Cost-effectiveness

One concern expressed about PEP is cost. Anti-HIV drugs are a lot more expensive than condoms. However, at around £600 for a month's triple combination therapy, the cost of one course of PEP for a single individual compares extremely favourably with the lifetime costs of treating the same individual for HIV.

A 2009 review¹ of the cost-effectiveness of PEP for the United Kingdom commented that “It is not possible to draw conclusions on the clinical effectiveness of non-occupational PEP for HIV because of the limited evidence in terms of the quantity and quality of studies.”

However it found that four economic evaluations using evidence on effectiveness taken from the use of PEP in the occupational setting indicate that PEP might be cost-effective with certain populations, though it cautioned on the generalisability of studies conducted in other countries.

The cost–effectiveness of an intervention such as PEP can only be meaningfully calculated in terms of the amount of money that would need to be spent to prevent a single infection. On average, no more than about one out of every 300 people who have a single episode of unprotected receptive anal sex with an HIV–positive person becomes infected as a result.² So if all 300 came forward for PEP after their risk exposure, 299 would be treated 'unnecessarily', because they would not have become infected regardless of whether or not they received PEP. If doctors have to treat 300 people in order to prevent the one single infection, the cost of preventing that infection would be 300 times £750, which makes £225,000. This begins to approximate the likely lifetime drug costs of treating someone with HIV, which for a 30-year post-treatment lifespan in the UK would be around £300,000. However the cost of PEP per infection prevented is still likely to be much lower when all the costs of lifetime treatment in addition to drugs (staff, monitoring etc.) are included.

The cost–effectiveness of PEP could be improved by using fewer or cheaper drugs; for example, if only two nucleoside reverse transcriptase inhibitors (NRTIs) were used, or if an additional protease inhibitor was reserved only for specific cases of the greatest risk, the cost per course of PEP would be approximately halved.

Moreover, PEP is more cost–effective if it is delivered only to people whose circumstances mean that they are most at risk of becoming infected (effectively reducing the proportion of recipients who are being treated 'unnecessarily'). Possible criteria for prioritisation include limiting PEP to cases in which people have had a risk encounter with someone who is definitely HIV positive. This is the case in UK national guidelines for any sexual exposure other than receptive anal intercourse, even though the US guidelines for occupational use do not carry such a restriction.

A study published in January 2004³ attempted to calculate the cost-effectiveness of PEP by looking at 401 people who had sought PEP in San Francisco.

The group included men and women who sought PEP for incidents of unprotected anal and/or vaginal intercourse and needle-sharing. The researchers concluded that, given their risk behaviour, PEP reduced the HIV infections that would have been expected in the group by 53%. They estimated that 2.36 HIV infections would have been expected in the 401 people during the study period, and PEP reduced this to 1.1 infections.

This 53% reduction saved 11.74 quality-adjusted life years (QALYs). This measurement, frequently used in cost-benefit calculations, means that, for those who used it successfully, PEP should lead to an extra 11.74 years of reasonable health. This in turn, it was calculated, would save a total of US$281,323 in future HIV-related medical costs. When all factors were taken into account, the cost of PEP per QALY saved was US$14,449. This is easily under the US threshold for the definition of medical cost-effectiveness, which is $40,000 to $60,000 per QALY (about £30,000 in the UK). By comparison, a similar cost-effectiveness study⁴ showed that HIV combination therapy resulted in a cost of US$23,000 per QALY saved.

This study found that PEP, given to the general at-risk population, did work out to be much less cost-effective than other HIV prevention methods. As an example, one risk-reduction programme for at-risk women attending an urban primary healthcare clinic, which produced a significant increase in condom use, cost about US$2000 per QALY.⁵ A similar programme for gay men,⁶ was cost-saving: the cost of likely future treatment and care of those infected without the programme outweighed the cost of delivering the programme to the whole group.

PEP for gay men in the San Francisco study was more cost-effective than for the group as a whole: US$8607 per QALY saved. However, when it came to gay men who had been receptive partners in unprotected anal sex, it found that PEP was actually cost-saving. The cost per infection averted for this group was US$177,293 – which is less than the likely cost of their lifetime HIV treatment if they had not received successful PEP. On the other hand, PEP for gay men on the insertive end of unprotected anal sex (i.e. ‘tops’) was not considered cost-effective.

The variation seen in cost-effectiveness between subgroups of different populations is not surprising, given that you need to provide PEP to the people most at-risk for it to be cost-effective. The Health Protection Agency⁷ estimates that gay men who are the passive partner in unprotected anal intercourse have a 1-in-33 risk of being infected with HIV if they are certain their partner is HIV-positive, but a 1-in-222 risk if they do not know the HIV status of their partner. They estimate that gay men who are the active partner in unprotected anal intercourse have a 1-in-555 risk of being infected with HIV if they are certain their partner is HIV-positive, but a 1-in-11,111 risk if they do not know the HIV status of their partner. However, other factors such as geographical location, sexually transmitted infections (STIs), viral load and bleeding may affect the risk estimate, so there is likely to be a range of risk of transmission rather than an exact value.

In short, if PEP in the UK is offered to gay men who have been the passive partner in unprotected anal intercourse and/or who have known HIV-positive partners, PEP could potentially save as much money as providing condoms and safer-sex education, as long as PEP is not routinely relied upon as a substitute for these other safer-sex practices.