Population pharmacokinetics of onercept in healthy subjects.

Objective: To develop a population pharmacokinetic model and to determine the covariates affecting the pharmacokinetics of onercept (recombinant human tumour necrosis factor [TNF] receptor-1) in healthy subjects.

Subjects And Methods: Onercept pharmacokinetics data were obtained from 48 healthy male and female subjects (four phase I studies). In study A, 12 subjects received increasing single intravenous doses of onercept either 5 and 50mg or 15 and 150mg. In study B, 12 subjects received single intravenous, subcutaneous and intramuscular doses of onercept 50mg. Study C investigated the pharmacokinetics of onercept following repeat subcutaneous administration of six doses of 50mg every 48 hours in 12 subjects. Study D investigated the pharmacokinetics of onercept following repeat subcutaneous administration of six doses of 100mg and 150mg over 2 weeks in 12 subjects. Nonlinear mixed-effects modelling software NONMEM was used to build a base model, while the final model was determined after selection of the covariates.

Results: The disposition of onercept was described using a two-compartment model with two absorption processes (a first-order followed by a zero-order) and included a constant baseline, accounting for the endogenous TNF receptor-1 levels. Slow absorption of onercept following subcutaneous and intramuscular administration was observed and suggested that absorption was the rate-limiting process. The population mean (coefficient of variation %) values for clearance, absorption rate constant, volume of distribution of the central compartment, bioavailability of onercept and baseline TNF receptor-1 levels were 4.03 L/h (13.3%), 0.04 h-1 (29.1%), 4.42L (6.2%), 0.90 (23.8%) and 1.68 microg/L (20.4%), respectively. The only significant covariates were found to be dose (which affected clearance), and day (which affected absorption rate constant); however, the effects were small (10-15%) and are unlikely to be of any clinical relevance.

Conclusion: The proposed population pharmacokinetic model characterises well the overall pharmacokinetic profile of onercept after intramuscular, subcutaneous and intravenous administration in healthy subjects. The pharmacokinetics of onercept showed modest intersubject variability.