Allopurinol

Description

Allopurinol is a xanthine oxidase inhibitor. The chemical name for allopurinol tablets is 1, 5-dihydro-4H-pyrazolo 3, 4-dpyrimidin-4-one, with a molecular weight of 136.11 g/mol. Allopurinol exhibits a solubility in water of 80.0 mg/dL at 37°C, which increases in alkaline solutions. The scored white, flat cylindrical tablet formulation contains 100 mg of allopurinol along with inactive ingredients including corn starch, lactose monohydrate, magnesium stearate, povidone, and purified water. The scored peach, flat cylindrical tablet formulation contains 300 mg of allopurinol and includes inactive ingredients such as corn starch, FD&C Yellow No. 6 Aluminium Lake, lactose monohydrate, magnesium stearate, povidone, and purified water.

Uses and Indications

Allopurinol Tablets are indicated for the management of adult patients exhibiting signs and symptoms of primary or secondary gout, including acute attacks, tophi, joint destruction, uric acid lithiasis, and/or nephropathy. Additionally, Allopurinol is indicated for both adult and pediatric patients diagnosed with leukemia, lymphoma, and solid tumor malignancies who are undergoing cancer therapy that results in elevated serum and urinary uric acid levels. Furthermore, it is indicated for adult patients with recurrent calcium oxalate calculi whose daily uric acid excretion exceeds 800 mg/day in males and 750 mg/day in females, despite implementation of lifestyle modifications.

Limitations of use include the recommendation against the use of Allopurinol Tablets for the treatment of asymptomatic hyperuricemia.

Dosage and Administration

For the management of gout, patients with normal kidney function should initiate treatment with 100 mg orally once daily. The dosage may be increased by 100 mg weekly increments until a target serum uric acid level of 6 mg/dL or less is achieved, with a maximum allowable dosage of 800 mg daily. In patients with impaired kidney function, the initial dosage is 50 mg orally once daily, with titration recommendations to be followed as outlined for renal impairment until the target serum uric acid level is reached.

For hyperuricemia associated with cancer therapy, adults may be prescribed a dosage range of 300 mg to 800 mg orally daily. Pediatric patients should receive 100 mg/m² orally every 8 to 12 hours, with a maximum daily dosage of 10 mg/kg or 800 mg.

In the case of recurrent calcium oxalate calculi, the recommended initial dosage for patients with normal kidney function is between 200 mg to 300 mg orally daily.

For patients with renal impairment, healthcare professionals should refer to the full prescribing information (FPI) for specific dosage modifications and recommendations.

Contraindications

Use of allopurinol is contraindicated in patients with known hypersensitivity to allopurinol or to any of the excipients present in allopurinol tablets. This contraindication is essential to prevent potential allergic reactions that may occur in susceptible individuals.

Warnings and Precautions

Allopurinol is associated with several significant warnings and precautions that healthcare professionals must consider to ensure patient safety.

Skin Rash and Hypersensitivity Allopurinol has been linked to serious and potentially fatal dermatological reactions. It is imperative that allopurinol tablets be discontinued immediately upon the first appearance of a skin rash or any other signs indicative of a hypersensitivity reaction.

Gout Flares Patients may experience gout flares during the initiation of allopurinol treatment. To mitigate this risk, concurrent prophylactic treatment with colchicine or anti-inflammatory agents is recommended.

Nephrotoxicity Allopurinol may adversely affect kidney function. Therefore, patients with impaired renal function should receive lower doses of allopurinol tablets to prevent further renal compromise.

Hepatotoxicity Reversible hepatotoxicity has been reported in patients taking allopurinol. Should any signs or symptoms of hepatotoxicity arise, it is essential to evaluate liver function promptly.

Myelosuppression There have been reports of bone marrow suppression associated with allopurinol use. Monitoring for signs of myelosuppression is advised.

Potential Effect on Driving and Use of Machinery Patients taking allopurinol may experience drowsiness, somnolence, or dizziness. Caution should be exercised when driving or operating machinery until the individual’s response to the medication is known.

Laboratory Tests In the event that signs and symptoms of hepatotoxicity develop, it is crucial to evaluate liver function to ensure patient safety and appropriate management.

Healthcare professionals are encouraged to remain vigilant regarding these warnings and to monitor patients accordingly to minimize risks associated with allopurinol therapy.

Side Effects

Patients receiving allopurinol may experience a range of adverse reactions, which can be categorized by seriousness and frequency.

Most commonly reported adverse reactions include nausea, diarrhea, and an increase in liver function tests. These reactions are generally mild but should be monitored during treatment.

