Festus A. Ogunbona

High-performance liquid chromatographic method for the determination of drotaverine in human plasma and urine

A simple and sensitive HPLC method for the determination of drotaverine in human plasma and urine has been developed. Alkalinized plasma or urine was extracted with organic solvent and the basic components in the organic phase were back-extracted into 0.1 M HCl. An aliquot of the aqueous layer was injected onto the column and the eluent was monitored at 254 nm. Separation was performed on a C18-column with 0.02 M sodium dihydrogen phosphate-methanol (30:70, v/v) containing perchlorate ion at pH 3.2 as mobile phase. Drotaverine was well resolved from the plasma constituents and internal standard. An excellent linearity was observed between peak-height ratios and plasma concentrations and the intra- and inter-assay coefficients of variation were always < 10%. The lowest limit of detection (signal-to-noise ratio 3:1) was 6 ng/ml. The method is suitable for therapeutic monitoring and pharmacokinetic studies of drotaverine in humans as well as in animal models.

Pharmacokinetics of quinine in African patients with acute falciparum malaria.

The pharmacokinetics of quinine were studied in six Nigerian patients during acute uncomplicated falciparum malaria and convalescent periods. An oral dose of 10 mg/kg quinine dihydrochloride administered 8‐hourly for 7 days gave parasite and fever clearance times of 36.0 ± 16.6 h and 18.0 ± 6.4 h, respectively. From the individual quinine plasma profiles the mean plasma concentration of quinine at the time of parasite clearance was estimated as 4.5 ± 1.1 μg/ml. Plasma quinine levels during malaria rose rapidly reaching a peak around the second and third days and declining thereafter as patients improved clinically. In acute malaria plasma quinine levels were more than two-fold higher than in convalescence; the mean AUC(0-12) in malaria was 37.9 ± 14.7 μg.h/ml compared to 17.9 ± 8.5μg.h/ml in convalescence. The apparent oral clearance (CL/F) and volume of distribution (Vd/F) duri ng the acute phase of the malaria (1.9 ± 0.7 ml/min/kg and 1.8 ± 0.9 l/kg, respectively) were significantly lower than in convalescence (4.5 ± 2.1 ml/min/kg and 4.2 ± 3.2 l/kg). The present data suggest that malaria parasites in African patients are still very sensitive to quinine and that the current dosage of quinine is effective for the treatment of acute falciparum malaria in African patients without augmenting therapy with any other drug such as tetracycline or sulphadoxine-pyrimethamine. It also confirms that malaria significantly alters the pharmacokinetics of quinine in humans.

Column liquid chromatographic analysis of quinine in human plasma, saliva and urine.

A new simple, selective and reproducible high-performance liquid chromatographic method for the determination of quinine in plasma, saliva and urine is described. The ion-pair method was carried out on a reversed-phase C18 column, using perchlorate ion as the counter ion and ultraviolet detection at 254 nm. Quinine was well resolved from its major metabolite, 3-hydroxyquinine, and the internal standard, primaquine. The limit of detection was 10 ng/ml and the recovery was greater than 90% from the three biological fluids.

Pharmacokinetic aspects of chloroquine-induced pruritus: influence of dose and evidence for varied extent of metabolism of the drug

The significance of a pharmacokinetics basis in chloroquine (CQ)-induced pruritus was investigated by determining the disposition of the drug in two groups of volunteers; pruritus positive and pruritus negative. Single oral dose of 600 mg CQ was administered to each of 36 volunteers, 18 for each of the two groups. After a washout period of 9 months, 150 mg single oral dose of the drug was given to 12 of the same volunteers, six each from the two groups. Blood and urine samples were collected at predetermined times following administration of each dose. Concentrations of CQ and its major metabolite, desethylchloroquine (CQM), were measured in plasma and urine using an established HPLC method. Results showed that the ratio, AUC (CQ)/AUC (CQM), as well as AUC(0-48 h) and 24-h urinary CQ excretion were all significantly higher (P<0.05) in pruritus-positive compared to pruritus-negative volunteers, following administration of the 600-mg CQ dose. Also, urinary drug-metabolite ratios monitored over 0-48 h postdose were markedly higher in the pruritus positive group. However, after administration of the 150-mg dose, 24-h urinary CQ collection and urinary drug-metabolite ratios were highly comparable between the two groups (P>0.1). This study indicates that there might be a decreased metabolism of CQ in subjects susceptible to CQ-induced pruritus following ingestion of a therapeutic dose. It also suggests that the extent of metabolism of CQ in this group may be influenced by the dose of the drug. Comparatively higher CQ levels in pruritus susceptible subjects may possibly be responsible for the pruritus experienced by such individuals when given therapeutic regimen.

