Key result
Oral propranolol achieves maximal tachycardia blockade at ~60% lower plasma levels than intravenous dosing.
Why the study?
Does the route of administration of propranolol affect the plasma levels required for beta-adrenergic blockade in normal people?
RCT (n=6)
Double-blind
Randomized balanced crossover
No
Does the route of administration of propranolol affect the plasma levels required for beta-adrenergic blockade in normal people?
Oral administration of propranolol requires lower plasma levels for beta-blockade than intravenous administration, indicating the formation of an active metabolite.
May inform route-specific propranolol dosing; leaves open active metabolite effects on beta-blockade.
Plasma propranolol levels associated with reductions in endogenous and exogenous cardiac beta-stimulation were determined in normal people. The levels associated with a given degree of blockade of exercise-induced tachycardia were about three times greater after intravenous administration than after oral administration. This shows that an active metabolite of propranolol is formed only after the drug is taken by mouth. The greatest reduction in the tachycardia of strenuous exercise was associated with plasma levels of 40 ng./ml. with oral administration and 100 ng./ml. with intravenously administered propranolol.The effect on isoprenaline-induced tachycardia following intravenously administered propranolol showed that the dose ratio for isoprenaline was about 30 with plasma levels of 100 ng./ml. and 10 with levels of 10-20 ng./ml. These plasma levels give 100% and 20-30% blockade of exercise-induced tachycardia. These findings suggest that some of the therapeutic effects of propranolol may be unrelated to beta-adrenergic blockade.
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Coltart et al. (1970) conducted an RCT in Healthy volunteers (n=6). Propranolol vs. Placebo or Saline was evaluated on Maximal reduction in exercise-induced tachycardia based on plasma concentration. Maximal blockade of exercise-induced tachycardia was associated with plasma propranolol levels of 40 ng/mL after oral administration and 100 ng/mL after intravenous administration.
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