Acetohydroxamic Acid
**Acetohydroxamic acid (AHA)** is a specialized medication primarily used as an adjunctive treatment in dogs for **persistent struvite urolithiasis** (bladder stones) and chronic urinary tract infections caused by **urease-producing bacteria** (e.g., *Staphylococcus* spp., *Proteus* spp., *Klebsiella*, *Morganella morganii*, and *Pseudomonas aeruginosa*). * **Clinical Pearl**: Because of its high side-effect profile, AHA is generally reserved for refractory cases where standard antibiotic therapy and calculolytic diets have failed. * **Warning**: It is strictly contraindicated in cats due to severe toxicity.
Mechanism: AHA acts as a potent, reversible inhibitor of the bacterial enzyme **urease**. * **Urease** normally hydrolyzes urea → ammonia + carbon dioxide. * By inhibiting **urease**, AHA → decreases urinary ammonia, bicarbonate, and carbonate concentrations → prevents the alkalinization of urine (keeps pH lower). * This acidic environment increases the solubility of struvite (magnesium ammonium phosphate) and carbonate-apatite crystals, and enhances the efficacy of concurrent antimicrobial therapy (e.g., carbenicillin, gentamicin, clindamycin, trimethoprim-sulfa, or chloramphenicol).
Dosing by species
- Adjunctive therapy of persistent struvite uroliths and persistent urease-producing bacteria after treating with antibiotics and calculolytic diets · 12.5 mg/kg twice daily PO · PO · twice daily
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Cats (highly toxic)
- Patients with poor renal function (e.g., serum creatinine >2.5 mg/dL)
- Pregnancy (FDA Category X - severe teratogenic effects)
Adverse effects
- Anorexia
- Vomiting
- Mouth and esophageal ulcers
- Hemolytic anemia
- Hyperbilirubinemia
- Bilirubinuria
- CNS disturbances (anxiety, depression, tremulousness)
- Reticulocytosis
- Bone marrow depression
- Phlebitis
- Skin rashes and alopecia
Drug interactions
- Iron salts · AHA may chelate iron salts in the gut if given concomitantly, reducing absorption.
- Methenamine · AHA may have a synergistic effect with methenamine in inhibiting urine pH increases caused by urease-producing Proteus spp., and may potentiate antibacterial effects.
- Alcohol · In humans, concurrent use of AHA with alcohol has resulted in skin rashes.
Monitoring
- CBC (Complete Blood Count)
- Renal function (including urinalysis)
- Hepatic function (specifically bilirubin levels)
Overdose
Acute overdoses can lead to severe hematologic and neurologic signs. * **Clinical Signs**: Anorexia, tremors, lethargy, vomiting, and anxiety. * **Hematologic Effects**: Increased reticulocyte counts and severe **hemolytic reactions**. Mild overdoses over several weeks can also result in hemolysis, particularly in patients with reduced renal function. * **Treatment**: Intensive hematologic monitoring with adjunctive supportive therapy, including possible blood transfusions.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.