Increased uptake of transdermal glyceryl trinitrate during physical exercise and during high ambient temperature

In a study of GTN absorption during exercise and high ambient temperature, 12 healthy volunteers carried 10 mg glyceryl trinitrate (GTN, nitroglycerin) transdermal patches for 6 hours during each of 3 days. During a control day the mean plasma GTN concentration ranged from 1.0 nmol/L (SD +/- 0.8 nmol/L) to 1.5 nmol/L (SD +/- 1.0 nmol/L), whereas during a bicycle ergometer day mean GTN concentration was increased to 3.1 nmol/L (SD +/- 1.7 nmol/L, p less than 0.001). During a sauna day volunteers stayed for 20 minutes in a sauna, and mean GTN concentration in plasma rose to 7.3 nmol/L (SD +/- 1.7 nmol/L, p less than 0.001). Systolic blood pressure increased during exercise (p less than 0.01) but decreased significantly in the sauna (p less than 0.01). Headache was noted frequently (9 of 12 subjects) and dizziness by a few (3 of 12). The demonstrated increased transdermal absorption in our study may infer an increased effect during workload. Whereas the increase in transdermally absorbed GTN may be beneficial to the exercising angina patient, increased effects of GTN may be undesirable in hot surroundings. A study on angina patients is justified to assess whether this phenomenon bears clinical relevance.