This week the NHS has to decide whether they will fund a new drug for HIV prevention after overruling the decision previously. The drug, called PrEP, is currently undergoing clinical trials. The drug will be given to high risk gay males to prevent contraction of the HIV retrovirus. The men classified as high risk are those who claim they have unprotected sex, have a partner who is HIV positive and those who use needles. However, they must not have the virus before treatment as PrEP is an abbreviation for pre-exposure prophylaxis; prophylaxis simply meaning prevention. It is this that is causing controversy within the NHS as officials don’t feel it is their responsibility to prescribe preventative medication for HIV.
PrEP is the common name for the combination drug Truvada. It is a once daily oral pill, sounding very similar to current contraceptive pills and so has good patient compliance.
HIV is a retrovirus which means it performs reverse transcription. Usually, in the process of DNA replication, the DNA unzips and undergoes transcription followed by translation to form another type of nucleic material called messenger RNA (mRNA). The mRNA then leaves the nucleus to make proteins and give the cell its function. However, when the HIV virus binds to a cell (specifically the T helper cells in the immune system) and enters it, reverse transcription occurs using reverse transcriptase; an enzyme carried by the virus. The reverse transcriptase does what it says on the tin. It reverses the process to form viral DNA from the viral RNA. The virus can then insert its DNA into the human DNA using another HIV-born enzyme called integrase, before forward transcription occurs again to form an mRNA with the HIV sequence integrated into it. The new sequence encodes HIV proteins to form the new virus and a budding and maturation process occurs producing more HIV viruses to infect other nearby cells. This repeats until the patient is immunosuppressed which is when AIDS is established.
With the knowledge of the life cycle, we can unpick each word: nucleosides are the DNA
subunits, the monomers that make the long strand of DNA before phosphorylation and
consist of one of the 4 bases (guanine, adenine, cytosine and thymine) bonded to a sugar unit (deoxyribose). As the drug is an analogue of a nucleoside it must mimic the structure of a nucleoside without being functional. The reverse transcriptase cannot use faulty nucleosides and so a chain of DNA cannot be made.
Truvada is highly effective and can reduce the contraction of HIV in high risk males by more than 90%, it is also cost effective. The cost of giving the drug (£400 a month before the patent runs out and it falls) is less than the lifelong treatments those who have contracted HIV and have established AIDS would receive. Some may say a condom is just as effective and cheaper, but even with the most cautious it can break and in a drunken fling it may simply be forgotten. By taking this pill, if a condom is not used the man is not at risk, in parallel with a woman taking the contraceptive pill to prevent pregnancy (not STI’s however). Again, this drug is for males at the highest risk so surely the decision is clear: bring out the drug, save money and most importantly lives. The quality of life of many gay men are hanging in the balance of this decision.