2.1 Recommended Dosage

Initiate therapy with allopurinol for injection 24 to 48 hours before the start of chemotherapy known to cause tumor cell lysis. Additionally, administer fluids sufficient to yield a daily urinary output of at least two liters in adults with a neutral or, preferably, slightly alkaline urine.

The recommended daily dose of allopurinol for injection is shown in Table 1. Administer the daily dose as single infusion or in equally divided infusions at 6-, 8-, or 12-hour intervals at a rate appropriate for the volume of infusate.

Table 1: Recommended Daily Dose of Allopurinol for Injection

The dosage of allopurinol for injection to lower serum uric acid to normal or near-normal varies with the severity of the disease. Monitor serum uric acid levels at least daily and administer allopurinol for injection at a dose and frequency to maintain the serum uric acid within the normal range. Discontinue allopurinol for injection when the patient is able to take oral therapy or when the risk of tumor lysis has abated.

2.2 Dosage Modifications in Patients with Renal Impairment

Reduce the dose of allopurinol for injection in patients with impaired renal function [see Use in Specific Populations (8.6) and Clinical Pharmacology (12.3)]. The recommended dosage reductions of allopurinol for injection in adult patients with renal impairment are shown in Table 2.

Table 2: Recommended Daily Dose of Allopurinol for Injection in Adult Patients with Renal Impairment

Treatment with allopurinol for injection has not been studied in pediatric patients with severe renal impairment or on dialysis. For pediatric patients with severe renal impairment or on dialysis, consider the risks and potential benefits before initiating treatment with allopurinol for injection [see Warnings and Precautions (5.2) and Use in Specific Populations (8.6)].

2.3 Preparation Instructions

Reconstitute and further dilute allopurinol for injection prior to intravenous infusion.

Reconstitution

• Reconstitute each vial of allopurinol for injection with 25 mL of Sterile Water for Injection, USP to obtain a concentration of 20 mg/mL of allopurinol.
• Inspect the reconstituted solution for discoloration and particulate matter. The reconstituted solution should appear as a clear, almost colorless solution with no more than a slight opalescence. Do not use if the reconstituted solution contains particulate matter or discoloration is present.

Dilution

• Dilute with 0.9% Sodium Chloride Injection, USP or 5% Dextrose for Injection, USP to obtain a final concentration of less than 6 mg/mL.
• Inspect the diluted solution for particulate matter or discoloration and discard if present.
• If not used immediately, the diluted allopurinol for injection solution can be stored at 20° to 25°C (68° to 77°F) for up to 10 hours after initial reconstitution. The storage includes time for infusion. Do not refrigerate the reconstituted and/or diluted product.
• If stored, the administration should be completed within 10 hours after reconstitution.
• Discard unused portion.

2.4 Administration Instructions

Do not mix allopurinol for injection with or administer it through the same intravenous port as agents which are incompatible in solution with allopurinol for injection. The following table lists drugs that are known to be physically incompatible in solution with allopurinol for injection.

Table 3: Drugs That Are Physically Incompatible in Solution with Allopurinol for Injection

5.1 Skin Rash and Hypersensitivity

Serious and sometimes fatal dermatologic reactions, including toxic epidermal necrolysis (TEN), Stevens-Johnson syndrome (SJS), and drug reaction with eosinophilia and systemic symptoms (DRESS) have been reported in patients taking allopurinol [see Adverse Reactions (6.1)]. These reactions occur in approximately 5 in 10,000 (0.05%) patients taking allopurinol. Other serious hypersensitivity reactions that have been reported include exfoliative, urticarial and purpuric lesions; generalized vasculitis; and irreversible hepatotoxicity. Discontinue allopurinol at the first appearance of skin rash or other signs which may indicate a hypersensitivity reaction.

The HLA-B*58:01 allele is a genetic marker for severe skin reactions indicative of hypersensitivity to allopurinol. Patients who carry the HLA-B*58:01 allele are at a higher risk of allopurinol hypersensitivity syndrome (AHS), but hypersensitivity reactions have been reported in patients who do not carry this allele. The frequency of this allele is higher in individuals of African, Asian (e.g., Han Chinese, Korean, Thai), and Native Hawaiian/Pacific Islander ancestry [see Clinical Pharmacology (12.5)]. The use of allopurinol is not recommended in HLA-B*58:01 positive patients unless the benefits clearly outweigh the risks.

