Detection of allopurinol and oxypurinol in canine urine by HPLC/MS-MS: Focus on veterinary clinical pharmacokinetics.

Allopurinol is the most commonly used drug for the treatment of hyperuricemia in people, and in view of the risks of fatal hypersensitivity in patients with renal dysfunction, doses based on the glomerular filtration rate are proposed. In veterinary medicine, allopurinol is used in the treatment of canine leishmaniasis (CanL) caused by Leishmania infantum owing to the drug action of inhibiting the parasite's RNA synthesis. However, renal dysfunction frequently ensues from disease progression in dogs. The purpose of the present study was to standardize and validate a sensitive high-performance liquid chromatography-mass spectrometric (HPLC-MS/MS) method to determine the concentration of allopurinol and its active metabolite oxypurinol in canine urine for clinical pharmacokinetic investigation. Urine samples of eleven (11) dogs with naturally occurring CanL and in the maintenance phase of the treatment with alopurinol were used. For the chromatographic analysis of urine, the mobile phase consisted of a solution of 0.1 % formic acid (88 %) in 10 mM ammonium acetate. Separation of allopurinol and oxypurinol occurred in a flow of 0.8 mL/min on a C8 reverse phase column 5 µm, and acyclovir was the internal standard. The HPLC-MS/MS method was validated by reaching the limits of detection and quantification, reproducibility and linearity. The lower limit of quantification achieved by the method was 10 µg/mL for both allopurinol and oxypurinol. Calibration curves were prepared in blank urine added with allopurinol at concentrations of 10-1000 µg/mL, and oxypurinol at 10-200 µg/mL. Coefficients of variation of less than 15 % between intracurrent and intercurrent accuracy values were observed for both allopurinol and oxypurinol. Urine test samples remained stable after being subjected to freeze-thaw cycles and remaining at room temperature for 4 h. The method proved to be adequate to quantify allopurinol and oxypurinol in urine samples from dogs under treatment.

Post-marketing assessment of generic tamoxifen in Brazilian breast cancer patients.

Generic formulations of tamoxifen are commonly prescribed to oestrogen receptor-positive breast cancer patients at the Brazilian National Cancer Institute (INCA). We carried out a post-marketing surveillance of the generic tamoxifen formulation in current use at INCA, by comparing plasma concentrations of the parent drug and metabolites obtained with the generic vs the reference formulation. Thirty patients participated in an open-label, bracketed protocol, comprising 3 successive phases of 30-32 days each: the generic formulation was used in phases 1 and 3 and the reference formulation in phase 2. Two blood samples were collected in the last 4 days of each phase, for LC-MS/MS quantification of tamoxifen and metabolites in plasma. The median plasma concentrations (ng/mL) for the reference formulation were as follows: tamoxifen, 135.0 (CI 95% 114.2-155.8); endoxifen, 35.3 (30.0-40.8); and 4-hydroxytamoxifen, 4.8 (4.2-5.4). The endoxifen/tamoxifen plasma concentration ratio was 0.27 (0.21-0.25). ANOVA detected no statistically significant difference in plasma concentrations of tamoxifen, metabolites or the endoxifen/tamoxifen ratio among the three phases. The genetic component (rGC) of the CYP2D6-mediated conversion of tamoxifen into endoxifen, estimated using the repeated drug administration procedure across the three phases, was 0.87, pointing to an important component of genetic variability. In conclusion, this first post-marketing surveillance trial of oncologic generic drugs carried out in Brazilian patients verified the switchability between the reference and the generic tamoxifen formulation currently used at our institution. The adopted bracketed protocol adds confidence to this conclusion and may serve as a frame for future trials of post-marketing assessment of other generic drug products.

Evaluation of potential herbal-drug interactions of a standardized propolis extract (EPP-AF®) using an in vivo cocktail approach.

