Combination of quinine, quinidine and cinchonine for the treatment of acute falciparum malaria: correlation with the susceptibility of Plasmodium falciparum to the cinchona alkaloids in vitro.

Thirteen patients with acute symptomatic uncomplicated falciparum malaria were enrolled in an open, randomized, phase 2, dose-finding clinical trial of a fixed dosage combination of quinine, quinidine and cinchonine (LA40221, Sanofi Recherche, France), which contained equal parts of the 3 alkaloids and was administered orally every 8 h in doses of 400 mg (7 patients) or 500 mg (6 patients) for 7 d. There was prompt clearance of parasitaemia and fever in all patients. The mean clearance times (+/- standard deviation) of parasitaemia, fever and other symptoms were 29 +/- 11.0 h, 10.7 +/- 4.1 h and 14.9 +/- 9.7 h respectively for the 400 mg dose group, and 35 +/- 20.0 h, 16 +/- 7.0 h and 17.6 +/- 8.7 h respectively for the 500 mg dose group. There was no recrudescence of parasitaemia during the 28 d observation period. Minor gastrointestinal side effects occurred in 2 patients, but there was no major side effect. Haematological, biochemical and other measurements were not adversely altered by treatment. QTc prolongation occurred in 3 patients--2 from the 400 mg and 1 from the 500 mg dose group. Testing in vitro against Plasmodium falciparum isolates from 47 patients (including the 13 patients enrolled in the trial) of the combination and its individual components suggested that the relative potencies in vitro, in decreasing order, were quinidine, LA40221, cinchonine and quinine. The minimum inhibitory concentrations were 0.32, 0.64, 0.64 and 1.28 mumol/litre of blood-medium mixture respectively, and the 50% inhibitory concentrations were 0.083, 0.11, 0.12 and 0.22 mumol/litre of blood-medium mixture. The respective 99% inhibitory concentrations were 0.27, 0.45, 0.50 and 1.20 mumol/litre of blood-medium mixture.

Assessment of a fixed-dosage combination of atenolol and chlorthalidone (Tenoretic) in hypertensive Nigerians.

The antihypertensive effect of a fixed dosage combination of the cardioselective beta-adrenoceptor blocker, atenolol, and the oral thiazide-like diuretic, chlorthalidone (Tenoretic) was studied in 24 hypertensive Nigerians in a double-blind, cross-over comparison with three other treatments. These were atenolol alone, 100 mg daily, chlorthalidone alone, 25 mg daily, and atenolol (100 mg) plus chlorthalidone (25 mg) daily taken as separate formulations. Tenoretic was taken as a once-daily tablet containing 100 mg atenolol plus 25 mg chlorthalidone. The order of administration of the drugs was randomized. Each drug was taken for 4 weeks. The results showed that atenolol and chlorthalidone lowered blood pressure to the same extent. Combination of the two drugs whether taken separately or in fixed-dosage combination was better than either product singly. The drugs were well tolerated.

Sensitivity of Plasmodium falciparum to mefloquine-sulphadoxine-pyrimethamine (Fansimef) in vivo and to mefloquine alone in vitro in Nigeria.

In Nigeria chloroquine remains the drug of choice for the treatment of falciparum malaria, since chloroquine resistance is not yet a problem. Nevertheless, in view of the rapid spread of multi-resistant Plasmodium falciparum in Africa it is desirable to test alternative drugs for efficacy and safety. To this end, we undertook a comparative controlled trial of the new triple combination, mefloquine-sulphadoxine-pyrimethamine (MSP, Fansimef) with chloroquine in a group of Nigerian children with symptomatic falciparum malaria. Our results showed that Fansimef was an effective blood schizontocide against the Nigerian strain of P. falciparum and was well tolerated. In particular, sinus bradycardia, which was frequently observed with Fanismef in the trials conducted in Zambia, was not seen in any of the Nigerian patients. In vitro sensitivity tests done on 26 P. falciparum isolates showed that all isolates were susceptible to complete inhibition by mefloquine, but the minimum concentration which produced complete inhibition in some isolates was higher than expected for fully sensitive parasites.

Sensitivity of Plasmodium falciparum to chloroquine, amodiaquine and mefloquine in Ibadan, Nigeria.

