Allopurinol is known chemically as 1,5-dihydro-4H-pyrazolo [3,4-d]pyrimidin-4-one. It is a xanthine oxidase inhibitor which is administered orally. It is available in 100 mg and 300 mg strengths. The 100mg tablets contain the inactive ingredients lactose, magnesium stearate, potato starch, and povidone. The 300mg tablets contain the inactive ingredients lactose, magnesium stearate, corn starch, and povidone. Its solubility in water at 37°C is 80.0 mg/dL and is greater in an alkaline solution.

Allopurinol has the following structural formula:

Allopurinol acts on purine catabolism, without disrupting the biosynthesis of purines. It reduces the production of uric acid by inhibiting the biochemical reactions immediately preceding its formation.

Allopurinol is a structural analogue of the natural purine base, hypoxanthine. It is an inhibitor of xanthine oxidase, the enzyme responsible for the conversion of hypoxanthine to xanthine and of xanthine to uric acid, the  end  product  of  purine  metabolism in  man. Allopurinol is metabolized to the corresponding  xanthine analogue, oxipurinol (alloxanthine), which also is an inhibitor of xanthine oxidase.

It has been shown that reutilization of both hypoxanthine and xanthine for nucleotide and nucleic acid synthesis is markedly enhanced when their oxidations are inhibited by allopurinol and oxipurinol. This reutilization does not disrupt normal nucleic acid anabolism, however, because feedback inhibition is an integral part of purine biosynthesis. As a result of xanthine oxidase inhibition, the serum concentration of hypoxanthine plus xanthine in patients receiving allopurinol for treatment for hyperuricemia is usually in the range of 0.3 to 0.4 mg/dL compared to a normal level of approximately 0.15 mg/dL. A maximum of 0.9 mg/dL  of these oxypurines has been reported when the serum urate was lowered to less than 2 mg/dL by high doses of allopurinol. These values are far below the saturation levels at which point their precipitation would be expected to occur (above 7 mg/dL).

The renal clearance of hypoxanthine and xanthine is at least 10 times greater than that of uric acid. The increased xanthine and hypoxanthine in the urine have not been accompanied by problems of nephrolithiasis. Xanthine crystalluria has been reported in only three patients. Two of the patients had Lesch-Nyhan syn- drome, which is characterized by excessive uric acid production combined with a  deficiency of  the enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGPRTase). This enzyme is required for the conversion of hypoxanthine, xanthine, and guanine to their respective nucleotides. The third patient had lymphosarcoma and produced an extremely large amount of uric acid because of rapid cell lysis during chemotherapy.

Allopurinol is approximately 90% absorbed from the gastrointestinal tract. Peak plasma levels generally occur at 1.5 hours and 4.5 hours for allopurinol and oxipurinol respectively, and after a single oral dose of 300 mg allopurinol, maximum plasma levels of about 3 mcg/mL of allopurinol and 6.5 mcg/mL of oxipurinol are produced.

Approximately  20% of the ingested allopurinol is excreted in the feces. Because of its rapid oxidation to oxipurinol and a renal clearance rate approximately that of glomerular filtration rate, allopurinol has a plasma half-life of about 1-2 hours. Oxipurinol, however, has a longer plasma half-life (approximately 15 hours) and therefore effective xanthine oxidase inhibition is maintained over a 24-hour period with single daily doses of allopurinol. Whereas allopurinol is cleared essentially by glomerular filtration, oxipurinol is reabsorbed in the kidney tubules in a manner similar to the reabsorption of uric acid.

The clearance of oxipurinol is increased by uricosuric drugs, and as a consequence, the addition of a uricosuric agent reduces to some degree the inhibition of xanthine oxidase by oxipurinol and increases to some degree the urinary excretion of uric acid. In practice, the net effect of such combined therapy may be useful in some patients in achieving minimum serum uric acid levels provided the total urinary uric acid load does not exceed the competence of the patient’s renal function.

Hyperuricemia may be primary, as in gout, or secondary to diseases such as acute and chronic leukemia, polycythemia vera, multiple myeloma, and psoriasis. It may occur with the use of diuretic agents, during renal dialysis, in the presence of renal damage, during starvation or reducing diets and in the treatment of neoplastic disease where rapid resolution of tissue masses may occur. Asymptomatic hyperuricemia is not an indication for treatment with allopurinol (see INDICATIONS AND USAGE).

