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Drugs Used to Treat Kidney and Urinary Tract Disorders

By Philip T. Reeves, BVSc (Hons), PhD, FANZCVS, Chief Regulatory Scientist, Veterinary Medicines and Nanotechnology, Australian Pesticides and Veterinary Medicines Authority ; Dawn Merton Boothe, DVM, PhD, Professor, Department of Anatomy, Physiology, and Pharmacology, College of Veterinary Medicine, Auburn University ; Maya M. Scott, BS, DVM, Resident, Clinical Pharmacology, Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine, Texas A&M University ; Ian Tizard, BVMS, PhD, DACVM, University Distinguished Professor of Immunology; Director, Richard M. Schubot Exotic Bird Health Center, Department of Veterinary Pathobiology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University ; Jozef Vercruysse, DVM, Professor, Faculty of Veterinary Medicine, Ghent University ; Jörg M. Steiner, DrMedVet, PhD, DACVIM, DECVIM-CA, AGAF, Associate Professor and Director, Gastrointestinal Laboratory, Department of Small Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A & M University

Drugs used to treat urinary disorders include antibiotics and antifungal medications for infections, diuretics for kidney failure, and a variety of other drugs for several other disorders.

Antibiotics

Antibiotic drugs are the basis of urinary tract infection treatment. Antibiotic treatment involves determining the type of bacteria present and choosing the appropriate drug. There are many types of antibiotics; your veterinarian will prescribe one that is excreted in an active form in the urine and is known to be effective against the particular bacteria present (see Table: Antibiotic Drugs Commonly Used to Treat Urinary Tract Infections in Dogs and Cats*).

Antibiotic Drugs Commonly Used to Treat Urinary Tract Infections in Dogs and Cats*

Drug

Typical Antibacterial Activity

Amoxicillin

Staphylococci, streptococci, enterococci, Proteus

Ampicillin

Staphylococci, streptococci, enterococci, Proteus

Amoxicillin/clavulanic acid

Staphylococci, streptococci, enterococci, Proteus

Cephalexin/cefadroxil

Staphylococci, streptococci, Proteus, Escherichia coli, Klebsiella

Ceftiofur

Escherichia coli, Proteus

Enrofloxacin

Staphylococci, some streptococci, some enterococci, Escherichia coli, Proteus, Klebsiella, Pseudomonas, Enterobacter

Gentamicin

Staphylococci, some streptococci, some enterococci, Escherichia coli, Proteus, Klebsiella, Pseudomonas, Enterobacter

Nitrofurantoin

Staphylococci, some streptococci, some enterococci, Escherichia coli, Klebsiella, Enterobacter

Tetracycline

Streptococci, some activity against staphylococci and enterococci at high urine concentrations

Trimethoprim/sulfa

Streptococci, staphylococci, Escherichia coli, Proteus, some activity against enterococci and Klebsiella

*Many of the drugs listed are not directly approved by the FDA for treatment of the bacteria listed. Veterinarians decide what drug and dosage to use for an animal based on their experience, published reports, and continuing education.

Many animals with recurrent urinary tract infections are treated with repeated courses of antibiotics. However, if the underlying cause of the infection is not found, the repeated courses of antibiotics can do more harm than good. Inappropriate treatment with the wrong antibiotic can cause bacteria to become resistant (see Guidelines for the Use of Antibiotic Drugs). Chronic urinary tract infections from highly resistant bacteria are very hard to treat.

If episodes occur more than once or twice yearly, and the causes of the urinary tract infections cannot be found or corrected, longterm low-dose treatment with oral antibiotics may be necessary to prevent new episodes.

Antifungal Drugs

Although uncommon, fungal urinary tract infections occur in dogs and cats. Treatment involves removing any predisposing factors (excessive corticosteroids, urinary catheters) and giving antifungal drugs, with or without urinary alkalinization (see Controlling Urine pH).

Cystine-binding Agents

Cystinuria, with the formation of cystine kidney stones, is caused by an inherited disorder. Cystine kidney stones are dissolved with changes in the diet, urinary alkalinization or neutralization, and the use of cystine-binding agents. Once stones are dissolved, changes in the diet can help prevent them from coming back.

Diuretics

Diuretics are used to remove excess water from animals with swelling or volume overload, such as that which occurs with kidney failure. There are several classes of diuretics, grouped by the way they act in the body (see Table: Diuretics*). Loop diuretics are named because of their effect on the ascending loop of Henle in the kidney. Carbonic anyhdrase inhibitors work by decreasing the formation of carbonic acid, making more sodium bicarbonate, which takes water with it when it is excreted. Carbonic anhydrase inhibitors also enhance potassium excretion. Thiazide diuretics are infrequently used, but they may be given to animals that cannot tolerate the more potent loop diuretics. Thiazides can be combined with loop or potassium-sparing diuretics. They may also be used to treat diabetes insipidus, which affects the kidneys. Potassium-sparing diuretics do not cause the loss of potassium, which is beneficial in some conditions in which potassium levels may be low. These are usually used in combination with other diuretics, rather than alone. Osmotic diuretics keep water from being reabsorbed in the kidneys.

Diuretics*

Drug

Chlorothiazide

Dimethyl sulfoxide

Furosemide

Hydrochlorothiazide

Mannitol

Spironolactone

*Many of the drugs listed are not directly approved by the FDA for treatment in all species. Veterinarians decide what drug and dosage to use for an animal based on their experience, published reports, and continuing education.

Other Drugs

Some angiotensin-converting enzyme (ACE) inhibitors (see Drugs Used to Treat Heart and Blood Vessel Disorders : Angiotensin-converting Enzyme (ACE) Inhibitors), may be helpful in treating chronic kidney failure, and may reduce excess protein in the urine in some animals. Dimethyl sulfoxide (DMSO) has been used in dogs with amyloidosis with variable results.

Natural and synthetic hormones may help treat urinary incontinence (). For example, a nonsteroidal estrogen derivative that closely resembles estradiol has been effective in treating urinary incontinence in female dogs. Alpha-adrenergic agents may also be helpful for this condition.

Muscle relaxants may help relieve urine retention due to tightening of the urethral muscles. Other drugs that may be tried include adrenergic antagonists or cholinergic agonists.

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