ETHNOPHARMACOLOGICAL RELEVANCE: Propolis has been employed extensively in many cultures since ancient times as antiseptic, wound healing, anti-pyretic and others due to its biological and pharmacological properties, such as immunomodulatory, antitumor, anti-inflammatory, antioxidant, antibacterial, antiviral, antifungal, antiparasite activities. But despite its broad and traditional use, there is little knowledge about its potential interaction with prescription drugs. AIM OF THE STUDY: The main objective of this work was to study the potential herbal-drug interactions (HDIs) of EPP-AF® using an in vivo assay with a cocktail approach. MATERIALS AND METHODS: Subtherapeutic doses of caffeine, losartan, omeprazole, metoprolol, midazolam and fexofenadine were used. Sixteen healthy adult volunteers were investigated before and after exposure to orally administered 125 mg/8 h (375 mg/day) EPP-AF® for 15 days. Pharmacokinetic parameters were calculated based on plasma concentration versus time (AUC) curves. RESULTS: After exposure to EPP-AF®, it was observed decrease in the AUC0-∞ of fexofenadine, caffeine and losartan of approximately 18% (62.20 × 51.00 h.ng/mL), 8% (1085 × 999 h.ng/mL) and 13% (9.01 × 7.86 h.ng/mL), respectively, with all 90% CIs within the equivalence range of 0.80-1.25. On the other hand, omeprazole and midazolam exhibited an increase in AUC0-∞ of, respectively, approximately 18% (18.90 × 22.30 h.ng/mL) and 14% (1.25 × 1.43 h.ng/mL), with the upper bounds of 90% CIs slightly above 1.25. Changes in pharmacokinetics of metoprolol or its metabolite α-hydroxymetoprolol were not statistically significant and their 90% CIs were within the equivalence range of 0.80-1.25. CONCLUSIONS: In conclusion, our study shows that EPP-AF® does not clinically change CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A activities, once, despite statistical significant, the magnitude of the changes in AUC values after EPP-AF® were all below 20% and therefore may be considered safe regarding potential interactions involving these enzymes. Besides, to the best of our knowledge this is the first study to assess potential HDIs with propolis.

Albendazole Sulfoxide Plasma Levels and Efficacy of Antiparasitic Treatment in Patients With Parenchymal Neurocysticercosis.

BACKGROUND: The efficacy of albendazole therapy in patients with parenchymal neurocysticercosis (NCC) is suboptimal. Plasma levels of albendazole sulfoxide (ASOX), the active metabolite of albendazole, are highly variable among patients. We hypothesized that high ASOX plasma levels during albendazole therapy may be associated with an increased antiparasitic efficacy. METHODS: ASOX plasma levels were measured at treatment day 7 in 118 patients with parenchymal NCC enrolled in a treatment trial. The relationships between increasing ASOX plasma levels with the proportion of cysts resolved and the proportion of patients with complete cyst resolution (evaluated by 6-month brain magnetic resonance) were assessed. RESULTS: There was a trend toward a higher proportion of cysts resolved and a higher proportion of patients cured with increasing quartiles of ASOX plasma levels. In patients with 3 or more brain cysts, the regression analysis adjusted by the concomitant administration of praziquantel (PZQ) showed a 2-fold increase in the proportion of cysts resolved (risk ratio [RR], 1.98; 95% confidence interval [CI], 1.01-3.89; P = .048) and 2.5-fold increase in the proportion of patients cured (RR, 2.45; 95% CI, .94-6.36; P = .067) when ASOX levels in the highest vs the lowest quartile were compared. No association was found in patients with 1-2 brain cysts. CONCLUSIONS: We suggest an association between high ASOX plasma levels and increased antiparasitic efficacy in patients with parenchymal NCC. Nonetheless, this association is also influenced by other factors including parasite burden and concomitant administration of PZQ. These findings may serve to individualize and/or adjust therapy schemes to avoid treatment failure.

Pharmacokinetics and pharmacodynamics of rocuronium in young adult and elderly patients undergoing elective surgery.

OBJECTIVE: To evaluate the impact of advanced age on rocuronium kinetic disposition in ASA I-III patients undergoing elective surgeries. METHODS: Young adult (20-50 years, n = 15) and elderly patients (65-85 years, n = 14) submitted to surgery under general anaesthesia were investigated. All patients were induced with individual intravenous doses of midazolam, rocuronium, fentanyl and propofol. Rocuronium-induced neuromuscular block was monitored by train of four stimulations of the adductor muscle of the thumb on the ulnar nerve. The pharmacokinetic parameters were calculated by non-compartmental analysis. The relationship between rocuronium plasma concentration and the neuromuscular blockade was described by a sigmoidal Emax model. KEY-FINDINGS: Elderly patients presented decreased Cl (2.1 ml/kg per min vs 2.8 ml/kg per min; P = 0.0123); increased AUC/dose (507.8 µg min/ml (mg/kg) vs 392.2 µg min/ml/(mg/kg); P = 0.0168) and reduced volume of distribution (285.4 ml/kg vs 435.6 ml/kg, P = 0.0434) compared to young adults. The concentrations required to achieve 50% of maximum neuromuscular block (EC50) were similar for young adult (338.8 ng/ml) and elderly (462.7 ng/ml) patients (P > 0.05). CONCLUSIONS: Elderly patients showed increased AUC/D and reduced total Cl compared to young adult patients due to the age-related reduced renal function. Differences in the PK-PD properties of rocuronium in elderly population are due to changes in drug disposition rather than to alterations in the sensitivity to the drug.

