We all know that the most effective on-demand prophylaxis is correct condom usage at the time of sexual activity, but other forms of prophylaxis are needed for when condoms are not used. IPERGAY suggests that oral TDF/FTC may also serve as a sort of on-demand prophylaxis, but this strategy requires lead time, and there is not yet enough data to differentiate on-demand PrEP from non-daily PrEP (4x/week).
If you could design an on-demand prophylaxis (alternative to condoms or oral TDF/FTC), what would you make? What do you think are the features critical to an effective on-demand prophylaxis (ease of use, cost, pharmacokinetics, efficacy)? Would you expect that a different drug, formulation, or strategy might work better for the goal of effective on-demand prophylaxis?