Orris

Methenamine hippurate can cause itching

Reading File
Finding Sources
Finding Sources
Searching PubMed

"methenamine hippurate" AND "urinary tract infections"

Reading File
Reading File
Searching the Web

Hiprex methenamine hippurate prescribing information adverse reactions rash pruritus

Yes, that's correct. Itching (pruritus) is a known but uncommon side effect of methenamine hippurate, usually along with a rash.
What the sources say
  • The DailyMed label says adverse effects occur in fewer than 3.5% of patients. In decreasing order of frequency, they are nausea, vomiting, and rarely pruritus, rash, and dysuria.
  • The Hiprex FDA label lists nausea, upset stomach, dysuria, and rash as minor reactions.
  • Drugs.com puts rash and pruritus in the uncommon range (0.1% to 1%). It also lists generalized skin rash and hypersensitivity reactions, both with frequency not reported.
  • Lippincott Illustrated Reviews: Pharmacology (p. 1044) says the main adverse effect is gastrointestinal distress. Albuminuria, hematuria, and rashes can develop at higher doses.
Practical points
  • Itching with a rash may be a hypersensitivity reaction. Look for urticaria, widespread rash, facial or lip swelling, wheeze, or fever. Any of these means stopping the drug and getting the patient assessed urgently.
  • If the itching is mild and isolated, a trial off the drug usually settles it. Reactions were reversible when the drug was stopped.
  • Consider other causes before blaming methenamine. These include other new drugs, especially sulfonamides, which should not be combined with methenamine. Katzung's Basic and Clinical Pharmacology notes they can form an insoluble compound with the formaldehyde methenamine releases.
  • Large doses (8 g daily for 3 to 4 weeks) have caused bladder irritation, painful frequent urination, albuminuria, and gross hematuria. The usual dose is 1 g twice daily.
  • The label says to avoid methenamine in hepatic insufficiency (Lippincott notes ammonia formation) and in severe dehydration. Katzung describes its role as preventing, not treating, UTI.
Recent evidence check PubMed returned three recent systematic reviews, including a 2025 meta-analysis of randomized trials in UTI prevention, plus 2024 reviews (PMIDs 38329493 and 37986168). I only read the titles, not the abstracts. Nothing I found suggests the safety profile above has changed. I did not check these reviews' tolerability data.
If you're asking about a specific patient, tell me the timing and any other symptoms and I can help think it through.
This is a shared conversation. Sign in to Orris to start your own chat.