Impact of metoprolol on insulin sensitivity in the ICU
Metoprolol (a cardio-selective 1-blocker) has been shown to reduce insulin sensitivity in ‘healthy’ individuals by 14-27%. It is regularly used in the Christchurch Hospital intensive care unit (ICU), but may unintentionally reduce insulin sensitivity and thus exacerbate stress-hyperglycaemia. This study used model-based methods to quantify the effect of metoprolol on insulin sensitivity in critically ill patients. A model-based measure of insulin sensitivity was used to quantify changes between two matched retrospective cohorts of 17 ICU patients. All patients were admitted to the Christchurch hospital ICU between 2005 and 2007 and spent at least 24 hours on the SPRINT glycaemic control protocol. A 9.7% reduction in whole-cohort median insulin sensitivity was seen between the control cohort and patients receiving metoprolol with a median dose of 100mg/d per patient. Comparing percentile patients as a surrogate for matched patients, reductions in median insulin sensitivity of less than 4% were observed for the 25th, 50th and 75th-percentile patients. These cohort and percentile patient reductions are less than the 14-27% reductions reported in ‘healthy’ subjects. The limited reduction of insulin sensitivity in critically ill patients could be a result of moderation of the physiological impact of metoprolol due to already reduced levels of peripheral glucose uptake and insulin receptor sensitivity. This limited reduction is not expected to have any clinical impact on the level of tight glycaemic control achieved with the SPRINT protocol.