Efficacy comparison of intravenous artelinate and artesunate in Plasmodium berghei-infected Sprague-Dawley rats.

This paper reports the comparative antimalarial efficacy of intravenous artelinate and artesunate in rats. Prior to efficacy experiments, a Plasmodium berghei-Sprague-Dawley rat model of malaria was developed, in which the clearance effects of intravenous drugs could be readily compared. In efficacy experiments, groups of P. berghei-infected rats were given 3 daily intravenous treatments of artelinate or artesunate at molar equivalent dose rates (total of 0-191.2 micromoles/kg). Artelinate was superior to artesunate in terms of clearance (100% clearance dose of 95.6 micromoles/kg (40 mg/kg) versus 191.2 micromoles/ kg for AS (73.4 mg/kg)) and parasite clearance time (1.7 +/- 0.5 days for AL versus 2.7 +/- 0.5 days for AS at a dose rate of 191.2 micromoles/kg, P < 0.01). No frank clinical toxicity was observed, though both artesunate and artelinate induced dose-related vascular necrosis at the site of injection. The necrosis was less severe and reversible when the drugs were administered via femoral, rather than tail/foot veins. The data suggest that the P. berghei-7-week-old Sprague-Dawley rat model of malaria is reproducible and useful for assessing the efficacy of antimalarials and that artelinate is at least as potent, and safe, as artesunate, the leading clinical treatment for severe malaria.

Neurotoxicity and efficacy of arteether related to its exposure times and exposure levels in rodents.

The neurotoxicity of beta-arteether (AE) is related to drug accumulation in blood due to slow and prolonged absorption from the intramuscular injection sites. In this efficacy and toxicity study of AE, the traditional sesame oil vehicle was replaced with cremophore to decrease the accumulation and toxicity of AE. Dihydroartemisinin (DQHS), a more toxic and active metabolite of AE, was also analyzed. When administered at a daily dosage of 25 mg/kg for seven days, blood accumulation of AE with sesame oil (AESO) was used had a 7.5-fold higher area under the curve (AUC) (on last versus first day dosing), while AE with cremophore (AECM) had only a 1.8-fold higher AUC. Although the accumulation of AECM was greatly reduced, its total exposure level (46.29 microg x h/ml) was 2.7-fold higher than with AESO (16.92 microg x h/ml) due to a higher bioavailability of AECM (74.5%) compared with AESO (20.3%). Total exposure time (calculated at over the minimal detected neurotoxicity level of 41.32 ng/ml) of AECM was 103 hours during the whole treatment period (192 hours), which was more than one-third (37%) less than with AESO (162 hours). Similar pharmacokinetic results were also shown with the active metabolite, DQHS. Anorexia and gastrointestinal toxicity with AESO were significantly more severe than with AECM (P < 0.001). Histopathologic examination of the brain demonstrated neurotoxic changes; the AESO rat group was significantly more severe than the AECM rat group. The brain injury scores with AECM were mild to moderate (2.3-3.0), and with AESO they were moderate to severe (3.0-4.7) on day 7 and day 10, respectively. In addition, the results of a 50% cure dose (CD50) against Plasmodium berghei in mice were 34.1 mg/kg for AESO and 14.2 mg/kg for AECM, indicating a significant higher efficacy was found in the AECM animals. Toxicity and efficacy of DQHS were also dependent on its exposure time and level, which was the same as its parent drug (AE). In conclusion, following the seven-day treatment in rats, AE and DQHS exposure time and level varied based on the vehicle used. The extension of drug exposure time and the low peak level of AE and DQHS were more associated with severe neurotoxicity and lower antimalarial efficacy, whereas the high level and short exposure time of AE and DQHS resulted in higher efficacy and milder toxicity.

Comparative pharmacokinetics and effect kinetics of orally administered artesunate in healthy volunteers and patients with uncomplicated falciparum malaria.

The single-dose pharmacokinetics of 100 mg of orally administered artesunate (AS) were studied in 6 patient volunteers with uncomplicated falciparum malaria and in 6 healthy volunteers. Plasma concentrations of both the parent drug, AS, and its major metabolite, dihydroartemisinin (DHA), were measured simultaneously by high-performance liquid chromatography (HPLC) with electrochemical detection (ECD). The antimalarial activity of each plasma sample measured by an in vitro bioassay (BA) was used to derive activity concentrations. Artesunate was absorbed rapidly and then almost completely hydrolyzed to DHA in patients, whereas hydrolysis was incomplete in healthy volunteers. The mean +/- standard deviation (SD) maximum concentration (Cmax) of AS was 296+/-110 nmol/L, the time to peak blood level (tmax was 0.71+/-0.66 hr, the half-life (t1/2,z) was 0.41+/-0.34 hr, and the bioavailability over 12 hr (area under the curve [AUC](0-12)) was 253+/-185 nmol hr/L. Measured by HPLC, the Cmax and AUC(0-12) values of DHA in patients with malaria were significantly greater than in volunteers (1,948+/-772 and 1,192+/-315 nmol/L; 4,024+/-1,585 and 1,763+/-607 nmol hr/L, respectively; P < or = 0.05). These differences were even greater when measured by BA. The Cmax for patients with malaria was 2,894+/-2,497 and 795+/-455 nmol/L for volunteers, and AUC(0-12) was 5,970+/-3,625 and 1,307+/-391 nmol hr/L, respectively (P < or = 0.05). In contrast, DHA parameter estimates for t1/2,z and tmax were similar between patients and healthy volunteers, with values of 0.80+/-0.30 versus 0.87+/-0.06 hr and 1.50+/-0.55 versus 1.13+/-0.52 hr, respectively (P > 0.5). Both drug metabolism and tissue protein binding could contribute to the differences between the antimalarial activity of artemisinin drugs in healthy volunteers and malaria infected patients.

