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Pre-Exposure Prophylaxis (PrEP)

Note:PrEP AIDS  Eile has previously published this article in our monthly edition September, 2013 – see sidebar icon or topbar “issues”

Dr. Shay Keating writes about the advantages and disadvantages of Pre-Exposure Prophylaxis in the treatment of HIV

Prophylaxis, in medical terms means preventing a disease or condition.  Post-exposure prophylaxis (PEP) is any prophylactic treatment started after an exposure to a disease. PEP is currently licensed under strict specialist supervision following HIV exposure either sexually or needle stick.

Pre-exposure prophylaxis (PrEP) on the other hand is a medical or public health procedure used before an exposure to prevent a disease rather than treat or cure it.  For example, a doctor might give medication used to treat a specific disease to a healthy person who is believed, not have the disease but to be at risk of contracting it.  A well known and commonly used example of PrEP is malaria medicine, given to travellers to countries where the disease is endemic such as Sub Saharan Africa.  PrEP is currently used in serodiscordant couples where one partner is HIV positive and the other negative and where the woman is keen to become pregnant.  PrEP is used by the negative partner for a defined time around the planned time of conception is a powerful tool to limit HIV infection from sexual intercourse. This has lessened the need for specialist and expensive sperm washing or artificial insemination in many cases.

What about using PrEP indefinitely as a HIV prevention tool? In 2007 the iPrEx study enrolled 2499 individuals to take part in a clinical trial. The trial involved 6 counties worldwide including the United States. This was the first trial to study the effectiveness of continuous PrEP use in preventing HIV infection.

All participants in the study received monthly HIV testing, safer sex counselling, condoms and STI treatment where appropriate. Half of the participants received a popular antiretroviral therapy (ART) and half received a placebo. The results of this study were interesting.  There was a 43.8% reduction in HIV infection in those taking ART.  This research was hailed by Time Magazine as the ‘most significant medical breakthrough of 2010’. It has been estimated that taking ART every day would be 99% effective in preventing HIV infection.  This is comparable to consistent and careful condom use, which apart from abstinence has up to now been the best sexually acquired HIV prevention strategy. Condoms can slip off or break and that’s when one remembers to use one.

The Centre for Disease Control (CDC) in Atlanta Georgia had a more tempered response to iPrEx.  They argued that PrEP has been shown to reduce HIV infection among men who have sex with men (MSM) and not heterosexuals or injecting drug users. The TDF2 trial in Botswana however, showed a 63% reduced risk of HIV infection in heterosexual men and women. Used correctly, PrEP appears to be effective.

The early PrEP data seems very promising but there are some problems. Adherence to PrEP is essential.  Studies found that high levels of adherence to ART i.e., no missed doses, correlated with high levels of protection against HIV infection and poor adherence to poor levels of protection. HIV resistance to PrEP can also be a problem. HIV resistance can only occur in the context of active infection.  It can occur if someone becomes infected with HIV either as a consequence of poor adherence or in the ‘window period’ where the person is infected following negative  antibody testing.  Furthermore the published PrEP studies used ART that is the backbone of many popular HIV treatment regimes. Resistance to this drug regime could seriously compromise treatment options going forward.

Another problem with PrEP is that in studies one in five MSM admitted that they would be less likely to use condoms with PrEP.  This would increase potential exposure to other sexually transmitted diseases such as syphilis, herpes or hepatitis. Side effects of PrEP are also a reality.  We can prescribe ART to those already affected by HIV and they will benefit hugely by the resolution of immune function but the real risk of adverse events in the otherwise well who do not have HIV may not warrant the long-term use of PrEP.

There are also cost implications.  It has been estimated that one year of PrEP could cost in the region of €10,000. The government, which funds HIV care, could treat someone who is HIV positive with this money. Current expert advice in Ireland is that long-term use to prevent HIV infection,  PrEP should be the last defence after considering condom use, regular HIV and STI testing and a reduction in the number of sexual partners.

I believe that until we know more, PrEP should only be given in very controlled clinical circumstances by specialists in the field.  Furthermore there is a concern that ad hoc prescribing or illicit procurement of PrEP will most certainly lead to abuse of the ARTs and ultimately to HIV infection and drug resistance.

Dr. James (Shay) N. Keating, BA Mod, MB, PhD. MRCP, Dip GUM, Dip Occ Med., has his clinic at the Harold’s Cross Surgery, Harolds Cross, Dublin 6W, and is an Associate Specialist in Genitourinary Medicine, at St. James’s Hospital, Dublin.

For more information contact stdclinic.ie Phone: 01-497 0022 or +353 87 234 5551

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