Pharmacokinetics of oral artesunate in thai patients with uncomplicated falciparum malaria

The pharmacokinetics of artesunate and its major plasma metabolite, dihydroartemisinin, were investigated in 11 Thai male patients with acute uncomplicated falciparum malaria during the acute and recovery phases. Patients were given an oral dose of 200mg artesunate (Guilin Pharmaceutical) on the first day, followed by 100mg 12 hours later, then 100mg daily for another 4 days (total dose of 700mg). All the patients showed a rapid initial response with median (range) parasite and fever clearance times of 30 (18 to 60) and 24 (4 to 94) hours, respectively; no patients showed reappearance of parasites during the 28-day follow-up period. No significant clinical adverse effects were detected in any patient. Acute phase malaria infection significantly influenced the pharmacokinetics of artesunate and its active metabolite, dihydroartemisinin. Maximum plasma drug concentration (C(max)), absorption half-life (t((1/2)a)), area under the plasma concentration-time curve from zero to the last observed time (AUC) and terminal elimination half-life (t((1/2)z)) of artesunate were decreased, while apparent total body clearance (CL/f) was increased during the acute phase, compared with the recovery phase. In addition, a decrease in the C(max) and an increase in the AUC(DHA/ARS ) ratio were found. Optimisation of therapy with oral artesunate should therefore be based on the kinetics of the drug and dihydroartemisinin in malaria patients with acute phase infection.

Pharmacokinetics of the four combination regimens of dihydroartemisinin/mefloquine in acute uncomplicated falciparum malaria

The pharmacokinetics of oral dihydroartemisinin and mefloquine were investigated in 40 patients (aged 16-30 y, weighing 45-60 kg) with acute uncomplicated falciparum malaria following the four combination regimens of dihydroartemisinin/ mefloquine [regimen-I: 300 mg dihydroartemisinin (h-0) plus 750 mg mefloquine (h-0); regimen-II: 300 mg dihydroartemisinin (h-0) plus 750 mg mefloquine (h-24); regimen-III: 300 mg dihydroartemisinin (h-0) plus 750 and 500 mg mefloquine (h-24 and 30); regimen-IV: 300 mg dihydroartemisinin (h-0) plus 750 and 500 mg mefloquine (h-0, 24)]. The four combination regimens were well tolerated. Patients in all treatment groups had a rapid initial response. However, 9 patients (4, 4, and 1 cases in regimens-I, II, and IV) had reappearance of parasitemia during the follow-up period. Significant changes in the pharmacokinetic parameters of both mefloquine and dihydroartemisinin were observed in patients with malaria compared with healthy subjects reported in a paralleled study. For mefloquine, Cmax (mg per dose), AUC0-day1 (mg per dose), and AUC0-day7 (mg per dose) were significantly higher in patients. Furthermore, tmax, was prolonged while V/F contracted and tl/2,z, MRT shortened in patients with malaria. For dihydroartemisinin, Cmax AUC, tmax and Vz/F were changed in the same direction as mefloquine, whereas t1/2z and MRT were prolonged. CL/F was also significantly reduced in patients with malaria. Absorption/disposition kinetics of oral dihydroartemisinin were similar among the various regimens. On the other hand, AUC0-day1 (mg per dose) of mefloquine after regimen-III was significantly higher than the other three regimens. Combination regimens with two divided doses of mefloquine (regimens-III and IV) resulted in a significantly delayed tmax (especially regimens-IV) compared with those with single dose regimens (regimens-I and II).

Absence of significant pharmacokinetic and pharmacodynamic interactions between artemether and quinoline antimalarials

The study was carried out to investigate the pharmacokinetic and pharmacodynamic interactions between artemether (ARTEM) and quinoline antimalarials namely mefloquine (MQ), quinine (QN) and primaquine (PQ) when given concurrently. A randomised comparative, seven way cross-over design was performed in eight healthy male Thais following the administrations of seven drug regimens on seven occasions i.e. a single oral dose of ARTEM (300 mg), or MQ (750 mg), or QN (600 mg), or PQ (45 mg) alone, or the combination of ARTEM (300 mg) with MQ (750 mg), or QN (600 mg), or PQ (45 mg). All clinical and laboratory parameters were normal in all subjects, before, during and after the study. The eight subject experienced no adverse effect after ARTEM, QN, PQ alone regimens, or combination of ARTEM with QN and PQ. After administration of MQ in either occasion, 3 subjects had weakness, nausea, abdominal pain, and diarrhoea; one subject complained of dizziness. All symptoms were mild and occurred during the first day of MQ administration. The fitting of the concentration-time curves of ARTEM, QN and PQ, to a one-compartment model with first order absorption yielded satisfactory results in all subjects. The best fit model for MQ was two-compartment model with first order absorption. The pharmacokinetics of all investigated drug, when given alone or in combination were not significantly different.

