The most common adverse effects of allopurinol are rashes, which are generally maculopapular or pruritic, and may be purpuric. The incidence of skin rashes may be increased in patients with renal insufficiency. More serious hypersensitivity reactions, including exfoliative rashes, Stevens-Johnson syndrome, toxic epidermal necrolysis, and drug reaction with eosinophilia and systemic symptoms (DRESS) may occur. Acute attacks of gout were also reported. Gastrointestinal adverse effects, such as diarrhea and nausea, are common, especially if allopurinol is taken before meals or on an empty stomach. Increases in liver enzymes and serum alkaline phosphatase were also observed.
Infections and infestations:
Cellulitis, furunculosis, furunculosis of the nose, infections, sepsis, septic shock, urinary tract infection.
Neoplasms benign, malignant and unspecified (including cysts and polyps):
Angioimmunoblastic lymphadenopathy, tumor lysis syndrome.
Blood and lymphatic system disorders:
Agranulocytosis, anemia, aplastic anemia, blast crisis, bone marrow aplasia, bone marrow suppression, clotting abnormalities, disseminated intravascular coagulation, ecchymosis, eosinophilia, eosinophilia hepato-splenomegaly, eosinophilic fibrohistiocytic bone marrow lesion, granulocytopenia, hemolytic anemia, leukocytosis, leukopenia, lymphadenopathy, lymphocytosis, neutropenia, pancytopenia, pseudolymphoma, reticulocytosis, splenomegaly, thrombocytopenia.
Immune system disorders:
Anaphylactic shock, angioedema, bronchospasm, erythema multiforme, hypersensitivity, pure red cell aplasia.
Metabolism and nutrition disorders:
Anorexia, diabetes mellitus, edema, electrolyte imbalance, hypercalcemia, hyperglycemia, hyperkalemia, hyperlipidemia, hypernatremia, hyperphosphatemia, hyperuricemia, hypervolemia, hypokalemia, hypomagnesemia, hyponatremia, hypovolemia, lactic acidosis, metabolic acidosis, water intoxication.
Confusion, depression, drowsiness, insomnia, somnolence.
Nervous system disorders:
Agitation, amnesia, ataxia, cerebral infarction, cerebrovascular accident, changes in mental status, coma, dizziness, dystonia, epilepsy, foot drop, generalized seizure, headache, myoclonus, neuritis (including peripheral), neuropathy (including peripheral), paralysis, paresthesia, seizures, status epilepticus, tremor, twitching, vertigo.
Amblyopia, cataract, conjunctivitis, iritis, macular changes, macular retinitis, maculopathy, optic neuritis, visual disturbance, visual impairment.
Ear and labyrinth disorders:
Angina (pectoris), bradycardia, cardiac failure, cardiorespiratory arrest, congestive heart failure, pericarditis, ventricular fibrillation.
Flushing, hemorrhage, hypersensitivity vasculitis, hypertension, hypotension, necrotizing angiitis, peripheral vascular disease, thrombophlebitis, vasculitis, vasodilation.
Respiratory, thoracic, and mediastinal disorders:
Acute respiratory distress syndrome, apnea, asthma, epistaxis, pharyngitis, pulmonary embolism, respiratory failure, respiratory insufficiency, rhinitis.
Abdominal distention, [intermittent] abdominal pain, ageusia, change in bowel habit, constipation, dysgeusia, dyspepsia, flatulence, gastritis, gastrointestinal hemorrhage, hematemesis, hemorrhagic pancreatitis, intestinal obstruction, pancreatitis, proctitis, salivary gland swelling, steatorrhea, stomatitis, tongue edema, vomiting.
Hepatic and hepatobiliary disorder:
Cholestatic jaundice, granulomatous hepatitis, hepatic dysfunction, hepatic necrosis, hepatitis, hepatocellular damage, hepatocellular necrosis, hepatomegaly, hepatotoxicity, hyperbilirubinemia, jaundice, liver failure, vanishing bile duct syndrome.
Skin and subcutaneous tissue disorders:
Alopecia, dermatitis (eczematoid, erythematous, exfoliative, hemorrhagic, purpuric, vesicobullous), drug eruption, eczema, hair color changes, hair discolored, ichthyosis, lichen planus, onycholysis, pruritus, purpura, rash (erythematous, scaly), skin edema, skin exfoliation, skin granuloma, toxic pustuloderma, urticaria.
Musculoskeletal and connective tissue disorders:
Arthralgia, gouty arthritis, hypotonia, myalgia, myopathy.
Renal and urinary disorders:
Albuminuria, arterial nephrosclerosis, azotemia, bilateral ureteral obstruction, decreased renal function, dysuria, glycosuria, hematuria, impaction of partly dissolved renal uric acid stones in the ureter, interstitial nephritis, nephritis, oliguria, oxipurinol stones, pyelonephritis, renal colic, renal failure, renal impairment, uremia, xanthine stone deposition.
Reproductive system and breast disorders:
Erectile dysfunction, gynecomastia (male), impotence, infertility (male), libido decreased, nocturnal emission.
General disorders and administration site conditions:
Asthenia, chills, death, diaphoresis, face edema, fever, hyperhidrosis, malaise, mucositis.
Abnormal electrocardiogram (ECG), abnormal liver function test results, decreased blood urea nitrogen, decreased prothrombin levels, decreased sulfobromophthalein excretion, decreased venous pressure, increased alanine aminotransferease, increased aspartate aminotransferase, increased blood urea nitrogen, increased creatinine, increased respiratory rate, increased urinary urobilinogen, liver biopsy findings of eosinophilia and noncaseating granulomas.