Info

Cardio-

Agonist

Stabilizing

ß-Blocker

selective

Activity

Activity

Propranolol

No

None

Yes

Acebutolol

Yes

Slight

None

Atenolol

Yes

None

None

Betaxolol

Yes

None

Slight

Carteolol

No

Slight

None

Esmolol

Yes

None

None

Levobunolol

No

None

None

Metoprolol

Yes

None

Slight

Nadolol

No

None

None

Penbutolol

No

Slight

None

Pindolol

No

Yes

Slight

Timolol

No

Slight

None

only 3 to 10% of an administered dose is recovered as unchanged drug. The metabolites are essentially inactive as p-receptor blocking agents and are eliminated primarily by renal excretion. Small amounts of the drug are present in the feces.

Timolol (Timoptic) is almost completely absorbed from the gastrointestinal tract. Peak plasma levels occur 2 to 4 hours after oral administration; the plasma halflife of timolol is approximately 5.5 hours. The extensive tissue distribution of timolol into lung, liver, and kidney is similar to that of other p-blockers. Approximately 70% of the drug is excreted in the urine within 24 hours, mostly as highly polar unconjugated metabolites. Only 6% of an administered dose is recovered in the feces. Although timolol is approved for the topical treatment of elevated intraocular pressure, there is limited information about its pharmacokinetics following administration by this route. The drug apparently can reach the systemic circulation after intraocular instillation, but plasma levels are only about 7% of those achieved in the aqueous humor.

About half of an orally administered dose of acebu-tolol (Sectral) is absorbed. Approximately 25% of the drug is bound to plasma proteins, and its plasma halflife is about 4 hours. Metabolism of acebutolol produces a metabolite with p-blocking activity whose half-life is 10 hours.

Roughly half of an orally administered dose of atenolol (Tenormin) is absorbed. The drug is eliminated primarily by the kidney and unlike propranolol, undergoes little hepatic metabolism. Its plasma half-life is approximately 6 hours, although if it is administered to a patient with impaired renal function, its half-life can be considerably prolonged.

Absorption of an oral dose of betaxolol (Kerlone, Betoptic) is almost complete. The drug is subject to a slight first-pass effect such that the absolute bioavailability of the drug is about 90%. Approximately 50% of administered betaxolol binds to plasma proteins, and its plasma half-life is about 20 hours; it is suitable for dosing once per day. The primary route of elimination is by liver metabolism, with only 15% of unchanged drug being excreted.

Carteolol (Cartrol) is a long-acting p-blocker that is suitable for dosing once per day. It is almost completely absorbed and exhibits about 30% binding to plasma proteins. Unlike many p-blockers, carteolol is not extensively metabolized. Up to 70% of an administered dose is excreted unchanged.

The p-blocker esmolol (Brevibloc) is unusual in that it is very rapidly metabolized; its plasma half-life is only 9 minutes. It is subject to hydrolysis by cytosolic esterases in red blood cells to yield methanol and an acid metabolite, the latter having an elimination half-life of about 4 hours. Only 2% of the administered esmolol is excreted unchanged. Because of its rapid onset and short duration of action, esmolol is used by the intravenous route for the control of ventricular arrhythmias in emergencies.

Nadolol (Corgard) is slowly and incompletely absorbed from the gastrointestinal tract, and only 30% of an orally administered dose is absorbed. Appreciable metabolism does not seem to occur; nadolol is excreted primarily unchanged in the urine and feces. The plasma half-life is quite long, approaching 24 hours, which permits dosing once per day.

Pindolol (Visken) is extensively absorbed from the gastrointestinal tract. First-pass metabolism is estimated at about 15%, and its plasma half-life is on the order of 3 to 4 hours. The binding of pindolol to plasma proteins is approximately 50%. The metabolic fate of pindolol is not completely understood, although 50% of an administered dose is recovered, primarily in the urine, as unchanged drug.

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