Xylometazoline Generic, Otrivin *α2 Agonists used in hypertension are listed in Chapter 11. β2 Agonists used in asthma are listed in Chapter 20. Norepinephrine transporter inhibitors are listed in Chapter 30.
The clinical picture is that of autonomic failure. The best indicator of this is the profound drop in orthostatic blood pressure without an adequate compensatory increase in heart rate. Pure autonomic failure is a neurodegenerative disorder selectively affecting peripheral autonomic fibers. Patients’ blood pressure is critically dependent on whatever residual sympathetic tone they have, hence the symptomatic worsening of orthostatic hypotension that occurred when this patient was given the α blocker tamsulosin. Conversely, these patients are hypersensitive to the pressor effects of α agonists and other sympathomimetics. For example, the α agonist midodrine can increase blood pressure signifi-cantly at doses that have no effect in normal subjects and can be used to treat their orthostatic hypotension. Caution should be observed in the use of sympathomimetics (includ-ing over-the-counter agents) and sympatholytic drugs.
David Robertson, MD, & Italo Biaggioni, MD*
A 38-year-old man has been experiencing palpitations and headaches. He enjoyed good health until 1 year ago when spells of rapid heartbeat began. These became more severe and were eventually accompanied by throbbing headaches and drenching sweats. Physical examination revealed a blood pressure of 150/90 mm Hg and heart rate of 88 bpm. During the physical examination, palpation of the abdomen elicited a sudden and typical episode, with a rise in blood pressure to 210/120 mm Hg, heart rate to 122 bpm, profuse sweating, and facial pallor. This was accompanied by severe headache. What is the likely cause of his episodes? What caused the blood pressure and heart rate to rise so high during the examination? What treatments might help this patient?
Catecholamines play a role in many physiologic and pathophysiologic responses, as described in Chapter 9. Drugs that block their receptors therefore have important effects, some of which are of great clinical value. These effects vary dramatically according to the drug’s selectivity for α and β receptors. The classification of adrenoceptors into α1, α2, and β subtypes and the effects of activating these receptors are discussed in Chapters 6 and 9. Blockade of peripheral dopamine receptors is of limited clinical importance at present. In contrast, blockade of central nervous system (CNS) dopamine receptors is very important; drugs that act on these receptors are discussed in Chapters 21 and 29. This chapter deals with pharmacologic antagonist drugs whose major effect is to occupy α1, α2, or β receptors outside the CNS and prevent their activation by catecholamines and related agonists.
For pharmacologic research, α1and α2-adrenoceptor antagonist drugs have been very useful in the experimental exploration of autonomic function. In clinical therapeutics, nonselective α antagonists are used in the treatment of pheochromocytoma * The authors thank Dr. Randy Blakely for helpful comments, Dr. Brett English for improving tables, and our students at Vanderbilt for advice on conceptual clarity.
(tumors that secrete catecholamines), and α1-selective antagonists are used in primary hypertension and benign prostatic hyperplasia. Beta-receptor antagonist drugs are useful in a much wider variety of clinical conditions and are firmly established in the treatment of hypertension, ischemic heart disease, arrhythmias, endocrinologic and neurologic disorders, glaucoma, and other conditions.
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