Comparative pharmacokinetics of phenylbutazone in healthy young-adult and geriatric horses.

OBJECTIVE: To evaluate the effects of aging on phenylbutazone (PBZ) disposition in older horses (≥ 25 years old) compared to young adults (4 to 10 years old) by characterizing the pharmacokinetic profile of PBZ and its active metabolite, oxyphenbutazone (OPBZ), following a 2.2-mg/kg dose, IV. We hypothesized that the disposition of PBZ will be affected by age. ANIMALS: 16 healthy horses (8 young adults aged 4 to 10 years and 8 geriatric horses ≥ 25 years old). METHODS: Horses were administered a single 2.2-mg/kg PBZ dose, IV. Plasma samples were collected at designated time points and frozen at -80 °C until assayed using liquid chromatography-tandem mass spectrometry. Pharmacokinetic analyses were performed using Phoenix WinNonlin, version 8.0 (Certara). Both clinical and pharmacokinetic data were compared between age groups using independent samples t tests, with P < .05 considered significant. RESULTS: Baseline characteristics did not differ between groups, with the exception of age, weight, and plasma total solids. Plasma concentrations of PBZ were best described by a two-compartment model. The maximum plasma concentration of OPBZ was reached at 5 hours for both age groups, and the metabolite-to-parent-drug area-under-the-curve ratios were approximately 20% for both groups. None of the pharmacokinetic parameters of PBZ or its metabolite, OPBZ, differed significantly between age groups. CLINICAL RELEVANCE: The hypothesis was rejected as there was no significant difference in PBZ disposition in young-adult horses compared to geriatric horses. Our data do not support the need for dose adjustments of PBZ in clinically healthy geriatric horses.

Clinical efficacy and pharmacokinetics of antimony in cutaneous leishmaniasis patients treated with sodium stibogluconate.

The efficacy and pharmacokinetics of antimony were explored in 12 young male patients with cutaneous leishmaniasis following intramuscular administration of sodium stibogluconate equivalent to 600 mg of antimony (Sb). Patients' cure rate was evaluated up to 6 weeks after treatment. Blood samples were collected at different time periods on the first and last days of a 3-week treatment. Twenty-four-hour urine samples were also collected on both occasions for the estimation of renal clearance (CL(r)). The blood concentrations of the Sb time profile were best described by a 2-compartment model with a first-order absorption rate. The mean absorption half-life was 0.21 ± 0.023 and 0.36 ± 0.18 hours for the first and last doses, respectively. A rapid distribution phase was followed by a slower elimination phase of a half-life of 9.4 ± 1.9 and 9.69 ± 2.3 hours for both days, respectively. An accumulation index of 2.33 was calculated. The fraction of dose excreted in urine was 0.386 ± 0.11 and 0.326 ± 0.05 on both occasions, respectively. The mean CL(r) was 4.88 ± 1.13 and 4.58 ± 1.05 L/h. In the current study, all of the patients were completely healed by week 6 after the end of treatment, as judged by the treating physician. In conclusion, the blood profile of antimony seems to be multicompartmental in nature.

The effect of chronic cadmium exposure on the pharmacokinetics of theophylline and ciprofloxacin in rats.

Cadmium has been associated with a number of adverse health effects but the impact of those effects on the pharmacokinetics of different drugs has not been investigated. Therefore, the pharmacokinetics of theophylline and ciprofloxacin were studied in cadmium-exposed and control rats (72 rats) following i.p. (6.5mg/kg) and p.o. (10mg/kg) administration, respectively. The third-generation offsprings of rats exposed to 100 microg/mL of cadmium chloride in drinking water were used in this study. Following 8 weeks of exposure, animals received the drugs as a single dose. Blood samples were withdrawn at different time-points and the plasma concentrations of both drugs were analyzed by HPLC. The pharmacokinetic parameters of theophylline and ciprofloxacin were altered significantly in the cadmium-exposed animals. For theophylline, a statistically significant increase (p<0.0001) in C(max) (69%) and AUC(0-)(infinity) (68%) of theophylline in the cadmium-exposed rats as compared to the control were observed. A corresponding significant (p<0.0001) reduction of 41% in clearance (CL/F) of theophylline was detected in the exposed group. Neither the half-life nor the mean residence time (MRT) showed any significant change due to the exposure to cadmium. For ciprofloxacin, no significant difference was seen in the C(max) of the exposed group as compared to the control animals. However, a delay in T(max) was observed in the exposed group (from 0.16(+/-0.003) to 0.37(+/-0.14)h). A small, but significant increase in t(1/2) (p<0.05) was detected (1.74(+/-0.25) vs. 1.45(+/-0.12)h). A significant reduction (p<0.05) of CL/F from 30.54(+/-1.9) to 24.01(+/-3.81)mL/min/kg was seen in the treated group. The current investigation showed that chronic exposure to cadmium could have a very significant impact on altering the pharmacokinetic parameters of various drugs. Therefore, in cadmium-polluted areas, dose adjustments and drug monitoring, especially for drugs with a narrow therapeutic window, should be carried out.