Side-effects

The most common side-effects of abacavir (Ziagen) are nausea, vomiting, lethargy and fatigue. Other commonly reported side-effects are fever, headache, diarrhoea and loss of appetite. In general, these appear in the first few weeks of treatment. They tend to resolve themselves and to be of mild or moderate severity.

Abacavir seems to damage mitochondria to a lesser extent than other nucleoside reverse transcriptase inhibitors (NRTIs).^[1] It is therefore less likely to cause side-effects related to mitochondrial damage, such as fat loss from under the skin, than are other NRTIs, such as d4T (stavudine, Zerit) and AZT (zidovudine, Retrovir).^[2] A number of studies have examined the effects of switching from these drugs to abacavir, with most showing modest improvements in fat levels.^[3][4][5][6]

There is conflicting evidence as to whether abacavir increases the risk of myocardial infarction (heart attack). In the D:A:D (Data Collection on Adverse events of Anti-HIV Drugs) observational multi-cohort study, an increased risk of myocardial infarction in those exposed to abacavir in the preceding six months (relative risk 1.9) was reported. An association was also seen in those taking didanosine (relative rate 1.5). No association was found between the use of zidovudine, stavudine, or lamivudine and cardiac events. Underlying cardiovascular risk factors were ruled out as a cause of excess risk and the risk was not present six months after discontinuing abacavir.^[7]

Results from SMART (Strategies for Management of Anti-Retroviral Therapy) study also found an excess risk of cardiovascular disease (CVD) with abacavir use as compared to other NRTIs. Events included myocardial infarction; stroke, coronary artery disease, congestive heart failure, peripheral vascular disease, and death. Researchers believe that abacavir may cause vascular inflammation, increasing the risk of cardiovascular events, particularly in those already highly vulnerable.^[8]

However, a 48-week interim study analysis of HEAT (Head-to-Head Epzicom and Truvada) failed to find excess CVD risk in the Epzicom (Kivexa) arm. Comparing the two NRTI backbones, each paired with Kaletra, Kivexa was found to be non-inferior to Truvada and lacking in any excess toxicity.^[9]

Lactic acidosis is a rare, but serious side-effect of all NRTIs including abacavir. Symptoms include an enlarged and tender liver, nausea and malaise. Lactic acidosis usually develops within a few months of starting treatment with NRTIs. It is more common in people with liver disease, obesity and women.

Three case reports of changes in mental state in patients starting abacavir have been reported. Although rare, symptoms include depression, suicidal thoughts, auditory hallucinations, psychosis, headaches and nightmares.^[10][11][12]