No other drugs or alcohol was allowed

No other drugs or alcohol was allowed to be taken throughout the duration of the study. Amodiaquine dihydrochloride and desethylamodiaquine dihydrochloride were obtained from Parke-Davis, USA and quinidine from BDH Laboratory Supplies, Poole, England. Amodiaquine dihydrochloride tablets (Parke-Davis, USA) were purchased from a retail pharmacy in Nigeria. HPLC grade acetonitrile and methanol, and analytical grade diethyl ether, perchloric acid, sodium hydroxide and hydrochloric acid were purchased from Sigma (Sigma–Aldrich chemical company, Germany). A Mersham Pharmacia Biotech IP-900 liquid chromatography (USA) (AKTA) fitted with a variable UV detector (model P-900)

was used for the analysis. The stationary phase was a reversed-phase C18 column Eclipse-XDB-C18–3.5 μm (200 × 4.6 mm I.D.). The solvent system for HPLC consisted of acetonitrile: 0.02 M potassium dihydrogen phosphate (10:90). The pH of the mobile phase was adjusted to 4.0 with orthophosphoric

acid. The mobile phase was pumped through the Transmembrane Transporters modulator column at a flow rate of 1.0 ml/min. The experiments were performed at ambient temperature. The method was a slight modification of Gitau et al (2004).10 Whirl mixer (Fissions), precisions pipettes (MLA), table centrifuge (Gallenkamp) and digital sonicator (Gallenkamp) were used for the extraction procedure. To 1 ml of plasma placed in a 15-ml screw capped extraction tube were added 20 μL of 500 μg/ml quinidine solution (internal standard) and 2 ml of acetonitrile before mixing for about 15 s, followed by mechanical tumbling for 15 min. After centrifuging for 10 min at 3000 g, the

liquid phase was transferred to a clean tube, to which was added 2 ml of ammonia. The mixture was then extracted by mechanical tumbling for 15 min, with 2 × 5 ml of diethyl ether. After centrifugation and separation, the combined organic phases were evaporated to dryness and the residue was reconstituted in 100 μL of methanol while a 50 μL aliquot was injected onto the HPLC column. Calibration curve based on peak area ratio was prepared by spiking drug-free Electron transport chain plasma with standard solutions of amodiaquine and monodesethylamodiaquine to give concentration ranges of 2–30 ng/ml and 20–300 ng/ml respectively. The samples were taken through the extraction procedure described above. The pharmacokinetic (PK) parameters for amodiaquine and monodesethylamodiaquine were calculated with the computer program WinNonLin (version 1.5). The data were analyzed using noncompartmental analysis. The parameters that could be established were as follows: time point of maximum observed concentration in plasma (Tmax); concentration in plasma corresponding to Tmax (Cmax); terminal half-life (T1/2); area under the plasma concentration versus time (C–t) curve (AUCT).

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