Pharmacokinetic and pharmacodynamic interactions of mefloquine and quinine

This study was carried out to investigate the pharmacokinetic and pharmacodynamic interactions between two antimalarial drugs, mefloquine and quinine. A randomized, comparative, three-way crossover study was performed in seven healthy male Thais after the administration of three drug regimens on three occasions i.e., a single oral dose of quinine sulfate (600 mg), mefloquine (750 mg) alone, or the combination of mefloquine (750 mg) and quinine (600 mg given 24 h after mefloquine). QTc interval was significantly prolonged in subjects following the combination regimen (at 2.5, 3, 4, 6, 8, 12, 18, 24 h after the quinine dose) but no abnormal clinical signs or symptoms were found. There were no significant changes in vital signs or routine laboratory values in any of the subjects. The pharmacokinetics of mefloquine and quinine were influenced by the presence of the other drug. Greater blood schizonticidal activities were collected from the sera of subjects on the combination regimen than from the sera of subjects the quinine or mefloquine regimens. The minimum inhibitory concentrations (MICs) of the equivalent concentrations (Eqs) of quinine or mefloquine, which completely inhibited the growth of the K1 strain of Plasmodium falciparum in vitro (MICs of quinine Eq and mefloquine Eq) were significantly lower in the sera of subjects on the combination regimens, than in the sera of subjects on mefloquine or quinine alone [MICs of quinine Eq: 41.2 (21.25-73.5) vs. 135 (118-150) ng/ml; MICs of mefloquine Eq: 18.2 (17-19.2) vs. 25.2 (24.4-26.8) ng/ml].

Pharmacokinetics of benflumetol given as a fixed combination artemether-benflumetol (CGP 56697) in Thai patients with uncomplicated falciparum malaria

The pharmacokinetics of benflumetol as a fixed combination, artemether-benflumetol (CGP 56697), following three regimens [regimen A: four tablets at 0, 8, 24 and 48 h (320 mg artemether, 1,920 mg benflumetol); regimen B: two tablets at 0, 8, 24 and 48 h (160 mg artemether, 960 mg benflumetol); regimen C: four tablets at 0, 8 and 24 h (240 mg artemether, 1,440 mg benflumetol)] were investigated in 39 patients with acute uncomplicated falciparum malaria. All patients showed a rapid initial response with a median parasite clearance time of 40, 41 and 39.5 h and a fever clearance time of 27.8, 32 and 24.5 h for regimens A, B and C, respectively. In nine patients (two, four and three patients in regimens A, B and C, respectively), however, parasitemia reappeared in the peripheral blood smear between days 9 and 23. The pharmacokinetics of benflumetol were highly variable, with coefficients of variation in pharmacokinetic parameters ranging from 14.9% to 144%. Absorption and elimination of benflumetol were relatively slow. Median Cmax per dose (first dose) was significantly higher in regimen B (6.29 ng/ml/mg dose) than in regimen A (2.6 ng/ml/mg dose) and regimen C (3.06 ng/ml/mg dose). Mean T1/2z in regimen C (2.65 h) was significantly shorter than in regimen A (4.5 h) and regimen B (3.89 h). In patients on regimens A and B who showed a sensitive response, plasma concentrations of benflumetol were significantly higher than in those with treatment failure.

Pharmacokinetic and pharmacodynamic interactions of mefloquine and dihydroartemisinin

Pharmacokinetic and pharmacodynamic interactions between dihydroartemisinin and mefloquine were investigated in 10 healthy Thai males. The study was of a three-way crossover design. Subjects were randomized to receive three drug regimens on three separate occasions as follows: regimen I: a single oral dose of 300 mg dihydroartemisinin; regimen II: a single oral dose of 750 mg mefloquine; regimen III: a single oral dose of 300 mg dihydroartemisinin, given concurrently with a single oral dose of 750 mg mefloquine. All regimens were well tolerated. Oral dihydroartemisinin was rapidly absorbed and disappeared from systemic circulation within 8-10 h. Mefloquine absorption and disposition were relatively slow processes. Pharmacokinetics of dihydroartemisinin and mefloquine when given concurrently were similar, except for the absorption rate of mefloquine which was faster in the presence of dihydroartemisinin. Pharmacodynamically, the combination of dihydroartemisinin and mefloquine resulted in a synergistic effect on ex vivo blood schizontocidal activity. Maximum activity (Amax) and area under effect-time curve (AUEC) of dihydroartemisinin and mefloquine were increased approximately two- and 20-fold (Amax), and four- and twofold, respectively, compared with each individual drug alone. AUEC of mefloquine during the first 24 h (AUEC 0-24 h) was increased approximately 50-fold in the presence of dihydroartemisinin.

Pharmacokinetic interactions of artemether and pyrimethamine in healthy male Thais

The pharmacokinetics of a single oral dose of artemether (300 mg) and pyrimethamine (100 mg) given as each individual drug alone or as a drug combination (artemether 300 mg plus pyrimethamine 100 mg), were investigated in 8 healthy male Thai volunteers. Both artemether and pyrimethamine were rapidly absorbed after oral administration. Elimination of pyrimethamine was however, a relatively slow process compared with artemether, and thus resulted in a long terminal phase elimination half-life (50-106 hours). Pharmacokinetics of artemether and dihydroartemisinin following a single oral dose of artemether alone or in combination with pyrimethamine were similar. In contrast, coadministration of artemether resulted in significantly increased Cmax (medians of 818 vs 1,180 ng/ml) and contracted the apparent volume of distribution (medians of 3 vs 2.56 l/kg) of pyrimethamine.