Gout is a metabolic disorder which is characterized by hyperuricemia and resultant deposition of monosodium urate in the tissues, particularly the joints and kidneys. The etiology of this hyperuricemia is the overproduction of uric acid in relation to the patient’s ability to excrete it. If progressive deposition of urates is to be arrested or reversed, it is necessary to reduce the serum uric acid level below the saturation point to suppress urate precipitation.

Administration of allopurinol generally results in a fall in both serum and urinary uric acid within two to three days. The degree of this decrease can be manipulated almost at will since it is dose-dependent. A week or more of treatment with allopurinol may be required before its full effects are manifested; likewise, uric acid may return to pretreatment levels slowly (usually after a period of seven to ten days following cessation of therapy). This reflects primarily the accumulation and slow clearance of oxipurinol. In some patients a dramatic fall in urinary uric acid excretion may not occur, particularly in those with severe tophaceous gout. It has been postulated that this may be due to the mobilization of urate from tissue deposits as the serum uric acid level begins to fall.

The action of allopurinol differs from that of uricosuric agents, which lower the serum uric acid level by increas- ing urinary excretion of uric acid. Allopurinol reduces both the serum and urinary uric acid levels by inhibiting the formation of uric acid. The use of allopurinol to block the formation of urates avoids the hazard of increased renal excretion of uric acid posed by uricosuric drugs.

Allopurinol can substantially reduce serum and urinary uric acid levels in previously refractory patients even in the presence of renal damage serious enough to render uricosuric drugs virtually ineffective. Salicylates may be given conjointly for their antirheumatic effect without compromising the action of allopurinol. This is in contrast to the nullifying effect of salicylates on uricosuric drugs.

Allopurinol also inhibits the enzymatic oxidation of mercaptopurine, the  sulfur-containing analogue of hypoxanthine, to 6-thiouric acid. This oxidation, which is catalyzed by xanthine oxidase, inactivates mercaptopurine. Hence, the inhibition of such oxidation by allopurinol may result in as much as a 75% reduction in the therapeutic dose requirement of mercaptopurine when the two compounds are given together.

THIS IS  NOT AN INNOCUOUS DRUG. IT  IS  NOT RECOMMENDED FOR THE TREATMENT OF ASYMPTOMATIC HYPERURICEMIA. Allopurinol reduces serum and urinary uric acid concentrations. Its use should be individualized for each patient and requires an understanding of its mode of action and pharmacokinetics (see CLINICAL PHARMACOLOGY, CONTRAINDICATIONS, WARNINGS and PRECAUTIONS).

Allopurinol is indicated in:

1. the management of patients with signs and symptoms of primary or secondary gout (acute attacks, tophi, joint destruction, uric acid lithiasis and/or nephropathy).

2. the management of patients with leukemia, lymphoma and malignancies who are receiving cancer therapy which causes elevations of serum and urinary uric acid levels. Allopurinol treatment should be discontinued when the potential for overproduction of uric acid is no longer present.

3. the management of patients with recurrent calcium oxalate calculi whose daily uric acid excretion exceeds 800 mg/day in male patients and 750 mg/day in female patients. Therapy in such patients should be carefully assessed initially and reassessed periodically to determine in each case that treatment is beneficial and that the benefits outweigh the risks.

Patients who have developed a severe reaction to allopurinol should not be restarted on the drug.

ALLOPURINOL SHOULD BE DISCONTINUED AT THE FIRST APPEARANCE OF SKIN RASH OR  OTHER SIGNS WHICH MAY INDICATE AN ALLERGIC REACTION. In some instances a skin rash may be followed by more severe hypersensitivity reactions such as exfoliative, urticarial and purpuric lesions as well as Stevens-Johnson syndrome (erythema multiforme exudativum), and/or generalized vasculitis, irre- versible hepatotoxicity and on rare occasions death.

