see also:

• viruses
• antiretroviral agents
• AIDS

• these medications are used to reduce the risk of getting HIV infection
• see https://www.cdc.gov/hiv/risk/prep/index.html
• examples include:
  • emtricitabine and tenofovir disoproxil fumarate
  • emtricitabine and tenofovir alafenamide
  • integrase inhibitors (INIs)
    • cabotegravir (Apretude)

• the following is derived from Landovitz and Currier, NEJM 2009; 361:1768-75;
• post-exposure prophylaxis appears to prevent ~80% of potential HIV transmissions but is expensive, often not well tolerated and thus the decision on prophylaxis is complicated and requires an estimate of risk-benefit for the individual patient.

• ELISA testing of known source
  • NB. recent high risk behaviour of source which may give false negative ELISA
  • if ELISA is negative and no recent high risk behaviour, then post-exposure prophylaxis is NOT indicated.
• characteristics of unknown source HIV status which generally are indicators for post-exposure prophylaxis:
  • men who have sex with men
  • men who have sex with both men and women
  • commercial sex workers
  • injection-drug users
  • persons with a history of incarceration
  • persons from a country where the seroprevalence of HIV is 1% or greater
  • perpetrators of sexual assault
  • persons who have a sexual partner belonging to one of these groups.

• the overall rate of HIV transmission through percutaneous inoculation is said to be 0.3%
  • higher rates may occur if either:
    • a needle that was used to cannulate a blood vessel in the source patient
    • advanced HIV disease in the source patient
    • a deep needlestick
    • visible blood on the surface of the instrument
• splashes of infectious material to mucous membranes (e.g. conjunctivae or oral mucosa) or broken skin also may transmit HIV infection (estimated risk per exposure = 0.09%)

• sexual exposure estimated risks of HIV transmission:
  • NB. there is almost zero risk of sexual transmission of HIV with viral loads of less than 1000 copies per mL in the source person¹⁾
  • 1-30% if receptive anal intercourse
  • 0.1 to 10.0% with insertive anal intercourse and receptive vaginal intercourse
  • 0.1 to 1.0% with insertive vaginal intercourse
  • possible with oral sex but data lacking
  • risk also depends upon:
    • presence or absence of concomitant genital ulcer disease
    • other disease states
    • cervical or anal dysplasia
    • circumcision status (cirumcision lowers risk)
    • the viral load in the genital compartment
    • the degree of viral virulence
• IVDU sharing needles:
  • risk estimated at 0.67% per needle-sharing contact.

• initiate as soon as possible after exposure (consider 1st dose if ELISA testing of source is likely to be delayed)
  • commencement before 36hrs appears more effective than commencing before 72 hours in monkeys
• postexposure prophylaxis should be continued for 28 days
• two drug regime appears to have the best cost-effective, clinical risk-benefit profile unless the source HIV population has > 15% viral resistance rates, in which case, a three-drug regime would be prudent.
• compliance with Rx is a major issue and at least weekly patient contact is advised to improve compliance

• tenofovir–emtricitabine:
  • once daily dosing, well tolerated but risk of nephrotoxicity
  • emtricitabine 200mg + tenofovir 300 mg orally, daily for 4 weeks
• zidovudine–lamivudine:
  • twice daily dosing, less well tolerated (more nausea, asthenia, neutropenia, anaemia, abnormal LFTs) but preferred in pregnancy

• baseline HIV status (and hepatitis B, C)
• baseline FBE, U&E, LFT if considering post-exposure prophylaxis
• vaccination against hepB if no or insufficient antibodies to hep B (plus IgG if source is hep B +ve)
• consider screening and Rx for sexually transmitted infections (STDs/STIs) if sexual exposure including RPR at 3 months
• follow up ELISA testing for HIV and HCV (hepatitis C) at 4-6 weeks, 3 months and 6 months after exposure
• use condoms and avoid sharing razors, toothbrushes, etc until te 6 month HIV test is negative