Comparative pharmacokinetics of enrofloxacin and ciprofloxacin in lactating dairy cows and beef steers following intravenous administration of enrofloxacin.

The comparative pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin were investigated in lactating cows and beef steers. The plasma elimination half-life of either enrofloxacin or ciprofloxacin was shorter in cows than in steers. The overall production of ciprofloxacin was slightly higher in steers than in cows (metabolite ratio: 64% and 59%, respectively). There was no significant difference in plasma protein binding of enrofloxacin between cows (percent bound: 59.4%) and steers (percent bound: 60.8%). Ciprofloxacin was more extensively bound to plasma proteins in steers (percent bound: 49.6%) than in cows (percent bound: 33.8%). The steady state volume of distribution of enrofloxacin is comparable in cows (1.55 L/kg) and steers (1.59 L/kg). Within either bovine class, plasma elimination half-life of enrofloxacin and ciprofloxacin are comparable, while plasma protein binding was higher for enrofloxacin than for ciprofloxacin. Ciprofloxacin was more concentrated in milk than enrofloxacin.

Dose-finding and efficacy study for i.m. artemotil (beta-arteether) and comparison with i.m. artemether in acute uncomplicated P. falciparum malaria.

AIMS: The antimalarial efficacy/pharmacodynamics and pharmacokinetics of intramuscular (i.m.) artemotil in Thai patients with acute uncomplicated falciparum malaria were studied to determine effective dose regimens and to compare these with the standard dose regimen of artemether. METHODS: In part I of the study three different artemotil dose regimens were explored in three groups of 6-9 patients for dose finding: 3.2 mg kg-1 on day 0 and 1.6 mg kg-1 on days 1-4 (treatment A), 1.6 mg kg-1 on day 0 and 0.8 mg kg-1 on days 1-4 (treatment B), 3.2 mg kg-1 on day 0 and 0.8 mg kg-1 on days 1-4 (treatment C). In part II of the study, artemotil treatments A and C were compared in three groups of 20-22 patients with standard i.m. artemether treatment: 3.2 mg kg-1 on day 0 and 0.8 mg kg-1 on days 1-4 (treatment R). RESULTS: Full parasite clearance was achieved in all patients in Part I, but parasite clearance time (PCT) and fever clearance time (FCT) tended to be longer in treatment B. Also the incidence of recrudescence before day 28 (RI) tended to be higher for treatment B. In part II, the mean PCT for each of the two artemotil treatments (52 and 55 h, respectively) was significantly longer than for artemether (43 h). The 95% CI for the difference A vs R was 0, 16 h (P=0.0408) and for difference C vs R it was 2, 19 h (P=0.0140). FCT was similar for the three treatments. The incidence of RI ranged from 5 out of 19 for treatment C to 3 out of 20 for treatment R. Plasma concentration-time profiles of artemotil indicated an irregular and variable rate of absorption after i.m. injection. A late onset of parasite clearance was associated with delayed absorption and/or very low initial artemotil plasma concentrations. Pharmacokinetic-pharmacodynamic evaluations supported a relationship between the rate of parasite clearance and exposure to artemotil during approximately the first 2 days of treatment, and suggested that artemotil has a slower rate of absorption than artemether. Safety assessment, including neurological and audiometric examinations showed no clinically relevant findings. Adverse events before and during treatment included headache, dizziness, nausea, vomiting and abdominal pain. These are characteristic of acute malaria infections and resolved during treatment. CONCLUSIONS: The optimum dose regimen for artemotil in this study was identical to the standard dose regimen of artemether. The findings that artemotil is more slowly absorbed from the i.m. injection site than artemether, and that early systemic availability may be insufficient for an immediate onset of parasite clearance contributed to the decision to choose a higher loading dose of artemotil (divided over two injection sites) and to omit the fifth dose in later studies. With this optimized dosing schedule, the more pronounced depot characteristics of i.m. artemotil can be an advantage, since it may allow shorter hospitalization.

Arteether-induced brain injury in Macaca mulatta. I. The precerebellar nuclei: the lateral reticular nuclei, paramedian reticular nuclei, and perihypoglossal nuclei.

