Absorption Metabolism and Excretion

Propranolol (Inderal) is suitable for both parental and oral administration. Absorption from the gastrointestinal tract is extensive. The peak therapeutic effect after oral administration occurs in 1 to 1.5 hours. The plasma half-life of propranolol is approximately 3 hours. The drug is concentrated in the lungs and to a lesser extent in the liver, brain, kidneys, and heart. Binding to plasma proteins is extensive (90%). The liver is the chief organ involved in the metabolism of propranolol, and the drug is subject to a significant degree of first-pass metabolism. At least eight metabolites have been recovered from the urine, the major excretory route.

The pharmacokinetic profile of metoprolol (Lopres-sor) is similar to that of propranolol. Metoprolol is readily and rapidly absorbed after oral administration and is subject to a significant amount of first-pass metabolism by the liver. Curiously, the duration of metoprolol's action is longer than one would predict from its plasma half-life, which ranges from 0.5 to 2.5 hours. The degree of binding of metoprolol to plasma proteins is modest (10%). The extensive distribution of metoprolol to the lungs and kidney is typical of a moderately lipophilic drug. Metoprolol undergoes considerable metabolism;

TABLE 11.2 Characteristics and

Preparations of ß-Blockers

TABLE 11.2 Characteristics and

Preparations of ß-Blockers

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