London, UK—Increasing resistance to the drug tenofovir, used to treat human immunodeficiency virus (HIV), has raised worldwide alarm.

That’s according to a new study published in the Lancet Infectious Diseases journal. A study team led by researchers from University College London and involving Stanford University and the London School of Hygiene and Tropical Medicine found tenofovir-resistant strains in 60% of patients in sub-Saharan Africa compared to 20% in patients treated in Europe.

The study involved 1,926 HIV patients from 36 countries with treatment failure between 1998 and 2015.The researchers note that about two-thirds of patients with tenofovir-resistant strains had also become resistant to other drugs in their regimens, indicating that their treatment had been completely compromised.

In Sub-Saharan Africa, the research suggests, up to 15% of HIV patients treated with tenofovir-based drug combinations will develop tenofovir resistance in the first year of treatment alone, and that the percentage tends to rise over time. The concern is that resistant strains could be passed on to others, becoming more widespread and potentially compromising global HIV-control strategies.

“Tenofovir is a critical part of our armamentarium against HIV, so it is extremely concerning to see such a high level of resistance to this drug,” explained lead author Ravi Gupta, MD, of the University College London. “It is very potent drug with few side-effects, and there aren't any good alternatives that can be deployed using a public health approach. Tenofovir is used not only to treat HIV but also to prevent it in high-risk groups, so we urgently need to do more to combat the problem of emerging resistance.”

Tenofovir is often a component of pre-exposure prophylaxis (PrEP), which is increasingly used in the United States and elsewhere.

Study authors explain that resistance to a drug usually occurs because of non- or inconsistent adherence to the drug regime. HIV medications should be regularly used at least 85% to 90% of the time, they said, because treatment interruption can allow the virus to develop a resistance to the drugs.

Study participants who already had compromised immune systems were 50% more likely to develop tenofovir resistance, as were patients on certain other antiretroviral drugs combined with the drugs. The researchers point out that, in many parts of Sub-Saharan Africa, particularly rural locations, supplies are limited so patients often can’t receive treatment until they have advanced HIV disease; in addition, the availability of second-line treatments is rare.

“Public health organizations and global funders have been very effective at expanding antiretroviral drug therapy to increasing proportions of patients in need,” noted Robert Shafer, MD, of the Stanford University School of Medicine. “This study highlights the need for efforts to ensure that the regimens used to treat HIV retain their effectiveness as long as possible.”

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