NPEP appears to be most effective when administered as soon as possible after exposure. In macaque monkeys, tenofovir initiated within 24 hours of a simian immunodeficiency virus (SIV) challenge provided 100% protection from infection vs 50% and 25% when initiated at 48 and 72 hours, respectively.^[14]  In seven human cases of seroconversion following NPEP, the median time from exposure to first dose of NPEP medication was 45.5 hours (range 14 – 72.4 hours) and three of the seroconversions to HIV in this series initiated NPEP after 48 hours post exposure although this difference was not statistically significant.^[12] Nurses should be aware of the critical nature of time with regard to PEP, educate accordingly, facilitate rapid referral if required and, in emergency departments, allocate a high triage priority to patients who present for PEP.