Single-dose pharmacokinetics and cardiovascular effects of oral pimobendan in healthy cats.

INTRODUCTION: To investigate the pharmacokinetics and pharmacodynamics of oral pimobendan in conscious, healthy cats. ANIMALS: Eight healthy adult cats. MATERIALS AND METHODS: A randomised, single-blinded, crossover design was used. Two oral doses of pimobendan (0.625-mg [LD], 1.25-mg [HD]) and a control substance (3-mL water) were administered to each cat. Blood collection, echocardiography, and oscillometric blood pressure measurements were performed repeatedly for 12 h following each dose. Plasma concentrations of pimobendan and the active metabolite, O-desmethylpimobendan (ODMP), were quantified using ultra-high-performance liquid chromatography tandem mass spectrometry. Cardiovascular parameters were evaluated for between- and within-treatment effects over time using linear mixed modelling. RESULTS: Pimobendan was rapidly absorbed and converted to ODMP with the pimobendan AUC0-∞ greater than ODMP AUC0-∞ (ODMP:pimobendan AUC0-∞ ratio 0.6 [LD] and 0.5 [HD]) despite a longer elimination half-life of ODMP (pimobendan t1/2 0.8 h vs. ODMP t1/2 1.6 h [LD]; pimobendan t1/2 0.7 h vs. ODMP t1/2 1.3 h [HD]). Averaged across all time points, pimobendan increased several measures of systolic function; however, its effect could not be further characterised. Although treatment was well-tolerated, two cats vomited following HD and another had a ventricular premature beat recorded following LD. CONCLUSIONS: The lower ODMP:pimobendan AUC0-∞ ratio compared to that observed previously in dogs suggests reduced metabolism in cats. Treatment effects were observed in measures of systolic function; however, the duration of action and differences in effects between the two pimobendan doses could not be characterised. Further studies are required to evaluate pimobendan in feline cardiovascular medicine.

Pharmacokinetics and cardiovascular effects following a single oral administration of a nonaqueous pimobendan solution in healthy dogs.

Pimobendan is an inodilator used in the treatment of canine congestive heart failure (CHF). The aim of this study was to investigate the pharmacokinetics and cardiovascular effects of a nonaqueous oral solution of pimobendan using a single-dose, operator-blinded, parallel-dose study design. Eight healthy dogs were divided into two treatment groups consisting of water (negative control) and pimobendan solution. Plasma samples and noninvasive measures of cardiovascular function were obtained over a 24-h period following dosing. Pimobendan and its active metabolite were quantified using an ultra-high-performance liquid chromatography-mass spectrometer (UHPLC-MS) assay. The oral pimobendan solution was rapidly absorbed [time taken to reach maximum concentration (Tmax ) 1.1 h] and readily converted to the active metabolite (metabolite Tmax 1.3 h). The elimination half-life was short for both pimobendan and its active metabolite (0.9 and 1.6 h, respectively). Maximal cardiovascular effects occurred at 2-4 h after a single oral dose, with measurable effects occurring primarily in echocardiographic indices of systolic function. Significant effects persisted for <8 h. The pimobendan nonaqueous oral solution was well tolerated by study dogs.

The rheumatoid arthritis susceptibility polymorphism PTPN22 C1858T is not associated with leflunomide response or toxicity.