The schizontocidal effect of chloroquine was compared to that of amodiaquine in vivo and mefloquine in vitro. In the in-vivo study, 32 patients were randomly given chloroquine whilst 29 received amodiaquine. The mean parasite clearance time was 2.5 days for chloroquine and 2.4 days for amodiaquine. These times were not significantly different. The cure rate in both groups up to day 14 was 100%. In the in-vitro study, three isolates of Plasmodium falciparum were compared for their sensitivity to chloroquine and mefloquine. In all three isolates schizogony was inhibited at a concentration of 0.8 x 10(-6) mol/l of either drug. It was concluded that chloroquine is still an effective schizontocide and should remain the drug of choice for the treatment of P. falciparum in the Ibadan area.

Comparison of the relative in vitro activity of chloroquine and amodiaquine against chloroquine-sensitive strains of P. falciparum.

The activities of chloroquine and amodiaquine against a sensitive strain of Plasmodium falciparum found in children in Ibadan were compared using an in vitro technique. The criterion for drug activity was the inhibition of maturation of the parasites. Three sets of experiments were performed with each of the two drugs. The minimum concentration of chloroquine causing 90% inhibition of maturation was 25 nmol as compared with 12 nmol for amodiaquine. This suggests a two-fold increase in activity of amodiaquine when compared with chloroquine against sensitive strains of P. falciparum. The implication is that amodiaquine is a much more potent tool in malaria chemotherapy than the erstwhile overused chloroquine.

The relationship of the pharmacokinetics of chloroquine to dose in the rabbit.

Four albino rabbits were treated with 4 different doses of chloroquine phosphate (30-50 mg kg-1) given intragastrically and 10 others were given the hydrochloride (2.5-12.5 mg kg-1 i.v.). The i.v. doses were given as bolus into the median ear vein over 5-8 min. Samples (3-5 mL) of whole blood were subsequently collected at intervals for up to 6 weeks and analysed by HPLC. From the results, log concentration-time curves were drawn and the i.v. data fitted by computer to 3-compartment (8 rabbits) or 2-compartment curves (2 rabbits). The area under the curve (AUC) and half-lives were calculated for the different doses. A plot of AUC versus dose yielded a straight line but the half-lives showed wide inter-individual variation from the same doses.

Influence of route of administration on the pharmaco-kinetics of chloroquine and desethylchloroquine.

The pharmacokinetics of chloroquine following a single oral dose of 600 mg or an intramuscular injection of 200 mg of the drug was studied in seven healthy adult Africans. Each subject received chloroquine by both routes, with an interval of at least 4 months between them. Intramuscular injection led to rapid absorption of chloroquine, which attained a maximum concentration in plasma after 15 minutes and occasionally reached toxic levels; plasma levels fell below therapeutically useful concentrations 2-4 hours after administration. In contrast, oral administration of chloroquine produced therapeutic levels of the drug within 30 minutes and were maintained for up to 3 days. Peak levels in plasma were not high enough to produce adverse reactions. The terminal half-life and renal clearance time of chloroquine were not influenced by route of administration.

Comparison of the pharmacokinetics of chloroquine after single intravenous and intramuscular administration in healthy Africans.

The pharmacokinetics of chloroquine were studied after intramuscular and intravenous administration of the drug to healthy African adults. Chloroquine was analysed in plasma using an h.p.l.c. method and pharmacokinetic parameters were derived from the concentration-time data using a non-linear computer programme. A two-compartment open model was assumed. Chloroquine was rapidly absorbed from an intramuscular site, producing a plasma concentration-time profile similar to that obtained after a 15 min i.v. infusion of a comparable dose. The pharmacokinetics of chloroquine after i.m. and i.v. administration were characterised by a long half-life and a very large volume of distribution. There was no significant difference between the values of each parameter obtained from the different routes. It is suggested that the high Cmax obtained after i.m. and i.v. administration of chloroquine might contribute to its toxicity when these routes are used in treatment.

In vitro assessment of the antimalarial activity of chloroquine and its major metabolites.

A quantitative assessment of the antimalarial activity of chloroquine and its two major metabolites, desethylchloroquine (DEC) and bis-desethylchloroquine (bis-DEC), was made using a semi-automated microdilution technique. Two isolates of Plasmodium falciparum were used: the multi-drug resistant Vietnam Smith LA 137 strain and the chloroquine-sensitive Camp LA 137 strain. Mefloquine served as the standard for the Vietnam Smith strain and chloroquine for the Camp strain. Chloroquine and DEC demonstrated nearly equivalent activities in their inhibition of the growth of the chloroquine-sensitive Camp strain. Bis-DEC was less active since its ID50 was more than twice that of chloroquine. Against the chloroquine-resistant Vietnam Smith strain, DEC showed a three-fold loss of activity and bis-DEC showed no activity at concentrations as high as 340 ng ml-1. A combination of chloroquine and DEC showed an additive effect against both the Vietnam Smith and Camp strains.