Plasma concentrations of artemether and its major plasma metabolite, dihydroartemisinin, following a 5-day regimen of oral artemether, in patients with uncomplicated falciparum malaria

Plasma concentrations of artemether and its active plasma metabolite (dihydroartemisinin) were measured in 49 male, Thai patients with acute, uncomplicated, multidrug-resistant, Plasmodium falciparum malaria, following their treatment with oral artemether (300 mg on the first day, then 100 mg daily for another 4 days). Four patients recrudesced (on days 19-22). After the first dose, artemether became undetectable in < or = 18 h and this drug was also undetectable in samples collected immediately before each dose. Although dihydroartemisinin followed similar trends, three patients had detectable plasma concentrations of this metabolite 24 h after the first dose (i.e. immediately before the second dose). Median (range) values for plasma concentrations of dihydroartemisinin 6 h [354 (150-751) v. 196 (178-220) ng/ml] and 12 h [158 (25-420) v. 54 (25-115) ng/ml] after the initial dose, estimated antimalarial activities (calculated as dihydroartemisinin equivalents) 6 h [331 (78.2-644.1) v. 23 (183.3-270) nmol/litre] and 12 h [98.3 (10-192.2) v. 56.7 (9.8-59.4) nmol/litre] after the initial dose, and the corresponding 'areas under the curves' (AUC) [3684 (1562-8216) v. 834 (1401-2030) ng.h/ml] were all significantly higher in the patients with sensitive responses than in those who recrudesced.

Pharmacokinetics and ex vivo anti-malarial activity of sera following a single oral dose of dihydroartemisinin in healthy Thai males

The pharmacokinetics of dihydroartemisinin (DHA) was studied in eight healthy male Thai subjects after a single oral dose of 300 mg. Absorption of oral DHA was rapid, Cmax of 679 (307-1000) ng/ml was observed at 1.5 (1-2.5) hours after dosing [median (range)]. Plasma concentrations declined monoexponentially and at 12 hours after administration, the levels were below the detection limit (3 ng/ml). A large variation in the AUC (approximately) 50% was observed. The median (range) AUC was 2010 (636-4079) ng h/ml. The lag time and absorption half-life (t1/2a) were 0.169 (0.111-0.277) hours and 0.709 (0.367-1.118) hours respectively. t1/2z was 1.25 (0.79-1.89) hours Vz/f and CL/f were 5.9 (3.5-8.2) l/kg and 45.3 (28.6-122.8) ml/min/kg, respectively. The pattern of its ex vivo serum activity coincided with the plasma concentrations of DHA.

Pharmacokinetics and bioavailability of oral and intramuscular artemether

OBJECTIVE

The pharmacokinetics and bioavailability of artemether and dihydroartemisinin were investigated in eight Thai males following the administration of single oral and intramuscular doses of artemether (300 mg) in a randomized two-way cross-over study.

RESULTS

Both oral and intramuscular artemether were well-tolerated. In most cases, artemether and dihydroartemisinin were detected in plasma after 30 min and declined to levels below the limit of detection within 18-24 h. Compared with intramuscular administration, oral administration of artemether resulted in a relatively rapid but incomplete absorption [Cmax: 474 vs 540 ng.ml-1; tmax: 2.0 vs 3.9 h; AUC: 2.17 vs 5.20 micrograms.h.ml-1]. Geographic means of lag-time and absorption half-life (t1/2a) of oral vs intramuscular artemether were 0.28 and 1.1 h vs 0.30 and 2 h, respectively, t1/2z was significantly shortened after the oral dose [2.8 vs 6.9 h]. Mean oral bioavailability relative to intramuscular administration was 43.2%. The ratio of the AUCs of artemether to dihydroartemisinin was significantly lower after the oral than after the intramuscular dose (geometric mean: 0.29 vs 0.60). artemisinin, which is commercially available in China, Vietnam, Thailand and some African countries. The drug is administered as solution in oil for intramuscular injection or as oral tablets. The clinical efficacy of artemether is dependent on the formulation, dosing scheme, duration of treatment, and the severity of the disease [1, 2]. Oral artemether is effective but with short-term treatment, the relapse rate is high. While the efficacy of intramuscular artemether against multidrug-resistant P. falciparum in either uncomplicated or severe cases has been confirmed, its pharmacokinetic documentation is limited. Formulations with high bioavailability and low costs are essential. With high-performance liquid chromatography and electrochemical detection, more sensitive and reliable assay of artemisinin and derivatives in biological fluids has been achieved [3-4]. In the present study, we have assessed the pharmacokinetics and bioavailability of oral and intramuscular artemether, in healthy Thai males.

