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Isoprenaline
See also Adrenoceptor agonists
General information
As a non-selective beta-adrenoceptor agonist, isoprenaline produces a wide range of adrenergic effects. Those that involve the heart present the most marked problems in practice. Doses of up to 10 micrograms/minute are used to improve the peripheral circulation in shock. In respiratory disease, isoprenaline in sublingual tablets (up to 10 mg) and inhalers were used in the past, but have been supplanted by selective beta 2 -adrenoceptor agonists. Isoprenaline inhalers sometimes provided more than the 20 micrograms needed for a maximum effect on the bronchi, resulting in adverse reactions. Oral isoprenaline was also used to treat some forms of heart block, but is now therapeutically obsolete.
Organs and systems
Cardiovascular
Tachycardia, dysrhythmias, palpitation, flushing, and attacks of angina pectoris were disadvantages of isoprenaline when it was used in respiratory disease. Users tended to raise the dose (hence increasing the degree of cardiac toxicity), possibly because a metabolite (3-alpha-methylisoprenaline), which may act as a weak beta-blocker, accumulates and makes the original doses ineffective. Isoprenaline produces electrocardiographic changes compatible with myocardial infarction or can lead to ventricular fibrillation or even cardiac muscle necrosis if infusions are not given with the utmost caution [ , ]. Exceptionally, the tachycardia produced by an infusion of isoprenaline can be overshadowed by a reflex bradycardia, even while the drug is being given [ ].
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