Arteether toxicokinetics and pharmacokinetics in rats after 25 mg/kg/day single and multiple doses.

Multiple doses of arteether (ARTE) at 25 mg/kg cause CNS and anorectic toxicities in rats. The same dose of ARTE was used to study the toxicokinetics (TK) after multiple injections and the pharmacokinetics (PK) following single administration. Animals were administered ARTE in sesame oil for 7 days, blood samples were collected using destructive sampling for up to 192 h after dosing and assayed by HPLC-ECD. Two other groups of rats were administered either a single 25 mg/kg i.v. or i.m. dose. In addition, the drug remaining in the i.m. injection site was measured. During the 7 day treatments, anorectic toxicity of ARTE was observed, and that caused significant reductions in food consumption and body weight after day 2. TK data on days 2-7 revealed marked changes compared to the PK parameters estimated on day 1. AUC (4367 ng x h/ml) on day 7 was 5-fold higher than AUC (905 ng x h/ml) on day 1. The volume of distribution at steady state (V(SS)) on day 7 (41.8 l) was 40% of the day 1 value of the V(SS) (104.3 l). Clearance (CL) was increased by 89% of the day 1 value, from 0.98 l/h to 1.85 l/h on day 7. The elimination t(1/2) of ARTE was also prolonged from 13.7 h (day 1) to 31.2 h (day 7). These data suggest that ARTE may have altered its distribution and elimination in rats as a result of the systemic toxicity. Analysis of the injection sites showed that 38% and 91% of the total amount of ARTE single dose remained in the muscles at 24 h (after first injection) and 168 h (at 24 h after 7 daily multiple doses), respectively. Fast and slow absorption phases from muscle were seen with t(1/2) of 0.97 h and 26.3 h, respectively. The apparent elimination t(1/2) of ARTE after i.m. injection (13.7 h) was much longer than that after i.v. dosing (0.67 h) due to the prolonged muscle absorption phase. Acute toxicity data of artemisinin drugs demonstrated that animals receiving a high single ARTE dose in sesame oil died between days 5-11, similar to artemether. When animals received dihydroartemisinin formulated in 50% DMAC/oil, or artesunic acid and artelinic acid in 0.9% saline vehicle, they died between days 1 and 2. This suggests that delayed onset toxicity and death in the ARTE rats may also be due to slow absorption and prolonged drug exposure. Therefore multiple i.m. administrations cause anorexia and drug accumulation, possibly affecting the toxicokinetics and efficacy of the drug.

Pharmacology and toxicology of artelinic acid: preclinical investigations on pharmacokinetics, metabolism, protein and red blood cell binding, and acute and anorectic toxicities.

The pharmacokinetics, metabolism, protein binding, red blood cell (RBC) binding, stability in vitro, and acute and anorectic toxicity of artelinic acid (ARTL) were investigated in various animal species and human blood samples. Absorption and distribution following 10 mg/kg intramuscular or oral administration in dogs and rats were very rapid with t1/2 0.12-0.54; there were also a high AUC (11,262 ng/h/mL) and Vss (9.5 L/kg), low CL (15 mL/min/kg) and long elimination time (t1/2 = 2.6 h), compared with rat data. Oral bioavailability of ARTL was 79.7% in dogs and 30.1% in rats. The conversion of ARTL to dihydroartemisinin (DART) in dogs (0.1-0.5% of total dose) after 3 routes of administration (intravenous, intramuscular and oral) was 10-fold lower than that in rats. In rats dosed with [14C]ARTL, unchanged ARTL accounted for less than 13% of the total radioactivity after all 3 administration routes, suggesting that ARTL was extensively biotransformed. The half-lives of total radioactivity (21-49 h) in urine were much longer than that of unchanged ARTL in plasma (1.4-3.7 h), indicating that some long-lasting metabolites of ARTL were formed in rats. The mass balance data showed that 77-83% of total radioactivity was recovered in urine and faeces. High binding capacity (79-95%) and low binding affinity (1.1-9.3 x 10-7 M) of ARTL were measured in rat, rabbit, dog, monkey and human plasma. The RBC/plasma ratios of [14C]ARTL were 0.35 and 0.44 for dog and human plasma, respectively. ARTL was much more stable than artesunic acid (ARTS) in rat and dog plasma, and both ARTL and ARTS were more stable in dog plasma than in rat plasma in vitro. The 50% lethal dose (LD50) of ARTL in rats was about 535 mg/kg. Multiple intramuscular dosing for 7 d of 50 mg/kg/d of ARTL caused mild anorectic toxicity compared to ARTS in rats. In contrast to 4 other artemisinin derivatives, ARTL seems to be a good antimalarial candidate as it has the highest plasma concentration, the highest binding capacities in RBC, the highest oral bioavailability, the longest elimination half-life, the lowest metabolism rate and the lowest toxicity at equivalent dose levels.

Metabolism of beta-arteether to dihydroqinghaosu by human liver microsomes and recombinant cytochrome P450.

beta-Arteether (AE) is an endoperoxide sesquiterpene lactone derivative currently being developed for the treatment of severe, complicated malaria caused by multidrug-resistant Plasmodium falciparum. Studies were undertaken to determine which form(s) of human cytochrome P-450 catalyze the conversion of beta-arteether to its deethylated metabolite, dihydroqinghaosu (DQHS), itself a potent antimalarial compound. In human liver microsomes, AE was metabolized to DQHS with a Km of 53.7 +/- 29.5 microM and a Vmax of 1.64 +/- 1. 78 nmol DQHS/min/mg protein. AE biotransformation to DQHS was inhibited by ketoconazole and troleandomycin. Ketoconazole was a competitive inhibitor, with an apparent Ki of 0.33 +/- 0.11 microM. Because AE is being developed for patients who fail primary treatment, it is possible that AE may be involved in life-threatening drug-drug interactions, such as the associated cardiotoxicity of mefloquine and quinidine. Coincubation of AE with other antimalarials showed mefloquine and quinidine to be competitive inhibitors with a mean Ki of 41 and 111 microM, respectively. Metabolism of AE using human recombinant P450s provided evidence that cytochrome P450s 2B6, 3A4, and 3A5 were the primary isozymes responsible for its deethylation. CYP3A4 metabolized AE to dihydroqinghaosu at a rate approximately 10 times that of CYP2B6 and approximately 4.5-fold greater than that of CYP3A5. These results demonstrate that CYP3A4 is the primary isozyme involved in the metabolism of AE to its active metabolite, DQHS, with secondary contributions by CYP2B6 and -3A5.

Age-associated changes in specific errors on the Benton Visual Retention Test.

While total errors on the Benton Visual Retention Test (BVRT) are known to increase in normal aging, there is little information on changes for specific error types. We examined the differential increase in seven specific error categories for 2,000 participants in the Baltimore Longitudinal Study of Aging. Cross-sectional analyses indicated that all errors increased with age, but differences between age groups in error profiles suggested relatively greater age effects for distortions, omissions, and rotations. There were also significant gender differences in error profiles, reflecting increased rotation and omission errors in females. Longitudinal analyses of age changes for a subset of 673 participants with three BVRT assessments were consistent with the cross-sectional data and indicated intra-individual increases with age in distortions, omissions, and rotations. While women made more omission errors, men showed steeper increases in omission errors with age. These findings suggest that cerebral aging impacts all categories of BVRT errors but has differential effects on particular error types.