Influence of surgery on plasma propranolol levels and protein binding

The influence of surgery and anesthesia on perioperative plasma propranolol levels was studied in 25 hyperthyroid and five euthyroid patients undergoing thyroidectomy. Propranolol levels fell markedly after surgery as a consequence of poor drug administration in the immediate postoperative period due largely to patients' nausea and inability to swallow. Propranolol was not detectable in the plasma of three hyperthyroid patients 8 hr after surgery. When propranolol was given through a nasogastric tube, propranolol levels were satisfactory throughout. Compared with preoperative levels, in all patients there was a two- to threefold rise in total and free propranolol levels 24 hr after surgery, suggesting decreased hepatic clearance of propranolol. The degree of plasma protein binding of propranolol had also increased on the day after surgery, leading to a 30% reduction in propranolol free fraction. Surgery and anesthesia greatly influence the handling of propranolol in the perioperative period.