Malaria poses a threat across several continents: Eurasia (Asia and parts of Eastern Europe), Africa, Central and South America. Bradley (1991) estimates human exposure at 2,073,000,000 with infection rates at 270,000,000, illnesses at 110,000,000, and deaths at 1,000,000. Significant mortality rates are attributed to infection by the parasite Plasmodium falciparum, with an estimated 90% among African children. A worldwide effort is ongoing to chemically and pharmacologically characterize a class of artemisinin compounds that might be promising antimalarial drugs. The U.S. Army is studying the efficacy and toxicity of several artemisinin semi-synthetic compounds: arteether, artemether, artelinic acid, and artesunate. The World Health Organization and the U.S. Army selected arteether for drug development and possible use in the emergency therapy of acute, severe malaria. Male Rhesus monkeys (Macaca mulatta) were administered different daily doses of arteether, or the vehicle alone (sesame oil), for a period of either 14 days, or 7 days. Neuropathological lesions were found in 14-day arteether treated monkeys in the precerebellar nuclei of the medulla oblongata, namely: (1) the lateral reticular nuclei (subnuclei magnocellularis, parvicellularis, and subtrigeminalis), (2) the paramedian reticular nuclei (subnuclei accessorius, dorsalis, and ventralis), and the perihypoglossal nuclei (n. intercalatus of Staderini, n. of Roller, n. prepositus hypoglossi). The data demonstrate that the simina meduallry precerebellar nuclei have a high degree of vulnerability when arteether is given for 14 days at dose levels between 8mg/kg per day and 24 mg/kg per day. The neurological consequences of this treatment regimen could profoundly impair posture, gait, and autonomic regulation, while eye movement disorders might also be anticipated.

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.

The pharmacokinetics and bioavailability of dihydroartemisinin, arteether, artemether, artesunic acid and artelinic acid in rats.

The pharmacokinetics and bioavailability of dihydroartemisinin (DQHS), artemether (AM), arteether (AE), artesunic acid (AS) and artelinic acid (AL) have been investigated in rats after single intravenous, intramuscular and intragastric doses of 10 mg kg(-1). Plasma was separated from blood samples collected at different times after dosing and analysed for parent drug. Plasma samples from rats dosed with AM, AE, AS and AL were also analysed for DQHS which is known to be an active metabolite of these compounds. Plasma levels of all parent compounds decreased biexponentially and were a reasonable fit to a two-compartment open model. The resulting pharmacokinetic parameter estimates were substantially different not only between drugs but also between routes of administration for the same drug. After intravenous injection the highest plasma level was obtained with AL, followed by DQHS, AM, AE and AS. This resulted in the lowest steady-state volume of distribution (0.39 L) for AL, increasing thereafter for DQHS (0.50 L), AM (0.67 L), AE (0.72 L) and AS (0.87 L). Clearance of AL (21-41 mL min(-1) kg(-1)) was slower than that of the other drugs for all three routes of administration (DQHS, 55-64 mL min(-1) kg(-1); AM, 91-92 mL min(-1) kg(-1); AS, 191-240 mL min(-1) kg(-1); AE, 200-323 mL min(-1) kg(-1)). In addition the terminal half-life after intravenous dosing was longest for AL (1.35 h), followed by DQHS (0.95 h), AM (0.53 h), AE (0.45 h) and AS (0.35 h). Bioavailability after intramuscular injection was highest for AS (105%), followed by AL (95%) and DQHS (85%). The low bioavailability of AM (54%) and AE (34%) is probably the result of slow, prolonged absorption of the sesame-oil formulation from the injection site. After oral administration, low bioavailability (19-35%) was observed for all five drugs. In-vivo AM, AE, AS and AL were converted to DQHS to different extents; the ranking order of percentage of total dose converted to DQHS was AS (25.3-72.7), then AE (3.4-15.9), AM (3.7-12.4) and AL (1.0-4.3). The same ranking order was obtained for all formulations and routes of administration. The drug with the highest percentage conversion to DQHS was artesunic acid. Because DQHS has significant antimalarial activity, relatively low DQHS production could still contribute significantly to the antimalarial efficacy of these drugs. This is the first time the pharmacokinetics, bioavailability and conversion to DQHS of these drugs have been directly compared after different routes of administration. The results show that of all the artemisinin drugs studied the plasma level was highest for artelinic acid; this reflects its lowest extent of conversion to DQHS and its slowest rate of elimination.

Dose-dependent brainstem neuropathology following repeated arteether administration in rats.

