Pharmacokinetic determinants of virological response to raltegravir in the in vitro pharmacodynamic hollow-fiber infection model system.

Daily administration (q24h) of raltegravir has been shown to be as efficacious as twice-daily administration (q12h) in the hollow-fiber infection model (HFIM) system. However, q24h regimens were not noninferior to q12h dosing in a clinical trial. We hypothesized that between-patient variability in raltegravir pharmacokinetics (PK) was responsible for the discordance in conclusions between the in vitro and in vivo studies. Hollow-fiber cartridges were inoculated with HIV-infected H9 cells and uninfected CEM-SS cells. Four cartridges received the total daily exposure (800 mg) q24h and four received half the daily exposure (400 mg) q12h. PK profiles with half-lives of 8, 4, 3, and 2 h were simulated for each dosing interval. Cell-to-cell viral spread was assessed by flow cytometry. Viral inhibition was similar between q24h and q12h dosing at the 8- and 4-h half-lives. The q24h dosing was not as efficacious as the q12h dosing when faster half-lives were simulated; a lack of viral suppression was observed at days 3 and 4 for the 2- and 3-h half-lives, respectively. The discrepancy in conclusions between the in vitro HFIM system studies and clinical trials is likely due to the large interindividual variation in raltegravir PK.