Testing for human leukocyte antigen (HLA) is required before starting a patient on abacavir, a nucleoside reverse transcriptase inhibitor (NRTI) used to inhibit viral replication in HIV infection. This stems from the identification 20 years ago of a gene variant, HLA-B*57:01, associated with hypersensitivity to abacavir.¹

Before routine screening was introduced in 2005, abacavir hypersensitivity syndrome (AHS) occurred in 5-7 per cent of patients prescribed abacavir. However, AHS has been eliminated by not using abacavir in patients with the HLA-B*57:01.

Two HLA gene variants have also been found that are associated with serious adverse effects with anti-epileptics.¹

A variant of the gene HLA-B*15:02, particularly prevalent among people in Southeast Asia, is strongly associated with the potentially fatal hypersensitivity reactions of Stevens–Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) following carbamazepine use. SJS-TEN reactions can also occur with oxcarbazepine and phenytoin.

Another gene variant, HLA-A*31:01, more prevalent among the Northern European population, is associated with other carbamazepine-induced hypersensitivity reactions such as common maculopapular rash.

Pharmacogenomic guidelines for prescribing carbamazepine and oxcarbazepine and the HLA genotype were published in 2018.¹⁹