Labetalol is a mixed adrenergic blocker that blocks alpha-1, beta-1 and beta-2 adrenergic receptors. Administration results in decreased peripheral vascular resistance and mean arterial pressure without significant changes in heart rate and cardiac output.
Peak plasma concentration at 2 hours after PO labetalol. Oral bioavailability varies with age. 30% in 30 year-old up to 65% in 80 year-old.
50% bound to plasma proteins.
Volume of distribution at equilibrium for labetalol mostly concentrated in extravascular compartments.
Low lipid solubility, so labetalol accumulates in lung, liver, and kidney; very little in brain.
Half-life of labetalol in plasma is 3 hours.
Extensive first pass metabolism via hepatic biotransformation to inactive metabolites and excreted via urine. Therefore, plasma clearance time is largely determined by hepatic blood flow. Patients with hepatic disease have increased plasma clearance times. Patients with renal disease have little to no effect on plasma clearance time.
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