Methenamine hippurate (UREX)

The UREX source contraindicates use in renal insufficiency without assigning a numeric clearance cutoff. It also contraindicates severe hepatic insufficiency and severe dehydration. Do not convert this unspecified restriction into an invented eGFR threshold. The usual adult regimen in the source is 1 g twice daily, but that is not an endorsement for a renally contraindicated patient. Antibacterial activity depends on acidic urine. UREX must not be the sole treatment for an acute renal-parenchymal infection with systemic symptoms. Differences from international product wording need explicit reconciliation rather than silent substitution.

The UK manufacturer prescribing information contraindicates severe renal failure at creatinine clearance or GFR below 10 mL/min, but permits use in the stated mild (20-50) and moderate (10-20) renal categories. This differs from the U.S.-source nonspecific renal-insufficiency restriction. Other contraindications include renal-parenchymal infection, hepatic dysfunction, severe dehydration, metabolic acidosis and gout. Avoid sulfonamides and alkalinizing agents such as potassium citrate; avoid acetazolamide because urinary alkalinization reduces the intended effect. These are UK product instructions, included to expose a disagreement, not to replace U.S. labeling or supply a U.S. renal cutoff.