Urinary tract infections

Drug Store News, Dec 11, 1989

Trimethoprim/sulfamethoxazole in a low daily dose or every other day is effective and has a minimal risk of emergence of resistant bacteria. Nitrofurantoin in doses of 50 mg/day is also effective. Some evidence does exist that long term use of nitrofurantoin is associated with a large number of adverse effects. These include the following: hypersensitive reactions, blood dyscrasias, neuropathies, liver damage and interstitial pneumonitis.

Patients receiving prophylactic therapy should be instructed to void completely before the dose is taken. This will accomplish the following: allow the highest possible concentration of drug in the bladder and reduce the number of bacteria in the bladder.

The duration of prophylaxis is indefinite. Common practice is to continue for six months followed by patient observation. If further recurrences occur prophylaxis may be continued for another 12 months or even longer. Cystitis can occur regularly in the female after sexual intercourse. This is managed by single doses of nitrofurantoin taken either immediately after or before intercourse.

Relapses (a recurrent UTI) occur because the offending organism was not completely eradicated from the urinary tract. Symptoms will usually recur within six weeks of the original infection. The treatment for this is longer courses of therapy. If the infection persists kidney stones, congenital abnormalities, prostatitis or some other structural defect may be responsible.

Methenamine mandelate has been used for prophylaxis therapy. It has a low order of toxicity and minimal incidence of resistance strains emerging. The oral dose is one gram four times a day. A single bedtime dose of one gram has been shown to be less effective than the other agents. When methenamine mandelate or the hippurate salt is used acidification of the urine is necessary because the effectiveness of methenamine depends upon its release of formaldehyde which occurs maximally when the urine pH is 5.5 or below. Vitamin C in divided daily doses of six grams per day, methionine in doses of 12-15 grams per day or ammonium chloride in doses of 2-3 grams every 6 hours are all agents used to acidify the urine.

Cranberry juice, which contains large quantities of hippuric acid, a urinary acidifier, is a good dietary beverage during methenamine therapy.

Whenever methenamine is used the urine pH should be checked because it is sometimes difficult to attain the pH of 5.5 or less. The difficulty in attaining this desired pH and the availability of other effective agents have decreased the prophylactic use of methenamine. [Figure A to B Omitted] [Tabular Data 1 to 4 Omitted]

Jerry A. Bennett, Pharm.D. Associate Professor of Clinical Pharmacy College of Pharmacy, University of Cincinnati Cincinnati, Ohio