Prior to starting allopurinol, consider testing for the HLA-B*58:01 allele in genetically at-risk populations. Screening is generally not recommended in patients from populations in which the prevalence of HLA-B*58:01 is low, or in current allopurinol users, as the risk of SJS/TEN/DRESS is largely confined to the first few months of therapy, regardless of HLA-B*58:01 status.

Hypersensitivity reactions to allopurinol may be increased in patients with decreased renal function receiving thiazide diuretics and allopurinol concurrently. In addition, concomitant use of the following drugs may increase the risk of skin rash, which may be severe: bendamustine, thiazide diuretics, ampicillin and amoxicillin [see Drug Interactions (7.1)]. Patients should stop allopurinol and seek medical attention if they develop a rash.

5.2 Renal Function Impairment

Treatment with allopurinol may result in renal impairment due to formation of xanthine calculi or due to precipitation of urates in patients receiving concomitant uricosuric agents. Patients with pre-existing renal disease, including renal impairment or history of kidney stones, may be at increased risk for worsening renal impairment due to xanthine calculi or precipitation of urates while receiving treatment with allopurinol.

Monitor serum creatinine at least daily during the early stages of allopurinol administration. Maintain fluid intake sufficient to yield a urinary output of at least 2 liters per day in adults. In patients with severely impaired renal function or increase in uric acid concentration associated with decreased urate clearance, reduce the dosage of allopurinol [see Use in Specific Populations (8.6) and Dosage and Administration (2.1, 2.2)].

5.3 Hepatotoxicity

Cases of reversible clinical hepatotoxicity have been noted in patients taking oral allopurinol. 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, evaluate liver enzymes. In patients with pre-existing liver disease, monitor liver enzymes periodically during the early stages of therapy. Discontinue allopurinol in patients with elevated liver enzymes.

5.4 Myelosuppression

Myelosuppression, manifested by anemia, leukopenia or thrombocytopenia, has been reported in patients receiving allopurinol [see Adverse Reactions (6.1)]. The cytopenias have occurred from as early as 6 weeks to as late as 6 years after the initiation of allopurinol therapy. Discontinue use of allopurinol in patients with unexplained cytopenias. Concomitant use with allopurinol with cytotoxic drugs associated with myelosuppression may increase the risk of myelosuppression. Monitor blood counts more frequently [see Drug Interactions (7)].

Concomitant use with allopurinol increases the exposure of either mercaptopurine or azathioprine which may increase the risk of myelosuppression. Reduce the dosage of mercaptopurine or azathioprine as recommended in the respective prescribing information when used concomitantly with allopurinol [see Drug Interactions (7)].

5.5 Drowsiness

Drowsiness has been reported in patients taking allopurinol [see Adverse Reactions (6.1)]. Advise patients to avoid operation of automobiles or other dangerous machinery and activities made hazardous by decreased alertness when starting allopurinol or increasing the dose until they know how the drug affects them. Advise patients that the central nervous system depressant effects of allopurinol may be additive to those of alcohol and other CNS depressants.

6.1 Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The safety of allopurinol was evaluated in an uncontrolled compassionate use study of 1,378 patients with advanced malignancies requiring treatment with cytotoxic chemotherapy and in patients with other serious conditions.

Adverse reactions were reported in 9% (125/1378) of the patients treated with allopurinol. The most common adverse reaction was skin rash. Two patients experience serious adverse reactions (decreased renal function and generalized seizure) and one patient experienced severe diarrhea. Approximately 1.1% of patients experienced allergic adverse reactions (including rash, eosinophilia, local injection site reaction).

