Julius O. Soyinka

Pharmacokinetic interactions between ritonavir and quinine in healthy volunteers following concurrent administration.

AIMS To evaluate the pharmacokinetic interactions between ritonavir and quinine in healthy volunteers. METHODS Ten healthy volunteers were each given 600-mg single oral doses of quinine alone, ritonavir alone (200 mg every 12 h for 9 days), and quinine in combination with ritonavir, in a three-period pharmacokinetic nonrandomized sequential design study. Quinine was co-administered with the 15th dose of ritonavir. Blood samples collected at predetermined time intervals were analysed for ritonavir, quinine and its major metabolite, 3-hydroxyquinine, using a validated high-performance liquid chromatography method. RESULTS Concurrent ritonavir administration resulted in about fourfold increases in both the C(max) and AUC(T)[C(max) 2.79 +/- 0.22 vs. 10.72 +/- 0.32 mg l(-1), 95% confidence interval (CI) 7.81, 8.04; AUC 50.06 +/- 2.52 vs. 220.47 +/- 6.68 mg h(-1) l(-1), 95% CI 166.3, 175.3], a significant increase (P < 0.01) in the elimination half-life (11.15 +/- 0.80 vs. 13.37 +/- 0.33 h, 95% CI 1.64, 2.77) and about a 4.5-fold decrease in CL/F (12.01 +/- 0.61 vs. 2.71 +/- 0.09 l h(-1)) of quinine. Also, with ritonavir, there was a pronounced reduction of AUC(metabolite)/AUC(unchanged drug) ratio of quinine (1.35 +/- 0.10 vs. 0.13 +/- 0.02) along with a marked decrease in C(max) (1.80 +/- 0.12 vs. 0.96 +/- 0.09 mg l(-1)) and AUC(0-48h) (62.80 +/- 6.30 vs. 25.61 +/- 2.44 mg h(-1) l(-1)) of the metabolite. Similarly, quinine caused modest but significant increases (P < 0.01) in the C(max), AUC and elimination T((1/2)) of ritonavir. CONCLUSIONS Downward dosage adjustment of quinine appears necessary when concurrently administered with ritonavir.

Effects of concurrent administration of nevirapine on the disposition of quinine in healthy volunteers

Objectives Nevirapine and quinine are likely to be administered concurrently in the treatment of patients with HIV and malaria. Both drugs are metabolised to a significant extent by cytochrome P450 (CYP)3A4 and nevirapine is also an inducer of this enzyme. This study therefore evaluated the effect of nevirapine on the pharmacokinetics of quinine.

Alteration of pharmacokinetics of proguanil in healthy volunteers following concurrent administration of efavirenz.

Efavirenz and proguanil are likely to be administered concurrently for the treatment of patients with HIV and malaria. The metabolism of proguanil is mediated principally by CYP2C19 while efavirenz is known to inhibit this enzyme. This study therefore investigated the effect of efavirenz on proguanil disposition. Fifteen healthy volunteers were each given 300 mg single oral doses of proguanil alone or with the 9th dose of efavirenz (400mg daily for 11 days) in a crossover fashion. Blood samples were collected at pre-determined time intervals and analyzed for proguanil and its major metabolite, cycloguanil, using a validated HPLC method. Co-administration of proguanil and efavirenz resulted in significant increases (p < 0.05) in C(max), T(max), AUC(T) and elimination half-life (T(1/2beta)) of proguanil compared with values for proguanil alone [C(max): 2.55+/-0.24 mg/l vs 3.75+/-0.48 mg/l; T(max): 2.80+/-0.99 h vs 4.80+/-0.99 h; AUC(T): 45.58+/-12.75 mgh/l vs 97.00+/-23.33 mgh/l; T(1/2beta): 16.50+/-4.55 h vs 23.24+/-4.08 h]. Also, efavirenz caused a pronounced decrease in the AUC(metabolite)/AUC(unchanged drug) ratio of proguanil along with a significant decrease (p < 0.05) in C(max) and AUC of the metabolite. These results indicate that efavirenz significantly alters the pharmacokinetics of proguanil. These suggest that the protection against malaria by proguanil may be decreased when the drug is co-administered with efavirenz and the antimalarial efficacy is dependent on cycloguanil plasma levels.

