Allopurinol

Description

Allopurinol is a xanthine oxidase inhibitor, chemically designated as 1,5-dihydro-4H-pyrazolo 3,4-d pyrimidin-4-one, with a molecular weight of 136.11 g/mol. This compound is administered orally and exhibits a solubility in water of 80.0 mg/dL at 37°C, with increased solubility in alkaline solutions. Each tablet for oral administration contains either 100 mg, 200 mg, or 300 mg of allopurinol, USP, along with inactive ingredients that include croscarmellose sodium, colloidal silicon dioxide, lactose monohydrate, magnesium stearate, pregelatinized starch, povidone, and FD&C Yellow No. 6 aluminum Lake (present only in the 300 mg formulation).

Uses and Indications

Allopurinol tablet is 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, it is indicated for both adult and pediatric patients with leukemia, lymphoma, and solid tumor malignancies who are undergoing cancer therapy that results in elevated serum and urinary uric acid levels.

This medication is also indicated for adult 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, despite implementation of lifestyle changes.

Allopurinol tablet is not recommended 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. For 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.

In the case of hyperuricemia associated with cancer therapy, adult patients may be prescribed a dosage range of 300 mg to 800 mg orally daily. For pediatric patients, the recommended dosage is 100 mg/m² orally every 8 to 12 hours, not exceeding a maximum of 800 mg per day (10 mg/kg/day).

For the prevention 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 for specific dosage modifications.

Contraindications

Use of allopurinol is contraindicated in patients with known hypersensitivity to allopurinol or to any of its ingredients. This contraindication is essential to prevent severe 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 be discontinued immediately at the first sign of a skin rash or any other indication of a hypersensitivity reaction.

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

Nephrotoxicity Allopurinol can impact kidney function. Patients with impaired renal function may require dosage adjustments to avoid further complications. Regular monitoring of renal function is advised for these patients.

Hepatotoxicity There have been reports of reversible hepatotoxicity associated with allopurinol use. Should any signs or symptoms indicative of liver dysfunction arise, it is essential to evaluate liver function promptly.

Myelosuppression Bone marrow suppression has been documented in patients receiving allopurinol. Clinicians should remain vigilant for signs of myelosuppression and consider appropriate monitoring.

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.

In summary, healthcare professionals should closely monitor patients for these potential adverse effects and adjust treatment as necessary to ensure safe and effective use of allopurinol.

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, with an incidence greater than 1%.

Serious adverse reactions associated with allopurinol include skin rash and hypersensitivity, which can lead to serious and sometimes fatal dermatological reactions. It is crucial to discontinue allopurinol 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 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 signs and symptoms of hepatotoxicity develop, 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 affect 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.

Drug Interactions

The concomitant use of certain medications may increase the risk of serious skin reactions. Specifically, the following drugs have been identified: bendamustine, thiazide diuretics, ampicillin, and amoxicillin. It is advisable to monitor patients closely for any signs of skin reactions when these agents are used in conjunction.

Capecitabine should be avoided in patients receiving this treatment due to the potential for adverse interactions.

For patients taking mercaptopurine or azathioprine, it is recommended to reduce the dosage of these medications as outlined in their respective prescribing information to mitigate the risk of toxicity.

In the case of pegloticase, it is essential to discontinue and avoid initiating treatment with allopurinol, as this combination may lead to significant complications.

For a comprehensive overview of significant drug interactions, please refer to the full prescribing information (FPI).

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

However, the safety and effectiveness of allopurinol have not been established for the treatment of signs and symptoms of primary or secondary gout in pediatric patients. Additionally, its use has not been validated for managing recurrent calcium oxalate calculi in this demographic. Furthermore, allopurinol's safety and effectiveness remain unestablished in pediatric patients with rare inborn errors of purine metabolism.

Geriatric Use

Elderly patients may require special consideration when initiating treatment with allopurinol, particularly those aged 65 and older or those with renal impairment. For these patients, the initial dosage should be 50 mg orally daily, with careful monitoring and gradual dose increases of 50 mg/day every 2 to 4 weeks until the target serum uric acid level is achieved. This approach is essential to minimize the risk of serious adverse reactions associated with the medication.

Close monitoring of kidney function is crucial for geriatric patients with chronic kidney disease when starting allopurinol. If there are any persistent abnormalities in kidney function, it may be necessary to decrease the dosage or discontinue the medication altogether. Additionally, patients with a history of kidney disease or kidney stones are at an increased risk for worsening kidney function or acute kidney injury due to the potential formation of xanthine calculi while on allopurinol.

The presence of the HLA-B5801 allele, which is associated with an increased risk of allopurinol-related hypersensitivity reactions such as Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) and Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis (SJS/TEN), should also be considered. The frequency of this allele varies among populations, with rates of 8% to 10% in Han Chinese, approximately 8% in Thai, and about 6% in Korean populations. Allopurinol is not recommended for patients who test positive for the HLA-B5801 allele unless the potential benefits clearly outweigh the risks.

Elderly patients should be advised to increase their fluid intake during therapy, aiming for at least 2 liters of liquids per day, to help prevent the formation of kidney stones. Furthermore, allopurinol should be permanently discontinued at the first sign of a skin rash or any other indication of a hypersensitivity reaction.

