Utilization of In Vitro, In Vivo and In Silico Tools to Evaluate the pH-Dependent Absorption of a BCS Class II Compound and Identify a pH-Effect Mitigating Strategy.

PURPOSE: To describe a stepwise approach to evaluate the pH effect for a weakly basic drug by in vitro, in vivo and in silico techniques and identify a viable mitigation strategy that addresses the risk. METHODS: Clinical studies included assessment of the pH effect with famotidine. In vitro dissolution was evaluated in various biorelevant media and in a pH-shift test. PK studies in dogs were conducted under pentagastrin or famotidine pre-treatment and GastroPlus was employed to model human and dog PK data and simulate the performance in human. RESULTS: Clinical data indicated considerable pH dependent absorption of the drug when dosed in the presence of H2-antagonists. In vitro dissolution and in vivo dog data confirmed that the observed pH effect was due to reduced dissolution rate and lower solubility at increased gastric and intestinal pH. A salt form was identified to overcome the effect by providing fast dissolution and prolonged supersaturation. GastroPlus simulations predicted a mitigation of the pH effect by the salt. CONCLUSIONS: The drug exhibited a strong pH-effect in humans. The in vitro, in vivo and modeling approach provides a systematic workflow to evaluate the risk of a new drug and identify a strategy able to mitigate the risk.

The effects of apremilast on the QTc interval in healthy male volunteers: a formal, thorough QT study.

OBJECTIVE: This study was conducted to evaluate the effect of apremilast and its major metabolites on the placebocorrected change-from-baseline QTc interval of an electrocardiogram (ECG). MATERIALS AND METHODS: Healthy male subjects received each of 4 treatments in a randomized, crossover manner. In the 2 active treatment periods, apremilast 30 mg (therapeutic exposure) or 50 mg (supratherapeutic exposure) was administered twice daily for 9 doses. A placebo control was used to ensure doubleblind treatment of apremilast, and an openlabel, single dose of moxifloxacin 400 mg was administered as a positive control. ECGs were measured using 24-hour digital Holter monitoring. RESULTS: The two-sided 98% confidence intervals (CIs) for ΔΔQTcI of moxifloxacin completely exceeded 5 ms 2 - 4 hours postdose. For both apremilast dose studies, the least-squares mean ΔΔQTcI was < 1 ms at all time points, and the upper limit of two-sided 90% CIs was < 10 ms. There were no QT/QTc values > 480 ms or a change from baseline > 60 ms. Exploratory evaluation of pharmacokinetic/pharmacodynamic data showed no trend between the changes in QT/QTc interval and the concentration of apremilast or its major metabolites M12 and M14. CONCLUSIONS: Apremilast did not prolong the QT interval and appears to be safe and well tolerated up to doses of 50 mg twice daily.

Population Pharmacokinetics Analysis To Inform Efavirenz Dosing Recommendations in Pediatric HIV Patients Aged 3 Months to 3 Years.

Efavirenz (EFV) is a nonnucleoside reverse transcriptase inhibitor approved worldwide for the treatment of HIV in adults and children over 3 years of age or weighing over 10 kg. Only recently EFV was approved in children over 3 months and weighing at least 3.5 kg in the United States and the European Union. The objective of this analysis was to support the selection of an appropriate dose for this younger pediatric population and to explore the impact of CYP2B6 genetic polymorphisms on EFV systemic exposures. A population pharmacokinetic (PPK) model was developed using data from three studies in HIV-1-infected pediatric subjects (n = 168) and one study in healthy adults (n = 24). The EFV concentration-time profile was best described by a two-compartment model with first-order absorption and elimination. Body weight was identified as a significant predictor of efavirenz apparent clearance (CL), oral central volume of distribution (VC), and absorption rate constant (Ka). The typical values of efavirenz apparent CL, VC, oral peripheral volume of distribution (VP), and Ka for a reference pediatric patient were 4.8 liters/h (4.5 to 5.1 liters/h), 84.9 liters (76.8 to 93.0 liters), 287 liters (252.6 to 321.4 liters), and 0.414 h(-1) (0.375 to 0.453 h(-1)), respectively. The final model was used to simulate steady-state efavirenz concentrations in pediatric patients weighing <10 kg to identify EFV doses that produce comparable exposure to adult and pediatric patients weighing ≥10 kg. Results suggest that administration of EFV doses of 100 mg once daily (QD) to children weighing ≥3.5 to <5 kg, 150 mg QD to children weighing ≥5 to <7.5 kg, and 200 mg QD to children weighing ≥7.5 to <10 kg produce exposures within the target range. Further evaluation of the impact of CYP2B6 polymorphisms on EFV PK showed that the identification of CYP2B6 genetic status is not predictive of EFV exposure and thus not informative to guide pediatric dosing regimens.

