12. urinary system drugs

Chapter 12

Urinary System Drugs

Copyright © 2011 Delmar, Cengage Learning

Basic Anatomy and Physiology

• The structures of the urinary system include paired kidneys, paired ureters, a single urinary bladder, and a single urethra

• Within each kidney are millions of individual structures, called nephrons, that do the actual work of the kidney– A nephron consists of a glomerulus, Bowman’s

capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and a collecting duct


Basic Anatomy and Physiology


Urinary System Disorders

• Include urinary tract infections, inflammation and irritation of the urinary tract, renal failure, urinary incontinence, and uroliths (urinary stones)

• Bacterial infections of the urinary system may lead to:– inflammation, pollakiuria (increased frequency of urination)– dysuria (painful urination) which may result in inappropriate

urination for household pets • These disorders affect the urinary tract resulting in clinical signs such

as inappropriate urination, inability to urinate, frequent urination, increased urination, or pain


Drugs Affecting the Urinary System

• Diuretics– Increase the volume of urine excreted by the kidneys

and promote release of water from tissues– Lower the fluid volume in tissues; are used to

decrease edema and lower blood pressure– May also be used to reduce udder edema in cattle

and promote voiding to enhance removal of toxins from the body

– Types of diuretics include thiazides, loop diuretics, potassium-sparing diuretics, carbonic anhydrase inhibitors, and osmotics



• Diuretics (cont.)– Thiazides

• Act directly on the renal tubules to block sodium reabsorption and promote chloride ion excretion

• Side effects include hypokalemia and cardiac dysfunction

• Examples include hydrochlorothiazide, chlorothiazide, hydroflumethiazide, and bendroflumethiazide



• Diuretics (cont.)– Loop diuretics

• Influence the reabsorption action at the loop of Henle, resulting in tremendous diuresis

• Side effects include electrolyte imbalances, especially hypokalemia

• An example is furosemide



• Diuretics (cont.)– Potassium-sparing diuretics

• Act on the distal convoluted tubules to promote sodium and water excretion and potassium retention (interfere with the sodium-potassium pump that is controlled by aldosterone)

• Main side effect is hyperkalemia• Examples include spironolactone, triamterene, and

amiloride



• Diuretics (cont.)– Carbonic anhydrase inhibitors

• Block the action of the enzyme carbonic anhydrase, which is used by the body to maintain acid-base balance

• Used to decrease intraocular pressure with open-angle glaucoma

• Main side effect is metabolic acidosis• Examples include acetazolamide and

dichlorphenamide



• Diuretics (cont.)– Osmotic diuretics

• Increase the osmolality (concentration) of the urine filtrate in the renal tubules, resulting in the excretion of chloride, potassium, and water

• Used to prevent kidney failure and to decrease intracranial and intraocular pressure

• Side effects include fluid and electrolyte imbalance and vomiting

• Examples include mannitol and glycerin



• Antihypertensive drugs– Drugs that decrease hypertension (lower blood

pressure)– Types of antihypertensive drugs include:

• Diuretics: promote sodium and water loss, which decreases fluid volume and blood pressure (covered previously in this chapter and Chapter 8)

• Angiotensin-converting enzyme inhibitors (ACE inhibitors): block the conversion of angiotensin I to angiotensin II, which results in decreased aldosterone secretion. Examples include enalapril, captopril, lisinopril, and benazepril



• Antihypertensive drugs (cont.)– Types of antihypertensive drugs include:

• Calcium-channel blockers: block the influx of calcium ions into the myocardial cells, resulting in an inhibition of cardiac and smooth muscle contractility; examples include diltiazem, verapamil, and nifedipine

• Direct-acting arteriole vasodilators: relax smooth muscles of blood vessels causing vasodilation; examples include hydralazine and minoxidil



• Antihypertensive drugs (cont.)– Types of antihypertensive drugs include:

• Beta-adrenergic antagonists (also known as beta-blockers): has side effect of decreasing blood pressure; an example of a nonselective beta-blocker is propranolol

• Alpha-adrenergic antagonists: block alpha-1 adrenergic receptors, resulting in vasodilation; examples include phenoxybenzamine, prazosin, and nicergoline



• Urolith treatment– Uroliths are abnormal mineral masses in the urinary

system– Types of uroliths include: struvite, calcium oxalate,

calcium phosphate, urate, cystine, and mixed– Each type of urolith may be treated differently and

may include dietary management as well as drug treatment

– Drug categories used to treat uroliths include urinary acidifiers, urinary alkalinizers, and xanthine oxidase inhibitors



• Urolith treatment (cont.)– Urinary acidifiers are used clinically to produce acid

urine, which dissolves and helps prevent formation of struvite uroliths; their use has declined with the use of urinary acidifying diets; examples include methionine and ammonium chloride

– Urinary alkalinizers are used clinically to treat calcium oxalate, cystine, and ammonium urate uroliths; an example is potassium citrate

– Xanthine oxidase inhibitors decrease the production of uric acid, which helps decrease the formation of ammonium urate uroliths; an example is allopurinol



• Urinary incontinence drugs– Urinary incontinence is the loss of voluntary

control of micturition– Urinary incontinence may be due to:

• Neurologic disorders resulting from trauma to the spinal cord, tumors of the nervous system, or degeneration of the nervous system tracts

• Nonneurologic disorders, which include hormone-responsive, stress, urge, ectopic ureter formation, or urinary bladder overdistention



• Drugs used to treat neurologically caused urinary incontinence:– Cholinergic agonists treat animals with damage to the

nerves that control relaxation of the urinary bladder• Promote voiding of urine from the urinary bladder• An example is bethanechol

– Anticholinergics treat urinary incontinence by promoting urine retention in the urinary bladder

• Block binding of ACh to its receptor site, causing muscle relaxation

• Examples include propantheline, dicyclomine, and butylhyoscine



• Drugs used to treat neurologically caused urinary incontinence (cont.):– Alpha-adrenergic antagonists decrease the tone of

internal urethral sphincters and are used to treat urinary incontinence due to decreased urinary tone as a result of overdistention of the urinary bladder

• Examples include phenoxybenzamine, prazosin, and nicergoline



• Drugs used to treat nonneurologically caused urinary incontinence:– Estrogen treats hormone-responsive urinary

incontinence seen mainly in F/S dogs; an example is diethylstilbestrol (DES)

– Testosterone treats hormone-responsive urinary incontinence seen mainly in M/C dogs; examples include testosterone cypionate and testosterone propionate



• Drugs used to treat nonneurologically caused urinary incontinence (cont.):– Alpha- and beta-adrenergic agonists stimulate these

receptors, which increases urethral tone; examples include phenylpropanolamine and ephedrine

– Skeletal muscle relaxants treat urge incontinence or urethral obstructions due to increased external urethral sphincter tone; examples include dantrolene, aminopropazine, and diazepam


Health & Medicine

12. urinary system drugs