In patients receiving Purinethol® (mercaptopurine) or Imuran® (azathioprine), the concomitant administration of 300-600 mg of allopurinol per day will require a reduction in dose to approximately one-third to one-fourth of the usual dose of mercaptopurine or azathioprine. Subsequent adjustment of doses of mercaptopurine or azathioprine should be made on the basis of therapeutic response and the appearance of toxic effects (see CLINICAL PHARMACOLOGY).

A few cases of reversible clinical hepatotoxicity have been noted in patients taking allopurinol, and in some patients asymptomatic rises in serum alkaline phosphatase or serum transaminase have been observed. If anorexia, weight loss or pruritus develop in patients on allopurinol, evaluation of liver function should be part of their diagnostic workup. In patients with pre-existing liver disease, periodic liver function tests are recommended during the early stages of therapy.

Due to  the  occasional occurrence of drowsiness, patients should be alerted to the need for due precaution when engaging in activities where alertness is mandatory.

The occurrence of hypersensitivity reactions to allopurinol may be increased in patients with decreased renal function receiving thiazides and allopurinol concurrently. For this reason, in this clinical setting, such combinations should be administered with caution and patients should be observed closely.

Data upon which the following estimates of incidence of adverse reactions are made are derived from experiences reported in the literature, unpublished clinical trials and voluntary reports since marketing of allopurinol began. Past experience suggested that the most frequent event following the initiation of allopurinol treatment was an increase in acute attacks of gout (average 6% in early studies). An analysis of current usage suggests that the incidence of acute gouty attacks has diminished to less than 1%. The explanation for this decrease has not been determined but may be due in part to initiating therapy more gradually (see PRECAUTIONS and DOSAGE AND ADMINISTRATION).

The most frequent adverse reaction to allopurinol is skin rash. Skin reactions can be severe and sometimes fatal. Therefore, treatment with allopurinol should be discontinued immediately if a rash develops (see WARNINGS). Some patients with the most severe reaction also had fever, chills, arthralgias, cholestatic jaundice, eosinophilia and mild leukocytosis or leukopenia. Among 55 patients with gout treated with allopurinol for 3 to 34 months (average greater than 1 year) and followed prospectively, Rundles observed that 3% of patients developed a type of drug reaction which was predominantly a pruritic maculopapular skin eruption, sometimes scaly or exfoliative. However, with current usage, skin reactions have been observed less frequently than 1%. The explanation for this decrease is not obvious. The incidence of skin rash may be increased in the presence of renal insufficiency.  The frequency of skin rash among patients receiving ampicillin or amoxicillin concurrently with allopurinol has been reported to be increased (see PRECAUTIONS).

Massive overdosing or acute poisoning by allopurinol has not been reported. In mice the 50% lethal dose (LD50) is 160 mg/kg given intraperitoneally (i.p.) with deaths delayed up to five days and 700 mg/kg orally (p.o.) (approximately 140 times the usual human dose) with deaths delayed up to three days. In rats the acute LD50 is 750 mg/kg  i.p. and 6000 mg/kg  p.o. (approximately 1200 times the human dose).

In the management of overdosage there is no specific antidote for allopurinol. There has been no clinical experience in the management of a patient who has taken massive amounts of allopurinol.

Both allopurinol and oxipurinol are dialyzable, however, the usefulness of hemodialysis or peritoneal dialysis in the management of an allopurinol overdose is unknown.

The dosage of allopurinol to accomplish full control of gout and to lower serum uric acid to normal or near-normal levels varies with the severity of the disease. The average is 200 to 300 mg per day for patients with mild gout and 400 to 600 mg per day for those with moderately severe tophaceous gout. The appropriate dosage may be administered in divided doses or as a single equivalent dose with the 300 mg tablet. Dosage requirements in excess of 300 mg should be administered in divided doses. The maximal recommended dosage is 800 mg daily. To reduce the possibility of flareup of acute gouty attacks, it is recommended that the patient start with a low dose of allopurinol (100 mg daily) and increase at weekly intervals by 100 mg until a serum uric acid level of 6 mg/dL or less is attained but without exceeding the maximal recommended dosage.