A validated HPLC-MS/MS assay for quantifying unstable pharmacologically active metabolites of clopidogrel in human plasma: application to a clinical pharmacokinetic study.

Clopidogrel is prescribed for the treatment of Acute Coronary Syndrome and recent myocardial infarction, recent stroke, or established peripheral arterial disease. A sensitive and reliable high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) assay was developed and validated to enable reliable quantification of four diastereomeric and chemically reactive thiol metabolites, two of which are pharmacologically active, in human plasma. The metabolites were stabilized by alkylation of their reactive thiol moieties with 2-bromo-3'-methoxyacetophenone (MPB). Following organic solvent mediated-protein precipitation in a 96-well plate format, chromatographic separation was achieved by gradient elution on an Ascentis Express RP-amide column. Chromatographic conditions were optimized to ensure separation of the four derivatized active metabolites. Derivatized metabolites and stable isotope-labeled internal standards were detected by positive ion electrospray tandem mass spectrometry. The HPLC-MS/MS assay was validated over concentration ranges of 0.125-125 ng/mL for metabolites H1-H3 and 0.101-101 ng/mL for H4. Intra- and inter-assay precision values for replicate quality control samples were within 14.3% for all analytes during the assay validation. Mean quality control accuracy values were within ±6.3% of nominal values for all analytes. Assay recoveries were high (>79%). The four derivatized analytes were stable in human blood for at least 2 h at room temperature and on ice. The analytes were also stable in human plasma for at least 25 h at room temperature, 372 days at -20 °C and -70 °C, and following at least five freeze-thaw cycles. The validated assay was successfully applied to the quantification of all four thiol metabolites in human plasma in support of a human pharmacokinetic study.

Effects of oral posaconazole on the pharmacokinetic properties of oral and intravenous midazolam: a phase I, randomized, open-label, crossover study in healthy volunteers.

