Medicine guide

Lithostat

250 mg · Tablet

Prescription only
Urease Inhibitor

Active substance: Acetohydroxamic Acid
Made by: Mission Pharmacal Company
Source: Official label

Quoted from the official source. Not yet reviewed by Mediclarum — the leaflet in your pack is authoritative.

At a glance

Quoted from the official label · 2026-01-08

What it is

Urease Inhibitor

Used for

Acetohydroxamic acid is indicated as adjunctive therapy in patients with chronic urea-splitting urinary infection.

The label’s usual adult dose

AHA should be administered orally, one tablet 3-4 times a day in a total daily dose of 10-15 mg/kg/day.

The maximum daily dose should be no more than 1.5 grams, regardless of body weight.

Full directions ↓

Do not take it if

Acetohydroxamic acid should not be used in:

All warnings ↓

Good to know

Prescription only
FDA enforcement reports list no ongoing recall, and none from the last two years, for this product code · checked 2026-10-02

Every line above is selected, not written, from the official label. Nothing is reworded. DailyMed

What it is for

Acetohydroxamic acid is indicated as adjunctive therapy in patients with chronic urea-splitting urinary infection.
AHA is intended to decrease urinary ammonia and alkalinity, but it should not be used in lieu of curative surgical treatment (for patients with stones) or antimicrobial treatment.
Long-term treatment with AHA may be warranted to maintain urease inhibition as long as urea-splitting infection is present.
Experience with AHA does not go beyond 7 years.
A patient package insert should be distributed to each patient who receives AHA.

From the official label · 2026-01-08 · DailyMed

How it works

From this product’s own US prescribing label.

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.

Peak level after0.25–1 h

How it leaves the body

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.

Quoted from the prescribing label, sections “Mechanism of Action” and “Pharmacokinetics”. DailyMed · 2026-01-08

Do not take it if

Acetohydroxamic acid should not be used in:
a. patients whose physical state and disease are amenable to definitive surgery and appropriate antimicrobial agents b. patients whose urine is infected by non-urease producing organisms c. patients whose urinary infections can be controlled by culture-specific oral antimicrobial agents d. patients whose renal function is poor (i.e., serum creatinine more than 2.5 mg/dl and/or creatinine clearance less than 20 ml/min) e. female patients who do not evidence a satisfactory method of contraception f. patients who are pregnant Acetohydroxamic acid may cause fetal harm when administered to a pregnant woman.
AHA was teratogenic (retarded and/or clubbed rear leg at 750 mg/kg and above and exencephaly and encephalocele at 1,500 mg/kg) when given intraperitoneally to rats.
AHA is contraindicated in women who are or may become pregnant.
If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be informed of the potential hazard to the fetus.

Quoted from the official label, section “Contraindications”.

How to take it

These directions are for this exact strength and form. Another one is different.

AHA should be administered orally, one tablet 3-4 times a day in a total daily dose of 10-15 mg/kg/day.
The recommended starting dose is 12 mg/kg/day, administered at 6-8 hour intervals at a time when the stomach is empty.
The maximum daily dose should be no more than 1.5 grams, regardless of body weight.
The dosage should be reduced in patients with reduced renal function.
Patients whose serum creatinine is greater than 1.8 mg/dl should take no more than 1.0 gm/day; such patients should be dosed at q-12-h intervals.
Further reductions in dosage to prevent the accumulation of toxic concentrations in the blood may also be desirable.
Insufficient data exists to accurately characterize the optimum dose and/or dose interval in patients with moderate degrees of renal insufficiency.
Patients with advanced renal insufficiency (i.e., serum creatinine more than 2.5 mg/dl) should not be treated with AHA.
The risk of accumulation of toxic blood levels of AHA seems to be greater than the chances for a beneficial effect in such patients.
In children an initial dose of 10 mg/kg/day is recommended.
Close monitoring of the patient’s clinical condition and hematologic status is recommended.
Titration of the dose to higher or lower levels may be required to obtain an optimum therapeutic effect and/or to reduce the risk of side effects.

Quoted from the official label, section “Dosage & Administration”.

