Cholinoceptor Blocking Drugs
antagonists, like agonists, are divided into muscarinic and nicotinic
subgroups on the basis of their specific receptor affinities. Ganglion blockers
and neuromuscular junction blockers make up the antinicotinic drugs.
subtypes of muscarinic receptors have been identified, primarily on the basis
of data from ligand-binding and cDNA-cloning experiments. A standard
terminol-ogy (M1 through M5) for these subtypes is now in
common use, and evidence—based mostly on selective agonists and antagonists—
indicates that functional differences exist between several of these subtypes.
M1 receptor subtype is located on central nervous system (CNS)
neurons, sympathetic postganglionic cell bodies, and many presynaptic sites. M 2
receptors are located in the myocar-dium, smooth muscle organs, and some
neuronal sites. M3 recep-tors are most common on effector cell
membranes, especially glandular and smooth muscle cells. M4 and M5
receptors are less prominent and appear to play a greater role in the CNS than
in the periphery.
JH, a 63-year-old architect, complains of urinary symptoms to his family physician. He has hypertension, and during the last 8 years, he has been adequately managed with a thiazide diuretic and an angiotensin-converting enzyme inhibitor. During the same period, JH developed the signs of benign prostatic hypertrophy, which eventually required prostatectomy to relieve symptoms. He now complains that he has an increased urge to urinate as well as urinary fre-quency, and this has disrupted the pattern of his daily life. What do you suspect is the cause of JH’s problem? What information would you gather to confirm your diagnosis? What treatment steps would you initiate?
CASE STUDY ANSWER
JH’s symptoms are
often displayed by patients following prostatectomy to relieve significant
obstruction of bladder outflow. Urge incontinence can occur in patients whose
pro-static hypertrophy caused instability of the detrusor muscle. He should be
advised that urinary incontinence and urinary frequency can diminish with time
after prostatectomy as detrusor muscle instability subsides. JH can be helped
by daily administration of a single tablet of extended-release tolterodine (4
mg/day) or oxybutynin (5–10 mg/day). A transdermal patch containing oxybutynin (3.9
mg/day) is also available.