BACKGROUND: Like itraconazole and ketoconazole, posaconazole, a broad-spectrum oral triazole antifungal, inhibits the activity of the cytochrome P450 (CYP) isozyme 3A4. Midazolam, a short-acting benzodiazepine, is metabolized by CYP3A4. Potential drug interactions can be expected in patients who are concurrently receiving inhibitors and substrates of CYP3A4 (eg, ketoconazole, posaconazole) and benzodiazepines (eg, midazolam). Because of the potential for drug interactions, it is important to determine the effects of posaconazole on the pharmacokinetic properties of midazolam. OBJECTIVE: The aim of this study was to compare the effects of oral administration of posaconazole versus ketoconazole on the pharmacokinetic properties of orally and intravenously administered midazolam. METHODS: This Phase I, randomized, open-label, crossover study was conducted at Swiss Pharma Contract Ltd., Allschwil, Switzerland. Healthy volunteers were randomly assigned to 1 of 2 treatment arms. Arm 1 received posaconazole 200 mg BID for 7 days, posaconazole 400 mg BID for 7 days, no drugs during a 28-day washout, and ketoconazole 400 mg once daily for 7 days. Arm 2 received posaconazole and ketoconazole in the reverse order, with a 28-day washout between treatments. An oral/IV midazolam sequence (oral midazolam 2 mg and IV midazolam 0.4 mg) was administered on days -2/-1, 6/7, 13/14 (arm 1), 36/17 (arm 2), 43/44, and 50/51 in both treatment arms. Blood samples were collected up to 24 hours after midazolam administration. Pharmacokinetic parameters, including C(max), C(min) (before azole administration), terminal-phase t(1/2) (t(1/2z)), and AUC to final measurable sampling time (AUC(tf)), were calculated using noncompartmental methods, and drug interactions were evaluated using analysis of variance. Adverse events were collected using physical examination, including vital sign measurements; clinical laboratory analysis; electrocardiography; and direct questioning at predefined time points throughout the study to assess tolerability. RESULTS: A total of 12 subjects were enrolled (11 men, 1 woman; all white; mean age, 42.8 years [range, 28-53 years]; mean weight, 80.6 kg; and mean body mass index, 25.6 kg/m(2)). All of the subjects completed the study. Based on point estimates of logarithm-transformed data, posaconazole 200 and 400 mg BID were associated with significant increases in midazolam C(max) (up to 1.3- and 2.4-fold) and AUC(tf) values (up to 4.6- and 6.2-fold), respectively. Ketoconazole 400 mg once daily was associated with significantly increased midazolam C(max) and AUC(tf) (up to 2.8- and 8.2-fold, respectively). When midazolam was concurrently administered with either azole, t(1/2z) was prolonged. Seven of 12 (58%) subjects reported > or =1 adverse event during the study (5 with posaconazole alone and 4 with posaconazole + midazolam). The most common adverse events were diarrhea (3 subjects [25%] with posaconazole alone, 2 [17%] with ketoconazole alone, and 1 [8%] with posaconazole + midazolam) and flatulence (1 [8%] with posaconazole alone and 1 [8%] with midazolam alone). CONCLUSIONS: The results from this study in a small, all-white population of healthy volunteers suggest that posaconazole was a potent inhibitor of CYP3A4, but to a lesser extent than was ketoconazole. Monitoring patients for adverse events, the need for dose adjustments, or both during coadministration with posaconazole may be warranted in patients being treated with benzodiazepines that are predominantly metabolized through CYP3A4 (eg, midazolam).

A novel HPLC assay for pentamidine: comparative effects of creatinine and inulin on GFR estimation and pentamidine renal excretion in the isolated perfused rat kidney.

PURPOSE: 1. To develop and validate an analytical method for pentamidine (PTM) by reversed-phase HPLC. 2. To compare the effects of creatinine and inulin on PTM excretion in the isolated perfused rat kidney. METHODS: The HPLC method utilized a base deactivated, 5 micro, C18 column and a mobile phase containing acetonitrile (24%) and 0.025 M monobasic phosphate buffer, pH 3.2 (76%). Mobile phase flow rate and UV detection wavelength were 1 mL/min and 270 nm, respectively. Sulfadiazine (SDZ) was used as the internal standard. The method was used to measure pentamidine in perfusate and urine samples generated from studies with the isolated perfused rat kidney (IPK) model. Perfusion experiments were conducted in the presence of two different GFR markers: creatinine and inulin (PTM dose 800 micro g). Both creatinine and inulin were assayed using colorimetric methods. RESULTS: The HPLC assay is rapid, sensitive and reproducible. The method was validated over two standard concentration ranges: 0.1 to 1 micro g/mL, and 1 to 10 micro g/mL. In control (drug-naïve) IPK perfusions, creatinine clearance was approximately 15% greater than inulin clearance (0.80+/- 0.21 mL/min vs. 0.69+/-0.17 mL/min, p > 0.05). In the presence of PTM, however, creatinine clearance was reduced to 0.56+/-0.27 (p < 0.05 compared to control). Inulin clearance was not altered by PTM administration (0.76+/-0.26 mL/min). Cumulative urinary excretion of PTM (% dose) was 3.0+/-0.47% and 9.6+/-4.2% in the presence of creatinine and inulin, respectively. PTM clearance was significantly reduced (0.06+/-0.01 mL/min vs. 0.13+/-0.01 mL/min, p < 0.05) and % kidney accumulation significantly enhanced (66+/-4.7% vs. 37+/-9.7%, p < 0.05) by creatinine. CONCLUSIONS: Creatinine overestimated GFR in the IPK. The altered renal excretion of PTM by creatinine is consistent with inhibition of PTM tubular secretion. Because of increased kidney accumulation, detrimental effects of PTM on renal function were observed. Based on these findings, creatinine should be used cautiously as an indicator of GFR in IPK experimentation.