We propose a model that characterizes and links the complexity and diversity of clinically observed hepatitis C viral kinetics to sustained virologic response (SVR)—the primary clinical end point of hepatitis C treatment, defined as an undetectable viral load at 24 weeks after completion of treatment)—in patients with chronic hepatitis C (CHC) who have received treatment with peginterferon α‐2a ± ribavirin. The new attributes of our hepatitis C viral kinetic model are (i) the implementation of a cure/viral eradication boundary, (ii) employment of all hepatitis C virus (HCV) RNA measurements, including those below the lower limit of quantification (LLOQ), and (iii) implementation of a population modeling approach. The model demonstrated excellent positive (99.3%) and negative (97.1%) predictive values for SVR as well as high sensitivity (96.6%) and specificity (99.4%). The proposed viral kinetic model provides a framework for mechanistic exploration of treatment outcome and permits evaluation of alternative CHC treatment options with the ultimate aim of developing and testing hypotheses for personalizing treatments in this disease. Clinical Pharmacology & Therapeutics (2010) 87 6, 706–713. doi:

AimsIbandronate, a highly potent nitrogen-containing bisphosphonate, is the subject of an ongoing clinical development programme that aims to maximize the potential of simplified, less frequent oral and intravenous (i.v.) administration in osteoporosis. A modelling and simulation project was undertaken to characterize further the clinical pharmacology of ibandronate and identify convenient intermittent oral and i.v. regimens for clinical evaluation. Methods and resultsUsing selected data from clinical studies involving 174 women with postmenopausal osteoporosis (PMO), a classical multicompartmental pharmacokinetic-pharmacodynamic (PK-PD) model was developed that accurately described the P K of i.v. ibandronate in plasma and urine and urinary excretion of the C-telopeptide of the a chain of type I collagen (uCTX), a sensitive biomarker of PD response to ibandronate. To reduce processing times, the classical PK-PD model was simplified using a 'kinetics of drug action' or kinetic (K)-PD model (i.e. a dose-response model as opposed to a dose-concentration-response model). The performance of the K-PD model was evaluated by fitting data simulated with the PK-PD model under various dosing regimens. The simplified model produced a virtually indistinguishable fit of the data from that of the PK-PD model. The K-PD model was extended to consider the influence of supplemental therapy (calcium with or without vitamin D) on the P D response and validated by retrospectively simulating the uCT X response in a prior Phase III and Phase II/III study of i.v. ibandronate, given once every 3 months, in 3380 women with PMO. The observed median uCTX responses at the scheduled assessment points in the completed studies were within the distribution of the simulated responses. The K-PD model for i.v. ibandronate was extended further to allow simultaneous fitting of uCTX responses after i.v. and oral administration in 676 postmenopausal women with osteoporosis, and validated by retrospectively simulating the data observed in a Phase I study of oral daily ibandronate in 180 women with PMO. The K-PD model adequately described the uCTX response after oral dosing. ConclusionsThis validated K-PD model is currently being used to evaluate a range of novel intermittent oral and i.v. ibandronate regimens in an ongoing clinical development programme.

We discontinued anticonvulsant drugs in 92 patients who had been free of seizures during two years of treatment with a single drug. All the patients had epilepsy that had previously been untreated, and had been randomly assigned to receive carbamazepine, phenytoin, or sodium valproate. Thirty-one patients relapsed, and 61 remained free of seizures. The mean duration of the follow-up in the patients remaining free of seizures was 35 months (range, 6 to 62). There was no significant difference between the relapse rate among adults (35 percent) and that among children (31 percent). Our results suggest that the number of seizures a patient had before control was achieved, the number of drugs tried as single-drug therapy, and the type of treatment withdrawn all influenced the outcome. Among the various types of seizures, complex partial seizures with secondary generalization carried the worst prognosis. In comparison, the risk of relapse was 65 percent lower in patients with generalized seizures and 97 percent lower in patients with complex or simple partial seizures in the absence of secondary generalized attacks. Among the four electroencephalographic classes, class 4 (abnormal before treatment and unchanged before withdrawal) carried the worst prognosis. The risk of relapse was 94 to 99 percent lower in patients in the other three electroencephalographic classes. Among the three anticonvulsants, withdrawal of sodium valproate carried the worst prognosis. In comparison, the odds of relapsing were 28 percent lower after withdrawal of phenytoin and 85 percent lower after withdrawal of carbamazepine. We conclude that withdrawal of anticonvulsant medication should be considered in patients free of seizures for two years.

The bioavailability of 5'-DFUR in the systemic circulation was practically identical after administration of the two tablet formulations. Therefore, the two formulations can be regarded as bioequivalent. The variables investigated (age, gender, body surface area, and creatinine clearance) had no clinically significant effect on the pharmacokinetics of capecitabine or its metabolites.

At the dose used in this study, the effect of concomitantly delivered Maalox on the extent and rate of gastrointestinal absorption of capecitabine is not clinically significant. Therefore, there is no need to adjust the dose or timing of capecitabine administration in patients treated with Maalox.