This is a case of phenobarbital-induced TEN in an HLA-B*15:02 and HLA-B*58:01 negative and CYP2C19*1/*2 intermediate metabolism patient; unlike previously reported similar cases, the patient’s cutaneous eruption was promptly recognized, and treated appropriately under close monitoring by physicians and clinical pharmacists, and the patients had a good prognosis. The gene discussed is CYP2C19; the disease is toxic epidermal necrolysis.