Abacavir, adverse reaction

Educate the patient on common adverse drug effects and a few of the key signs and symptoms of severe toxicity (i.e., jaundice and abacavir hypersensitivity reaction). Tell them to call their provider immediately if any of those symptoms occur. Make sure they have the correct telephone number for the clinic. 

Severe or fatal hypersensitivity reactions can occur within hours after reintroduction of abacavir in patients who have no identified history or unrecognized symptoms of hypersensitivity to abacavir therapy (see Warnings and Adverse Reactions). Zidovudine has been associated with hematologic toxicity, including neutropenia and severe anemia, particularly in patients with advanced HIV disease (see Warnings). Prolonged use of zidovudine has been associated with symptomatic myopathy. 

Abacavir sulfate has been associated with fatal hypersensitivity reactions. Do not restart abacavir following a hypersensitivity reaction (see Warnings and Adverse Reactions). 

Abacavir (t) 2 h) may be the most potent reverse transcriptase inhibitor. It is usually well-tolerated, but adverse effects may include hypersensitivity reactions especially during the first 6 weeks of therapy. 

The effects of abacavir have been evaluated in a study in over 13 000 adults who no longer responded to commercially available treatment regimens (2). By month 2 of treatment with abacavir, plasma HIV-1 RNA concentrations fell by at least half a log unit in 31% of patients, and in 5.6% of the patients HIV-1 RNA concentrations fell to under 400 copies/ml. Serious drug-related adverse events were reported by 7.7% of patients. The most common were nausea, skin rash, diarrhea, malaise or fatigue, and fever. About 4.6% of patients had a hypersensitivity reaction that was possibly drug-related. 

The efficacy and safety of abacavir (NRTI) and efavirenz (NNRTI) plus background therapy have been retrospectively evaluated in 50 patients, who had previously been treated with HAART (3). There was some immunological benefit, albeit limited, in most of the patients. Adverse effects were not mentioned in detail, but the dropout rate during the first 4 weeks of treatment was high, owing to skin rashes and hypersensitivity reactions. 

In a 24-week open, single-arm trial, 108 antiretroviral therapy-naive, HIV-infected prisoners were given a combination tablet of lamivudine -I- zidovudine (150 mg/300 mg) and a tablet of abacavir 300 mg bd (2). The plasma HIV-1 RNA concentration remained at 400 copies/ml or less in 85% of the patients and at less than 50 copies/ml in 75%. Nausea was the most common adverse effect (n = 40). Four patients withdrew prematurely because of one or more of the following abdominal discomfort and pain abdominal distension neutropenia malaise or fatigue nausea and vomiting. Two patients had a suspected hypersensitivity reaction to abacavir and were withdrawn. 

Hughes AR, Brothers CH, Mosteller M, et al. Genetic association studies to detect adverse drug reactions Abacavir hypersensitivity as an example. Pharmacogenomics. 2009 10(2) 225-233. 

---