A warning was issued last month by the US Food and Drug Administration that once daily ddI tablets may not be equivalent to twice daily ddI tablets in efficacy, following the announcement of 48 week data from a study comparing ddI/d4T/nelfinavir with AZT/3TC/nelfinavir. The warning stressed that once daily ddI could still be used in cases where individuals had difficulty in adhering to twice daily ddI dosing.
The AI454-148 study did not compare once daily ddI to twice daily ddI, but did compare once daily ddI with AZT/3TC. After 48 weeks those in the ddI arm were significantly less likely to have undetectable viral load by intention to treat analysis (50% vs 59%; p=0.05).
The results prompted US regulators to issue a warning about the potentially reduced potency of once daily ddI when compared to twice daily ddI, but European regulators have taken a different view. They have not asked Bristol-Myers-Squibb to issue a warning, and in a letter to UK doctors issued last week, BMS pointed out that the FDA ignored a number of factors which should be taken into account before jumping to the conclusion that once daily ddI is inferior to twice daily dosing.
If the study had been analysed using a switch equals failure intention to treat analysis, in which everybody who changed from their initial treatment was considered to have failed the initial regimen, the two regimens would be similar, said BMS. Eight per cent of those randomised to AZT opted to switch to d4T during the study, while only 3% opted to switch from d4T to AZT. This difference was highly statistically significant (p=0.007). In the original design of the trial, it was expected that these switches would be evenly distributed between the study arms, and that they would not affect the final outcome.
Similarly, if all those who failed to start the study medication despite randomisation had been excluded from the analysis, the two regimens would have been similar. While 2% failed to start in the AZT arm, 4% of the ddI arm failed to start the study regimen, yet were treated as `on drug' by the 48 week analysis.
Finally, BMS point out that the nelfinavir regimen used in the study was three times daily, imposing a much higher burden on the ddI arm than the AZT arm. Nelfinavir must be taken separately from ddI, making the ddI/d4T/nelfinavir arm a four times daily regimen.
The findings do not affect the recent European approval of once daily ddI capsules, which are a different formulation from the 200mg reduced mass tablets used in the AI454 study.