Pharmacokinetics of chloroquine diphosphate in the dog.

Chloroquine diphosphate was administered i.v. and orally to seven male beagle dogs. Approximately 2 mg/kg was administered i.v. and 4 weeks later a single 150-mg (tablet) dose was administered orally. Blood sampling was carried out for 28 and 42 days, respectively, and whole blood drug levels were assayed by fluorometry. After i.v. injection, the chloroquine blood concentration-time profile exhibited a biexponential decay. The mean terminal T 1/2 was 12.6 days using i.v. data alone and 14.5 days with simultaneous fitting of oral and i.v. data. Pharmacokinetic parameters calculated using model-independent methods showed good agreement with model-dependent methods. The model-independent value for blood clearance was 2.67 liters/kg/day. A mean Vdss of 53.3 liters/kg indicates that the drug is widely distributed to tissues. Using a specific thin-layer chromatographic method, chloroquine and its major metabolite, desethylchloroquine, could be detected in blood for 42 days after oral chloroquine administration. These data suggest a long T 1/2 for the metabolite, as well as the parent drug. Chloroquine, desethylchloroquine and bisdesethylchloroquine were tested for in vitro activity against clinically derived chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum. Against chloroquine-sensitive P. falciparum, desethylchloroquine was as active as chloroquine, whereas bisdesethylchloroquine was less active. Against a chloroquine-resistant strain, desethylchloroquine was less active than chloroquine and bisdesethylchloroquine possessed no detectable activity.

A micro-modification for quantification of chloroquine in whole blood by fluorimetric assay.

The use of whole blood in fluorimetric assays for chloroquine is discussed. Since whole blood contains a much higher concentration of chloroquine than plasma (Fitch, 1969), such use allows for a longer period of sampling following a single oral dose of chloroquine. Chloroquine can be reproducibly quantified (coefficient of variation: 5%) from samples collected for up to 4-6 weeks after a single oral dose. This prolonged sampling provides for a more complete characterization of the true terminal slope of the chloroquine concentration-time curve. The usual fluorimetric methods of assay (Brodie et al., 1947; McChesney, Banks & McAuliff, 1962; Schulman & Young, 1974; Vogel & Konigk, 1975) do not differentiate very accurately concentrations of chloroquine below 50 ng/ml (coefficient of variation 20%). This micro-modification enables the determination of chloroquine concentrations below 50 ng/ml with a degree of accuracy much better (coefficient of variation 5%) than that of the usual fluorimetric methods.

Comparative bio-availability characteristics of different brands of chloroquine available in Nigeria.

The disintegration, dissolution and bio-availability characteristics of six of the most popular brands of chloroquine used in Nigeria were determined in order to test the hypothesis that there are no significant differences among the different brands. The disintegration times of all the six brands ranged from 8.9 to 40.4 min while the dissolution times ranged from 17.5 to 60 min. All passed the U.S. Pharmacopoiea (USP) XX disintegration test. Bio-availability studies done on two brands, Avloclor (ICI) with the fastest dissolution rate and Pfizerquine (Pfizer) with the slowest dissolution rate, showed similar areas under the curve (AUC). Furthermore, their peak height concentration (Cmax) and time of peak height concentration (Tmax) did not show any significant differences. Consequently, statements about any of these six brands of cloroquine having a greater efficacy than the other may be pure conjecture.

Double-blind placebo substitution: withdrawal of fluphenazine decanoate in schizophrenic patients.

In a double-blind placebo substitution study, 27 chronic schizophrenic patients successfully treated for more than 2 years with fluphenazine decanoate were withdrawn from the drug. These patients showed a significantly higher relapse rate than the matched control group of 26 patients who continued to receive fluphenazine (56% versus 19%, p less than .001). This high rate of relapse is viewed as indicating the need for continued medication in most chronic schizophrenic patients.

The relative importance of genetic and environmental factors in hypertension in black subjects.

