1. Fundamentals of Pharmacology for Veterinary Technicians
Chapter 12
Urinary System Drugs
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

2. 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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

3. Basic Anatomy and Physiology
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

4. 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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

5. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

6. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

7. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

8. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

9. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

10. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

11. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

12. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

13. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

14. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

15. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

16. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

17. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

18. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.

19. Drugs Affecting the Urinary System
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
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.