Activity of artemether-azithromycin versus artemether-doxycycline in the treatment of multiple drug resistant falciparum malaria

The efficacy of the combination of artemether with doxycycline or azithromycin was evaluated in 60 patients with acute uncomplicated falciparum malaria who attended malaria clinic in Mae Sot, Tak Province (Thai-Myanmar border). Patients (30 each) were randomized to receive (a) 300 mg artemether together with 100 mg doxycycline as initial doses, followed by 100 mg artemether plus 100 mg doxycycline at 12 hours later, then 100 mg doxycycline every 12 hours for another 4 days, or (b) 300 mg artemether together with 500 mg azithromycin, followed by 250 mg azithromycin at 24 and 48 hours. The follow-up period was 28 days. Patients in either group had a rapid initial response to treatment with comparable PCT and FCT. The cure rate of artemether-azithromycin regimen was significantly lower than that of artemether-doxycycline regimen (14.8 vs 53.3%). Low cure rate from artemether-azithromycin combination in this study was likely to be due to inadequate azithromycin dosage. However, with the low incidence of gastrointestinal adverse effects, the once daily dose of azithromycin could still be increased in order to enhance its clinical efficacy. The simplicity of drug administration and lesser incidence of adverse effects make azithromycin a more proper partner of artemether than doxycycline. Further dose-finding and pharmacokinetic study with the artemether-azithromycin combination is encouraging.

ParaSight-F test for the detection of treatment failure in multidrug resistant Plasmodium falciparum malaria

The ParaSight-F test for the detection of Plasmodium falciparum was evaluated for its accuracy and usefulness in predicting treatment outcome in 75 patients (70 males, 5 females) with acute uncomplicated malaria who attended a malaria clinic in Mae Sot, Tak province, on the Thai-Myanmar border. All patients were admitted to the clinic for 28 d to exclude reinfection. The test was performed using blood samples collected into ethylenediaminetetraacetic acid from the patients on admission, and on days 1, 2, 7, and 14. The presence of microscopically detectable parasitaemia was used as the reference for sensitivity and specificity of the test. The reappearance of parasites on day 28 was used to determine the accuracy of predicting the outcome of artemether treatment on day 14. The sensitivity of the ParaSight-F test on admission, and on days 1, 2, 7, and 14, was 98.7%, 96.7%, 100%, 100% and 100%, respectively, with corresponding specificities of 50%, 24.2%, 47.1% and 72.9%. The sensitivity for predicting recrudescence by using the test on day 14 was 100%, with 97.7% specificity, and the sensitivity of predicting a sensitive response on day 14 was 97.7%, with 100% specificity. The test seems to permit more precise detection of treatment failure under 'field' conditions if used on day 14 after the start of treatment.

Quinine-tetracycline for multidrug resistant falciparum malaria

Plasmodium falciparum in Southeast Asia is highly resistant to chloroquine and sulfadoxine/ pyrimethamine. Quinine-tetracycline has been used as a second line treatment for uncomplicated falciparum malaria, but duration of treatment varies from place to place. The 7-days course of this combination has been shown to be very effective. However, due to the cinchonism adverse effects, the patient compliance has not been satisfactory. We have evaluated the efficacy of a 7-days course of tetracycline in combination with either 5 or 7-days course of quinine. Ninety male Thai patients who were admitted to the Bangkok Hospital for Tropical Diseases were randomized to receive tetracycline 250 mg qid for 7 days in combination with either quinine 600 mg tid for 5 days (Q5T7; group A) or quinine 600 mg tid for 7 days (Q7T7; group B). The patients were hospitalized for 28 days. Patients in both groups had a comparable initial response to treatment, with the clearance of fever and parasites within 4 days. There were 46 and 40 patients in group A and B, respectively, who completed the 28 day of follow-up. The cure rates were 87 and 100%, respectively for group A and B. No serious adverse effects were found in either group; transient nausea, vomiting and tinnitus were common findings. The incidence of adverse effects was not different between the two groups. The results from the present study suggest that a short course treatment of quinine (Q5T7) had significantly decreased the cure rate. In areas with quinine resistant falciparum malaria, a full course of 7-days quinine, in combination with 7-days course of tetracycline is recommended for hospital treatment. However, an alternative shorter course of antimalarials is suggested for home treatment.

Artemether-pyrimethamine in the treatment of pyrimethamine-resistant falciparum malaria

