Allergy to chlorpromazine and valproic acid following carbamazepine hypersensitivity in a patient with an HLA-B*4601 allele

A 73-year-old man, exhibiting psychomotor excitement after traumatic brain injury, developed allergic cutaneous eruptions and hepatic inflammation that did not resolve after the cessation of carbamazepine (CBZ). Fusing maculopapular erythema was observed in the face, neck, presternal region, and bilaterally in the forearms and feet. A drug-induced lymphocyte stimulation test revealed hypersensitivity to chlorpromazine (CPZ) and valproic acid (VPA), as well as to CBZ. The allergic reaction with eosinophilia to CPZ and VPA was suspected to have emerged following CBZ hypersensitivity, since previous treatment with CPZ and VPA prior to the introduction of CBZ had not been associated with adverse reactions earlier in the course of treatment. Recent studies have indicated linkages between severe CBZ hypersensitivity – but not mild CBZ hypersensitivity – and specific leukocyte antigens, HLA-B*1502 and HLA-A*3101, in Asian and European populations. The present case exhibited the HLA-B*4601 allele, which is associated with a high relative risk for the development of CBZ-induced maculopapular eruptions in Japanese and Han Chinese populations. Although cross-hypersensitivity among aromatic compounds, including CBZ and CPZ, is well-established, data regarding CBZ allergy-associated hypersensitivity to VPA are limited. In the present case, a cutaneous allergy to mianserin (a tetracyclic antidepressant) was also observed later in the course of treatment, suggesting additional cross-reactivity exists among aromatic psychotropic drugs. Thus, the association between the HLA-B*4601 allele and allergic reactions to VPA, aromatic psychotropic drugs, and CBZ should be further examined in future studies.