Abacavir resistance: what it means and what to do next

If you're taking abacavir (an NRTI used in HIV treatment) and your viral load starts to rise, resistance might be the reason. Resistance means the virus has changed so the drug no longer controls it well. That doesn’t mean you’re out of options — but you do need clear steps and timely testing.

How resistance happens and what mutations matter

Resistance develops when HIV copies itself imperfectly and selects versions that survive drug pressure. For abacavir, several reverse transcriptase mutations are commonly linked to reduced effect. The ones clinicians watch for most are L74V, Y115F, K65R and M184V. Any of these can lower abacavir activity, and when they appear together the effect gets stronger.

Keep in mind two things: (1) M184V is best known for affecting lamivudine/emtricitabine, but it can also change how other NRTIs work; (2) the pattern of mutations matters more than a single change. That’s why a lab report listing mutations is useful — it shows the whole picture, not just one name.

Testing, timing, and practical next steps

If your viral load rises above your normal suppression (clinicians often act when it’s consistently above roughly 200–500 copies/mL), ask for genotypic resistance testing. Genotypic tests read the virus’s genetic code and list mutations. Some clinics also do phenotypic tests, which measure the virus’s actual drug sensitivity, but genotyping is faster and widely used.

When results come back, your doctor will compare the mutation pattern to known resistance profiles and recommend a new regimen if needed. Common moves include switching to an integrase inhibitor–based regimen (for example, dolutegravir), or to a boosted protease inhibitor like darunavir with a good resistance barrier. Often clinicians pick drugs from different classes so cross-resistance won’t be a problem.

Don’t forget basics that actually help: check adherence first (missed doses are the most common cause of resistance), review possible drug interactions that lower antiretroviral levels, and confirm prescription accuracy. Also, before anyone starts abacavir, HLA-B*57:01 testing is required to avoid a dangerous hypersensitivity reaction — that’s not about resistance but it matters for safe use.

If you’re worried about resistance, talk openly with your provider. Bring recent lab results, a list of medications (including over-the-counter and supplements), and an honest log of missed doses. With timely testing and a smart switch, most people regain viral suppression and keep long-term treatment options open.