Busulfan dosing algorithm and sampling strategy in stem cell transplantation patients.

AIM: The aim of this investigation was to develop a model-based dosing algorithm for busulfan and identify an optimal sampling scheme for use in routine clinical practice. METHODS: Clinical data from an ongoing study (n = 29) in stem cell transplantation patients were used for the purposes our analysis. A one compartment model was selected as basis for sampling optimization and subsequent evaluation of a suitable dosing algorithm. Internal and external model validation procedures were performed prior to the optimization steps using ED-optimality criteria. Using systemic exposure as parameter of interest, dosing algorithms were considered for individual patients with the scope of minimizing the deviation from target range as determined by AUC(0,6 h). RESULTS: Busulfan exposure after oral administration was best predicted after the inclusion of adjusted ideal body weight and alanine transferase as covariates on clearance. Population parameter estimates were 3.98 h(-1), 48.8 l and 12.3 l h(-1) for the absorption rate constant, volume of distribution and oral clearance, respectively. Inter-occasion variability was used to describe the differences between test dose and treatment. Based on simulation scenarios, a dosing algorithm was identified, which ensures target exposure values are attained after a test dose. Moreover, our findings show that a sparse sampling scheme with five samples per patient is sufficient to characterize the pharmacokinetics of busulfan in individual patients. CONCLUSION: The use of the proposed dosing algorithm in conjunction with a sparse sampling scheme may contribute to considerable improvement in the safety and efficacy profile of patients undergoing treatment for stem cell transplantation.

Effect of type 2 diabetes mellitus on the pharmacokinetics of metformin in obese pregnant women.

BACKGROUND AND OBJECTIVE: The use of metformin throughout gestation by women with polycystic ovary syndrome (PCOS) and type 2 diabetes mellitus (T2DM) significantly reduces the number of first-trimester spontaneous abortions and the rate of occurrence of gestational diabetes and hypertensive syndromes. Metformin is taken up into renal tubular cells by organic cation transport 2 (OCT2) and eliminated unchanged into the urine. The objective of this study was to analyse the influence of T2DM on the pharmacokinetics of metformin in obese pregnant women and in a control group of non-diabetic obese pregnant women with PCOS. METHODS: Eight non-diabetic obese pregnant women with PCOS and nine obese pregnant women with T2DM taking oral metformin 850 mg every 12 h were evaluated throughout gestation. Serial blood samples were collected over a 12-h period during the third trimester of pregnancy. Steady-state plasma concentrations of metformin were determined by high-performance liquid chromatography with a UV detector. The pharmacokinetic results of the two groups, reported as median and 25th and 75th percentile, were compared statistically using the Mann-Whitney test, with the level of significance set at p < 0.05. RESULTS: The pharmacokinetic parameters detected for PCOS versus T2DM patients, reported as median, were, respectively: elimination half-life 3.75 versus 4.00 h; time to maximum concentration 2.00 versus 3.00 h; maximum concentration 1.42 versus 1.21 µg/mL; mean concentration 0.53 versus 0.56 µg/mL; area under the plasma concentration-time curve from time zero to 12 h 6.42 versus 6.73 µg·h/mL; apparent total oral clearance 105.39 versus 98.38 L/h; apparent volume of distribution after oral administration 550.51 versus 490.98 L; and fluctuation (maximum-minimum concentration variation) of 179.56 versus 181.73 %. No significant differences in pharmacokinetic parameters were observed between the groups. CONCLUSION: T2DM in the presence of insulin use does not influence the pharmacokinetics of metformin in pregnant patients, demonstrating the absence of a need to increase the dose, and consequently does not influence the OCT2-mediated transport in pregnant women with PCOS.