WHAT IS KNOWN AND OBJECTIVE: A common polymorphism (C1858T) in the gene that encodes the protein tyrosine phosphatase non-receptor type 22 (PTPN22) is associated with altered T-cell responses and increased susceptibility to rheumatoid arthritis (RA) and other autoimmune diseases. Teriflunomide, the active metabolite of leflunomide, reduces T-cell responses through inhibition of tyrosine kinase p56LCK. We examined a potential association between PTPN22 genotype and response or toxicity to leflunomide in Caucasian RA patients taking leflunomide in combination with other disease-modifying antirheumatic drugs (DMARDs). METHODS: Patients enrolled in the Royal Adelaide Hospital RA inception cohort and taking leflunomide were eligible for inclusion. Participants were followed for 12 months after leflunomide initiation or until either another DMARD was added or leflunomide was ceased. Clinical response according to change in 28-joint Disease Activity Score (DAS28) and cessation due to toxicity were assessed. RESULTS AND DISCUSSION: A total of 94 participants were included in the study, 75 of whom carried the CC genotype, 18 the CT, whereas one individual carried the TT genotype. Over the first 12 months of leflunomide treatment, there was no statistically significant relationship between carrying the T allele and change in DAS28 (-0·84 vs. -1·15, P = 0·446) nor with cessation of leflunomide treatment due to side effects (P = 0·433). These results indicate that PTPN22 C1858T genotype has no effect on response or toxicity outcomes in leflunomide-treated RA patients. WHAT IS NEW AND CONCLUSION: This is the first study to evaluate the biologically plausible hypothesis that PTPN22 genotype might be a predictor of response/toxicity to leflunomide therapy. Despite this, PTPN22 genotype was not associated with leflunomide response or toxicity in patients with RA.

Lack of influence of CYP2D6 genotype on the clearance of (R)-, (S)- and racemic-methadone.

OBJECTIVE: To investigate the influence of CYP2D6 genotype on the oral clearance of (R)-, (S)- and rac-methadone. METHODS: In this retrospective study, CYP2D6 genotypes were identified in 56 methadone maintained subjects. Plasma concentrations of (R)-, (S)- and rac-methadone were determined by stereoselective HPLC and sufficient data were available to estimate the apparent oral clearances of (R)-, (S)- and rac-methadone using a population kinetic model in 37 of the genotyped subjects. RESULTS: The CYP2D6 allele frequencies were similar to those previously reported in Caucasians, the most common being: CYP2D6*1 (35.2%), CYP2D6*2 (12.0%) and CYP2D6*4 (22.2%). Three unknown SNPs were found in four subjects: 1811G > A (n = 1), 1834C > T (n = 1) and 2720G > C (n = 2). The oral clearances of (R)-, (S)- and rac-methadone varied 5.4-, 6.8- and 6.1-fold, respectively. No significant differences in methadone oral clearance were found between CYP2D6 genotypic PM, IM and EM (p = 0.57, 0.40 and 0.43 for (R)-, (S)- and rac-methadone, respectively). Only 1 subject had duplication of functional CYP2D6 alleles and the oral clearance of the three analytes was not markedly altered. CONCLUSIONS: CYP2D6 poor, intermediate and extensive metabolizer genotypes did not appear to impact on the oral clearance of (R)-, (S)- or rac-methadone. In addition, methadone dosage requirements were not influenced by CYP2D6 genotypes in these subjects. However, the impact of duplication of functional CYP2D6 alleles on oral clearance and dosage requirements requires further investigation.

Blood-brain distribution of morphine-6-glucuronide in sheep.

BACKGROUND AND PURPOSE: At present there are few data regarding the rate and extent of brain-blood partitioning of the opioid active metabolite of morphine, morphine-6-glucuronide (M6G). In this study the cerebral kinetics of M6G were determined, after a short-term intravenous infusion, in chronically instrumented conscious sheep. EXPERIMENTAL APPROACH: Five sheep received an intravenous infusion of M6G 2.2 mg kg(-1) over a four-minute period. Non-linear mixed-effects analysis, with hybrid physiologically based kinetic models, was used to estimate cerebral kinetics from the arterio-sagittal sinus concentration gradients and cerebral blood flow measurements. KEY RESULTS: A membrane limited model was selected as the final model. The blood-brain equilibration of M6G was relatively slow (time to reach 50% equilibration of the deep compartment 5.8 min), with low membrane permeability (PS, population mean, 2.5 ml min(-1)) from the initial compartment (V1, 13.7 ml) to a small deep distribution volume (V2) of 18.4 ml. There was some between-animal variability (%CV) in the initial distribution volume (29%), but this was not identified for PS or V2. CONCLUSION AND IMPLICATIONS: Pharmacokinetic modelling of M6G showed a delayed equilibration between brain and blood of a nature that is primarily limited by permeability across the blood-brain-barrier, in accordance with its physico-chemical properties.