Pharmacokinetics and pharmacodynamics of qinghaosu derivatives: how do they impact on the choice of drug and the dosage regimens?

The critical decisions of which artemisinin derivative(s) to use and by which route(s) of administration for falciparum malaria are complex scientifically and politically. Despite the need for additional pharmacokinetic, pharmacodynamic and toxicokinetic data, these drugs are too important to delay concise, rational recommendations any longer. These types of decisions must be made now, implemented on a multinational level with WHO leadership, and revised as new findings emerge. For acute, uncomplicated disease, per os dosing of artesunate or artemether for three days is recommended, but only in combination with other antimalarial drugs like mefloquine. For severe falciparum malaria, intravenous administration is the preferred route, yet current formulations for intravenous dosing are not optimal and should be an area for future development emphasis. Clearly intramuscular administration of artemether has proven effective for severe disease, yet dosing regimens shouldn't be designed with ultimate parasitological cure as the aim and the problem of bioavailability of the sesame oil formulations must be examined further. Once the life-saving reduction in parasitemia and pathophysiological sequelae have been achieved, the patient can be given oral medication to affect radical cure. Much more data will be required to define the role of per rectum dosing for the treatment of severe malaria, yet this approach holds great promise as a life-saving intervention in rural areas where this disease has it most dramatic impact.

Plasmodium falciparum: evaluation of lactate dehydrogenase in monitoring therapeutic responses to standard antimalarial drugs in Nigeria.

The correlation of P. falciparum lactate dehydrogenase (pLDH) activities and patent infections was evaluated for monitoring therapeutic responses and drug resistance in 70 patients with microscopically confirmed P. falciparum malaria in Nigeria. Each patient was treated with standard dosages of artemether (53 patients), chloroquine (7 patients), sulfadoxine-pyrimethamine (6 patients), or halofantrine (4 patients). Response of infection to treatment was monitored by microscopic examination of thick and thin blood smears, clinical symptoms, and levels of pLDH activities in blood products. pLDH activity was determined using an antibody capture technique and 3-acetyl pyridine adenine dinucleotide developed to enhance sensitivity of the enzyme detection. All patients treated with artemether were cured while 5 patients treated with chloroquine, 1 treated with sulfadoxine-pyrimethamine, and 2 treated with halofantrine suffered recrudescent infections after treatment. pLDH activity was detected in blood products obtained from patients with patent or recrudescent infections determined by microscopy and clinical symptoms. Levels of pLDH activities in whole blood and packed cells from the patients correlated with qualitative detection of parasites in blood smears and in patients with high gametocyte counts. Gametocyte counts in the patients after treatment ranged from 40 gametocytes/microliter of blood to 4923 gametocytes/microliter of blood. There is a consistent relationship between patent infection and pLDH activities that could easily be determined in whole blood and packed cells from the patients. Further development of the procedure will enhance its valuable application in clinical management of drug-resistant malaria in the endemic areas.

Randomized trial of mefloquine-doxycycline, and artesunate-doxycycline for treatment of acute uncomplicated falciparum malaria.

One hundred nine adult patients with acute uncomplicated falciparum malaria were randomly selected to receive combinations of either doxycycline plus mefloquine or doxycycline plus artesunate. Fifty-four patients received mefloquine (1,250 mg divided between two doses of 750 and 500 mg six hours apart) with doxycycline and 55 patients received artesunate (300 mg total for 2.5 days; 100 mg followed by 50 mg every 12 hr for 2.5 days) with doxycycline. Doxycycline was administered in doses of 200 mg once a day for seven days. All patients were admitted to the hospital for 28 days to exclude reinfection. Ninety-seven patients completed the study; 12 patients left prior to completion of follow-up for reasons unrelated to their treatment. Cure rates for the two groups were 96% (46 of 48) for mefloquine plus doxycycline and 80% (39 of 49) for artesunate plus doxycycline. Mean fever and parasite clearance times were significantly shorter in the group that received artesunate plus doxycycline (38.7 and 41.3 hr) than mefloquine plus doxycycline (64.3 and 69.0 hr), respectively. In vitro drug sensitivity testing of selected isolates obtained prior to treatment indicated that eight of nine admission isolates were resistant to mefloquine; all isolates were susceptible to artesunate. Recrudescent isolates failed to show a pattern of decreased sensitivity to the drugs to which the parasites had been exposed during treatment; the studies showed decreased sensitivity to doxycycline in only two of eight isolates tested.(ABSTRACT TRUNCATED AT 250 WORDS)

