LHPG Comment: Unlike the Videx chewable/dispersible tablets, the new formulation of ddI (Videx EC) does not contain antacids. Interactions with the old formulation that were due to the presence of antacid should not apply to the new formulation. Timing of administration of Videx EC with other medications will still be dependent on food requirements, but no longer on gastric pH requirements.

Specific interaction studies have not been performed with efavirenz and NRTIs other than lamivudine, zidovudine, and tenofovir disoproxil fumarate. Clinically significant interactions are not expected since the NRTIs are metabolised via a different route than efavirenz and would be unlikely to compete for the same metabolic enzymes and elimination pathways. No dosage adjustment is necessary for either medicinal product.
Sustiva Summary of Product Characteristics, Bristol-Myers Squibb Pharmaceuticals Ltd, April 2015.
Sustiva Prescribing Information, Bristol-Myers Squibb Company, March 2015.

Didanosine + Emtricitabine

The coadministration of emtricitabine (200 mg once daily), didanosine (400 mg once daily for patients ¡Ý60 kg; 250 mg once a daily for patients <60 kg) and efavirenz (600 mg once daily) was studied in 9 treatment na§áve, HIV+ patients. When compared to historical data for each drug alone, the pharmacokinetics of emtricitabine were not affected, didanosine AUC and Cmax were higher than expected and efavirenz Cmax, Cmin and AUC were lower than expected. The authors suggest the efavirenz concentrations may have been underestimated as they delayed dosing by 12 hours for ease of sampling.
Pharmacokinetics of emtricitabine, didanosine and efavirenz administered once-daily for the treatment of HIV-infected adults (pharmacokinetic substudy of the ANRS trial). Molina J-M, Peytavin G, Perusat S et al. HIV Medicine, 2004, 5: 99-104.