Abacavir is associated with hypersensitivity reaction (ABC-HSR) in around 8% of patients who start it and usually the symptoms occur quickly, on average ten days after drug initiation and worsen with each administered dose (13). Rash is presented in 70% of cases and in rare instances may be accompanied by general symptoms, but eosinophilia and hepatitis are uncommon. If the hypersensitivity reaction is related to abacavir all the symptoms disappear within 72 hours of discontinuation. Restarting abacavir after ABC-HSR may result in a life-threatening condition including hypotension and is strongly contraindicated (14).
A specific human genetic variation (HLA-B*5701 allele) was found to be strongly associated with susceptibility to ABC-HSR. Therefore a genetic test for HLA-B*5071 can accurately predict whether the patient is at risk for ABC-HSR. HLA-B*5701 carriage rate is highest in Caucasians (6-8%) and lower in those of African/Asian ethnicity (<1%, 2.5% for African-Asian).
Results from PREDICT-1 trial (15) show that screening for HLA-B*5701 reduces the rate of ABC-HSR from 7.8% to 3.4%. In this study none of the patients who tested negative developed ABC-HSR and less then half of the patients tested as positive did. These results are generalizable across ethnicity (16).
DIHS/DRESS related to nevirapine is the most common treatment-limiting toxicity and occurs in around 5% of patients starting this ART. The most common organ involvement is hepatitis (17). SJS/TEN occurs in around 0.3% of patients on nevirapine (12).
Skin rashes related to efavirenz are usually mild or moderate maculopapular eruptions which occur in the first 2 weeks after drug initiation and usually resolve spontaneously. More severe hypersensitivity reactions occurred in less than 1% of patients taking efavirenz and SJS in approximately 0.14% (18). Efavirenz should be discontinued only when a severe rash with blistering, fever and mucosal involvement is present. Skin rash is more likely to occur if switching ART from efavirenz to nevirapine, then other way around (20).
In addition to the drugs mentioned above, skin rash as an adverse reaction has been reported for the following:
In addition, enfuviritide (fusion inhibitor), the only ART injected subcutaneously, can cause reactions at the injection site, including redness, itching and hard lumps.
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