Development, validation and clinical application of a novel method for the quantification of efavirenz in dried breast milk spots using LC-MS/MS

OBJECTIVES This manuscript describes the development, validation and clinical application of a novel method for the quantification of the antiretroviral drug efavirenz in dried breast milk spots using LC-MS. METHODS Dried breast milk spots were prepared by spotting 30 μL of human breast milk on each circle of Whatman 903 Protein Saver cards. Chromatographic separation was achieved on a reverse-phase C18 column with 1 mM ammonium acetate in water/acetonitrile using a solvent gradient at a flow rate of 400 μL/min and detection was by TSQ Quantum Access triple quadrupole mass spectrometer equipped with a heated electrospray ionization source. The method was applied to characterize the breast milk pharmacokinetic profile of efavirenz in HIV-positive nursing mothers receiving regimens containing 600 mg of efavirenz once daily. RESULTS The assay was validated over the concentration range 50-7500 ng/mL. Accuracy ranged between 95.2% and 102.5% and precision ranged between 1.05% and 9.53%. The average recovery of efavirenz from dried breast milk spots was 106.4% and the matrix effect was 8.14%. Stability of efavirenz in dried breast milk spots and processed samples at room temperature, -40°C and -80°C was demonstrated. In the pharmacokinetic study, the mean (SD) AUC0-24, Cmax and Cmin of efavirenz in breast milk were 59,620 ng·h/mL (17,440), 4527 ng/mL (1767) and 1261 ng/mL (755.9), respectively. The mean (range) milk-to-plasma concentration ratio over the dosing interval was 0.78 (0.57-1.26). CONCLUSIONS The dried breast milk spot method is simple, robust, accurate and precise, and can be used in settings with limited resources.

Validation and clinical application of a method to quantify nevirapine in dried blood spots and dried breast-milk spots

OBJECTIVES The validation and clinical application of an LC-MS/MS method for the quantification of nevirapine in dried blood spots (DBS) and dried breast-milk spots (DBMS) are presented. METHODS DBS and DBMS were prepared from 50 and 30 μL of nevirapine-spiked whole blood and human breast milk, respectively. Chromatographic separation was achieved on a reverse-phase C18 column with 0.1% formic acid in water/acetonitrile using a solvent gradient programme at a flow rate of 400 μL/min, and detection was by a TSQ Quantum Access triple quadrupole mass spectrometer. The clinical application was evaluated in HIV-positive nursing mothers and their breastfed infants. RESULTS The assay was validated over the concentration range 50-10,000 ng/mL. Accuracy ranged from 93.3% to 113.4% and precision ranged from 1.9% to 12.0%. The mean (percentage coefficient of variation) recovery of nevirapine from DBS and DBMS was ≥ 70.7% (≤ 8.2) and the matrix effect was ≤ 1.04 (≤ 6.1). Nevirapine was stable in DBS and DBMS for ≥ 15 months at room temperature and -80°C. Mean (SD) AUC0-12, Cmax and Cmin in maternal plasma versus breast milk were 57,808 ng · h/mL (24,315) versus 55,817 ng · h/mL (22,368), 6140 ng/mL (2605) versus 5231 ng/mL (2215) and 4334 ng/mL (1880) versus 4342 ng/mL (2245), respectively. The milk-to-plasma concentration ratio over the dosing interval was 0.94 (0.15). Infant plasma concentrations 2 and 8 h after maternal dosing were 580.6 ng/mL (464.7-1607) and 584.1 ng/mL (381.5-1570), respectively. CONCLUSIONS These methods further extend opportunities for conducting clinical pharmacokinetic studies in nursing mother-infant pairs, especially in resource-limited settings.

Effect of hypoxia on metabolic rate, core body temperature, and c-fos expression in the naked mole rat.

Recent investigations of hypoxia physiology in the naked mole rat have opened up an interesting line of research into the basic physiological and genomic alterations that accompany hypoxia survival. The extent to which such findings connect the effect of hypoxia to metabolic rate (O2 consumption), core body temperature (Tb), and transcripts encoding the immediate early gene product (such as c‐fos) under a constant ambient temperature (Ta) is not well known. We investigated this issue in the current study. Our first sets of experiments measured Tb and metabolic rates during exposure of naked mole rats to hypoxia over a constant Ta. Hypoxia significantly decreased metabolic rates in the naked mole rat. Although core Tb also decreased during hypoxia, the effect of hypoxia in suppressing core Tb was not significant. The second series of experiments revealed that c‐fos protein and mRNA expression in the hippocampus neurons (CA1) increased in naked mole rats that were repeatedly exposed to 3% O2 for 60 min per day for 5 days when compared to normoxia. Our findings provide evidence for the up‐regulation of c‐fos and suppression of metabolic rate in hypoxia tolerating naked mole rats under constant ambient temperature. Metabolic suppression and c‐fos upregulation constitute part of the physiological complex associated with adaptation to hypoxia.

Simultaneous liquid chromatographic analysis of ritonavir, quinine and 3-hydroxyquinine in human plasma.