A listing of the adverse reactions reported from clinical trials follows:

Incidence Greater Than 1%:
Cutaneous/Dermatologic: rash (1.5%)

Genitourinary: renal failure/insufficiency (1.2%)

Gastrointestinal: nausea (1.3%), vomiting (1.2%)

Incidence Less Than 1%:
Body as a Whole: fever, pain, chills, alopecia, infection, sepsis, enlarged abdomen, mucositis/pharyngitis, blast crisis, cellulitis, hypervolemia

Cardiovascular: heart failure, cardiorespiratory arrest, hypertension, pulmonary embolus, hypotension, decreased venous pressure, flushing, headache, stroke, septic shock, cardiovascular disorder, ECG abnormality, hemorrhage, bradycardia, thrombophlebitis, ventricular fibrillation 

Cutaneous/Dermatologic: urticaria, pruritus, local injection site reaction

Gastrointestinal: diarrhea, gastrointestinal bleeding, hyperbilirubinemia, splenomegaly, hepatomegaly, intestinal obstruction, jaundice, flatulence, constipation, liver failure, proctitis

Genitourinary: hematuria, increased creatinine, oliguria, kidney function abnormality, urinary tract infection

Hematologic: leukopenia, marrow aplasia, thrombocytopenia, eosinophilia, neutropenia, anemia, pancytopenia, ecchymosis, bone marrow suppression, disseminated intravascular coagulation

Metabolic: hypocalcemia, hyperphosphatemia, hypokalemia, hyperuricemia, electrolyte abnormality, hypercalcemia, hyperglycemia, hypernatremia, hyponatremia, metabolic acidosis, edema, glycosuria, hyperkalemia, lactic acidosis, water intoxication, hypomagnesemia

Neurologic: seizure, status epilepticus, myoclonus, twitching, agitation, mental status changes, cerebral infarction, coma, dystonia, paralysis, tremor

Pulmonary: respiratory failure/insufficiency, ARDS, increased respiration rate, apnea 

Musculoskeletal: arthralgia

Other: hypotonia, diaphoresis, tumor lysis syndrome

7.1 Drugs Known to Affect the Occurrence of Skin Rash and Hypersensitivity

Concomitant use of the following drugs may increase the risk of skin rash, which may be severe: bendamustine, thiazide diuretics, ampicillin and amoxicillin. Renal impairment may further increase risk with concomitant use of thiazide diuretics [see Warnings and Precautions (5.1) (5.2) and Clinical Pharmacology (12.2)].

Monitor renal function and reduce the dose of allopurinol in patients with concomitant thiazide diuretic use and impaired renal function [see Dosage and Administration (2.2)].

Discontinue allopurinol at the first appearance of skin rash or other signs which may indicate a hypersensitivity reaction when use concomitantly with these drugs.

7.2 Other Drugs Known to Have Clinically Important Drug Interactions with Allopurinol

Table 4: Interventions for Clinically Important Drug Interactions with Allopurinol

8.1 Pregnancy

Risk Summary

Based on findings in animals, allopurinol may cause fetal harm when administered to a pregnant woman. Adverse developmental outcomes have been described in exposed animals (see Data). Allopurinol and its metabolite oxypurinol have been shown to cross the placenta following administration of maternal allopurinol.

Available limited published data on allopurinol use in pregnant women do not demonstrate a clear pattern or increase in frequency of adverse developmental outcomes. Among approximately 50 pregnancies described in published literature, 2 infants with major congenital malformations have been reported with following maternal allopurinol exposure. Advise pregnant women of the potential risk to a fetus.

All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. 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.

Data

Animal Data

There was no evidence of fetotoxicity or teratogenicity in rats or rabbits treated during the period of organogenesis with oral allopurinol at doses up to 200 mg/kg/day and up to 100 mg/kg/day, respectively (about three times the human dose on a mg/m2 basis). However, there is a published
report in pregnant mice that single intraperitoneal doses of 50 or 100 mg/kg (about 1/3 or 3/4 the human dose on a mg/m2 basis) of allopurinol on gestation days 10 or 13 produced significant increases in fetal deaths and teratogenic effects (cleft palate, harelip, and digital defects). It is uncertain whether these findings represented a fetal effect or an effect secondary to maternal toxicity. In another published study with no reported maternal toxicity, allopurinol administered orally at 15 or 45 mg/kg to pregnant rats during organogenesis caused embryonic resorptions, growth retardation, decreased fetal weight, and skeletal, liver, kidney, and brain abnormalities. In rats, maternal treatment with allopurinol in normoxic pregnancy has been shown to increase the cardiac protein levels of sarcoplasmic/endoplasmic reticulum calcium ATPase 2 (SERCA2a) in the adult male offspring. The mechanism underlying this effect is not understood. However, this effect was not matched by an increase in left ventricular end diastolic pressure or sympathetic dominance in hearts of adult male offspring of normoxic pregnancy treated with allopurinol.

