PT  - JOURNAL ARTICLE
AU  - Brian J. Kirby
AU  - Ann C. Collier
AU  - Evan D. Kharasch
AU  - Vaishali Dixit
AU  - Pankaj Desai
AU  - Dale Whittington
AU  - Kenneth E. Thummel
AU  - Jashvant D. Unadkat
TI  - Complex Drug Interactions of HIV Protease Inhibitors 2: In Vivo Induction and In Vitro to In Vivo Correlation of Induction of Cytochrome P450 1A2, 2B6, and 2C9 by Ritonavir or Nelfinavir
AID  - 10.1124/dmd.111.038646
DP  - 2011 Dec 01
TA  - Drug Metabolism and Disposition
PG  - 2329--2337
VI  - 39
IP  - 12
4099  - http://dmd.aspetjournals.org/content/39/12/2329.short
4100  - http://dmd.aspetjournals.org/content/39/12/2329.full
SO  - Drug Metab Dispos2011 Dec 01; 39
AB  - Drug-drug interactions (DDIs) with the HIV protease inhibitors (PIs) are complex, paradoxical (e.g., ritonavir/alprazolam), and involve multiple mechanisms. As part of a larger study to better understand these DDIs and to devise a framework for in vitro to in vivo prediction of these DDIs, we determined the inductive effect of ∼2 weeks of administration of two prototypic PIs, nelfinavir (NFV), ritonavir (RTV), and rifampin (RIF; induction positive control) on the cytochrome P450 enzymes CYP1A2, CYP2B6, CYP2C9, and CYP2D6 and the inductive or inductive plus inhibitory effect of NFV, RTV, or RIF on CYP3A and P-glycoprotein in healthy human volunteers. Statistically significant induction of CYP1A2 (2.1-, 2.9-, and 2.2-fold), CYP2B6 (1.8-, 2.4-, and 4-fold), and CYP2C9 (1.3-, 1.8-, and 2.6-fold) was observed after NFV, RTV, or RIF treatment, respectively (as expected, CYP2D6 was not induced). Moreover, we accurately predicted the in vivo induction of these enzymes by quantifying their induction by the PIs in human hepatocytes and by using RIF as an in vitro to in vivo scalar. On the basis of the modest in vivo induction of CYP1A2, CYP2B6, or CYP2C9, the in vivo paradoxical DDIs with the PIs are likely explained by mechanisms other than induction of these enzymes such as induction of other metabolic enzymes, transporters, or both.