Pregnancy

Based on findings in animal studies, allopurinol may cause fetal harm when administered to pregnant patients. Adverse developmental outcomes have been observed in exposed animals, and both allopurinol 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 demonstrate a clear pattern or increase in the frequency of adverse developmental outcomes. Among approximately 50 pregnancies described in the literature, two infants with major congenital malformations have been reported following maternal exposure to allopurinol. Therefore, healthcare professionals should advise pregnant women of the potential risks to the fetus.

All pregnancies carry a background risk of birth defects, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 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 published in 2011 described the outcome of a full-term pregnancy in a 35-year-old woman with a history of recurrent kidney stones who took 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 provided data on 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 had severe malformations similar to those described 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 period of organogenesis 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 published report 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 represent a direct fetal effect or an effect secondary to maternal toxicity.

Lactation

There is no specific information available regarding the use of this medication in nursing mothers or its effects on lactation. Additionally, no data are provided concerning the excretion of this medication in breast milk or its potential 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 nephrotoxicity associated with allopurinol. It is essential to consider that individuals with reduced kidney function require lower doses of allopurinol to mitigate the risk of adverse effects. Careful monitoring of renal function is recommended in this population to ensure appropriate dosing and to prevent potential complications.

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 impairment and to guide further management. Adjustments to dosing or treatment may be necessary based on the results of these evaluations.

Overdosage

In the event of an allopurinol overdosage, 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 treatment of allopurinol overdose remains uncertain.

Management of an overdose should focus on supportive care and symptomatic treatment. Continuous monitoring of the patient’s clinical status is essential, and appropriate interventions should be implemented based on the symptoms presented. Given the lack of a specific antidote, healthcare providers should remain vigilant for any signs of toxicity and manage them accordingly.

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, with a mean duration of treatment of 40 months, nor in an in vitro assay with human lymphocytes.

Oral doses of allopurinol at 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

Postmarketing experience has identified serious and, in some cases, fatal dermatologic reactions associated with allopurinol tablets. Patients are advised to discontinue the medication and seek immediate medical attention 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 other signs and symptoms indicative of hypersensitivity reactions.

There is a recognized risk of nephrotoxicity with allopurinol tablets; therefore, patients are encouraged to increase fluid intake during therapy to help prevent kidney stones. Additionally, hepatotoxicity has been reported, prompting patients to report any signs and symptoms of liver failure, such as jaundice, pruritus, bleeding, bruising, or anorexia.

Myelosuppression is another potential risk associated with allopurinol, and patients should be vigilant for signs and symptoms of infection, fever, bleeding, shortness of breath, or significant fatigue. Central nervous system effects, including drowsiness, somnolence, and dizziness, have also been reported. These effects may be additive when allopurinol is used in conjunction with alcohol or other central nervous system depressants.

Furthermore, there are risks of adverse effects when allopurinol tablets are co-administered with certain medications, including dicumarol, warfarin, sulfinpyrazone, mercaptopurine, azathioprine, ampicillin, amoxicillin, pegloticase, theophylline, and thiazide diuretics.

Patient Counseling

Patients should be advised to take allopurinol tablets after meals to minimize gastric irritation. In the event that a single dose is occasionally forgotten, 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, 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 these flares. Patients should be advised to continue treatment with both allopurinol and the prophylactic therapy as prescribed, even if gout flares occur. It is important to reassure them that it may take several months to achieve control of the flares, but typically, the flares 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, such as jaundice, pruritus, bleeding, bruising, or anorexia, to their healthcare provider.

There is also a risk of myelosuppression with allopurinol. Patients should be advised to 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. The central nervous system depressant effects of allopurinol may be additive to those of alcohol and other CNS depressants. Therefore, 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 or increasing the dose, until they understand how the medication affects them.

Finally, patients should be informed of the risks of adverse effects when allopurinol is 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 closely.

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 handling and storage conditions are essential to ensure the product remains within the specified parameters.

Additional Clinical Information

Clinicians should consider screening for HLA-B*5801 prior to initiating allopurinol treatment in patients from populations with a high prevalence of this allele. Frequent monitoring of kidney function is recommended during the early stages of allopurinol administration for patients managing gout or recurrent calcium oxalate calculi, and daily monitoring is advised for those receiving allopurinol for tumor lysis syndrome. Additionally, liver enzymes should be monitored periodically in patients with pre-existing liver conditions.

Patient counseling should emphasize the importance of discontinuing allopurinol and seeking immediate medical attention if a rash develops. Patients should be informed that it may take several months to achieve control of gout flares and that they should continue allopurinol and any prophylactic treatments during this time. It is also important to advise patients about the potential additive central nervous system depressant effects of allopurinol with alcohol and other CNS depressants, and to caution them against operating vehicles or engaging in hazardous activities until they are aware of how the medication affects their alertness.

FDA Insert (PDF)

This document is the official FDA-approved prescribing information for Allopurinol as submitted by Zydus Lifesciences Limited. It includes detailed information about indications, dosage, contraindications, warnings, and clinical pharmacology.

View full prescribing information (PDF)