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ZYLOPRIM (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, irreversible hepato-toxicity, and, on rare occasions, death.
In patients receiving PURINETHOL® (mercaptopurine) or IMURAN® (azathioprine), the concomitant administration of 300 to 600 mg of ZYLOPRIM (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 ZYLOPRIM (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 ZYLOPRIM (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 ZYLOPRIM (allopurinol) may be increased in patients with decreased renal function receiving thiazides and ZYLOPRIM (allopurinol) concurrently. For this reason, in this clinical setting, such combinations should be administered with caution and patients should be observed closely.
General: An increase in acute attacks of gout has been reported during the early stages of administration of ZYLOPRIM (allopurinol) , even when normal or subnormal serum uric acid levels have been attained. Accordingly, maintenance doses of colchicine generally should be given prophylactically when ZYLOPRIM (allopurinol) is begun. In addition, it is recommended that the patient start with a low dose of ZYLOPRIM (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 maximum recommended dose (800 mg per day). The use of colchicine or anti-inflammatory agents may be required to suppress gouty attacks in some cases. The attacks usually become shorter and less severe after several months of therapy. The mobilization of urates from tissue deposits which cause fluctuations in the serum uric acid levels may be a possible explanation for these episodes. Even with adequate therapy with ZYLOPRIM (allopurinol) , it may require several months to deplete the uric acid pool sufficiently to achieve control of the acute attacks.
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 to (1) avoid the theoretical possibility of formation of xanthine calculi under the influence of therapy with ZYLOPRIM (allopurinol) and (2) help prevent renal precipitation of urates in patients receiving concomitant uricosuric agents.
Some patients with pre-existing renal disease or poor urate clearance have shown a rise in BUN during administration of ZYLOPRIM (allopurinol) . Although the mechanism responsible for this has not been established, patients with impaired renal function should be carefully observed during the early stages of administration of ZYLOPRIM (allopurinol) and the dosage decreased or the drug withdrawn if increased abnormalities in renal function appear and persist.
Renal failure in association with administration of ZYLOPRIM (allopurinol) has been observed among patients with hyperuricemia secondary to neoplastic diseases. Concurrent conditions such as multiple myeloma and congestive myocardial disease were present among those patients whose renal dysfunction increased after ZYLOPRIM (allopurinol) was begun. Renal failure is also frequently associated with gouty nephropathy and rarely with hypersensitivity reactions associated with ZYLOPRIM (allopurinol) . Albuminuria has been observed among patients who developed clinical gout following chronic glomerulonephritis and chronic pyelonephritis.
Patients with decreased renal function require lower doses of ZYLOPRIM (allopurinol) than those with normal renal function. Lower than recommended doses should be used to initiate therapy in any patients with decreased renal function and they should be observed closely during the early stages of administration of ZYLOPRIM (allopurinol) . In patients with severely impaired renal function or decreased urate clearance, the half-life of oxipurinol in the plasma is greatly prolonged. Therefore, a dose of 100 mg per day or 300 mg twice a week, or perhaps less, may be sufficient to maintain adequate xanthine oxidase inhibition to reduce serum urate levels.
Bone marrow depression has been reported in patients receiving ZYLOPRIM (allopurinol) , most of whom received concomitant drugs with the potential for causing this reaction. This has occurred as early as 6 weeks to as long as 6 years after the initiation of therapy of ZYLOPRIM (allopurinol) . Rarely, a patient may develop varying degrees of bone marrow depression, affecting one or more cell lines, while receiving ZYLOPRIM (allopurinol) alone.
Laboratory Tests: The correct dosage and schedule for maintaining the serum uric acid within the normal range is best determined by using the serum uric acid as an index.
In patients with pre-existing liver disease, periodic liver function tests are recommended during the early stages of therapy (see WARNINGS).
ZYLOPRIM (allopurinol) and its primary active metabolite, oxipurinol, are eliminated by the kidneys; therefore, changes in renal function have a profound effect on dosage. In patients with decreased renal function or who have concurrent illnesses which can affect renal function such as hypertension and diabetes mellitus, periodic laboratory parameters of renal function, particularly BUN and serum creatinine or creatinine clearance, should be performed and the patient's dosage of ZYLOPRIM (allopurinol) reassessed.
The prothrombin time should be reassessed periodically in the patients receiving dicumarol who are given ZYLOPRIM (allopurinol) .
Pregnancy: Teratogenic Effects: Pregnancy Category C. Reproductive studies have been performed in rats and rabbits at doses up to twenty times the usual human dose (5 mg/kg per day), and it was concluded that there was no impaired fertility or harm to the fetus due to allopurinol. There is a published report of a study in pregnant mice given 50 or 100 mg/kg allopurinol intraperitoneally on gestation days 10 or 13. There were increased numbers of dead fetuses in dams given 100 mg/kg allopurinol but not in those given 50 mg/kg. There were increased numbers of external malformations in fetuses at both doses of allopurinol on gestation day 10 and increased numbers of skeletal malformations in fetuses at both doses on gestation day 13. It cannot be determined whether this represented a fetal effect or an effect secondary to maternal toxicity. There are, however, no adequate or well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.
Experience with ZYLOPRIM (allopurinol) during human pregnancy has been limited partly because women of reproductive age rarely require treatment with ZYLOPRIM (allopurinol) . There are two unpublished reports and one published paper of women giving birth to normal offspring after receiving ZYLOPRIM (allopurinol) during pregnancy.
Nursing Mothers: Allopurinol and oxipurinol have been found in the milk of a mother who was receiving ZYLOPRIM. Since the effect of allopurinol on the nursing infant is unknown, caution should be exercised when ZYLOPRIM (allopurinol) is administered to a nursing woman.
Pediatric Use: ZYLOPRIM (allopurinol) is rarely indicated for use in children with the exception of those with hyperuricemia secondary to malignancy or to certain rare inborn errors of purine metabolism (see INDICATIONS and DOSAGE AND ADMINISTRATION).
Last reviewed on RxList: 10/11/2010
This monograph has been modified to include the generic and brand name in many instances.
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