Serious adverse reactions associated with allopurinol include skin rash and hypersensitivity, which can lead to severe and sometimes fatal dermatological reactions. It is crucial to discontinue allopurinol tablets at the first appearance of a skin rash or any other signs of hypersensitivity. Gout flares may also occur during the initiation of treatment; therefore, concurrent prophylactic treatment with colchicine or anti-inflammatory agents is recommended to mitigate this risk.

Nephrotoxicity is another serious concern, as allopurinol may adversely affect kidney function. Patients with decreased kidney function require careful dose adjustments to avoid further complications. Additionally, cases of reversible hepatotoxicity have been reported; if patients exhibit signs or symptoms of hepatotoxicity, liver function should be evaluated promptly. Myelosuppression, or bone marrow suppression, has also been documented in patients taking allopurinol.

Furthermore, patients may experience drowsiness, somnolence, and dizziness, which could potentially impair their ability to drive or operate machinery safely.

It is important to note that allopurinol is contraindicated in patients with known hypersensitivity to allopurinol or any of its ingredients. Monitoring for these adverse reactions is essential to ensure patient safety and effective management during treatment.

Drug Interactions

There are currently no documented drug interactions associated with this medication. Additionally, there are no known interactions with laboratory tests. As such, no specific recommendations for dosage adjustments or monitoring are necessary at this time.

Packaging & NDC

The table below lists all NDC Code configurations of Allopurinol, the U.S. brand-name prescription product. Columns show Packaging, Formulation Type, and Active Ingredient Strength.

Pediatric Use

The safety and effectiveness of allopurinol have been established in approximately 200 pediatric patients with leukemia, lymphoma, and solid tumor malignancies undergoing cancer therapy that leads to elevated serum and urinary uric acid levels. The efficacy and safety profile in this population is comparable to that observed in adults.

However, the use of allopurinol tablets for the treatment of signs and symptoms of primary or secondary gout in pediatric patients has not been established. Additionally, its safety and effectiveness have not been determined for managing recurrent calcium oxalate calculi or in pediatric patients with rare inborn errors of purine metabolism.

Geriatric Use

Elderly patients often present with impaired kidney function, which is a common consideration when prescribing allopurinol. Dosage adjustments are necessary for this population to ensure safety and efficacy. For patients with renal impairment, the initial dosage of allopurinol should be 50 mg orally daily, with titration based on individual kidney function.

In patients with gout and varying degrees of renal impairment, the recommended initial dosages are as follows: for those with an estimated glomerular filtration rate (eGFR) greater than 60 mL/minute, no dosage modification is required. For patients with an eGFR between 30 to 60 mL/minute, the initial dosage is 50 mg daily. For those with an eGFR between 15 to 30 mL/minute, the dosage should be adjusted to 50 mg every other day. In cases where the eGFR is between 5 to 15 mL/minute, the dosage should be further reduced to 50 mg twice weekly, and for patients with an eGFR less than 5 mL/minute, the recommended dosage is 50 mg once weekly.

Due to the prevalence of decreased kidney function in elderly patients, careful monitoring of renal function is essential to avoid potential toxicity. Allopurinol has been associated with nephrotoxicity, particularly in individuals with pre-existing kidney disease, which is more common in the geriatric population. Additionally, the risk of serious skin reactions, including hypersensitivity, may be heightened in elderly patients, especially those with compromised kidney function.

Elderly patients may also exhibit increased sensitivity to side effects such as drowsiness, somnolence, and dizziness, which can impair their ability to drive or operate machinery safely. Therefore, it is recommended that kidney function be monitored frequently during the early stages of allopurinol administration in elderly patients to prevent acute kidney injury and ensure appropriate dosage adjustments are made as needed.

Pregnancy

Based on findings in animal studies, allopurinol tablets may pose a risk of fetal harm when administered to pregnant women. Adverse developmental outcomes have been observed in animal models exposed to allopurinol. The drug and its metabolite, oxypurinol, have been shown to cross the placenta following maternal administration.

Limited published data on allopurinol use in pregnant women do not indicate a clear pattern or an increased frequency of adverse developmental outcomes. Among approximately 50 pregnancies documented in the literature, two infants with major congenital malformations were reported following maternal exposure to allopurinol. Therefore, healthcare professionals should advise pregnant women of the potential risks to the fetus.

It is important to note that all pregnancies carry a background risk of birth defects, loss, or other adverse outcomes. The background risk of major birth defects and miscarriage for the population using allopurinol is not well defined. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is approximately 2% to 4% and 15% to 20%, respectively.