Pharmacokinetics of combined treatment with praziquantel and albendazole in neurocysticercosis.

AIMS: Neurocysticercosis is the most common cause of acquired epilepsy in the world. Antiparasitic treatment of viable brain cysts is of clinical benefit, but current antiparasitic regimes provide incomplete parasiticidal efficacy. Combined use of two antiparasitic drugs may improve clearance of brain parasites. Albendazole (ABZ) has been used together with praziquantel (PZQ) before for geohelminths, echinococcosis and cysticercosis, but their combined use is not yet formally recommended and only scarce, discrepant data exist on their pharmacokinetics when given together. We assessed the pharmacokinetics of their combined use for the treatment of neurocysticercosis. METHODS: A randomized, double-blind, placebo-controlled phase II evaluation of the pharmacokinetics of ABZ and PZQ in 32 patients with neurocysticercosis was carried out. Patients received their usual concomitant medications including an antiepileptic drug, dexamethasone, and ranitidine. Randomization was stratified by antiepileptic drug (phenytoin or carbamazepine). Subjects had sequential blood samples taken after the first dose of antiparasitic drugs and again after 9 days of treatment, and were followed for 3 months after dosing. RESULTS: Twenty-one men and 11 women, aged 16 to 55 (mean age 28) years were included. Albendazole sulfoxide concentrations were increased in the combination group compared with the ABZ alone group, both in patients taking phenytoin and patients taking carbamazepine. PZQ concentrations were also increased by the end of therapy. There were no significant side effects in this study group. CONCLUSIONS: Combined ABZ + PZQ is associated with increased albendazole sulfoxide plasma concentrations. These increased concentrations could independently contribute to increased cysticidal efficacy by themselves or in addition to a possible synergistic effect.

Pharmacokinetic interaction between albendazole sulfoxide enantiomers and antiepileptic drugs in patients with neurocysticercosis.

The aim of the present investigation was to determine the interaction between the antiepileptic drugs (AEDs) phenytoin, carbamazepine, and phenobarbital and the enantioselective metabolism of albendazole. Thirty-two adults with a diagnosis of the active form of intraparenchymatous neurocysticercosis and treated with albendazole at the dose of 7.5 mg/kg every 12 hours for 8 days were studied. The patients were divided into four groups based on the combined use of AEDs or not: control group (n = 9), phenytoin group (n = 9 patients treated with 3-4 mg/kg/d sodium phenytoin), carbamazepine group (n = 9 patients treated with 10-20 mg/kg/d carbamazepine), and phenobarbital group (n = 5 patients treated with 1.5-4.5 mg/kg/d phenobarbital). Serial blood collections were carried out on day 8 of albendazole treatment during the last 12-hour dose interval. Plasma concentrations of the (+)- and (-)-albendazole sulfoxide (ASOX) and albendazole sulfone (ASON) metabolites were determined by high-performance liquid chromatography using a chiral phase column and fluorescence detection. The pharmacokinetic parameters were analyzed by analysis of variance followed by the Tukey-Kramer test. The results are reported as means. The following differences (P < 0.05) were observed between the control and the phenytoin, carbamazepine, and phenobarbital groups, respectively: (+)-ASOX area under the concentration-time curve for 0 to 12 hours after treatment (AUC(0-12)) 6.1, 2.1, 3.1, 2.4 microg/h/mL; (+)-ASOX maximum plasma concentration (C(max)) 0.8, 0.3, 0.4, 0.3 microg/mL; (+)-ASOX half-life (t1/2) 8.0, 3.8, 4.1, 4.9 h; (-)-ASOX AUC(0-12) 1.8, 0.4, 0.6, 0.5 microg/h/mL; (-)-ASOX C(max) 0.2, 0.06, 0.1, 0.1 microg/mL; (-)-ASOX (t(1/2)) 4.3, 1.9, 2.2, 2.1 h; ASON AUC(0-12) 0.5, 0.2 microg/h/mL; ASON C(max) 0.8, 0.3, 0.4, 0.3 microg/mL; ASON (t(1/2)) 8.0, 3.8, 4.1 h. The results show that phenytoin, carbamazepine, and phenobarbital induce to approximately the same extent the oxidative metabolism of albendazole in a nonenantioselective manner. Notably, a significant reduction in the plasma concentration of the active ASOX metabolite was observed in patients with neurocysticercosis treated with these AEDs.