Acetohydroxamic acid

AHA reversibly inhibits the bacterial enzyme urease, thereby inhibiting the hydrolysis of urea and production of ammonia in urine infected with urea-splitting organisms. The reduced ammonia levels and decreased pH enhance the effectiveness of antimicrobial agents and allow an increased cure rate of these infections.

Acetohydroxamic acid has been evaluated clinically in patients with urea-splitting urinary infections, often accompanied by struvite stone disease, that were recalcitrant to other forms of medical and surgical management. In these clinical trials, AHA reduced the pathologically elevated urinary ammonia and pH levels that result from the hydrolysis of urea by the enzyme, urease.

AHA does not acidify urine directly nor does it have a direct antibacterial effect. The usefulness of reducing ammonia levels and decreasing urinary pH is suggested by single (not yet replicated) clinical trials in which urease inhibition 1) allowed successful antibiotic treatment of urea-splitting Proteus infections after surgical removal of struvite stones in patients not cured by 3 months of antibacterial treatment alone, and 2) reduced the rate of stone growth in patients who were not candidates for surgical removal of stones.

AHA is well absorbed from the gastrointestinal tract after oral administration; peak blood levels occur from 0.25 to 1 hour after dosing. The compound is distributed throughout body water, and there is no known binding to any tissue. AHA chelates with dietary iron within the gut. This reaction may interfere with absorption of AHA and with iron. Concomitant hypochromic anemia should be treated with intramuscular iron.

In rodents, the metabolic fate of AHA is well known; 55% is excreted unchanged in urine, 25% is excreted as acetamide or acetate and 7% is excreted by the lungs as carbon dioxide. Less than 1% is excreted in the feces. Approximately 5% of the administered dose is unaccounted for. In rodents, AHA shows a dose-related change in pharmacokinetics; with increasing dose, there is an increase in the half-life and an increase in the percent of the administered dose recovered in urine as unchanged AHA.

Pharmacokinetics in man are generally similar to rodents including the dose-related increase in half-life, but they are not as well characterized as in the rodent. Thirty-six to sixty-five percent (36-65%) of the oral dosage is excreted unchanged in the urine. It is unaltered AHA in the urine that provides the therapeutic effect, but the precise concentration of AHA in urine that is necessary to inhibit urease is incompletely delineated. Therapeutic benefit may be obtained from concentrations as low as 8 mcg/ml; higher concentrations (i.e., 30 mcg/ml) are expected to provide more complete inhibition of urease. The plasma half-life of AHA is approximately 5-10 hours in subjects with normal renal function and is prolonged in patients with reduced renal function.