Impotence is most commonly caused by which antihypeensive agent

b blockers Mel Harrison 16th/e p 273) Among the anti hypeensive agents thiazide diuretics and fl lockers are implicated most commonly for impotence. Erection requires increased blood flow into the erectile tissues of the penis i.e. corpora cavernosa and corpora spongiosa. The erectile tissue are large cavernous sinusoids which are normally relatively empty of blood but becomes dilated tremendously when aerial blood flows rapidly into them under pressure while the venous outflow is paially occluded. Erection is caused by parasympathetic impulses that pass from sacral poion of spinal cord. These parasympathetic nerve fibres in contrast to most other parasympathetic fibres are believed to secrete nitric oxide and/or vasoactive intestinal peptide in addition to acetylcholine. The nitric oxide especially relaxes the aeries of the penis as well as relaxes the trabecular meshwork of smooth muscle fibres in the erectile tissue of the corpora cavernosa and corpora spongiosum. 13 blockers inhibit this vasodilation and cause erectile dysfunction. Medicated induced erectile dysfunction is estimated to occur in 25% of men. Among the antihypeensive agents the thiazide diuretics and fiblockers have been implicated most frequently. Calcium channel blockers and angiotensin conveing enzyme inhibitors are less frequently cited. Drugs associated with erectile dysfunction : Diuretics Tranquilizers Thiazide * Butyrophenones Spironolactone * Phenothiazines Antihypeensives H2 antagonists Calcium channel blockers * Ranitidine Methyldopa * Cimetidine Clonidine Hormones Reserpine * Progesterone 13 blockers * Estrogens Guanethidine * Coicosterolds Cardiac/antihyperlipidemics * GnRH agonists Digoxin * 5a reductase inhibitors Gemifibrozil * Cyprote rune acetate Clofibrate Cytotoxic agents Antidepressants * Cvclophosphamide Selective serotonin reuptake inhibitors * Methotrexate Tricyclic antidepressants * Roferon-A Lithium Recreational M.A.O. inhibitors * Ethanol Cocaine Marijuancs Antimetabolites These are synthetic analogues of normal metabolites related to components of DNA or of coenzymes involved in nucleic acid synthesis. They act by competition i.e. they "deceive" or "defraud" bodily processes. Instead of the natural substrate they get themselves incorporated, forming dysfunctional molecules. These drugs act on the S phase of the cell cycle, thus only dividing cells are responsive