Daily dosing for PrEP seems to be taking precedence over other dosing schedules. This was cast into some doubt when the IPERGAY and PROUD studies were presented at CROI revealing and 86% reduction in transmission for both daily and event driven PrEP. But discussion about frequency of dosing remains. HPTN067 the ADAPT trial reported 2 of 3 arms comparing daily, twice weekly + one dose after event and one dose before and one dose after event dosing. The sites were Harlem and Bangkok. Daily dosing was best in both studies. Doses after sex event were most frequently missed. No risk compensation.
Less than daily dosing is probably effective at some level, but determining that level is the challenge. Having sufficient drug on board to maintain an effective therapeutic dose is the issue and this may be impacted by other host factors such as weight and metabolic rate. If 3 or 4 doses are sufficient to provide protection then this would provide significant cost savings against the cost of Truvada
On the topic of risk compensation, a passing comment was made that if anyone is going to see risk compensation and reduction in condom use it will be the Australians as they are the only people who use condoms.