Other warnings

A Coombs negative hemolytic anemia has occurred in patients receiving AHA.
Gastrointestinal upset characterized by nausea, vomiting, anorexia and generalized malaise have accompanied the most severe forms of hemolytic anemia.
Approximately 15% of patients receiving AHA have had only laboratory findings of an anemia.
However, most patients developed a mild reticulocytosis.
The untoward reactions have reverted to normal following cessation of treatment.
A complete blood count, including a reticulocyte count, is recommended after two weeks of treatment.
If the reticulocyte count exceeds 6%, a reduced dosage should be entertained.
A CBC and reticulocyte count are recommended at 3-month intervals for the duration of treatment.
General Hematologic Effects:
Bone marrow depression (leukopenia, anemia, and thrombocytopenia) has occurred in experimental animals receiving large doses of AHA, but has not been seen in man to date.
AHA is a known inhibitor of DNA synthesis and also chelates metals - notably iron.
Its bone marrow suppressant effect is probably related to its ability to inhibit DNA synthesis, but anemia could also be related to depletion of iron stores.
To date, the only clinical effect noted has been hemolysis, with a decrease in the circulating red blood cells, hemoglobin and hematocrit.
Abnormalities in platelet or white blood cell count have not been noted.
However, clinical monitoring of the platelet and white cell count is recommended.
Monitoring Liver Function:
Abnormalities of liver function have not been reported to date.
However, a chloro-benzene derivative of acetohydroxamic acid caused significant liver dysfunction in an unrelated study.
Therefore, close monitoring of liver function is recommended.
(See Carcinogenesis for discussion of possible hepatic carcinogenesis.) Use In Patients With Renal Impairment:
Since AHA is eliminated primarily by the kidneys, patients with significantly impaired renal function should be closely monitored, and a reduction of daily dose may be needed to
avoid excessive drug accumulation.
(See Dosage and Administration.)
General Hematologic Effects:
Bone marrow depression (leukopenia, anemia, and thrombocytopenia) has occurred in experimental animals receiving large doses of AHA, but has not been seen in man to date.
AHA is a known inhibitor of DNA synthesis and also chelates metals - notably iron.
Its bone marrow suppressant effect is probably related to its ability to inhibit DNA synthesis, but anemia could also be related to depletion of iron stores.
To date, the only clinical effect noted has been hemolysis, with a decrease in the circulating red blood cells, hemoglobin and hematocrit.
Abnormalities in platelet or white blood cell count have not been noted.
However, clinical monitoring of the platelet and white cell count is recommended.
Monitoring Liver Function:
Abnormalities of liver function have not been reported to date.
However, a chloro-benzene derivative of acetohydroxamic acid caused significant liver dysfunction in an unrelated study.
Therefore, close monitoring of liver function is recommended.
(See Carcinogenesis for discussion of possible hepatic carcinogenesis.) Use In Patients With Renal Impairment:
Since AHA is eliminated primarily by the kidneys, patients with significantly impaired renal function should be closely monitored, and a reduction of daily dose may be needed to
avoid excessive drug accumulation.
(See Dosage and Administration.)

Quoted from the official label, section “Warnings”.

Pregnancy and breastfeeding

(See Contraindications.)
It is not known whether AHA is secreted in human milk.
Because many drugs are excreted in human milk, and because of the potential for serious adverse reactions in nursing infants from AHA, a decision should be made to discontinue nursing or the drug, taking into account the significance of the drug to the mother’s well being.

Quoted from the official label, section “OTC — Pregnancy or Breast Feeding”.

Other medicines

AHA has been used concomitantly with insulin, oral and parenteral antibiotics, and progestational agents.
No clinically significant interactions have been noted, but until wider clinical experience is obtained, AHA should be used with caution in patients receiving other therapeutic agents.
AHA taken in association with alcoholic beverages has resulted in a rash.
(See Adverse Reactions.) AHA chelates heavy metals-notably iron.
The absorption of iron and AHA from the intestinal lumen may be reduced when both drugs are taken concomitantly.
When iron administration is indicated, intramuscular iron is probably the product of choice.

Quoted from the official label, section “Drug Interactions”.

If you take too much

In an emergency, call your local emergency number or a poison control centre.

Acute deliberate overdosage in man has not occurred, but would be expected to induce the following symptoms:
anorexia, malaise, lethargy, diminished sense of well being, tremulousness, anxiety, nausea and vomiting.
Laboratory findings are likely to include an elevated reticulocyte count and a severe hemolytic reaction requiring hospitalization, symptomatic treatment, and possibly blood transfusions.
Concomitant reduction in platelets and/or white blood cells should be anticipated.
Milder overdosages resulting in hemolysis have occurred in an occasional patient with reduced renal function after several weeks or months of continuous treatment.
The acute LD 50 of AHA in animals (rats) is 4.8 gm/kg.
Recommended treatment for an overdosage reaction consists of (1) cessation of treatment, (2) close monitoring of hematologic status, (3) symptomatic treatment, and (4) blood transfusions as required by the clinical circumstances.
The drug is probably dialyzable, but this property has not been tested clinically.

Quoted from the official label, section “Overdosage”.

Use in children

Children with chronic, recalcitrant, urea-splitting urinary infection may benefit from treatment with AHA.
However, detailed studies involving dosage and dose intervals in children have not been established.
Children have tolerated a dose of 10 mg/kg/day, taken in two or three divided doses, satisfactorily for periods up to one year.
Close monitoring of such patients is mandatory.

Quoted from the official label, section “Pediatric Use”.