In vitro susceptibility and clinical response of multidrug resistant Plasmodium falciparum to the combination artemether-pyrimethamine were evaluated in patients with acute uncomplicated falciparum malaria. Sixty patients were randomized to receive 3 oral regimens of the combination artemether-pyrimethamine as follows: Regimen-I: artemether (300 mg) plus pyrimethamine (100 mg) on the first day, then placebo on the two consecutive days; Regimen-II: artemether (300 mg) plus pyrimethamine (100 mg) on the first day, then artemether (150 mg) plus pyrimethamine (50 mg) on the second day, and placebo on the third day; Regimen-III: artemether (300 mg) plus pyrimethamine (100 mg) on the first day, then artemether (150 mg) plus pyrimethamine (50 mg) on the second and third days. All patients had a rapid initial response to treatments with 95% of parasitemia being cleared within the first 24 hours. PCT24hours and PCT48hours were similar among the three drug regimens (11 vs 4, 6 vs 12, and 9 vs 11 patients for a 1-day, 2-day, and 3-day combination regimen, respectively). Fever was cleared within 48 hours in all patients in either group. Transient mild nausea, vomiting and loss of appetite were found in a few patients during the first 2 days of treatment. Seven patients did not complete the 28 day follow-up period (5 vs 2 in a 1-day vs 2-day regimen), the reason for withdrawal was not associated with drug-related adverse effects. Only 53 patients were therefore qualified for the efficacy assessment. There was 15, 13 and 5 patients in a 1-day, 2-day and 3-day combination regimens, respectively, who had reappearance of the parasitemia between days 11 and 21. The cure rates of the 3 treatment groups were statistically significantly different (0, 27.8, and 75% for a 1-day, 2-day and 3-day combination regimen, respectively). Two patients developed P. vivax malaria on days 20 and 24. All of the isolates were highly resistant to pyrimethamine, with MIC of 10(-5) M. There is potential advantage of this combination therapy in reducing the dosage and treatment period of artemisinin derivative, which is therefore likely to improve complaince in clinical practice. The use of a 3-day combination regimen (300 mg artemether plus 100 mg pyrimethamine on the first day, then 150 mg artemether plus 50 mg pyrimethamine on the second and third days) seems to be a good alternative regimen to sulfadoxine/ pyrimethamine in areas where P. falciparum is sensitive to pyrimethamine eg in Africa.

A comparative clinical trial of artemether and the sequential regimen of artemether-mefloquine in multidrug resistant falciparum malaria

A randomized, comparative clinical trial for assessment of the efficacy of two antimalarial regimens, artemether alone and the sequential regimen artemethermefloquine, was carried out in 109 Thai male patients with acute uncomplicated, multidrug resistant falciparum malaria who were admitted to the Bangkok Hospital for Tropical Diseases. Fifty-three patients received oral artemether at a total dose of 700 mg (300 mg initially, followed by 100 mg daily for 4 days), and 56 patients received the sequential regimen of artemether-mefloquine (300 mg oral artemether initially, followed by 750 mg oral mefloquine after 24 h). Patients in both groups had a rapid initial response to treatment, with a median parasite clearance time of 40 h compared with 43.5 h for the sequential regimen. Median fever clearance times were 42.5 h and 32.5 h for artemether and the sequential regimen respectively. Parasitaemia reoccurred in patients of both groups during the follow up period, six in the artemether and three in the sequential regimen (cure rates were 88 and 94%). No serious adverse effects were observed in either group of patients.

Pharmacokinetics of mefloquine, when given alone and in combination with artemether, in patients with uncomplicated falciparum malaria

The pharmacokinetics of mefloquine at a single oral dose of 750 mg, when given alone or 24 hours after a single oral dose of artemether (300 mg) was investigated in 27 Thai patients with acute uncomplicated falciparum malaria (17 with mefloquine alone, 10 with the combination). The oral bioavailabiiity of mefloquine was significantly decreased when administered 24 hours after an oral dose of artemether. This was evident by the significantly lower values of Cmax, AUC[0-24 h], AUC[0-48 h], AUC[0-72 h], as well as total AUC[Cmax: 1,290 (827-2,619) vs 1,820 (1,283-2,531) ng.ml-1; AUC[0-24 h]: 0.99 (0.64-1.41) vs 1.33 (1.07-1.95) micrograms.day.ml-1; AUC[0-48 h]: 1.78(1.23-2.58) vs 2.67 (2.09-3.84) micrograms.day.ml-1; AUC[0-72 h]: 2.74 (1.63-3.6) vs 4.54 (2.88-5.38) micrograms.day.ml-1; AUC: 11.11 (6-20.96) vs 15.29 (9.3-36.71) micrograms.day.ml-1]. Tmax was also delayed with the combination regimen [14 (5-24) vs 6 (4-16) h]. Terminal elimination half-lives were comparable [t1/2z: 11.1 (6.8-14.3) vs 13.4 (10.5-19.1) h].

Comparison of artemether and quinine in the treatment of severe falciparum malaria in south-east Thailand

One hundred and two Thai patients with severe falciparum malaria (92 males and 10 females) were allocated at random to receive either the standard regimen of quinine infusion (52 cases) or intramuscular artemether (50 cases). The patients in both groups had comparable admission clinical and laboratory data. Artemether gave a better survival rate (87.2% vs. 63.3%) and parasite clearance time (54 vs. 78 h) than quinine. Fever clearance times (79 h vs. 84 h) and time to recovery of consciousness (48 h in both groups) were comparable. Previous treatment with quinine or mefloquine had no influence on treatment outcome. The most common adverse effect in patients treated with quinine was tinnitus. Two patients had severe hearing impairment which resolved within 1 week after the end of treatment. Mild, transient pain was noted at the injection site of artemether but no abscess formed. QTc wave prolongation was seen in most patients receiving quinine; however, no arrhythmia was observed despite the high concentration of quinine in some patients who had received quinine before admission. Complications developed in 7 survivors in each treatment group. No patient in the artemether group had neurological sequelae after recovery of consciousness, but 2 in the quinine group had left facial palsy and one had a myasthenia gravis-like syndrome. No patient died with complications in he artemether group, but 7 died with pulmonary complications in the quinine group.