Histopathological effects of the artemisinin antimalarial, beta-arteether, were evaluated in rats. Arteether (3.125-12.5 mg/kg/day, IM, in sesame oil) was administered for 7 consecutive days. Seven days following the last injection, histological evaluation of the brainstem was performed. Rats treated with 12.5 mg/kg showed significant neuropathology, including chromatolysis, in the nucleus trapezoideus and nucleus superior olive. To a lesser extent, neuropathology was present in the nucleus ruber. Mild neuropathology was also detected in other brainstem regions examined. Although no statistically significant neuropathology was found for the groups treated with 6.25 mg/kg/day and 3.125 mg/kg/day, substantial neuropathology was observed in a single rat in each of these treatment conditions. These results confirm and extend previous studies demonstrating brainstem neurotoxicity from artemisinin antimalarials. Furthermore, these results suggest that, in rats, brainstem auditory pathways may be particularly vulnerable. Early detection of arteether neuropathology may, therefore, require examination of auditory functions.

Biomimetic metabolism of artelinic acid by chemical cytochrome P-450 model systems.

PURPOSE: To study the reaction of artelinic acid with chemical model systems of cytochrome P-450 as a means of obtaining authentic samples of the putative metabolites necessary for identification of the mammalian metabolites of artelinic acid. METHODS: Artelinic acid was reacted with different organic complexes of iron(II). The reaction products were isolated and characterized by NMR and thermospray mass spectroscopy. RESULTS: Five compounds which are putative metabolites of artelinic acid were isolated from these reactions and unambiguously identified, while the identity of two other compounds await final confirmation. CONCLUSIONS: Standards of possible metabolites of artelinic acid can be produced by the reaction of the compound with ferrous complexes that may simulate cytochrome P-450 catalyzed metabolism of xenobiotics. This approach may provide a simple and versatile method for the formation of metabolites of artemisinin compounds which is more advantageous than previous approaches with fungal-based systems.

Arteether: risks of two-week administration in Macaca mulatta.

Male rhesus monkeys (Macaca mulatta) were administered daily doses of the antimalarial drug arteether. The 14-day treated group received either 24 mg/kg/day, 16 mg/kg/day, or 8 mg/kg/day. The seven-day treatment group received either 24 mg/kg/day or 8 mg/kg/day. All control cases in each group received the sesame oil vehicle alone. Neurologic signs were absent for animals in the seven and 14-day treatment groups except for one monkey which showed diffuse piloerection on day 14, and another monkey receiving 24 mg/kg/day for seven days showed mild lethargy after the fourth day. Mild, sporadic anorexia was noted in all animals by day 14, and a single animal showed diffuse piloerection on day 14. Surgical anesthesia preceded killing by exsanguination and was accompanied by perfusion fixation of the central nervous system. Brain sections were cut and then stained for study by light microscopy. Evidence of neuronal pathology, both descriptive and numerical, was collected. The neuroanatomic and neuropathologic findings demonstrated that arteether produced extensive brainstem injury when administered for 14 days. The magnitude of brainstem neurotoxicity was dose-dependent, where injury was greatest at the 24 mg/kg/day dose level, less at the 16 mg/kg/day dose level, and least at the 8 mg/kg/day dose level. Arteether induced multiple systems injury to brainstem nuclei of 1) the reticular formation (cranial and caudal pontine nuclei, and medullary gigantocellular and paragigantocellular nuclei); 2) the vestibular system (medial, descending, superior, and lateral nuclei); and 3) the auditory system (superior olivary nuclear complex and trapezoid nuclear complex). The vestibular nuclei and the reticular formation were most severely injured, with the auditory system affected less. The cranial nerve nuclei (somatic and splanchnic) appeared to escape damage, with the exception of the abducens nerve nucleus. The same brainstem nuclear groups of seven-day treated monkeys appeared normal. The statistical data are concordant with the descriptive data in demonstrating neurotoxic effects. In summary, no neurologic deficits were detected in any of the vehicle control monkeys (14-day and seven-day cases). Monkeys in the 14-day treatment group were free of clinical neurologic signs throughout the first week. At day 14, fine horizontal nystagmus was seen in one monkey, and another monkey exhibited diffuse piloerection. Monkeys in the seven-day treatment group were free of clinical neurologic signs except for one case. This monkey was treated with 24/mg/kg/day of arteether and exhibited lethargy after the fourth day. These indications of dysfunction arose too late to be practical indicators of neurotoxicity.

Comparative bioavailability of oral, rectal, and intramuscular artemether in healthy subjects: use of simultaneous measurement by high performance liquid chromatography and bioassay.

