Coadministration of lamotrigine and Reyataz/ritonavir may decrease lamotrigine plasma concentrations due to UGT1A4 induction. Lamotrigine should be used with caution in combination with Reyataz/ritonavir. If necessary, monitor lamotrigine concentrations and adjust the dose accordingly. No dose adjustment of lamotrigine is required if Reyataz without ritonavir is administered.

Coadministration of lamotrigine and Reyataz with ritonavir is expected to decrease lamotrigine plasma concentrations. Dose adjustment of lamotrigine may be required when coadministered with Reyataz and ritonavir. Coadministration of lamotrigine and Reyataz without ritonavir is not expected to decrease lamotrigine plasma concentrations. No dose adjustment of lamotrigine is required when coadministered with Reyataz without ritonavir.

The effects of atazanavir alone and with ritonavir on lamotrigine conjugation were investigated in 21 HIV- subjects given lamotrigine alone (100 mg single dose) and with atazanavir (400 mg once daily) and atazanavir/ritonavir (300/100 mg once daily). Atazanavir alone had no significant effect on lamotrigine AUC (12% decrease) or Cmax (1% decrease). In contrast, atazanavir/ritonavir decreased lamotrigine AUC (32%) and Cmax (6%).