A comparative clinical trial of two different regimens of artemether plus mefloquine in multidrug resistant falciparum malaria

Plasmodium falciparum in Thailand is highly resistant to available antimalarial drugs. Artemether, a derivative of artemisinin, is a promising compound currently used to cope with this situation but the course of treatment has to be at least 5 d. An effective short treatment course of this drug is possible when used in combination with mefloquine. We now report a trial of different regimens of the combination artemether/mefloquine. Fifty-seven male Thai patients, admitted to the Bangkok Hospital for Tropical Diseases, were allocated at random to receive oral artemether 300 mg as an initial dose, followed by either the standard dose of mefloquine (750 mg) at 24 h or a higher dose of mefloquine (750 mg at 24 h, then 500 mg at 30 h). Patients were followed up in hospital for 42 d. Two patients, both in the high dose mefloquine group, were excluded as they failed to attend for follow-up. All patients had a rapid initial response to treatment with median parasite clearance times of 37 and 40 h, median fever clearance times of 33.5 and 30.5 h, and cure rates of 75 and 96% (P = 0.0248), for the standard and high doses of mefloquine respectively. No serious adverse effect was found; mild and transient dizziness, nausea, vomiting and diarrhoea were noted in half of the patients in each group. The results suggest that a 30 h short course of artemether plus mefloquine at high dose should be used in areas with documented mefloquine resistance.

Artemether 5 versus 7 day regimen for severe falciparum malaria

Twenty-eight male Thai patients with severe falciparum malaria were randomized to receive either artemether for a 5 (300 mg initial dose followed by 100 mg for another 4 days) or a 7 days regimen (160 mg initial dose, followed by 80 mg daily for another 6 days). Thirteen patients received a 5 day regimen and 15 received 7 day regimen. The follow-up period was 28 days. The patients in both groups were comparable in age, body weight, admission parasitemia, hematocrit and white cell count. There were 4 patients in each group who presented with cerebral malaria. The median values of parasite and fever clearance times (PCT and FCT) in the 5 and 7 days regimens were 52 vs 60 hours, and 85 vs 68 hours, respectively. There were 8 and 4 patients, respectively who had recrudescence during days 15 to 25. The cure rates were 38% (95% CI = 14-68%) and 73% (95% CI - 50-96%), respectively for 5 and 7 day regimens. None died in either group. No patients in either group had neurological sequelae after recovery of consciousness. Clinically adverse effects in either group were transient pain at the site of injection. No drug related biochemical or ECG changes were noted in either group. The duration of treatment is the determinant of the cure rate; however, the duration of even 7 days still resulted in high recrudescence rate. It may be necessary to combine artemether with other longer half-life antimalarials to improve the cure rate.

The pharmacokinetics of chloroquine in healthy Thai subjects and patients with Plasmodium vivax malaria

The pharmacokinetics of chloroquine (CQ) and desethylchloroquine (DECQ) were studied in seven male Thai patients with P. vivax malaria and seven healthy male Thais, after the standard oral dosage regimen of CQ (a total dose of 1500 mg given over 3 days). All patients showed a rapid initial response to the treatment with median (range) values of fever and parasite clearance times of 13.7 (2-47) and 58 (33-38) h, respectively. In the patients, the median range Cmax value was significantly higher (1547 (996-2446) vs 838 (656-1587) ng ml-1), and AUC(0,28d) was greater (281 (250-515) vs 122 (103-182) micrograms ml-1 h). In addition, the median (AUC(0,28d) of DECQ was significantly greater (170 (72-265) vs 77 (49-140) micrograms ml-1 h). The AUC(0,28d) ratio of DECQ to CQ in patients was significantly higher than that in healthy subjects (0.67 (0.43-0.90) vs 0.51 (0.29-0.61)).

Quinine toxicity when given with doxycycline and mefloquine

The pharmacokinetic and dynamic interactions among 3 antimalarials, ie quinine, doxycycline and mefloquine was observed in a 26-year-old Thai male patient with falciparum malaria. During the acute episode of the infection, the patient was treated with an intravenous dose of quinine hydrochloride at 600 mg qid, together with an oral dose of doxycycline 100 mg bid. Due to nausea, tinnitus and the persistence of parasitemia in peripheral blood smears, the dose of quinine was reduced 2 days after the first treatment to 300 mg; concurrently oral mefloquine 750 mg was given as 2 divided doses at 24 hours apart. During the course of treatment, the patient developed hearing loss; deafness of the right ear lasted for one week after stopping quinine administration. Higher plasma quinine and lower whole blood mefloquine concentrations than would be expected from the simulation profiles were detected 4 days after the first treatment. However, the concentration of mefloquine was increased upon the cessation of quinine treatment.