1. The pharmacokinetic and effect kinetic properties of oral (p.o.), intramuscular (i.m.), and intrarectal (i.r.) artemether (5 mg kg-1) were compared in a crossover study in eight healthy adult volunteers. Plasma concentrations of artemether (AM) and its active metabolite dihydroartemisinin (DHA) were measured by high performance liquid chromatography with reductive mode electrochemical detection (h.p.l.c.-ECD), and plasma antimalarial activity in vitro (effect) was assessed on the same samples by a sensitive bioassay (BA). 2. Artemether was absorbed rapidly after oral administration with a mean (95% CI) Cmax for the parent compound of 406 (249 to 561) nmol l-1 and for DHA of 1009 (639 to 1379) nmol l-1 with tmax values of 1.7 (1.2 to 2.2) and 1.8 (1.4 to 2.2) h respectively. The mean (95% CI) elimination half-life of AM was 2.6 (1.8 to 3.4) h and for DHA was 1.9 (1.4 to 2.4) h. Plasma concentration and effect profiles with h.p.l.c.-ECD and BA were similar suggesting that other unidentified bioactive metabolites contributed little to antimalarial activity in vivo. 3. Absorption was slower, more variable, and DHA concentrations were lower following the i.m. and i.r. routes of administration. The mean (95% CI) relative bioavailability compared with oral artemether in the 6 h following administration AUC (0.6h) was 25 (9 to 41)% following i.m. and 35 (10 to 60)% following i.r. artemether. 4. These data demonstrate that oral artemether undergoes extensive first pass metabolism to the more active metabolite DHA. Plasma antimalarial activity following oral administration is significantly greater than following i.m. administration. The i.r. route of administration provided similar bioavailability to i.m. injection but there was considerable variability in absorption following both routes. Further studies are needed to determine whether i.r. artemether would be an effective treatment of severe malaria in the rural tropics in situations where oral or parenteral administration is not possible.

Primary toxic effects of anthraquinone-2-sulfonic acid in rat liver microsomes.

(1) The endogenous, NADPH-supported production of H2O2 and of O2-.-radicals in rat liver microsomes was very strongly enhanced in the presence of anthraquinone-2-sulfonic acid (AQSA). (2) This induction of H2O2 and of O2-.-radicals was catalyzed by the microsomal NADPH:cytochrome P450 oxidoreductase (EC 1.6.2.4). (3) AQSA was reduced to AQSA radicals by reductase; AQSA radicals reduce molecular oxygen to O2-.-radicals, which are readily dismutated to H2O2 by the microsomal superoxide dismutase. (4) O2-.-radicals are the sole precursors of all AQSA-induced production of H2O2 in liver microsomes.

Metabolism of a candidate 8-aminoquinoline antimalarial agent, WR 238605, by rat liver microsomes.

The in vitro metabolism of the 8-aminoquinoline, 8-(4-amino-1- methylbutylamino-2,6-dimethoxy-4-methyl-5-(3-trifluromethyl- phenoxy)quinoline (WR 238605), by rat liver microsomes was studied. After incubation of WR 238605 with rat liver microsomes, the metabolites were isolated either by direct solvent extraction or by extraction in the presence of ethyl chloroformate. WR 238605 was extensively metabolized to aminophenolic compounds, which underwent air oxidation during the isolation process to a mixture of quinones and quinoneimines. Because of the instability of the metabolites toward air oxidation, most of them could only be isolated as the ethoxycarbonyl derivatives by in situ derivatization with ethyl chloroformate. The metabolism of WR 238605 involved the expected metabolic pathways, such as O-demethylation, N-dealkylation, N-oxidation, and oxidative deamination. In addition, C-hydroxylation involving the 8-aminoalkylamino side chain, which was previously unknown for 8-aminoquinoline analogs, was found to be an important metabolic pathway for WR 238605. Most of the metabolites retained the 5-(m-trifluoromethyl)phenoxy group of WR 238605. Direct and indirect supporting evidence for the structure of the metabolites of WR 238605 came from the concomitant study of the in vitro metabolism of six other compounds that are putative metabolites of WR 238605.

Side-chain hydroxylation in the metabolism of 8-aminoquinoline antiparasitic agents.