8.2 Lactation

Risk Summary

Allopurinol and oxypurinol are present in human milk. Based on information from a single case report, allopurinol and its active metabolite, oxypurinol, were detected in the milk of a mother at five weeks postpartum at an estimated relative infant dose of 0.14 and 0.2 mg/kg of allopurinol and between 7.2 to 8 mg/kg of oxypurinol daily. There was no report of effects of allopurinol on the breastfed infant or on milk production. Because of the potential for serious adverse reactions in a breastfed child, advise women not to breastfeed during treatments with allopurinol and for one week after the last dose.

8.4 Pediatric Use

The safety and effectiveness of allopurinol have been established in approximately 200 pediatric patients. The efficacy and safety profile observed in this patient population were similar to that observed in adults.

8.5 Geriatric Use

Clinical studies of allopurinol did not include sufficient numbers of patients 65 years and older to determine whether they respond differently than younger patients.

8.6 Renal Impairment

Allopurinol and its primary active metabolite, oxypurinol, are eliminated by the kidneys [see Clinical Pharmacology (12.3)]. Therefore, changes in renal function will likely increase allopurinal and oxypurinol exposure. In patients with decreased renal function, or who have concurrent illnesses that can affect renal function such as hypertension and diabetes mellitus, perform periodic laboratory parameters of renal function, particularly BUN and serum creatinine or creatinine clearance, should be performed.

In patients with severely impaired renal function or decreased urate clearance, the half-life of oxypurinol in the plasma is greatly prolonged. Reduce the dose of allopurinol in patients with creatinine clearance ≤ 20 mL/min [see Dosage and Administration (2.2)]. Patients should be treated with the lowest effective dose, in order to minimize possible side effects.

12.1 Mechanism of Action

Allopurinol is a structural analogue of the natural purine base, hypoxanthine. Allopurinol and its oxypurinol metabolite inhibitor 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 humans. Allopurinol does not disrupt the biosynthesis of purines.

The action of oral allopurinol differs from that of uricosuric agents, which lower the serum uric acid level by increasing 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.

12.2 Pharmacodynamics

Allopurinol reduces the production of uric acid by inhibiting the biochemical reactions immediately preceding its formation in a dose dependent manner. The pharmacological action of allopurinol is generally believed to be mediated by its oxypurinol metabolite. 

Effect on Hypoxanthine and Xanthine

Reutilization of both hypoxanthine and xanthine for nucleotide and nucleic acid synthesis is markedly enhanced when their oxidations are inhibited by allopurinol and oxypurinol. This reutilization does not disrupt normal nucleic acid anabolism 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 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 allopurinol. These values are far below the saturation levels, at which point their precipitation would be expected to occur (above 7 mg/dL). The increased xanthine and hypoxanthine in the urine in patients who were treated with oral allopurinol have not been accompanied by problems of nephrolithiasis; however, there are isolated case reports of xanthine crystalluria.

Drug Interaction Studies

Fluorouracil: Based on non-clinical data, allopurinol may decrease anti-tumor activity due to suppression of phosphorylation of 5-fluorouracil.

Pegloticase: Concomitant use of allopurinol and pegloticase may potentially blunt the rise of serum uric acid levels required for monitoring the safe use of pegloticase.

Cytotoxic Agents: Enhanced bone marrow suppression by cyclophosphamide and other cytotoxic agents has been reported among patients with neoplastic disease, except leukemia, in the presence of allopurinol.

Thiazide Diuretics: Reports that the concomitant administration of allopurinol and thiazide diuretics contributed to increased allopurinol toxicity were reviewed; however, a causal mechanism or cause-and-effect relationship was not found.

