Worry that replacing daily oral PrEP with an injectable might sacrifice protection as the injection concentration declines toward the next dose is understandable but isn’t supported by the clinical results. The approved intervals were deliberately set so that drug levels remain adequate through the end of the interval; the downward concentration curve is expected and already built into the regimen.
There is no demonstrated end-of-cycle falloff in protection when injections are received on schedule. However, against perfectly taken oral PrEP, the biological advantage, in spite of statistically demonstrated superiority, may be small or unknowable because both approaches are already extremely effective. That said, Yeztugo trials were open label and there is no way to determine whether research subjects adjusted exposure risk towards dosing cycle finish lines. None of these methodologies are flawless.
The idea suggested upthread, as basis for caution held by some making decisions, is confidence in a pharmacokinetic dosing protective buffer …
“Confidence interval” does not refer to the degree of confidence in protection based on dosing intervals. In this context, confidence attaches to an estimated trial effect, often a hazard ratio or incidence-rate ratio, describing sampling uncertainty around the overall comparative incidence of infection, for example Apretude compared to TDF/FTC (aka Gilead’s pre-generic Truvada), or Yeztugo compared to background subpopulation incidence. To illustrate, one trial with Apretude compared to TDF/FTC: about 66% lower HIV incidence; hazard ratio 0.34 (95% confidence interval 0.18-0.62). Not to be confused with time windows and waning protection.
My preference for oral PrEP, even if no out-of-pocket for injectable versions were possible, is based on my capacity for 100% adherence, but it’s moot because I apply that capacity to on-demand uptake.