People taking PrEP as prescribed would generally not be eligible for PEP. However, those at risk of HIV acquisition taking PrEP may present for PEP in the context of suboptimal adherence to PrEP.103
Clinical104 and pharmacokinetic data101,105,106 provide good evidence of levels of adherence to PrEP required to effectively prevent HIV acquisition via anal and vaginal sex.
There are few data regarding front hole sex in trans men or neovaginal sex in trans women but levels of adherence required can be extrapolated from protective tissue concentrations in peripheral blood mononuclear cells.106 Time to protection of tenofovir disoproxil is shortest in lower gastrointestinal tract tissues, followed by peripheral blood mononuclear cells and then female genital tract tissues. Due to persistence of tenofovir and emtricitabine in rectal tissues, levels of PrEP adherence required for protection of HIV acquisition from anal sex are lower than those required for vaginal, front hole or neovaginal sex.
Evaluating the need for PEP involves an assessment of the:
(a) site and nature of exposure
(b) number and timing of PrEP doses taken in the seven days before the risk exposure
(c) correct dosage and timing of on-demand PrEP taken before and after the exposure.
Refer to Table 5 for guidance.
Table 5. PEP in the context of PrEP
| Anal sex and other exposures (includes vaginal, frontal or neovaginal sex and percutaneous exposures) | ||
|---|---|---|
| Risk exposure (refer to: Table 1) | Adherence to PrEP | Recommendations |
| Requires 3-drug PEP | Anal sex: At least 4 doses in the 7 days immediately before the risk exposure(s) Other exposures: At least 6 doses in the 7 days immediately before the risk exposure(s) | Continue PrEP Test for HIV at clinic presentation and 3 months |
| Requires 3-drug PEP | Anal sex: Fewer than 4 doses in the 7 days immediately before the risk exposure(s) OR Incomplete adherence to on-demand PrEP before or after exposure Other exposures: Fewer than 6 doses in the 7 days immediately before the risk exposure(s) | Transition to three-drug PEP if last risk exposure is within the 72-hour PEP window Assess context of adherence difficulty, intervene and consider increased frequency of monitoring If usually taking on-demand PrEP but was not taken as required before or after most recent exposure, consider recommending daily PrEP to improve adherence (NOTE: ON-DEMAND PrEP IS NOT RECOMMENDED FOR PEOPLE HAVING VAGINAL, FRONT HOLE OR NEOVAGINAL SEX) Test for HIV at PEP initiation and completion Re-commence PrEP on completion of 28 days of PEP |
| Requires 2-drug PEP | Anal sex: At least 4 doses in the 7 days immediately before the risk exposure(s) Other exposures: At least 6 doses in the 7 days immediately before the risk exposure(s) | Continue PrEP Test for HIV at clinic presentation and 3 months |
| Requires 2-drug PEP | Anal sex: Fewer than 4 doses in the 7 days immediately before the risk exposure(s) OR Incomplete adherence to on-demand PrEP before or after exposure Other exposures: Fewer than 6 doses in the 7 days immediately before the risk exposure(s) | Immediately commence daily TDF-FTC as PEP for at least 28 days, if last risk exposure is within the 72-hour PEP window; consider recommending ongoing DAILY PrEP to improve adherence Assess context of adherence difficulty, intervene and consider increased frequency of monitoring. If usually taking on-demand PrEP but was not taken as required before or after most recent exposure, consider recommending daily PrEP to improve adherence (NOTE: ON-DEMAND PrEP NOT RECOMMENDED FOR PEOPLE HAVING VAGINAL, FRONT HOLE OR NEOVAGINAL SEX) Test for HIV at PEP initiation and completion Re-commence PrEP on completion of 28 days of PEP |
