ZYLOPRIM (allopurinol) has the following structural formula:

ZYLOPRIM 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.  Each  scored white  tablet  contains  100  mg  allopurinol and the inactive ingredients lactose, magnesium stearate, potato starch, and povidone. Each scored peach tablet contains 300 mg allopurinol and the inactive ingredients corn starch, FD&C Yellow No. 6 Lake, lactose, magnesium stearate, and povidone. Its solubility in water at 37°C is 80.0 mg/dL and is  greater in  an alkaline solution.

ZYLOPRIM 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.

ZYLOPRIM is a structural analogue of the natural  purine  base, hypoxanthine. It is  an inhiboitor 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. ZYLOPRIM 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 ZYLOPRIM 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  ZYLOPRIM  for  treatment  of  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 ZYLOPRIM. 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 syndrome, which is characterized by excessive uric acid production combined with a deficiency of the enzyme, hypoxanthineguanine 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.

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

Approximately 20% of the ingested ZYLOPRIM is excreted in the feces. Because  of its  rapid oxidation to  oxipurinol and  a renal  clearance  rate  approximately that of glomerular filtration rate, ZYLOPRIM has a plasma half-life of about 1 to  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 ZYLOPRIM. Whereas ZYLOPRIM 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 ZYLOPRIM (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 ZYLOPRIM generally results in a fall in both serum and urinary uric acid within 2 to 3 days. The degree of this decrease can be  manipulated almost at will since  it is  dose-dependent. A  week or more of treatment with ZYLOPRIM may be required before its full effects  are  manifested; likewise, uric acid may return to pretreatment levels slowly (usually after a period of 7 to 10 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 ZYLOPRIM differs from that of uricosuric agents, which lower the serum uric acid level by increasing urinary excretion of uric acid. ZYLOPRIM reduces both the serum and urinary uric acid levels by inhibiting the formation of uric acid. The use of ZYLOPRIM to block the formation of urates avoids the hazard of increased renal excretion of uric acid posed by uricosuric drugs.

ZYLOPRIM 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 ZYLOPRIM. This is in contrast to the nullifying effect of salicylates on uricosuric drugs.

ZYLOPRIM 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 ZYLOPRIM 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.

ZYLOPRIM 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).

ZYLOPRIM 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. Treatment with ZYLOPRIM 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 ZYLOPRIM should not be restarted on the drug.

ZYLOPRIM 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), Drug Rash with Eosinophilia and Systemic Symptoms (DRESS) and/or generalized vasculitis, irreversible hepatotoxicity, and, on rare occasions, death (see ADVERSE REACTIONS).

In patients receiving PURINETHOL® (mercaptopurine) or IMURAN® (azathioprine), the concomitant administration of 300 to 600 mg of ZYLOPRIM 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 ZYLOPRIM, 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 ZYLOPRIM, 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  ZYLOPRIM may  be  increased in patients  with decreased renal function receiving thiazides and  ZYLOPRIM 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 ZYLOPRIM (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 ZYLOPRIM is skin rash. Skin reactions can be severe and sometimes fatal. Therefore, treatment with ZYLOPRIM 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 ZYLOPRIM 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 ZYLOPRIM has been reported to be increased (see PRECAUTIONS).



Drug rash with eosinophilia and systemic symptoms (DRESS) syndrome or drug hypersensitivity syndrome (DHS) has been reported in association with allopurinol use. The syndrome includes many of the severe reactions described above, and is potentially life-threatening and fatal. The syndrome is often characterized by fever, severe and profuse skin rash, elevated leukocyte counts and in particular, elevated eosinophil counts, lymphadenopathy, and multi-organ pathologies. Systemic symptoms often included, but were not limited to, the hepatic and renal systems. Symptoms involving the cardiac, gastrointestinal, lymphatic, pulmonary, and ophthalmic systems were also reported as occurring as part of the syndrome. It has been reported that symptoms may develop in approximately 1 week from initiating allopurinol therapy, but longer latency periods have also been reported.

To report SUSPECTED ADVERSE REACTIONS, contact Casper Pharma LLC at 1-844-5-CASPER (1-844-522-7737) or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

Most Common Reactions* Probably Causally Related:

• Gastrointestinal: Diarrhea, nausea, alkaline phosphataseincrease, SGOT/SGPT increase.
• Metabolic and Nutritional: Acute attacks of gout.
• Skin and Appendages: Rash, maculopapular rash.

*Early clinical studies and incidence rates  from early clinical experience  with ZYLOPRIM suggested that these adverse reactions were found to occur at a rate of greater than 1%. The most frequent event observed was acute attacks of gout following the initiation of therapy. Analyses of current usage suggest that the incidence of these adverse reactions is now less than 1%. The explanation for this decrease has not been determined, but it may be due to following recommended usage (see ADVERSE REACTIONSintroduction, INDICATIONS AND USAGE, PRECAUTIONS, and DOSAGE AND ADMINISTRATION).