Primaquine, 8-(4-amino-1-methylbutylamino)-6-methoxyquinoline, is an antimalarial 8-aminoquinoline derivative. Although it has been in use since 1952, its metabolism has not been clearly defined. This is due to the instability of the expected aminophenol metabolites and their amphoteric nature, which makes their isolation difficult. Recent studies on the metabolism of WR 238605, a new primaquine analog, has shown that these problems may be solved by extracting the metabolites in the presence of ethyl chloroformate. Subsequent identification of the ethoxycarbonyl derivatives of the metabolites has made it possible to define the in vitro metabolism of primaquine. The primary metabolic pathways of primaquine involved hydroxylation of the phenyl ring of the quinoline nucleus and C-hydroxylation of the 3'-position of the 8-aminoalkylamino side chain. Ring-hydroxylation of primaquine gives rise to 5-hydroxyprimaquine, which on demethylation produces 5-hydroxy-6-demethylprimaquine. Side-chain hydroxylation of primaquine gives rise to 3'-hydroxyprimaquine, which also undergoes O-demethylation to 3'-hydroxy-6-demethylprimaquine. 6-Demethylprimaquine, a putative metabolite of primaquine, also underwent metabolism involving 3'-hydroxylation of the side chain. WR 6026, 8-(6-diethylaminohexylamino)-6-methoxy-4-methylquinoline, is an antileishmanial 8-aminoquinoline derivative. The in vitro metabolism of WR 6026 also results in the formation of side chain-oxygenated metabolites. The present results, together with previous observations on the metabolism of WR 238605 and closely related primaquine analog, suggest that side-chain oxygenation is an important metabolic pathway of antiparasitic 8-aminoquinoline compounds in general.

Fatal neurotoxicity of arteether and artemether.

Artemisinin (qinghaosu) and several derivatives have been developed and are in use as antimalarial drugs but scant information is available regarding animal or human toxicity. Following a eight-day, multiple-dose, pharmacokinetic study of arteether (AE) (10 mg/kg/day [n = 6] and 20 mg/kg/day [n = 6]) in dogs, all high-dose animals displayed a progressive syndrome of clinical neurologic defects with progressive cardiorespiratory collapse and death in five of six animals. Neurologic findings included gait disturbances, loss of spinal and pain response reflexes, and prominent loss of brain stem and eye reflexes. Animals had prolongation of QT interval corrected for rate (QTc) on electrocardiograms (ECGs) with bizarre ST-T segment changes. Prominent neuropathic lesions were noted to be primarily limited to the pons and medulla. Similar lesions with dose-related severity were noted in eight other dogs studied in a second study with intramuscular (IM) administration of AE in sesame oil during a 28-day, dose-ranging study using 5, 10, 15, and 20 mg/kg/day. Injury, graded by a pathologist blinded to the dose group, showed a dose-related, region-specific injury in all animals that was most pronounced in the pons. Further studies in Sprague-Dawley rats using IM administration of AE and artemether (AM) at a dose of 12.5-50 mg/kg/day for 28 days confirmed the onset of a clinical neurologic syndrome with dose-related changes in body weight, activity, and seizure-like activity, stereotypic movement disorders, and ECG changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotoxicity in animals due to arteether and artemether.

Several artemisinin (qinghaosu) derivatives have been developed and are in use as antimalarial drugs but scant animal or human toxicity data are available. We noted a progressive syndrome of clinical neurological defects with cardio-respiratory collapse and death in 5/6 dogs dosed daily for 8 d with intramuscular arteether (AE) at 20 mg/kg/d in a pharmacokinetic study. Neurological findings included gait disturbances, loss of spinal reflexes, pain response reflexes and prominent loss of brain-stem and eye reflexes. Electrocardiography showed prolongation of the QT interval corrected for rate (QTc). Prominent neuropathic lesions were sharply limited to the pons and medulla. Neurological injury, graded by a pathologist 'blinded' to dose group, showed a dose-related region-specific injury which was most pronounced in the pons and medulla in all animals. Rats treated with AE and artemether (AM) at 12.5 to 50 mg/kg/d for 28 d confirmed clinical neurological abnormalities with high doses (> 25 mg/kg/d) after 6-14 d. Neuropathological examination of rat brain sections at 5 levels from the rostral cerebrum to the caudal medulla showed a dose-related pattern of injury characterized by hyalinized neuron cell bodies and loss of Nissl substance; changes congruent with those noted in dogs. No significant difference was noted in the extent, type, or distribution of lesions in the brains of rats treated with equivalent doses of AE or AM.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and kinetic-dynamic modeling of an 8-aminoquinoline candidate anticyanide and antimalarial drug (WR242511).