Experience with allopurinol during human pregnancy has been limited, as women of reproductive age rarely require treatment with this medication. A case report from 2011 described a full-term pregnancy in a 35-year-old woman with a history of recurrent kidney stones who was treated with allopurinol throughout her pregnancy. The child was born with multiple complex birth defects and died at 8 days of life. A subsequent report in 2013 detailed 31 prospectively ascertained pregnancies involving mothers exposed to allopurinol for varying durations during the first trimester. The overall rate of major fetal malformations and spontaneous abortions was reported to be within the normal expected range; however, one child exhibited severe malformations similar to those noted in the earlier case report.

Animal studies have shown no evidence of fetotoxicity or teratogenicity in rats or rabbits treated with oral allopurinol during the organogenesis period at doses up to 200 mg/kg/day and 100 mg/kg/day, respectively, which is approximately 2.4 times the human dose on a mg/m² basis. However, a study in pregnant mice indicated that single intraperitoneal doses of 50 mg/kg or 100 mg/kg (approximately 0.3 or 0.6 times the human dose on a mg/m² basis) administered on gestation days 10 or 13 resulted in significant increases in fetal deaths and teratogenic effects, including cleft palate, harelip, and digital defects. It remains uncertain whether these findings were due to direct fetal effects or secondary to maternal toxicity.

Lactation

There is no specific information available regarding the use of this medication in nursing mothers. Additionally, there is no data on the potential for excretion of this medication in breast milk or its effects on breastfed infants. Healthcare professionals should consider the lack of information when advising lactating mothers about the use of this medication.

Renal Impairment

Patients with renal impairment may experience alterations in kidney function due to allopurinol. It is essential to consider that individuals with decreased kidney function require lower doses of allopurinol tablets to mitigate the risk of adverse effects and ensure therapeutic efficacy. Monitoring of renal function is recommended in this patient population to guide appropriate dosing adjustments.

Hepatic Impairment

Patients with hepatic impairment may experience reversible hepatotoxicity. In the event that signs and symptoms of hepatotoxicity develop, it is essential to evaluate liver function promptly. Monitoring of liver function tests should be conducted to assess the extent of any hepatic compromise. Based on the evaluation, appropriate clinical decisions should be made regarding the continuation or modification of therapy in these patients.

Overdosage

In the event of an overdosage of allopurinol tablets, it is important to note that there is no specific antidote available. Healthcare professionals should be aware that both allopurinol and its active metabolite, oxipurinol, are dialyzable. However, the efficacy of hemodialysis or peritoneal dialysis in the management of an allopurinol overdose remains uncertain.

Given the lack of a specific antidote, the focus should be on supportive care and symptomatic management. Monitoring of the patient’s clinical status is essential, and appropriate interventions should be initiated based on the symptoms presented. Healthcare providers are advised to consider the potential need for renal function assessment, as impaired renal function may exacerbate the effects of an overdose.

In summary, while dialysis may be an option due to the dialyzability of the compounds, the overall management strategy should prioritize supportive care and close monitoring of the patient’s condition.

Nonclinical Toxicology

No evidence of tumorigenicity was observed in male or female mice or rats that received oral allopurinol for the majority of their life spans (greater than 88 weeks) at doses up to 20 mg/kg/day, which corresponds to 0.1 and 0.2 times the maximum recommended human dose (MRHD) on a mg/m² basis in mice and rats, respectively.

Allopurinol tested negative in several genotoxicity assays, including the in vitro Ames assay, the in vitro mouse lymphoma assay, and the in vivo rat bone marrow micronucleus assay. Additionally, allopurinol administered intravenously to rats at a dose of 50 mg/kg was not incorporated into rapidly replicating intestinal DNA. No evidence of clastogenicity was observed in lymphocytes taken from patients treated with allopurinol for a mean duration of 40 months, nor in an in vitro assay with human lymphocytes.

Allopurinol oral doses of 20 mg/kg/day had no effect on male or female fertility in rats or rabbits, which corresponds to approximately 0.2 or 0.5 times the MRHD on a mg/m² basis, respectively.

Postmarketing Experience

Serious and sometimes fatal dermatologic reactions have been reported in patients taking allopurinol tablets. Gout flares may occur during the initiation of treatment, even when serum uric acid levels are normal. Allopurinol tablets have been associated with potential effects on kidney function; therefore, patients are advised to increase fluid intake during therapy to help prevent kidney stones.

There is a noted risk of hepatotoxicity with allopurinol tablets, and patients should be vigilant for signs and symptoms of liver failure, including jaundice, pruritus, bleeding, bruising, or anorexia. Myelosuppression is also a risk, and patients are encouraged to report any signs and symptoms of infection, fever, bleeding, shortness of breath, or significant fatigue.