A nonhuman primate model for human cerebral malaria: effects of artesunate (qinghaosu derivative) on rhesus monkeys experimentally infected with Plasmodium coatneyi.

We studied the effects of artesunate on rhesus monkeys infected with Plasmodium coatneyi. Sixteen rhesus monkeys were divided in four groups. Group I consisted of three monkeys that were splenectomized and were treated with three doses (loading dose: 3.3 mg/kg, maintenance doses: 1.7 mg/kg) of artesunate, group II consisted of three monkeys that were treated with three doses of artesunate (same as group I), group III consisted of two monkeys that were treated with one dose (3.3 mg/kg) of artesunate, and group IV consisted of five untreated monkeys. Parasitemias of these groups ranged from 13.3% to 19.5% before treatment. Twenty-four hours after administration, the parasitemia was reduced to 2.2% in group I and to < 0.1% in group II; parasitemia was lowered to 10.6% in group III only 3 hr after drug administration. The rate of sequestration in the cerebral microvessels, which was 29.4% in untreated animals, was < 0.1% in groups I and II (24 hr after treatment), and 2.0% in group III (3 hr after treatment). These data clearly indicate that artesunate not only reduced parasitemia, but also reduced the rate of parasitized red blood cell (PRBC) sequestration in cerebral microvessels. In an immunohistologic study, endothelial-leukocyte adhesion molecule-1 (ELAM-1) was not detected in group I after treatment with artesunate, although the presence of CD36, thrombospondin, intercellular adhesion molecule-1, IgG, and C3 in the cerebral microvessels was not altered. This is the first in vivo study to show that artesunate interferes with continued PRBC sequestration in the cerebral microvessels in cerebral malaria.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of acute uncomplicated falciparum malaria with a short course of artesunate followed by mefloquine.

The clinical results of this study indicate that a half-dose regimen of artesunate followed by mefloquine produces an acceptable cure rate when compared to other commonly available drugs for treating acute uncomplicated falciparum malaria in Thailand. The 90% cure rate was comparable to the results with either a full dose of artesunate (600 mg over 5 days) or mefloquine (25 mg/kg in divided doses six hours apart) as well as the combination of quinine-tetracycline administered for seven days. This abbreviated regimen, however was less effective than the full dose regimen of both drugs previously reported.

Treatment of patients with recrudescent falciparum malaria with a sequential combination of artesunate and mefloquine.

A sequential combination of artesunate followed by mefloquine was evaluated prospectively in 24 patients with acute recrudescent falciparum malaria. The sequential combination was used to minimize possible side effects and to take advantage of the ability of artesunate to rapidly clear parasitemia and the prolonged effect of mefloquine to clear residual parasites. All patients had experienced one or more treatment failures with one or more courses of the following drugs (administered alone or in combination): quinine, tetracycline, mefloquine, artesunate, and sulfadoxine/pyrimethamine. Sequential treatment with artesunate (600 mg over five days) followed by mefloquine (750 mg and 500 mg six hours apart) cured all 24 patients. Each patient was followed for 28 days and 10 were observed for at least 35 days without clinical or parasitologic evidence of recrudescence. Fever and parasite clearance times after treatment with the sequential combination were 32.8 +/- 19.3 hr (mean +/- SD) and 40.0 +/- 16.2 hr, respectively. Susceptibility testing of selected parasite isolates indicated that all of the isolates tested were resistant to one or more antimalarial drugs. These results suggest that sequential treatment with artesunate followed by mefloquine is effective and well-tolerated in patients with recrudescent falciparum malaria.

Innate resistance to new antimalarial drugs in Plasmodium falciparum from Nigeria.

The rapid dissemination of chloroquine-resistant Plasmodium falciparum in West Africa has been well documented and represents a significant health threat to autochthonous populations. The methodical development of alternative chemotherapeutic agents demands that dispensing new antimalarial drugs (mefloquine, halofantrine, and artemisinine [qinghaosu]) be closely monitored in order to protect their clinical utility. Indeed, mefloquine-resistant strains of P. falciparum have been reported. We present data from experiments in vitro on the innate resistance of P. falciparum isolates to mefloquine as well as a disturbing observation of transient resistance to artemisinine. The implications for the extended efficacy of these new antimalarial drugs are addressed.