Multiple drugsLack of drug effect and serum sickness: case report A 33-year-old man exhibited a lack of drug effect during treatment with immune-globulin, azathioprine and prednisolone for pemphigus vulgaris. Additionally, he developed serum sickness during treatment with rituximab for refractory pemphigus vulgaris [not all routes stated].The man was hospitalised with fever, malaise, arthralgia and myalgia for one day. Two weeks prior the admission, he started receiving IV rituximab 1000mg 2 times a week for severe refractory pemphigus vulgaris. Previously, he had received treatment with IV immune-globulin [IVIg] 2 g/kg every cycle, azathioprine 2.5 mg/kg and prednisolone 2 mg/kg/day for pemphigus vulgaris for two years. However, the pemphigus vulgaris became refractory. Therefore, rituximab was added to his treatment. Examinations showed fever, haemodynamic instability with sinus tachycardia, generalised body rash and pain, and mild tachypnoea. He had severe pain on movement. Initially, he started receiving piperacillin/tazobactam for suspected sepsis; however, it was stopped after the admission. His laboratory tests showed an increase in leukocyte, erythrocyte counts, CRP, uric acid and creatinine. Other lab tests were nonsignificant. Therefore, rituximab-induced serum sickness was diagnosed.Therefore, the man started receiving methylprednisolone, paracetamol, morphine and fentanyl patches. Following 2 days, his condition resolved. After 4 days, he was discharged from the hospital.