Pharmacokinetics of artemether after oral administration to healthy Thai males and patients with acute, uncomplicated falciparum malaria

1. The pharmacokinetics of artemether were investigated (a) in six healthy male Thai volunteers after single 200 mg oral doses and (b) in eight male Thai patients with acute uncomplicated falciparum malaria after an initial 200 mg oral dose followed by 100 mg at 12 h then 100 mg daily for 4 days. 2. In the healthy subjects, median (range) maximum plasma concentrations of artemether of 118 (112-127) ng ml-1 were reached at 3 (1-10) h. Thereafter, drug concentrations declined monoexponentially with a median (range) t1/2.z of 3.1 (1.0-9.6) h. The median (range) AUC and MRT values were 1.10 (0.33-4.44) micrograms ml-1 h and 8.3 (3.5-20.8) h. The median Cmax value of dihydroartemisinin, an active metabolite, was 379 (162-702) mg ml-1 at 6 (2-12) h. Its median AUC value was 6.6 (0.83-38.7) micrograms ml-1 h; the apparent t1/2.z was 10.6 (4.7-19.2) h and the median MRT value was 16.0 (5.0-41.0) h. 3. In the patients, a higher Cmax value of parent drug than those observed in healthy subjects (median and range of 231 (116-411) ng ml-1), was reached at 3 (1-3) h after the first dose. Steady state was reached after the third dose (24 h) and concentrations fluctuated over the range of 36-60 ng ml-1. The respective median (range) values of AUC and t1/2.z were 5.8 (3.76-12.9) micrograms ml-1 h and 4.2 (2.5-5.3) h.(ABSTRACT TRUNCATED AT 250 WORDS)

High dose of primaquine in primaquine resistant vivax malaria

The efficacy of low dose chloroquine, characteristic pattern of relapse and the relapse rate in vivax malaria after high dose primaquine were investigated in 167 Thai patients. 87 patients were allocated at random to receive 300 mg, and 80 received 450 mg of chloroquine on the first day of admission. All patients in both groups showed a rapid response with comparable fever clearance times (27.3 vs. 26.1 h) and parasite clearance times (67.1 vs. 58.1 h). After recovery and clearance of parasitaemia, the patients were allocated at random (double blind) to receive 2 dosage regimens of primaquine, a daily dose of 15 mg or 22.5 mg for 14 d. Relapses in both groups occurred within 6 months; no patient relapsed beyond that period. The relapse rate in the primaquine 15 mg group was significantly higher than that in the 22.5 mg group (17.5% vs. 2.4%).

Pharmacokinetics of primaquine in G6PD deficient and G6PD normal patients with vivax malaria

The pharmacokinetics of primaquine have been studied in 13 G6PD normal and 13 G6PD deficient Thai male patients with Plasmodium vivax malaria who were given daily doses of 15 mg of primaquine over 14 d, following a full course of chloroquine. After the first dose (15 mg), primaquine underwent rapid absorption. Mean values (SD in parentheses) of maximum plasma concentration of 57.7 (7.7) vs. 55.7 (7.4) ng/mL were reached at 2.2 (0.6) vs. 2.2 (0.6) h, for the G6PD deficient and G6PD normal groups, respectively. Thereafter, drug levels declined rapidly and monoexponentially with a t1/2 lambda of 6.4 (1.9) vs. 6.3 (2.7) h. The respective mean values (SD in parentheses) for MRT, AUC0-varies; is directly proportional to Cl/f, and Vz/f were 6.8 (0.4) vs. 6.8 (0.5) h, 0.547 (0.070) vs. 0.521 (0.090) micrograms/h/mL, 8.54 (0.37) vs. 8.97 (1.46) mL/min/kg and 4.8 (1.7) vs. 5.1 (1.2) L/kg. There was no difference in the plasma concentrations or pharmacokinetics of primaquine between patients with normal G6PD and G6PD deficiency. In the G6PD deficient group, no relationship between the severity of haemolysis (< 20% or > 20% haemolysis) and the concentrations/pharmacokinetics of primaquine was observed.

Comparison of oral artesunate and quinine plus tetracycline in acute uncomplicated falciparum malaria

In Thailand Plasmodium falciparum malaria is highly resistant to available antimalarials. Investigations on the efficacy of existing antimalarials and of alternative drugs are urgently needed. Artesunate has been shown to be effective against falciparum malaria, but is associated with a high recrudescence rate. We have carried out a comparative clinical trial of the standard regimen of quinine + tetracycline versus oral artesunate at a 700-mg total dose given over 5 days to patients with acute uncomplicated falciparum malaria. The 64 male patients who took part in the study were randomized to receive either quinine-tetracycline (33 patients) or oral artesunate (31 patients). All the patients were admitted to the Bangkok Hospital for Tropical Diseases for 28 days. Oral artesunate had faster parasite and fever clearance times than the combination quinine-tetracycline, but the cure rate was not significantly different for the two regimens. However, the occurrence of adverse effects, such as tinnitus, was significantly higher in the quinine-tetracycline group. Surprisingly nausea and dizziness were rather common with artesunate. The possibility of neurological adverse effects for artesunate should also be borne in mind. Oral artesunate (700 mg given over 5 days) is effective and better tolerated than the combination quinine-tetracycline. The cure rate we obtained is higher than that reported in previous studies with 600 mg of oral artesunate given over 5 days. Oral artesunate can be considered as an alternative drug for multiple-drug-resistant falciparum malaria; however, adverse effects, particularly neurotoxicity, should be closely monitored before its widespread use can be recommended.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of mefloquine alone or in combination with artesunate

