RESUMEN

On 30 June 2015, the US Food and Drug Administration Pregnancy and Lactation Labeling Rule (PLLR) took effect. This rule sets new and improved standards for the inclusion of information about the use of prescription drugs and biological products during pregnancy and lactation. The new labeling requirements have important implications for clinical pharmacology as there is a subheading that is dedicated to inclusion of clinical pharmacology information that inform dosing during pregnancy and the postpartum period, if available.

Asunto(s)

RESUMEN

Pharmacokinetic (PK)-pharmacodynamic modeling and simulation were used to establish a link between methadone dose, concentrations, and Fridericia rate-corrected QT (QTcF) interval prolongation, and to identify a dose that was associated with increased risk of developing torsade de pointes. A linear relationship between concentration and QTcF described the data from five clinical trials in patients on methadone maintenance treatment (MMT). A previously published population PK model adequately described the concentration-time data, and this model was used for simulation. QTcF was increased by a mean (90% confidence interval (CI)) of 17 (12, 22) ms per 1,000 ng/ml of methadone. Based on this model, doses >120 mg/day would increase the QTcF interval by >20 ms. The model predicts that 1-3% of patients would have ΔQTcF >60 ms, and 0.3-2.0% of patients would have QTcF >500 ms at doses of 160-200 mg/day. Our predictions are consistent with available observational data and support the need for electrocardiogram (ECG) monitoring and arrhythmia risk factor assessment in patients receiving methadone doses >120 mg/day.

Asunto(s)

RESUMEN

Besides logistical and ethical concerns, evaluation of safety and efficacy of medications in pregnant women is complicated by marked changes in pharmacokinetics (PK) of drugs. For example, CYP3A activity is induced during the third trimester (T3). We explored whether a previously published physiologically based pharmacokinetic (PBPK) model could quantitatively predict PK profiles of CYP3A-metabolized drugs during T3, and discern the site of CYP3A induction (i.e., liver, intestine, or both). The model accounted for gestational age-dependent changes in maternal physiological function and hepatic CYP3A activity. For model verification, mean plasma area under the curve (AUC), peak plasma concentration (Cmax), and trough plasma concentration (Cmin) of midazolam (MDZ), nifedipine (NIF), and indinavir (IDV) were predicted and compared with published studies. The PBPK model successfully predicted MDZ, NIF, and IDV disposition during T3. A sensitivity analysis suggested that CYP3A induction in T3 is most likely hepatic and not intestinal. Our PBPK model is a useful tool to evaluate different dosing regimens during T3 for drugs cleared primarily via CYP3A metabolism.CPT: Pharmacometrics & Systems Pharmacology (2012) 1, e3; doi:10.1038/psp.2012.2; advance online publication 26 September 2012.

RESUMEN

PURPOSE: Docetaxel, a potent antimicrotubule agent widely used in the treatment of ovarian, breast and lung cancer, is extensively metabolized in various animal species, including humans. The metabolism of docetaxel to its primary metabolite, hydroxydocetaxel, is mediated by cytochrome P450 isozymes CYP3A2 and CYP3A4 in rats and humans, respectively. Several substrates of enzymes belonging to the CYP3A subfamily are known to induce different CYP isozymes, including CYP3A enzymes. Recently, paclitaxel, a compound structurally related to docetaxel, has been shown to significantly elevate the expression of CYP3A in rat and human hepatocytes. In this study we investigated the influence of docetaxel, employed at clinically relevant concentrations, on the level and the activity of cytochrome P450 3A in primary cultures of rat hepatocytes. METHODS: Rat hepatocytes were treated with different concentrations of docetaxel, paclitaxel and other CYP3A inducers. Testosterone 6beta-hydroxylase activity of intact hepatocytes was used as a marker for CYP3A. The immunoreactive CYP3A levels in the S-9 fractions were determined by Western blot analysis. RESULTS: We observed that by day 3 of drug treatment, docetaxel at concentration in the range of 2.5-10 microM increased the CYP3A enzymatic activity and the immunoreactive CYP3A levels in a concentration-dependent manner. At the 10 microM level, docetaxel caused a twofold increase in the CYP3A activity and a threefold increase in the immunoreactive CYP3A levels. However, the docetaxel-mediated CYP3A activity and enzyme level increase were significantly lower than those mediated by paclitaxel and dexamethasone. A comparison of the testosterone 6beta-hydroxylation activity in hepatocytes treated with these agents at a concentration of 5 microM each yielded the following rank order of induction capacity: dexamethasone > paclitaxel > docetaxel (15-fold, 5-fold, 2.2-fold, respectively). CONCLUSIONS: Taken together, our findings raise the possibility that docetaxel at clinically relevant concentrations increases CYP3A activity. The potential for docetaxel-mediated changes in the metabolism of other coadministered drugs and its own metabolism, in relation to that due to paclitaxel, are discussed.

Asunto(s)