b Receptor antagonists, particularly propranolol, are used in the treatment of hypertrophic obstructive cardiomyopathy, for relieving angina, palpitations, and syncope. b Blockers also may attenuate catecholamine-induced cardiomyopathy in pheochromocytoma.
b Blockers are used frequently in the medical management of acute dissecting aortic aneurysm; their usefulness comes from reduction in the force of myocardial contraction and in SP/St. Patients with Marfan's syndrome may develop progressive dilation of the aorta, which may lead to aortic dissection and regurgitation, a major cause of death in these patients; chronic treatment with propranolol may slow the progression of aortic dilation and its complications.
Glaucoma b Receptor antagonists are very useful in the treatment of chronic open-angle glaucoma. Six drugs currently are available: carteolol (ocupress, others), betaxolol (betaoptic, others), levobunolol (betagan, others), metipranolol (optipranolol, others), timolol (timoptic, others), and levobetax-olol (betaxon). Timolol, levobunolol, carteolol, and metipranolol are nonselective; betaxolol and levobetaxolol are b1 selective; none has significant membrane-stabilizing or intrinsic sympathomimetic activity. Topically administered b blockers have little or no effect on pupil size or accommodation and are devoid of blurred vision and night blindness often seen with miotics. These agents decrease the production of aqueous humor, which appears to be the mechanism for their clinical effectiveness. For details of the treatment of glaucoma, see Chapter 63.
Other Uses b Receptor antagonists control many of the cardiovascular signs and symptoms of hyperthyroidism and are useful adjuvants to more definitive therapy. Propranolol, timolol, and metoprolol are effective for the prophylaxis of migraine; the mechanism of this effect is not known; these drugs are not useful for treating acute migraine attacks. By reducing signs of increased sympathetic activity (tachycardia, muscle tremors, etc.), propranolol and other b blockers are effective in controlling acute panic symptoms in individuals who are required to perform in public or in other anxiety-provoking situations. Propranolol also may be useful in the treatment of essential tremor.
b Blockers may be of some value in the treatment of patients undergoing withdrawal from alcohol or those with akathisia. Propranolol and nadolol are efficacious in the primary prevention of variceal bleeding in patients with portal hypertension caused by hepatic cirrhosis.
For a complete Bibliographical listing see Goodman & Gilman's The Pharmacological Basis of Therapeutics, 11th ed., or Goodman & Gilman Online at www.accessmedicine.com.
5-Hydroxytryptamine (5-HT, serotonin, 3-[f3-aminoethyl]-5-hydroxyindole) is widely distributed, occurring in vertebrates, tunicates, mollusks, arthropods, coelenterates, fruits, and nuts. In humans, 5-HT is found in enterochromaffin cells throughout the gastrointestinal (GI) tract, in storage granules in platelets, and broadly throughout the central nervous system (CNS). 5-HT is also present in venoms (e.g., those of the common stinging nettle, wasps, and scorpions).
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