Additionally, drowsiness, somnolence, and dizziness have been reported in patients taking allopurinol tablets, which may be additive to the effects of alcohol and other central nervous system depressants. The use of allopurinol tablets in conjunction with certain medications, including dicumarol, warfarin, sulfinpyrazone, mercaptopurine, azathioprine, ampicillin, amoxicillin, pegloticase, theophylline, and thiazide diuretics, may increase the risk of adverse effects.

Patient Counseling

Healthcare providers should advise patients to take allopurinol tablets after meals to minimize gastric irritation. In the event that a single dose is occasionally forgotten, patients should be informed that there is no need to double the dose at the next scheduled time.

It is important to inform patients that allopurinol tablets may increase the risk of serious and potentially fatal dermatologic reactions. Patients should be instructed to discontinue the medication and seek medical attention immediately at the first sign of a skin rash, blisters, fever, painful urination, blood in the urine, irritation of the eyes, swelling of the lips or mouth, or any other signs and symptoms of hypersensitivity reactions.

Patients should also be made aware that gout flares may occur during the initiation of treatment with allopurinol tablets, even if their serum uric acid levels are normal. The concurrent use of additional medications such as colchicine or other anti-inflammatory agents can help prevent gout flares. Patients should be advised to continue treatment with both allopurinol tablets and any prophylactic therapy as prescribed, even if gout flares occur. Reassurance should be provided that it may take several months to achieve control of the flares, but they typically become shorter and less severe over time.

Additionally, patients should be informed that allopurinol tablets may affect kidney function. They should be advised to increase their fluid intake during therapy, aiming for at least 2 liters of liquids per day, to stay well hydrated and help prevent kidney stones.

Patients should be made aware of the risk of hepatotoxicity associated with allopurinol. They should report any signs and symptoms of liver failure, including jaundice, pruritus, bleeding, bruising, or anorexia, to their healthcare provider.

The risk of myelosuppression should also be communicated to patients, who should report any signs and symptoms of infection, fever, bleeding, shortness of breath, or significant fatigue to their healthcare provider.

Patients should be informed that drowsiness, somnolence, and dizziness have been reported in individuals taking allopurinol tablets. They should be cautioned that the central nervous system depressant effects of allopurinol may be additive to those of alcohol and other CNS depressants. Patients should be advised to avoid operating automobiles or other dangerous machinery and engaging in activities that may be hazardous due to decreased alertness when starting allopurinol tablets or increasing the dose, until they understand how the medication affects them.

Healthcare providers should inform patients of the risks of adverse effects when allopurinol tablets are used in conjunction with certain medications, including dicumarol, warfarin, sulfinpyrazone, mercaptopurine, azathioprine, ampicillin, amoxicillin, pegloticase, theophylline, and thiazide diuretics. Patients should be encouraged to disclose all medications they are currently using and to follow their physician's instructions.

Pregnant women should be advised of the potential risks to a fetus and should notify their healthcare provider if they become pregnant or intend to become pregnant during treatment with allopurinol tablets. Furthermore, women should be advised not to breastfeed during treatment with allopurinol tablets and for one week after the last dose.

Storage and Handling

The product is supplied in a tight container as defined by the United States Pharmacopeia (USP). It should be stored at a temperature range of 20°C to 25°C (68°F to 77°F) in a dry place to maintain its integrity and efficacy. Proper storage conditions are essential to ensure the product remains within the specified parameters.

Additional Clinical Information

Patients initiating treatment with allopurinol tablets should be screened for the HLA-B5801 allele, particularly in populations with a high prevalence of this genetic marker. Screening is not recommended for patients from populations with low prevalence or for current allopurinol users, as the risk of serious skin reactions such as Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), or drug reaction with eosinophilia and systemic symptoms (DRESS) is primarily associated with the initial months of therapy, independent of HLA-B5801 status.

Clinicians should counsel patients to discontinue allopurinol tablets immediately if a skin rash develops and to seek medical attention promptly. Patients are advised to continue taking allopurinol tablets and any prophylactic treatments even during gout flares, as it may take time to achieve effective control. Maintaining adequate fluid intake to ensure a urinary output of at least 2 liters per day is essential to prevent xanthine calculi formation and renal precipitation of urates, especially in those on concomitant uricosuric agents. Additionally, patients should be informed about the potential additive central nervous system depressant effects of allopurinol tablets with alcohol and other CNS depressants, and they should avoid operating vehicles or engaging in hazardous activities until they understand how the medication affects their alertness.

FDA Insert (PDF)

This document is the official FDA-approved prescribing information for Allopurinol as submitted by Heritage Pharmaceuticals Inc. d/b/a Avet Pharmaceuticals Inc.. It includes detailed information about indications, dosage, contraindications, warnings, and clinical pharmacology.

View full prescribing information (PDF)