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Pre-exposure prophylaxis for HIV infection (PrEP)

  • these medications are used to reduce the risk of getting HIV infection
  • examples include:
    • emtricitabine and tenofovir disoproxil fumarate
    • emtricitabine and tenofovir alafenamide
    • integrase inhibitors (INIs)
      • cabotegravir (Apretude)

Post-exposure prophylaxis for HIV infection

  • 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.

risk of source HIV transmissibility

  • 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.

risks of transmission

occupational exposure

  • 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%)

non-occupational exposure

  • 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.

post-exposure prophylaxis regime

  • 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

two main drug regimes for low risk exposures

  • 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

patient testing (recipient) and follow up

  • 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
hiv.txt · Last modified: 2024/01/29 06:32 by gary1

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