Pharmacokinetics and bioavailability of drotaverine in humans

SummaryThe pharmacokinetics and bioavailability of drotaverine was studied in 10 healthy volunteers after administration of single 80 mg oral and intravenous doses of the HCl salt of the drug, in a crossover fashion. Plasma and urine samples were analyzed for the unchanged drug by HPLC. The pharmacokinetic parameters, such as elimination half-life, plasma clearance, renal clearance and apparent volume of distribution, were not influenced by the route of drug administration. The drug was mainly eliminated by non-renal routes since renal clearance accounted for only 0.31±0.13% of the total plasma clearance. The absolute bioavailability was variable and ranged from 24.5–91% with a mean of 58.2±18.2% (mean ±SD). It is suggested that the high variation in the bioavailability of drotaverine HCl after oral administration may result in significant interindividual differences in therapeutic response.

Evidence for increased metabolism of chloroquine during the early third trimester of human pregnancy

Objective  To examine the possibility of a different extent of chloroquine (CQ) metabolism in human pregnancy by determining blood level profiles of the drug and its major metabolite, desethylchloroquine (CQM).

Sensitive high performance liquid chromatographic method for the determination of proguanil and its metabolites, cycloguanil and 4-chlorophenylbiguanide in biological fluids

A new simple, sensitive, cost-effective and reproducible high performance liquid chromatographic (HPLC) method for the determination of proguanil (PG) and its metabolites, cycloguanil (CG) and 4chlorophenylbiguanide (4-CPB) in urine and plasma is described. The extraction procedure is a simple three-step process that has eliminated the need for costly extraction and evaporation equipment. The mobile phase consisted largely of buffer, making the method cheap to run. The calibration plots were linear over the concentration range up to 3.0 µg/ml PG, CG and 4-CPB in urine and concentration range up to 1000 ng/ml in plasma. The correlation coefficients (r) were of the order of 0.99 and above for PG and 4-CPB and 0.98 for CG. The ion pair method was carried out on a 5 µ reversed-phase C-18 column, using perchlorate ion as the counter ion and ultra violet detection at 254 nm. The method was reproducible with coefficient of variation for PG, CG and 4-CPB, being less than 10% in urine and plasma. PG was well resolved from its metabolites, CG and 4-CPB, and the internal standard, pyrimethamine. The limit of detection of PG was 10 ng/ml and the recovery was greater than 90% in urine and plasma. The analytical method therefore, exhibits good precision and sensitivity and is one of the few methods that can detect PG and the two metabolites CG and 4-CPB. The analytical method developed in this study was used to determine PG bioavailability after rectal administration in humans.

Lack of pharmacokinetic interaction between chloroquine and imipramine.

The pharmacokinetic interaction between chloroquine (CQ) and imipramine was investigated in six healthy volunteers who received 300 mg of CQ, 50 mg of imipramine, and combined doses of both drugs in a randomized, crossover design. Blood and urine samples were collected at predetermined time intervals and were analyzed for the drugs and their metabolites by high-performance liquid chromatography methods. The results revealed that the plasma concentrations of CQ and its pharmacokinetic parameters were not significantly altered when CQ was coadministered with imipramine (p > 0.1). The plasma concentration-time profiles and the disposition characteristics of imipramine also were not altered after coadministration with CQ. The results suggest that there appears to be no pharmacokinetic interaction between CQ and imipramine given as single oral doses.

Relationship between plasma and saliva quinine levels in humans.

The relationship between saliva and plasma levels of quinine was studied in four healthy volunteers. After a single oral dose of quinine sulfate (600 mg) to the volunteers, quinine was determined in both saliva and plasma simultaneously over a 48-h period by an ion pair reverse-phase high performance liquid chromatography method. The tmax (4.3 +/- 0.5 h) and elimination half-life (11.8 +/- 2.9 h) of quinine derived from saliva levels were comparable with those obtained from plasma levels (tmax = 2.8 +/- 0.2 h, t1/2 = 12.9 +/- 2.3 h). A significant correlation existed between the plasma and saliva concentrations of the drug (r = 0.93, n = 20, p < 0.001). The mean saliva/plasma quinine concentration ratio was 0.24 +/- 0.02. The results suggest that quinine is passively secreted into saliva and that saliva level determination may be useful as a noninvasive method in the evaluation of pharmacokinetic parameters and therapeutic drug monitoring of quinine.

Dose linearity of quinine in healthy human subjects

Abstract The pharmacokinetics of quinine were assessed in seven healthy volunteers after administration of single oral doses of 250, 500, 750 and 1000 mg quinine in a randomized cross-over design. Serial blood samples were collected at predetermined times before and after the doses. Plasma quinine concentrations were assayed by a reversed-phase HPLC method with UV detection and the data were evaluated by non-compartmental methods to determine pharmacokinetic parameters. The mean elimination half-lives t 1 2 ) of quinine, which did not vary with the dose, were 10.1 ± 4.3, 12.3 ± 1.6, 9.0 ± 2.8 and 13.4 ± 7.0 h, respectively after the four doses. The peak plasma levels ( C max ) and area under the plasma level versus time curve (AUC) data showed dose-proportional response. The time to peak plasma concentration ( t max ), oral clearance ( CL F ) and apparent volume of distribution ( V d F ) were all similar regardless of the administered dose ( P > 0.05). There were minor side effects which increased with increase in dose but the effects were all reversible. These findings suggest that quinine disposition is linear over the dose range studied.