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Methenamine Hippurate
Each yellow capsule-shaped tablet contains 1 g Methenamine Hippurate
which is the Hippuric Acid Salt of Methenamine (hexamethylene tetramine).
The tablet also contains inactive ingredients. FD&C Yellow No.5 (tartrazine,
see PRECAUTIONS), Magnesium Stearate,
Povidone, and Saccharin Sodium.
Microbiology HIPREX (methenamine hippurate tablets USP) has antibacterial activity because the methenamine component is hydrolyzed to formaldehyde in acid urine. Hippuric acid, the other, component, has some antibacterial activity and also acts to keep the urine acid. The drug is generally active against E. coli, enterococci and staphylococci. Enterobacter aerogenes is generally resistant. The urine must be kept sufficiently acid for urea-splitting organisms such as Proteus and Pseudomonas to be inhibited. Human PHARMACOLOGY Within 1/2 hour after ingestion of a single 1-gram dose of HIPREX, antibacterial
activity is demonstrable in the urine. Urine has continuous antibacterial
activity when HIPREX is administered at the recommended dosage schedule
of 1 gram twice daily. Over 90% of methenamine moiety is excreted in the
urine within 24 hours after administration of a single 1-gram dose. Similarly,
the hippurate moiety is rapidly absorbed and excreted, and it reaches
the urine by both tubular secretion and glomerular filtration. This action
may be important in older patients or in those with some degree of renal
impairment.
HIPREX is indicated for prophylactic or suppressive treatment of frequently recurring urinary tract infections when long-term therapy is considered necessary. This drug should only be used after eradication of the infection by other appropriate antimicrobial agents.
1 tablet (1.0 g) twice daily (morning and night) for adults and pediatric patients over 12 years of age. 1/2 to 1 tablet (0.5 to 1.0 g) twice daily (morning and night) for pediatric patients 6 to 12 years of age. Since the antibacterial activity of HIPREX is greater in acid urine, restriction of alkalinizing foods and medications is desirable. If necessary, as indicated by urinary pH and clinical response, supplemental acidification of the urine should be instituted. The efficacy of therapy should be monitored by repeated urine cultures. HOW SUPPLIED 1-gram scored, capsule-shaped yellow tablets debossed MERRELL 277 in
bottles of 100 (NDC 0068-0277-61)
Minor adverse reactions have been reported in less than 3.5% of patients treated. These reactions have included nausea, upset stomach, dysuria, and rash.
No information provided.
Large doses of methenamine (8 grams daily for 3 to 4 weeks) have caused bladder irritation, painful and frequent micturition, albuminuria, and gross hematuria.
1. Care should be taken to maintain an acid pH of the urine, especially when treating infections due to urea-splitting organisms such as Proteus and strains of Pseudomonas. 2. In a few instances in one study, the serum transaminase levels were slightly elevated during treatment but returned to normal while the patients were still taking HIPREX. Because of this report, it is recommended that liver function studies be performed periodically on patients taking the drug, especially those with liver dysfunction. 3. Use in Pregnancy: In early pregnancy the safe use of HIPREX is not established. In the last trimester, safety is suggested, but not definitely proved. No adverse effects on the fetus were seen in studies in pregnant rats and rabbits. HIPREX taken during pregnancy can interfere with laboratory tests of urine estriol (resulting in unmeasurably low values) when acid hydrolysis is used in the laboratory procedure. This interference is due to the presence in the urine of methenamine and/or formaldehyde. Enzymatic hydrolysis, in place of acid hydrolysis, will circumvent this problem 4. This product contains FD&C Yellow No. 5 (tartrazine), which may cause
allergic-type reactions (including bronchial asthma) in certain susceptible
individuals. Although the overall incidence of FD&C Yellow No.5 (tartrazine)
sensitivity in the general population is low, it is frequently seen in
patients who also have aspirin hypersensitivity.
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