Side effects

Experience with AHA is limited.
About 150 patients have been treated, most for periods of more than a year.
Adverse reactions have occurred in up to thirty percent (30%) of the patients receiving AHA.
In some instances the reactions were symptomatic; in others only changes in laboratory parameters were noted.
Adverse reactions seem to be more prevalent in patients with preexisting thrombophlebitis or phlebothrombosis and/or in patients with advanced degrees of renal insufficiency.
The risk of adverse reactions is highest during the first year of treatment.
Chronic treatment does not seem to increase the risk nor the severity of adverse reactions.
The following reactions have been reported:
NEUROLOGICAL:
Mild headaches are commonly reported (about 30%) during the first 48 hours of treatment.
These headaches are mild, responsive to oral salicylate-type analgesics, and usually disappear spontaneously.
The headaches have not been associated with vertigo, tinnitus, or visual or auditory abnormalities.
Tremulousness and nervousness have also been reported.
GASTROINTESTINAL:
Gastrointestinal symptoms, nausea, vomiting, anorexia, and malaise have occurred in 20-25% of patients.
In most patients the symptoms were mild, transitory, and did not result in interruption of treatment.
Approximately 3% of patients developed a hemolytic anemia of sufficient magnitude to warrant interruption in treatment; several of these patients also had symptoms of gastrointestinal upset.
HEMATOLOGICAL:
Approximately 15% of patients have had laboratory findings characteristic of a hemolytic anemia.
A mild reticulocytosis (5- 6%) without anemia, is even more prevalent.
The laboratory findings are occasionally accompanied by systemic symptoms such as malaise, lethargy and fatigue, and gastrointestinal symptoms.
Symptoms and laboratory findings have invariably improved following cessation of treatment with AHA.
The hematological abnormalities are more prevalent in patients with advanced renal failure.
DERMATOLOGICAL:
A nonpruritic, macular skin rash has occurred in the upper extremities and on the face of several patients taking AHA on a long-term basis, usually when AHA has been taken concomitantly with alcoholic beverages, but in a few patients in the absence of alcohol consumption.
The rash commonly appears 30-45 minutes after ingestion of alcoholic beverages; it characteristically disappears spontaneously in 30-60 minutes.
The rash may be associated with a general sensation of warmth.
In some patients the rash is sufficiently severe to warrant discontinuation of treatment, but most patients have continued treatment, avoiding alcohol or using smaller quantities of it.
Alopecia has also been reported in patients taking AHA.
CARDIOVASCULAR:
Superficial phlebitis involving the lower extremities has occurred in several patients on AHA during the early (Phase II) clinical trials.
Several of the affected patients had had phlebitic episodes prior to treatment.
One patient developed deep vein thrombosis of the lower extremities.
The patient with phlebothrombosis had an associated traumatic injury to the groin.
It is unclear whether the phlebitis was related to or exacerbated by treatment with AHA.
No patient in the three (3) year controlled (Phase III) clinical trial developed phlebitis.
In all instances these vascular abnormalities returned to normal following appropriate medical therapy.
Embolic phenomena have been reported in three patients taking AHA in the Phase II trial.
The phlebitis and emboli resolved following discontinuation of AHA and implementation of appropriate medical therapy.
Several patients have resumed treatment with AHA without ill effect.
Palpitations have also been reported in patients taking AHA.
RESPIRATORY: No symptoms have been reported.
Radiographic evidence of small pulmonary emboli has been seen in three patients with phlebitis in their lower legs.
PSYCHIATRIC:
Depression, anxiety, nervousness, and tremulousness have been observed in approximately 20% of patients taking AHA.
In most patients the symptoms were mild and transitory, but in about 6% of patients the symptoms were sufficiently distressing to warrant interruption or discontinuation of treatment.

Quoted from the official label, section “Adverse Reactions”.

What it looks like and how it is packed

LITHOSTAT ® , NDC 0178-0500-01, is available for oral administration as 250 mg white, round tablets, in unit of use packages of 100 tablets.
Each LITHOSTAT ® tablet is debossed MPC 500 on one side and blank on the other side.
LITHOSTAT ® should be stored in a dry place at room temperature, 15° - 30°C (59° - 86°F).
Container should be closed tightly.
Rx only L050001R0824

Quoted from the official label, section “How Supplied”.

What is in it

Acetohydroxamic acid (AHA) is a stable, synthetic compound derived from hydroxylamine and ethyl acetate.
Its molecular structure is similar to urea:
AHA is weakly acidic, highly soluble in water, and chelates metals - notably iron.
The molecular weight is 75.068.
AHA has a pKa of 9.32 and a melting point of 89-91° C.
AHA is a urease inhibitor.
Available as 250 mg tablets.
Acetohydroxamic acid struct

Quoted from the official label, section “Description”.

Ingredients people check for

Lactose, gluten, dyes, sugars and other ingredients that matter with an allergy, intolerance or diet — as this product’s FDA label lists them.

The stored label for this product has no list of inactive ingredients. The list on the pack is the one to check.

Quoted from the FDA label. A label that does not name an ingredient is not a guarantee that the product is free of it, and formulations change. With an allergy, check the pack and ask a pharmacist.

Details

Made by	Mission Pharmacal Company
Active substance	Acetohydroxamic Acid
Strength	250 mg
Form	Tablet
Route	Oral
Packs	100 TABLET in 1 BOTTLE
NDC	0178-0500

Source: NDC Directory · 2026-09-13 · not reviewed by a clinician

Source: US Food and Drug Administration, NDC Directory. Reuse terms: US government work (FDA).

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