12.3 Pharmacokinetics

Following single 100 mg and 300 mg intravenous and oral administration of allopurinol, the relative intravenous Cmax was approximately 3-fold and 3.8-fold and AUC0-inf was approximately 1.9-fold higher for allopurinol at both dosages, respectively. The relative intravenous oxypurinol Cmax and AUC0-inf was approximately 1 compared to oral administration at both dosages.

The Cmax and AUC0-inf for both allopurinol and oxypurinol following intravenous administration of allopurinol were dose proportional in the dose range of 100 to 300 mg.

Distribution

The steady-state allopurinol volume of distribution (mean ± S.D.) is approximately 0.87 ± 0.13 L/Kg following intravenous administration.

Elimination

The half-life (mean ± S.D.) of allopurinol and oxypurinol are approximately 1.21 ± 0.33 and 23.5 ± 4.5 hours following intravenous administration, respectively. The net renal clearance of oxypurinol about 30 mL/min.

Metabolism 

Allopurinol is a weak CYP1A2 inhibitor. Allopurinol is rapidly eliminated from the systemic circulation primarily via oxidative metabolism to oxypurinol.

The oxypurinol (alloxanthine) metabolite is also a xanthine oxidase inhibitor and is present in systemic circulation in much higher concentrations and for a much longer period than allopurinol. In general, the ratio of the area under the plasma concentration vs time curve (AUC0-inf) between oxypurinol and allopurinol was in the magnitude of 30 to 40.

Excretion

Approximately 12% of an allopurinol intravenous dose was excreted unchanged, 76% excreted as oxypurinol, and the remaining dose excreted as riboside conjugates in the urine. Oxypurinol was primarily eliminated unchanged in urine by glomerular filtration and tubular reabsorption.

Drug Interaction Studies

Capecitabine: Concomitant use with allopurinol may decrease concentration of capecitabine’s active metabolites, which may decrease capecitabine efficacy.

Cyclosporine: Concomitant use of allopurinol increases cyclosporine concentrations which may increase the risk of adverse reactions.

Mercaptopurine or Azathioprine: Allopurinol inhibits xanthine oxidase mediated metabolism of mercaptopurine and azathioprine. Concomitant use of allopurinol increases the exposure of either mercaptopurine or azathioprine which may increase the risk of their adverse reactions including myelosuppression.

Theophylline: Concomitant use of allopurinol doses greater than or equal to 600 mg/day may decrease the clearance of theophylline.

Uricosuric Agents: Uricosuric agents increase the excretion of the active allopurinol metabolite oxypurinol. Concomitant use with uricosuric agents decreases oxypurinol exposure which may reduce the inhibition of xanthine oxidase by oxypurinol and increases the urinary excretion of
uric acid.

Warfarin: Allopurinol may inhibit the metabolism of warfarin, possibly enhancing its anticoagulant effect.

12.5 Pharmacogenomics

The HLA-B*58:01 allele is a genetic marker for severe skin reactions indicative of hypersensitivity to allopurinol [see Warnings and Precautions (5.1)]. The frequency of the HLA-B*58:01 allele ranges from 8 to 10% in Han Chinese populations, about 8% in Thai populations, and about 6% in Korean populations based upon published literature and available databases. The frequency of the HLA-B*58:01 allele is about 4% in Blacks, about 1 to 2 % in indigenous peoples of the Americas and Hispanic populations, and <1% in people from European descent and Japanese.

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Allopurinol was administered at doses up to 20 mg/kg/day to mice and rats for the majority of their life span. No evidence of carcinogenicity was seen in either mice or rats (at doses about 1/6 or 1/3 the recommended human dose on a mg/m2 basis, respectively).

Allopurinol administered intravenously to rats (50 mg/kg) was not incorporated into rapidly replicating intestinal DNA. No evidence of clastogenicity was observed in an in vivo micronucleus test in rats, or in lymphocytes taken from patients treated with allopurinol (mean duration of treatment 40 months), or 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 (about 1/3 or 1/2 the human dose on a mg/m2 basis, respectively).