In regions with high prevalence of HIV and malaria, co-infection of both diseases is common; hence, there is a high possibility of concurrent administration of antiretroviral and antimalarial drugs. This study describes a new ion-pair reversed-phase high-performance liquid chromatographic (HPLC) method for simultaneous determinations of ritonavir (RTV), quinine (QN), and its major metabolite, 3-hydroxyquinine (3-HQN), in human plasma. Following a simple extraction with diethyl-ether under alkaline conditions, chromatographic separation was achieved on a 5-mum particle size C-18 column (200 mm x 4.6mm I.D.) using a mobile phase consisting of methanol:acetonitrile:0.02 M potassium dihydrogen phosphate (15:10:75) containing 75 mmol/L perchloric acid (pH 2.8). Retention times for RTV, 3-HQN, QN and the internal standard were 2.8, 4.0, 7.0 and 12 min, respectively. The limits of detection and validated lower limits of quantitation were 10 and 12.5 ng/ml for RTV while the corresponding values were 5 and 70 ng/ml for both QN and 3-HQN, respectively. The new HPLC method is simple, rapid, selective, reproducible and cost-effective. As demonstrated in three volunteers, it will facilitate the conducting of simultaneous therapeutic monitoring of quinine and ritonavir in patients concurrently receiving both drugs.

Molecular and Physiological Factors of Neuroprotection in Hypoxia-tolerant Models: Pharmacological Clues for the Treatment of Stroke

The naked mole-rat possesses several unique physiological and molecular features that underlie their remarkably and exceptional resistance to tissue hypoxia. Elevated pattern of Epo, an erythropoietin (Epo) factor; c-fos; vascular endothelial growth factor (VEGF); and hypoxia-inducible factors (HIF-1α) contribute to the adaptive strategy to cope with hypoxic stress. Moreover, the naked mole-rat has a lower metabolic rate than any other eutherian mammal of comparable size that has been studied. The ability to actively reduce metabolic rate represents a strategy widely used in the face of decreased tissue oxygen availability. Understanding the different molecular and physiological factors that induce metabolic suppression could guide the development of pharmacological agents for the clinical management of stroke patient.

Alteration of the Disposition of Quinine in Healthy Volunteers After Concurrent Ciprofloxacin Administration.

This study evaluated the effects of concurrent ciprofloxacin administration on the disposition of quinine in healthy volunteers. Quinine (600-mg single dose) was administered either alone or with the 11th dose of ciprofloxacin (500 mg every 12 hours for 7 days) to 15 healthy volunteers in a crossover fashion. Blood samples collected at predetermined time intervals were analyzed for quinine and its major metabolite, 3-hydroxquinine, using a validated high-performance liquid chromatographic method. Administration of quinine plus ciprofloxacin resulted in significant increases (P < 0.05) in the total area under the concentration–time curve, maximum plasma concentration (Cmax), and terminal elimination half-life (T1/2b) of quinine compared with values with quinine dosing alone (AUC: 27.93 ± 8.04 vs. 41.62 ± 13.98 h·mg/L; Cmax: 1.37 ± 0.24 vs. 1.64 ± 0.38 mg/L; T1/2b: 16.28 ± 2.66 vs. 21.43 ± 3.22 hours), whereas the oral plasma clearance markedly decreased (23.17 ± 6.49 vs. 16.00 ± 5.27 L/h). In the presence of ciprofloxacin, there was a pronounced decrease in the ratio of AUC (metabolite)/AUC (unchanged drug) and highly significant decreases in Cmax and AUC of the metabolite (P < 0.05). Ciprofloxacin may increase the adverse effects of concomitantly administered quinine, which can have serious consequences on the patient. Thus, a downward dosage adjustment of quinine seems to be necessary when concurrently administered with ciprofloxacin.

Effect of dehusked Garcinia kola seeds on the overall pharmacokinetics of quinine in healthy Nigerian volunteers.

We investigated the effect of concurrent ingestion of Garcinia kola seed on the pharmacokinetics of quinine. In a randomized crossover study, 24 healthy Nigerian volunteers were assigned into 2 groups (A and B; n = 12 per group) on the basis of G. kola dose orally ingested. Each subject received 600 mg quinine sulfate before and after ingesting 12.5 g of G. kola once daily for 7 days (group A) or 12.5 g twice daily for 6 days and once on the seventh day (group B). Blood samples were collected and analyzed for plasma quinine and its metabolite (3‐hydroxyquinine) using a validated high performance liquid chromatography method. Concurrent administration of quinine with G. kola reduced quinine tmax by 48% (group A), mean Cmax by 19% and 26% in groups A and B, respectively, and slight reduction in mean AUC0–∞ of quinine in both groups. 3‐hydroxyquinine Cmax also reduced by 29% and 32%; AUC0–∞ by 13% and 9%, respectively. The point estimates of the T/R ratio of the geometric means for all Cmax obtained and only the AUC0–∞ at a higher dose of G. kola were outside the 80%–125% bioequivalence range. In conclusion, an herb–drug interaction was noted with concurrent quinine and G. kola administration.