Incidence Less Than 1% Probably Causally Related:

• Body As a Whole: Ecchymosis, fever, headache.
• Cardiovascular: Necrotizing angiitis, vasculitis.
• Gastrointestinal: Hepatic necrosis, granulomatous hepatitis, hepatomegaly, hyperbilirubinemia, cholestatic jaundice, vomiting, intermittent abdominal pain, gastritis, dyspepsia.
• Hemic and Lymphatic: Thrombocytopenia, eosinophilia, leukocytosis, leukopenia.
• Musculoskeletal: Myopathy, arthralgias.
• Nervous: Peripheral neuropathy, neuritis, paresthesia, somnolence.
• Respiratory: Epistaxis.
• Skin and Appendages: Erythema multiforme exudativum (Stevens-Johnson syndrome), toxic epidermal necrolysis (Lyell's syndrome), hypersensitivity vasculitis, purpura, vesicular bullous dermatitis, exfoliative dermatitis, eczematoid dermatitis, pruritus, urticaria, alopecia, onycholysis, lichen planus.
• Special Senses: Taste loss/perversion.
• Urogenital: Renal  failure, uremia  (see PRECAUTIONS).

Incidence  Less  Than 1%  Causal Relationship Unknown:

• Body As a Whole: Malaise.
• Cardiovascular: Pericarditis, peripheral vascular disease, thrombophlebitis, bradycardia, vasodilation.
• Endocrine: Infertility (male), hypercalcemia, gynecomastia (male).
• Gastrointestinal: Hemorrhagic pancreatitis, gastrointestinal bleeding, stomatitis, salivary gland swelling, hyperlipidemia, tongue edema, anorexia.
• Hemic and Lymphatic: Aplastic anemia, agranulocytosis, eosinophilic fibrohistiocytic lesion of bone marrow, pancytopenia, prothrombin decrease, anemia, hemolytic anemia, reticulocytosis, lymphadenopathy, lymphocytosis.
• Musculoskeletal: Myalgia.
• Nervous: Optic neuritis, confusion, dizziness, vertigo, foot drop, decrease in libido, depression, amnesia, tinnitus, asthenia, insomnia.
• Respiratory: Bronchospasm, asthma, pharyngitis, rhinitis.
• Skin and Appendages: Furunculosis, facial edema, sweating, skin edema.
• Special Senses: Cataracts, macular retinitis, iritis, conjunctivitis, amblyopia.
• Urogenital: Nephritis, impotence, primary hematuria, albuminuria.

Massive overdosing or acute poisoning by ZYLOPRIM has not been reported.

In mice, the 50% lethal dose (LD50) is 160 mg/kg  given intraperitoneally (IP) with deaths  delayed up to  5 days and 700 mg/kg  orally (PO) (approximately 140 times  the  usual human dose) with deaths  delayed up to 3 days. In rats, the acute LD50 is 750 mg/kg IP and 6000 mg/kg PO (approximately 1200 times the human dose).

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

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

The dosage of ZYLOPRIM 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/day for patients with mild gout and 400 to 600 mg/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 minimal effective dosage is 100 to 200 mg daily and the  maximal  recommended dosage is 800 mg  daily.  To reduce  the  possibility of flare-up of acute  gouty attacks, it is  recommended that the  patient start with a low dose of ZYLOPRIM (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 1 to 3 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 ZYLOPRIM 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 ZYLOPRIM, the dose of the uricosuric agent should  be gradually reduced over a period of several weeks  and  the  dose  of ZYLOPRIM gradually increased to the required dose needed to maintain a normal serum uric acid level.

It should also be noted that ZYLOPRIM is generally better tolerated if taken following meals. A fluid intake sufficient to yield a daily urinary output of at least 2 liters and the maintenance of a neutral or, preferably, slightly alkaline urine are desirable.

Since ZYLOPRIM and its metabolites are primarily eliminated only by the  kidney, accumulation of  the drug can occur in renal failure, and the dose of ZYLOPRIM should consequently be reduced. With a creatinine clearance of 10 to 20 mL/min, a daily dosage of 200 mg of ZYLOPRIM 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  clearance  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 is 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 2 or 3 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 ZYLOPRIM 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, oxalaterich 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 ZYLOPRIM 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.

100-mg (white) scored, flat cylindrical tablets imprinted with "ZYLOPRIM 100" on a raised hexagon, bottles of 90 (NDC 70199-015-90).

Store at 20° to 25°C (USP Controlled Room Temperature) (68° to 77°F) in a dry place.

300-mg (peach) scored, flat, cylindrical tablets imprinted with "ZYLOPRIM 300" on a raised hexagon, bottles of 90 (NDC 70199-016-90) and 500 (NDC 70199-016-05).

Store at 20° to 25°C (USP Controlled Room Temperature) (68° to 77°F) in a dry place and protect from light.

Casper Pharma LLC

Manufactured by

Patheon Mfg. Services LLC

Greenville, NC 27834

for Casper Pharma LLC

East Brunswick, NJ 08816



ZYLOPRIM is a registered trademark of Casper Pharma LLC, East Brunswick, NJ

IMURAN is a registered trademark of Sebela International Bermuda Limited, Hamilton, Bermuda

PURINETHOL is a registered trademark of Stason Pharmaceutical, Inc., Irvine, CA



Made in U.S.A.

PIB01605-02

Revised: 12/2018

ZYLOPRIM® (allopurinol)

100 mg 90 Tablets Bottle

NDC 70199-015-90

Rx Only





ZYLOPRIM® (allopurinol)

300 mg 90 Tablets Bottle

NDC 70199-016-90

Rx Only