Reyataz may increase plasma levels of carbamazepine due to CYP3A4 inhibition. Due to carbamazepine inducing effect, a reduction in Reyataz exposure cannot be ruled out. Carbamazepine should be used with caution in combination with Reyataz. If necessary, monitor carbamazepine serum concentrations and adjust the dose accordingly. Close monitoring of the patient's virologic response should be exercised. Coadministration of Reyataz without ritonavir is not recommended with carbamazepine.

Ritonavir is expected to increase plasma levels of carbamazepine. If patients beginning treatment with Reyataz/ritonavir have been titrated to a stable dose of carbamazepine, a dose reduction for carbamazepine may be necessary. Plasma concentrations of atazanavir may be decreased when carbamazepine is administered with Reyataz without ritonavir. Coadministration of carbamazepine and Reyataz without ritonavir is not recommended.

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. Trough concentrations for atazanavir were ~65% lower when compared with HIV-infected patients not treated with antiepileptic drugs (190 ± 91 versus 546 ± 380 ng/ml, respectively). Co-administration of carbamazepine or oxcarbazepine with atazanavir should be avoided owing to the potential risk of virological failure; the adoption of TDM is strongly advisable, eventually combining with increased antiretroviral doses.