HIV: Drug Market Dynamics

Ever since the discovery of the human immunodeficiency virus (HIV) in 1984, the prevalence of HIV patients has been increasing worldwide, and by 2006 there were 39.5 million with the disease (1). The six major Western markets (6MM) (2) represent the largest HIV drug market, generating approximately $8.2 billion of sales in 2006, following a strong compound annual growth rate (CAGR) of 13.1 per cent between 2003 and 2006 (3).

Although small compared to sectors such as the antibacterial market, the HIV market is one of the fastestgrowing within the infectious diseases sector. Factors driving this growth include the growing number of heterosexual transmissions, immigration from countries with a high HIV prevalence, and a suggested increase in high-risk sexual behaviour among homosexual men. At the same time, the lifeprolonging effects of antiretroviral therapies have turned HIV into a chronic disease.

Although the 6MM represent the most commercially significant HIV markets, they account for only three to six per cent of the globally infected population – over 95 per cent of HIV patients live in the developing world, with sub-Saharan Africa accounting for the vast majority (4). The growth in patient numbers in the Western markets is lower than the six per cent global growth in patient population from 2004 to 2006 as a result of greater disease awareness (1). Meanwhile, growth in emerging markets is driven by the fact that there are fewer and less well-funded HIV/AIDS educational programmes, the drug distribution infrastructure is less effective and drugs are unaffordable for patients.

COMBINATION DRUGS

The HIV market has witnessed a rapid development since the introduction of the first antiretroviral in 1987 (GlaxoSmithKline’s Retrovir, zidovudine). This drug belongs to the nucleoside reverse transcriptase inhibitor class (NRTIs). Since this was the first class of antiretrovirals to become available, the majority of patients were placed on high doses of monotherapy, which eventually led to toxicity and resistance. The introduction of protease inhibitors (PIs) in 1995 provided physicians with extra options to treat patients and initiated the use of a combination of drugs from different classes, more commonly known as highly active antiretroviral therapy (HAART).

This class’s novel mechanism of action enabled synergistic action with NRTIs in combination therapy, which partly addressed the problem of resistance. However, there were a number of issues when the first PIs launched, including patient compliance due to high pill burden, pharmacokinetic problems and side effects – such as lipodystrophy, liver toxicity and diabetes. Recently launched PIs have been designed to address these issues: drugs such as Kaletra, Reyataz and Prezista (developed by Abbott Laboratories, Bristol Meyers-Squibb (BMS) and Tibotec respectively) have more favourable side-effect profiles and have a significantly lower pill burden compared to the older PIs.