Coadministration of efavirenz (600 mg once daily) with atorvastatin (10 mg once daily) decreased the AUC and Cmax of atorvastatin by 43% and 12%, respectively; of 2-hydroxy atorvastatin by 35% and 13%, respectively; of 4-hydroxy atorvastatin by 4% and 47%, respectively; and of total active HMG-CoA reductase inhibitors by 34% and 20%, respectively. Coadministration did not affect efavirenz AUC or Cmax values. Cholesterol levels should be periodically monitored. Dosage adjustments of atorvastatin may be required (refer to the SmPC for atorvastatin). No dosage adjustment is necessary for efavirenz. 

Coadministration of atorvastatin (10 mg once daily for 4 days) and efavirenz (600 mg for 15 days) was studied in 14 subjects. There were decreases in atorvastatin Cmax, AUC and Cmin of 14%, 43% and 69%, respectively. Total active drug (including metabolites) decreased by 15% (Cmax), 32% (AUC) and 48% (Cmin). There was no change in efavirenz Cmax, AUC or Cmin. Consult the complete prescribing information for atorvastatin for guidance on individualising the dose.

Coadministration of efavirenz (600 mg once daily) and atorvastatin (10 mg once daily) was studied in 14 HIV-negative subjects. Efavirenz reduced atorvastatin AUC0-24h by 43% (P<0.001) and the total active atorvastatin exposure by 34% (P=0.005). Atorvastatin had no effect on non-steady-state efavirenz concentrations. The reduced inhibition of HMG-CoA reductase activity may result in diminished antilipid efficacy at usual doses of atorvastatin.