Canada. Bristol-Myers Squibb Canada and Gilead Sciences have issued a 'Dear Health-care Professional' letter to highlight that new clinical data show the potential for drug interactions between didanosine (delayed- release capsules enteric coated beadlets, Videx EC) and tenofovir disoproxil fumarate (Viread), with or without efavirenz (Sustiva) or nevirapine (Viramune). According to reports from recent investigator-sponsored studies, the coadministration of tenofovir and didanosine with either efavirenz or nevirapine may be associated with a potentially high virological failure rate and emergence of resistance in antiretroviral-näive adults with HIV-infection, low CD4+ cell counts and high baseline viral loads. Results of pharmacokinetic studies show that tenofovir and didanosine coadministration increases systemic didanosine exposure by 40 60%, and could potentiate didanosine-related adverse events (AEs). The companies recommend that the coadministration of didanosine and tenofovir be undertaken with caution, that patients who are receiving both drugs be monitored carefully for continued efficacy and for AEs, and that didanosine be discontinued in patients who develop AEs associated with the drug. The companies advise that the Canadian didanosine (Videx EC) and tenofovir disoproxil fumarate (Viread) product monographs have been revised to include this information, along with recommended didanosine dosage adjustments for coadministration with tenofovir.
'Dear Health-care Professional' letter from Bristol Myers Squibb and Gilead Sciences, Canada, 9 June 2005 (http://www.hc-sc.gc.ca).