Essential hypertension is the most important cardiovascular disease in black subjects. The types of presentation, the pattern of organ involvement and the subsequent complications are similar in black races. The response (or lack of response) to different types of treatment are also alike in blacks when compared with caucasians. Striking racial differences are observed in the plasma and intracellular electrolytes, cation transmembrane transport, salt taste threshold, plasma renin activity and urinary kallikrein activity. The similarities within the black racial groups are very likely to be genetic, although the pattern of inheritance remains controversial. Differences, however, occur in the prevalence and severity of the disease among the black racial groups. That these differences are due partly to environmental causes can not be disputed because even within the same ethnic groups changing patterns are observed in the prevalence of hypertension, in the course of urbanization of rural communities, or on moving from a previously rural to an urban environment. Consequently, genetic factors may be the only important considerations in the severity of hypertension in black subjects.

Chloroquine sensitivity of Plasmodium falciparum in Ibadan, Nigeria: II. Correlation of in vitro with in vivo sensitivity.

Plasmodium falciparum malaria was treated in 82 children with 25 mg/kg chloroquine orally over three days. They were observed for 28 days during which blood films were examined periodically for malaria parasites. Asexual forms of P. falciparum, present in the blood films of all the patients before commencing treatment, disappeared rapidly and by the third day no parasites were seen in blood films from any of them. Among the patients observed for more than three days, blood films remained negative throughout the observation period. In vitro tests of sensitivity of blood samples from 10 patients showed chloroquine concentrations of 0.5 to 0.8 nmol/ml to inhibit completely maturation from ring forms to schizonts. This suggests that P. falciparum in the Ibadan area is probably still fully sensitive to chloroquine.

Chloroquine sensitivity of Plasmodium falciparum in Ibadan, Nigeria.

Thirty-five children with Plasmodium falciparum malaria were treated with 25 mg/kg chloroquine over three days and observed for seven days during which blood films were examined daily for malaria parasites. Asexual forms of P. falciparum which were present in the blood films of all the patients before commencing treatment disappeared rapidly from the blood so that by the third day no parasites were seen in the blood film. The blood films remained negative for the rest of the seven-day observation period. Plasma chloroquine determination in eight of the patients showed high blood levels during the first three days. The results do not confirm the suspicion of chloroquine-resistant P. falciparum in the area studied although RI level of resistance by WHO criteria was not excluded.

Comparative beta-adrenoreceptor-blocking effects and pharmacokinetics or propranolol and pindolol in hypertensive Africans.

1. The beta-adrenoreceptor-blocking effects of pindolol were compared with those of propranolol and a placebo in a double-blind cross-over trial involving nine hypertensive African patients. 2. Heart rate, systolic blood pressure and diastolic blood pressure were measured at rest and immediately after exercise before and at intervals up to 6 h after oral administration of the drugs. In addition, plasma pindolol and propranolol concentrations were determined at the same intervals. 3. Pindolol diminished systolic blood pressure at rest and after exercise and antagonized exercise-induced tachycardia, but had no effect on resting heart rate. Propranolol diminished systolic blood pressure predominantly after exercise and reduced both resting and exercise heart rate. Both drugs had no effect on diastolic pressure. 4. The mean plasma concentration reached a peak at 2 h for each drug and this coincide with the interval at which maximal beta-adrenoreceptor-blocking effect was observed.

Abnormal cation composition and transport in erythrocytes from hypertensive patients.

Red cell sodium and potassium were determined in 100 untreated subjects with uncomplicated essential hypertension and compared with the values from 908 healthy normotensive control subjects. Red cell sodium concentration (expressed as mmol/l of erythrocytes) was significantly higher in hypertensive than in normotensive subjects. Red cell potassium concentration (in mmol/l of erythrocytes) was not significantly different in the two groups. Passive efflux of red cell potassium into buffered isotonic sucrose solution determined in eight hypertensive and nine normotensive subjects showed a lower potassium efflux rate in the hypertensive subjects. Comparison of active sodium efflux in sixteen hypertensive and fourteen normotensive subjects showed that ouabain-sensitive active sodium efflux was higher in red cells of normotensive than in those of hypertensive subjects.

Plasma and erythrocyte cations and permeability of the erythrocyte membrane to cations in essential hypertension.

Untreated African patients with essential hypertension were found to have high plasma sodium and low plasma potassium. The red cel contents of these cations determined from the same sample of blood were found to be high for sodium and normal for potassium. The passive permeability of the erythrocytes for potassium was lower in hypertensives than in controls. The ouabain-sensitive active sodium efflux was lower in hypertensives than in controls. The relationships between the erythrocyte cation content and the total body content of the cations, and between the membrane function in red cells and other cells of the body are discussed.