indication

Used in the treatment of high blood pressure.

pharmacology

Penbutolol is a non-selective beta blocker. Beta-blockers work by affecting the response to some nerve impulses in certain parts of the body. As a result, they decrease the heart's need for blood and oxygen by reducing its workload. They also help the heart to beat more regularly.

mechanism of action

Penbutolol competes with adrenergic neurotransmitters such as catecholamines for binding at beta(1)-adrenergic receptors in the heart and vascular smooth muscle and beta(2)-receptors in the bronchial and vascular smooth muscle. Beta(1)-receptor blockade results in a decrease in resting and exercise heart rate and cardiac output, a decrease in both systolic and diastolic blood pressure, and, possibly, a reduction in reflex orthostatic hypotension.

toxicity

Symptoms of overdose include drowsiness, vertigo, headache, and atriventricular block.

biotransformation

Metabolized in the liver by hydroxylation and glucuroconjugation forming a glucuronide metabolite and a semi-active 4-hydroxy metabolite.

absorption

Oral bioavailability is 90%.

half life

Phase 1: 2.5 hours; phase 2: 24 hours

route of elimination

The metabolites are excreted principally in the urine.

drug interactions

Aminophylline: Antagonism of action and increased effect of theophylline

Chlorpropamide: The beta-blocker, penbutolol, may decrease symptoms of hypoglycemia.

Clonidine: Increased hypertension when clonidine stopped

Dihydroergotamine: Ischemia with risk of gangrene

Disopyramide: The beta-blocker, penbutolol, may increase the toxicity of disopyramide.

Epinephrine: Hypertension, then bradycardia

Ergotamine: Ischemia with risk of gangrene

Fenoterol: Antagonism

Formoterol: Antagonism

Gliclazide: The beta-blocker, penbutolol, may decrease symptoms of hypoglycemia.

Glyburide: The beta-blocker, penbutolol, may decrease symptoms of hypoglycemia.

Ibuprofen: Risk of inhibition of renal prostaglandins

Indomethacin: Risk of inhibition of renal prostaglandins

Insulin Glargine: The beta-blocker, penbutolol, may decrease symptoms of hypoglycemia.

Methyldopa: Possible hypertensive crisis

Methysergide: Ischemia with risk of gangrene

Orciprenaline: Antagonism

Oxtriphylline: Antagonism of action and increased effect of theophylline

Pipobroman: Antagonism

Piroxicam: Risk of inhibition of renal prostaglandins

Prazosin: Risk of hypotension at the beginning of therapy

Repaglinide: The beta-blocker, penbutolol, may decrease symptoms of hypoglycemia.

Terazosin: Increased risk of hypotension. Initiate concomitant therapy cautiously.

Terbutaline: Antagonism

Theophylline: Antagonism of action and increased effect of theophylline

Treprostinil: Additive hypotensive effect. Monitor antihypertensive therapy during concomitant use.