1983 Volume 14 Issue 4 Pages 637-648
The pharmacokinetics and effects of guanabenz on blood pressure, heart rate and increases of plasma catecholamine levels and double products during physical exercise by ergometer were evaluated by 8 mg single oral dose of drug in 10 healthy male volunteers. Following results were obtained:
Mean plasma levels of unchanged guanabenz were reached to peak of 2.14±0.60ng/ml at 2 hrs and decreased with a half-life of 5.37 hrs. Individual differences in peak levels and AUC0-48 of the plasma levels of unchanged guanabenz were about 12-15 times, indicating the extensive “first-pass effect”.
Mean of cumulated urinary excretion of guanabenz and its metabolites for 48 hrs was 41.2% of the administered dose, in which unchanged guanabenz was only 0.4% of the dose. Individual differences of this cumulated urinary excretion were rather small (1.9 times) than those of plasma peak levels and AUC0-48, suggesting that individual differences of absorption are negligible.
Maximal reduction of blood pressure was-16.4/-16.8mmHg at 5 hrs, and blood pressure at 24 hrs still showed significantly lower level (-6.5/-6.0mmHg). Heart rates showed no significant changes at any time of observation . Increases of blood pressure and heart rate during physical exercise were not affected by guanabenz.
Resting plasma noradrenaline level was significantly decreased, while significant increase of plasma adrenaline level during physical exercise was blocked by guanabenz.
Double product at rest was significantly reduced by guanabenz, probably due to the result of its hypotensive effect. No influence of guanabenz was however observed on the increase of double product during physical exercise.
These results indicate that guanabenz has no effect on the circulatory regulations during physical exercise at the dose level which produces significant and long-lasting hypotensive effect in normotensive subjects.
