and low birth weight infants due to malaria in this area.

ELISA tests for dapsone and pyrimethamine and their application in a malaria chemoprophylaxis programme.

Enzyme-linked immunosorbent asays (ELISAs) are described for determining levels of dapsone and pyrimethamine in urine. Both assays have a sensitivity of about 20 mug/l and are reproducible, but each produces some false positives. The problem of false positive reactions was partially obviated by requiring positive results in both assays. In a pilot study involving 50 children aged 3 months to 4 years who were given a single dose of Maloprim (pyrimethamine + dapsone), 75% were positive for dapsone 7 days after administration of the drug, while 25% were still positive 15 days after its administration. The corresponding proportions for pyrimethamine were 73% and 30%, respectively. Comparison of the results obtained in a larger chemoprophylaxis trial with those from the pilot study indicated that the assays described could be used to investigate whether antimalarials had been taken.

Pyrimethamine pharmacokinetics and its tissue localization in mice: effect of dose size.

The plasma pharmacokinetics and mass fate of [14C]pyrimethamine were investigated in the mouse, following dosage with 12.5, 25, 50, and 75 mg kg-1 (i.p.). Peak plasma concentrations of pyrimethamine were reached between 1 and 2 h and then declined monoexponentially. The mean values for AUC0----30 h increased linearly in relation to the administered dose of pyrimethamine (r = 0.979, P less than or equal to 0.001). The mean values for intraperitoneal clearance and half-life were not significantly different between dose groups, indicating that the plasma pharmacokinetics of pyrimethamine were independent of dose. The percentage of the administered dose excreted in urine as pyrimethamine (1.3-3.5%) and 14C-radioactivity (21.7-29.1%) did not change with increasing dose. In contrast, the cumulative percentage of the dose excreted as 14C-radioactivity in faeces (16.7-22.8%) after the three highest doses 25, 50 and 75 mg kg-1 was significantly less than that seen with the lowest dose of 12.5 mg (50.3%). This suggests extensive biliary excretion of radioactivity, and that the capacity of this process may have been exceeded with the highest doses. Seven days after the administration of each of the three highest doses, a significantly greater percentage of [14C]pyrimethamine was localized in the soft tissues; i.e. heart, lung and kidney (7.8-13.8%), gut (5.4-9.4%) and particularly the liver (25.0-27.9%) when compared with the lowest dose of the drug (1.2, 1.0, 0.3% respectively). Following each dose, between 85 and 97% of the administered radioactivity was accounted for.(ABSTRACT TRUNCATED AT 250 WORDS)

High-performance liquid chromatographic assay of pyrimethamine, sulfadoxine and its N4-acetyl metabolite in serum and urine after ingestion of Suldox.

A sensitive and selective reversed-phase high-performance liquid chromatographic assay has been developed to determine the concentration of pyrimethamine, sulfadoxine and N4-acetylsulfadoxine in serum and urine after oral administration of the antimalarial remedy Suldox. Hitherto the literature describes no method being able to quantitate all three compounds in these fluids. The compounds are extracted successively from the same sample and subjected to liquid chromatography followed by ultraviolet detection (280 nm). Calibration curves were linear (r2 = 0.999; S.E.M. less than 3%; n = 10) in the range 0-300 micrograms/ml (sulfadoxine) and 0-1000 ng/ml (N4-acetylsulfadoxine and pyrimethamine). The limits of quantitation for the latter compounds were as low as about 5 ng/ml and 1 ng/ml, respectively. At therapeutic serum concentrations of 30 micrograms/ml (sulfadoxine), 350 ng/ml (N4-acetylsulfadoxine) and 120 ng/ml (pyrimethamine) an interassay reproducibility below 8% (relative standard deviation) was found for all three compounds. The assay was evaluated in a pilot study and proved convenient for pharmacokinetic studies in man following oral co-administration of pyrimethamine and sulfadoxine.

Highly sensitive and specific determination of mefloquine in biological fluids using gas chromatography mass spectrometry with selected ion monitoring.

A highly sensitive and specific assay for the determination of racemic erythro-alpha-(2-piperidyl)-2,8-bis(trifluoro-methyl)-4-quinoline-methanol in whole blood, plasma and urine has been developed. The method involves the extraction of the drug together with an internal standard, formation of the corresponding O-trimethylsilyl-N-trifluoroacetyl derivatives, gas chromatographic separation and mass spectrometric measurement of the peaks by selected ion monitoring. The method has a sensitivity of 1 ng ml-1 for plasma and 3 ng ml-1 for whole blood or urine. It has been applied to the analysis of mefloquine in plasma following an oral dose of 250 mg of the drug to healthy subjects. No interference was observed from the simultaneous administration of Fansidar.

Quantitative thin-layer chromatography of pyrimethamine and related diaminopyrimidines in body fluids and tissues.

Several 2,4-diaminopyrimidines which inhibit the enzyme dihydrofolate reductase are quantitated following extraction and separation on silica gel thin-layer chromatographic plates. These compounds are candidates for the treatment of brain tumors and meningeal leukemia, because they have the ability to cross the blood-brain barrier. The ultraviolet absorption of the pyrimidine ring at 275 nm is utilized to quantitate these compounds on thin-layer chromatographic plates with a scanning instrument. This method offers the advantages of speed, specificity, versatility and sensitivity, and has proven to be satisfactory for the measurement of as little as 10 ng/ml of these compounds in biological fluids.