Theophylline Increased serum levels with iodine 131-induced hypothyroidism: case report

A thin, 39-year-old man who was on salbutamol [albuterol], 2 Inhalations qid and oral aminophylline 400,ug qld, for asthma, had a 2-month history of diarrhoea, Iodine 131 was prescribed for treatment of Graves' disease,

Three months later, the patient experienced symptoms of hypothyroidism. His diarrhoea, after an Initial Improvement, had returned and he experienced nausea and cramps,

Serum theophylline level on presentation with diarrhoea was 168 ,ug/ml and 3 days prior to Iodine 131 therapy was 15.2 ,ug/ml with a terminal half-life of 4,95 hours, When the patient presented with hypothyroidism, serum theophylline level was 30,9 ,ug/ml and terminal half-life was 10,04 hours,

Thyroxine 0,15 mg/day was Initiated, The patient abstained from theophylline for 12 hours and then resumed at a reduced dosage of 200 mg/6 hours, One week later, his theophylline level was 16,1 ,ug/ml and the terminal half-life was 9,76 hours The nausea, cramping and diarrhoea had resolved, Two months later, he was euthyroid but had wheezing and shortness of breath, Serum theophylline level was 64 ,ug/ml and terminal half-life was 4,91 hours, His aminophylline dosage was Increased to 400 ,ug/6 hours and 3 days later serum theophylline level was 13,9 ,ug/ml and terminal half-life was 505 hours HIS medication was then changed to controlled-release theophylline and he remained well

'Serum theophylline concentrations and potential symptoms of theophylline toxicity should be monitored closely during drug-induced alterations of thyroid function.'

Johnson CE Cohen IA Theophylline loxlclly after

Iodine 131 Irealment for hyperthyroidism Clinical

Pharmacy 7 620622 Aug 1988

0757-7277/88/7779-0007/0$07,00/0 © ADIS Press REACTIONS' 79 Nov 7988 7