Category:Beta Blockers: Difference between revisions

The beta blockers, more formally the beta-adrenergic receptor antagonists, are a class of medicines that blunt the effect of adrenaline and the related stress hormones on the heart and other organs. They are the textbook case of a medicine designed deliberately from a theory rather than stumbled upon, and the theory came first. In 1948, at the Medical College of Georgia, the American pharmacologist Raymond Ahlquist proposed that adrenaline and noradrenaline act through two distinct kinds of receptor, which he named alpha and beta; the beta receptors, he argued, were the ones that quickened and strengthened the heartbeat.^[1] The idea met caution at first, because no medicine then existed that could block one kind of receptor and spare the other, and so prove the distinction real.^[2]

That medicine was found by the Scottish pharmacologist James Black. In 1958 Black joined the pharmaceutical division of Imperial Chemical Industries in England and set Ahlquist's theory against a practical problem: angina, the chest pain that comes when the heart's demand for oxygen outruns its supply. Rather than widen the arteries, as the medicines of the day did, Black reasoned that blocking the beta receptors of the heart would make the heart work less hard, and so need less oxygen. An early compound, pronethalol, proved the principle and was set aside; its successor, propranolol, reached the market in 1965 as the first widely successful beta blocker.^[2] The achievement was twofold. Propranolol changed the treatment of angina and was soon found to help in disordered heart rhythm and in high blood pressure; and beyond the medicine itself, Black had shown a method, beginning from an understanding of how the body works and designing a molecule to act on it. That method became a model for the whole pharmaceutical industry, and in 1988 Black received the Nobel Prize in Physiology or Medicine.^[2]

Black's first beta blockers, propranolol among them, blocked beta receptors throughout the body: both the beta-1 receptors concentrated in the heart and the beta-2 receptors of the airways and elsewhere. Blocking the beta-2 receptors could be a liability, above all in people with asthma. The cardioselective beta blockers that followed, among them atenolol, metoprolol, and bisoprolol, were built to act more on the heart's beta-1 receptors and less on the rest, though the selectivity is relative and fades as the dose rises. A later group again, sometimes called the third generation and including carvedilol, labetalol, and nebivolol, adds a widening of the blood vessels to the beta blockade.^[3]

Beta blockers are now used across a wide range of conditions. Within the heart they treat angina, several disorders of heart rhythm, and the period after a heart attack, and certain agents, shown in large trials to lengthen life, are a mainstay of treatment for chronic heart failure. They lower high blood pressure, although many present-day guidelines no longer place them first for raised blood pressure alone.^[3] Beyond the cardiovascular system they prevent migraine, settle the bodily signs of an overactive thyroid, lessen essential tremor, and, because they quiet the racing heart and trembling of an adrenaline surge, ease performance anxiety, a use well known among musicians and other performers though never formally approved for it.^[4]

All of this follows from a single action. A beta blocker binds to the beta-adrenergic receptors and occupies them without switching them on, so that adrenaline and noradrenaline can no longer reach them. Blocking the heart's beta-1 receptors slows the rate and softens the force of each beat, and so lowers the heart's workload; that much is well established, and it accounts plainly for the effect in angina and in disorders of heart rhythm. The benefit in high blood pressure, and above all the survival gained in heart failure, are understood to draw on more than this, including actions on the hormones that govern blood pressure and on the slow remodeling of the heart muscle, and the full account is still being worked out. A firm practical point is that a beta blocker is not stopped abruptly after regular use: sudden withdrawal can rebound into a dangerous worsening of heart rate, blood pressure, and chest pain, and the dose is instead lowered by degrees.^[3] This category collects the wiki's beta-blocker pages and groups them, as cardiology does, by generation and selectivity.

The beta blockers are grouped, as cardiology groups them, by generation: by whether a medicine blocks beta receptors throughout the body or chiefly in the heart, and whether it also widens the blood vessels.

• Non-selective (first generation): block the beta-1 and beta-2 receptors alike. propranolol; also nadolol, timolol, and sotalol.
• Cardioselective (beta-1-selective): act more strongly on the heart's beta-1 receptors. metoprolol, bisoprolol; also atenolol and esmolol.
• Vasodilating (third generation): add a widening of the blood vessels to the beta blockade. nebivolol; also carvedilol and labetalol.

This category indexes the beta-adrenergic receptor antagonists: medicines whose defining action is the blockade of beta receptors. The grouping above is by generation and selectivity, the axis cardiology itself uses.

Some members carry a second action as well. Carvedilol and labetalol block alpha-adrenergic receptors in addition to beta, and sotalol is also a class III antiarrhythmic; they are indexed here because beta blockade is central to what they do, and they may also be indexed under whatever other categories their pharmacology warrants. Beta blockers treat a number of conditions outside cardiology, among them migraine and essential tremor, but a medicine is indexed here for what it is, a beta blocker, and not for every condition it is used to treat.

Each beta blocker indexed here has, or will have, its own page, built on the wiki's standard structure for a medicine: a history-first account, then pharmacology, indications, adverse effects, and interactions. The wiki's medicine-page coverage of this class is still being filled in, which is why several agents above are named without a link.

This is one of the wiki's MedCategory class-overview pages. It carries the MedCategory and MedCategoryFull marker tags; the second suppresses the member list that MediaWiki would otherwise generate automatically, leaving the curated index above as the only one the reader sees. The category sits beneath Medicines and beneath Pharmaceutical, the origin category for medicines that came into use through scientific discovery rather than traditional practice. Few medicines belong there more plainly than the beta blockers, which were designed from a theory in a laboratory.