A randomized comparative trial of the pharmacokinetics and pharmacodynamics of oral doses of mefloquine and of mefloquine in combination with artesunate was carried out on 20 Thai male patients with acute, uncomplicated falciparum malaria. The patients were randomized to receive either mefloquine alone (8 patients; 1250 mg of mefloquine--initial dose, 750 mg; followed 6 hours later by 500 mg), or in combination with oral artesunate (12 patients--initial dose, 200 mg of artesunate; followed by 750 mg and 500 mg of mefloquine 6 hours and 12 hours later, respectively). The patients who received mefloquine alone all showed initially good responses to the treatment, with mean +/- SD values for the fever clearance time (FCT) and parasite clearance time (PCT) of 44.7 +/- 43.1 hours and 82.3 +/- 52.3 hours, respectively. Two patients had recrudescences on day 20 and day 31 (RI response). The cure rate was 75%, and one patient had Plasmodium vivax in his peripheral blood on day 52. The patients who received the combination treatment were clinically markedly improved, with a relatively shorter FCT (31.2 +/- 12.4 hours) and significantly shorter PCT (47.5 +/- 19.6 hours). Four had recrudescences on days 12, 18, 26 and 33; the cure rate was 66%. Artesunate caused three significant changes in mefloquine pharmacokinetics: a decrease in the maximum concentration (Cmax: 1623 ng.ml-1 versus 2212 ng.ml-1); an increase in the clearance rate (Cl/f:2.9 ml.min-1.kg-1 versus 1.1 ml.min-1.kg-1); and an expansion of the volume of distribution (Vdz/f: 31.8 l.kg-1 versus 25.0 l.kg-1).

The pharmacokinetics of quinine in patients with hepatitis

The pharmacokinetics of quinine were studied in six patients with hepatitis B infection (during acute and convalescent periods) and six healthy subjects. A single 10 mg kg-1 dose of quinine was given intravenously over 2 h. Pharmacokinetic parameters of quinine during the acute phase of the infection were not different from those during the recovery phase. However, when compared with those obtained from healthy subjects, significant changes were found. The terminal elimination half-life was prolonged (17 and 15 vs 10 h) and clearance was lower (2.9 and 2.3 vs 3.5 ml min-1 kg-1). Unbound quinine concentration in plasma at 2 h was approximately 10% of the total concentration in all subjects in the three study groups. A prolonged QTc interval (< 25%) was observed in all groups. The present data suggest that current dosage regimens of quinine used in the treatment of falciparum malaria may not be suitable for malaria patients with acute hepatitis or those who have had hepatitis within the past 3 months.

Comparison of oral artemether and mefloquine in acute uncomplicated falciparum malaria

Plasmodium falciparum malaria in Thailand is highly resistant to available antimalarials, and alternative drugs are needed urgently. Artemether is effective against falciparum malaria but associated with a high recrudescence rate. The proper dosage regimen remains to be defined. We have done a clinical trial comparing mefloquine 1250 mg in divided doses with oral artemether at 700 mg total dose given over 5 days in acute uncomplicated falciparum malaria. 46 patients, admitted to the Bangkok Hospital for Tropical Diseases, were randomised to receive either mefloquine (12) or artemether (34). Hospital follow-up was 28 days for the artemether group and 42 days for the mefloquine group. Oral artemether gave a significantly faster parasite clearance time than mefloquine (30 vs 64 h), and a significantly better cure rate (97 vs 64%) with fewer episodes of dizziness and vomiting. Oral artemether at 700 mg given over 5 days is effective and well tolerated. The cure rate with this regimen is higher than that reported by previous studies with 600 mg intramuscular artemether given over 5 days. Oral artemether can be considered as an alternative drug for multiple-drug-resistant falciparum malaria.

Pharmacokinetics of mefloquine in treatment failure

The pharmacokinetics of mefloquine at the therapeutic dose of 750 mg single orally were compared between cured and recrudescent patients with acute uncomplicated falciparum malaria. Mefloquine was well-tolerated during the study. The side-effects found were nausea, vomiting and diarrhea. Five patients showed R-I and two showed R-II types of response. All recrudescent patients came from the eastern border of Thailand. The time taken to clear the parasites (PCT) was significantly longer in patients with recrudescence (99.6 +/- 36.9 and 63.0 +/- 8.9 hours); however, there was no difference regarding fever clearance time (FCT: 39.0 +/- 16.1 and 31.0 +/- 21.3 hours). The maximum concentration (Cmax) and the concentration on the first and second days in cured patients were significantly higher than those of treatment failure patients. Other pharmacokinetic parameters appeared to be similar in both groups. The present study indicates the existence of mefloquine-resistant falciparum malaria in the eastern border of Thailand. Inadequate mefloquine concentration may play an important role in this aspect. In addition, this study also suggests that Cmax or the concentrations on the first or second day of treatment may be used as guidelines to predict the outcome of treatment.