Coadministration of carbamazepine (200 mg twice daily) and darunavir/ritonavir increased carbamazepine AUC, Cmax and Cmin by 45%, 43% and 54%, respectively. There was no change in darunavir AUC or Cmax, but Cmin decreased by 15%. No dose adjustment for darunavir/ritonavir is recommended. If there is a need to combine darunavir/ritonavir and carbamazepine, patients should be monitored for potential carbamazepine-related adverse events. Carbamazepine concentrations should be monitored and its dose should be titrated for adequate response. Based upon the findings, patients should be monitored for potential carbamazepine related adverse events. Based upon the findings, the carbamazepine dose may need to be reduced by 25% to 50% in the presence of darunavir/ritonavir.

Coadministration of carbamazepine (200 mg twice daily) and darunavir/ritonavir (600/100 mg twice daily) was studied in 16 subjects. Darunavir Cmax increased by 4%, AUC decreased by 1% and Cmin decreased by 15%. The AUC, Cmax and Cmin of carbamazepine increased by 45%, 43% and 54%, respectively; carbamazepine epoxide AUC and Cmax decreased by 54% and Cmin decreased by 52%. The dose of either darunavir/ritonavir or carbamazepine does not need to be adjusted when initiating coadministration with darunavir/ritonavir and carbamazepine. Clinical monitoring of carbamazepine concentrations and its dose titration is recommended to achieve the desired clinical response.

The drug-drug interactions between antiretrovirals and carbamazepine or oxcarbazepine were evaluated in a clinical setting using therapeutic drug monitoring (TDM) trough concentrations collected from HIV+ patients treated concomitantly with carbamazepine or oxcarbazepine and antiretrovirals for at least 3 months. HIV-infected patients not concomitantly treated with antiepileptic drugs and who underwent TDM for antiretrovirals in the previous 2 years were considered as controls. Eleven HIV-positive patients prescribed carbamazepine (n=7) or oxcarbazepine (n=4) were identified. All the TDM evaluations for carbamazepine and oxcarbazepine were within the therapeutic ranges. TDM results of darunavir measured in these patients were comparable with values usually measured in the control group.