Malaria is a major cause of health problems in a large portion of the world. The 8-aminoquinoline compound, primaquine, is one of the only compounds useful for relapses of Plasmodium vivax and Plasmodium ovale malaria. Primaquine has several toxicities that include methemoglobinemia and hemolytic anemia. The induction of methemoglobinemia is a treatment for cyanide poisoning. We studied the pharmacokinetics and pharmacodynamics (percentage methemoglobin) for WR242511, an 8-aminoquinoline primaquine replacement and potential anticyanide compound. The drug's pharmacokinetics and pharmacodynamics are described for oral and intravenous dosing, and two kinetic-pharmacodynamic models are shown to describe the single dose data. A significant lag occurs between the onset of appearance of drug in the plasma and the onset of methemoglobinemia. Peak drug concentrations occurred within 4 hr for oral dosing, and peak effect (percentage methemoglobin) did not occur for 72-96 hrs for both the oral and intravenous routes. Elimination half-life for the drug was 30 +/- 14 hr. Two kinetic-dynamic models, one with an effect compartment relating drug concentration to effect and one with metabolite causing a first-order conversion of hemoglobin to methemoglobin, are compared as to their ability to predict multiple dose pharmacokinetics and pharmacodynamics. Both models were useful in predicting drug concentrations and methemoglobin levels for multiple-dose experiments.

High-performance liquid chromatographic method for the determination of a candidate 8-aminoquinoline antimalarial drug (WR 242511) using oxidative electrochemical detection.

WR 242511 (or I) is a new compound of the 8-aminoquinoline class designed to replace primaquine for the treatment of malaria. In order to perform preclinical and clinical testing, an assay was needed to determine drug levels in plasma samples. A simple and reliable reversed-phase high-performance liquid chromatographic (HPLC) method for the measurement of I in plasma using oxidative electrochemical detection is described. A 250-microliters plasma sample containing WR 256408 (or II) as internal standard was extracted with tert.-butyl methyl ether-2-propanol. A 25-microliters aliquot of the extractant was used for HPLC analysis. The mobile phase was 50:50 acetonitrile-sodium acetate (50 mM, pH 6) with 1 mM EDTA. Compounds I and II were separated within 10 min. The limit of detection for I was 10 ng/ml (plasma) with a recovery around 72%. The method was validated in a dog experiment where levels were followed for 48 h. The method is sensitive and robust and can be used for routine drug analysis during pharmacokinetic studies.

Reduction of 1-nitroso-2-naphthol by NADPH in the presence of liver microsomes.

1. The endogenous, NADPH-supported production of H2O2 and of O2-.-radicals in liver microsomes, was very strongly enhanced in the presence of 1-nitroso-2-naphthol. 2. A 30-fold induction by NON was the consequence of its direct reduction to NON-radicals, catalyzed by microsomal NADPH:cytochrome P450 reductase. 3. Nitroso radicals reduce molecular oxygen to superoxide anion radicals, which were readily dismutated by superoxide dismutase to hydrogen peroxide. 4. O2-.-radicals were the sole precursors of all NON-induced production of H2O2 in liver microsomes.

The effects of age on the pharmacokinetics and biotransformation of theophylline in vivo and in vitro in the Mongolian gerbil (Meriones unguiculatus).

The effect of post maturational aging on the in vivo disposition of theophylline was examined in the Mongolian gerbils (Meriones unguiculatus) aged 30-39 (old), 12-18 (middle-aged) and 3 (young) months following a 20 mg/kg i.p. dose. Biotransformation of theophylline was also examined in liver microsomes from non-induced and 3-methylcholanthrene induced gerbils. Analysis of theophylline plasma kinetics showed decreased clearance, increased half-life and increased volume of distribution in old vs. young animals. Clearance to the 1,3-dimethyluric acid metabolite was similar for all age groups, while clearance to the 1-methyluric acid metabolite was significantly lower in the middle-aged group compared to that of young and old gerbils. Urinary recovery of 1-methylurate was increased in old vs. young and middle-aged animals while recovery of theophylline was decreased. 3-Methylcholanthrene induction resulted in decreased recovery of theophylline and increased recovery of 1,3-dimethylurate and 1-methylurate in young and middle-aged gerbils compared to non-induced controls. Decreased microsomal protein content was observed in old vs. young and middle-aged gerbils and an age-related decrease in cytochrome P-450 content (nmol P-450/g liver) was also observed. The rate of dimethylurate formation was decreased 37% in microsomes from old vs. young and middle-aged gerbils. 3-Methylcholanthrene administration resulted in a 2- and 1.5-fold increase in the rate of 1,3-dimethylurate formation in young and middle-aged gerbils, respectively. The results of these experiments indicate that the Mongolian gerbil may be useful for the study of the biochemical mechanisms underlying age-related changes in the biotransformation and kinetics of theophylline.