Normal serum urate levels are usually achieved in one to three weeks. The upper limit of normal is about 7 mg/dL for men and postmenopausal women and 6 mg/dL for premenopausal women. Too much reliance should not be placed on a single serum uric acid determination since, for technical reasons, estimation of uric acid may be difficult. By  selecting the appropriate dosage and, in certain patients, using uricosuric agents concurrently, it is possible to reduce serum uric acid to normal or, if desired, to as low as 2 to 3  mg/dL and keep it there indefinitely.

While adjusting the dosage of allopurinol in patients who are being treated with colchicine and/or  anti-inflammatory agents, it is wise to continue the latter therapy until serum uric acid has been normalized and there has been freedom from acute gouty attacks for several months.

In transferring a patient from a uricosuric agent to allopurinol, the dose of the uricosuric agent should be gradually reduced over a period of several weeks and the  dose of allopurinol gradually increased to  the required dose needed to maintain a normal serum uric acid level.

It should also be noted that allopurinol is generally better tolerated if taken following meals. A fluid intake sufficient to yield a daily urinary output of at least two liters and the maintenance of a neutral or, preferably, slightly alkaline urine are desirable.

Since allopurinol and its metabolites are primarily eliminated only by the kidney, accumulation of the drug can occur in renal failure, and the dose of allopurinol should consequently be reduced. With a creatinine clearance of 10 to 20 mL/min, a daily dosage of 200 mg of allopurinol is suitable. When the creatinine clearance is less than 10 mL/min, the daily dosage should not exceed 100 mg. With extreme renal impairment (creatinine clear- ance less than 3 mL/min) the interval between doses may also need to be lengthened.

The correct size and frequency of dosage for maintaining the serum uric acid just within the normal range are best determined by using the serum uric acid level as an index.

For the prevention of uric acid nephropathy during the vigorous therapy of neoplastic disease, treatment with 600 to 800 mg daily for two or three days is advisable together with a high fluid intake. Otherwise similar considerations to the above recommendations for treating patients with gout govern the regulation of dosage for maintenance purposes in secondary hyperuricemia.

The dose of allopurinol recommended for management of recurrent calcium oxalate stones in hyperuricosuric patients is 200 to 300 mg/day in divided doses or as the single equivalent. This dose may be adjusted up or down depending upon the resultant control of the hyperuricosuria based upon subsequent 24 hour urinary urate determinations. Clinical experience suggests that patients with recurrent calcium oxalate stones may also benefit from dietary changes such as the reduction of animal protein, sodium, refined sugars, oxalate-rich foods, and excessive calcium intake as well as an increase in oral fluids and dietary fiber.

Children, 6 to 10 years of age, with secondary hyperuricemia associated with malignancies may be given 300 mg allopurinol daily while those under 6 years are generally given 150 mg daily. The response is evaluated after approximately 48 hours of therapy and a dosage adjustment is made if necessary.

Allopurinol Tablets, USP; 100 mg, round, flat, off-white, scored tablet, debossed ‘0524’ over ‘0405’.

Bottles of 100                 NDC 55111-729-01

Bottles of 1000               NDC 55111-729-10

300 mg; round, convex, off-white tablet, debossed ‘AL3’.

Bottles of 100                 NDC 55111-730-01

Bottles of 500                 NDC 55111-730-05

Bottles of 1000               NDC 55111-730-10

Store at 15°-30°C (59°-86°F) and protect from moisture.

QUESTIONS OR COMMENTS? Call toll free 1-888-375-3784.You may report side effects to FDA at 1-800-FDA-1088.

Rx Only 

Manufactured by

Dr. Reddy’s Laboratories Louisiana, LLC

Shreveport, LA 71106 USA

Issued August, 2014                                                        

150019989-03

Please reference the How Supplied section listed above for a description of individual tablets. This drug product has been received by Aphena Pharma - TN in a manufacturer or distributor packaged configuration and repackaged in full compliance with all applicable cGMP regulations. The package configurations available from Aphena are listed below:

Store between 20°-25°C (68°-77°F). See USP Controlled Room Temperature. Dispense in a tight light-resistant container as defined by USP. Keep this and all drugs out of the reach of children.

Repackaged by:



Cookeville, TN 38506



20181212JH

NDC 71610-194 - Allopurinol, USP 100 mg - Rx Only