More frequently reported side effects include: acute gout attack. See below for a comprehensive list of adverse effects.

Applies to allopurinol: oral tablet

Other dosage forms:

• intravenous powder for solution

Along with its needed effects, allopurinol may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking allopurinol:

More common

• Ankle, knee, or great toe joint pain
• joint stiffness or swelling
• rash
• rash with flat lesions or small raised lesions on the skin

Rare

• Abdominal or stomach pain
• agitation
• ammonia-like breath odor
• anxiety
• bleeding gums
• blistering, peeling, or loosening of the skin
• blood in the urine or stools
• bloody nose
• bloody or black, tarry stools
• blue or pale skin
• bruising
• changes in skin color
• chest pain or discomfort
• chest pain, possibly moving to the left arm, neck, or shoulder
• chills
• clay-colored stools
• cloudy urine
• coma
• confusion
• constipation
• cough or hoarseness
• coughing up blood
• cracks in the skin
• dark urine
• decreased urine output
• depression
• diarrhea
• difficulty with breathing
• dizziness
• drowsiness
• dry mouth
• feeling faint, dizzy, or lightheaded
• feeling of warmth or heat
• fever
• fever with or without chills
• flushing or redness of the skin, especially on the face and neck
• general feeling of discomfort or illness
• general feeling of tiredness or weakness
• headache
• hostility
• incoherent speech
• increased urination
• irritability
• itching
• joint or muscle pain
• large, flat, blue or purplish patches in the skin
• lethargy
• light-colored stools
• loss of appetite
• loss of heat from the body
• lower back or side pain
• metallic taste
• muscle twitching
• muscle weakness
• nausea or vomiting
• pain, tenderness, or swelling of the foot or leg
• painful or difficult urination
• pinpoint red or purple spots on the skin
• rapid weight gain
• rash
• red, irritated eyes
• red, swollen skin
• redness, soreness, or itching skin
• right upper abdominal or stomach pain and fullness
• scaly skin
• seizures
• severe stomach pain
• shortness of breath
• slow or irregular heartbeat
• sore throat
• sores, ulcers, or white spots on the lips or in the mouth
• sores, welting, or blisters
• stupor
• sweating
• swelling of the face, ankles, hands, or lower legs
• swollen or painful glands
• swollen, painful, or tender lymph glands in the neck, armpit, or groin
• thirst
• tightness in the chest
• unpleasant breath odor
• unusual bleeding or bruising
• unusual weight gain or loss
• vomiting of blood or material that looks like coffee grounds
• wheezing
• yellow eyes or skin

Some side effects of allopurinol may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Rare

• Bad, unusual, or unpleasant (after) taste
• blindness
• blue-yellow color blindness
• blurred vision
• body aches or pain
• burning feeling in the chest or stomach
• burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
• burning, dry, or itching eyes
• burning, numbness, tingling, or painful sensations
• change in taste
• change in vision
• congestion
• continuing ringing or buzzing or other unexplained noise in the ears
• decreased interest in sexual intercourse
• decreased vision
• difficulty with moving
• discharge or excessive tearing
• feeling of constant movement of self or surroundings
• hair loss or thinning of the hair
• hearing loss
• hives or welts
• impaired vision
• inability to have or keep an erection
• indigestion
• lack or loss of strength
• loss in sexual ability, desire, drive, or performance
• loss of appetite
• loss of memory
• multiple swollen and inflamed skin lesions
• muscle aching or cramping
• muscle pain or stiffness
• muscular pain, tenderness, wasting, or weakness
• noisy breathing
• problems with memory
• redness, pain, or swelling of the eye, eyelid, or inner lining of the eyelid
• runny nose
• sensation of spinning
• sensitivity to light
• sleepiness or unusual drowsiness
• sleeplessness
• sneezing
• stomach upset
• stuffy nose
• sweating
• swelling of the breasts or breast soreness in both females and males
• swelling of the salivary glands
• swelling or inflammation of the mouth
• swollen joints
• tearing
• tender, swollen glands in the neck
• tenderness in the stomach area
• throbbing pain
• tightness in the chest
• trouble getting pregnant
• trouble with sleeping
• trouble with swallowing
• unable to sleep
• unsteadiness or awkwardness
• voice changes
• weakness in the arms, hands, legs, or feet
• weight loss

Applies to allopurinol: intravenous powder for injection, oral tablet

The most commonly reported adverse reactions include skin rash, diarrhea, nausea, alkaline phosphatase, and transaminase elevation.

Skin rash is one of the most common adverse reactions and may occur at any time during treatment. Some skin reactions can be severe and sometimes fatal. In patients with the most severe reactions, systemic symptoms such as fever, chills, arthralgia, cholestatic jaundice, eosinophilia and mild leukocytosis, or leukopenia accompany the rash. Among 55 patients with gout who received this drug for an average of 1 year (3 to 34 months), 3% developed pruritic maculopapular skin eruptions, sometimes scaly or exfoliative. The incidence of skin rash appears to be greater in patients with renal insufficiency.

Angioedema has been reported with and without signs and symptoms of a more generalized hypersensitivity reaction. Skin reactions associated with exfoliation, fever, lymphadenopathy, arthralgia, and/or eosinophilia resembling Stevens-Johnson and/or Lyell syndromes have occurred rarely. Associated vasculitis and tissue responses may manifest as hepatitis, interstitial nephritis, and very rarely epilepsy.

DRESS also known as drug hypersensitivity syndrome has been reported. The syndrome is potentially life-threatening and fatal. It has been reported that symptoms may develop in approximately 1 week from initiating allopurinol therapy, but longer latency periods have also been reported.

Common (1% to 10%): Rash, maculopapular rash

Uncommon (0.1% to 1%): Ecchymosis

Rare (less than 0.1%): Steven-Johnson syndrome, Lyell syndrome

Very rare (less than 0.01%): Alopecia, discolored hair, angioedema, fixed drug eruption

Frequency not reported: DRESS (Drug reaction with eosinophilia and systemic symptoms), sweating

Rare (less than 0.1%): Generalized hypersensitivity

Very rare (less than 0.01%): Anaphylaxis, angioedema

Frequency not reported: Hypersensitivity reaction

Generalized hypersensitivity including skin reactions associated with exfoliation, fever, lymphadenopathy, arthralgia, and/or eosinophilia resembling Stevens-Johnson and/or Lyell syndromes have occurred rarely. Associated vasculitis and tissue responses may manifest as hepatitis, interstitial nephritis, and very rarely epilepsy. When generalized hypersensitivity reactions have occurred, renal and or/hepatic disorders have often been present, particularly when the outcome has been fatal.

Angioedema has been reported with and without signs and symptoms of a more generalized hypersensitivity reaction.

Common (1% to 10%): Increases in alkaline phosphatase and serum transaminases

Rare (less than 0.1%): Hepatic dysfunction including hepatitis (hepatic necrosis and granulomatous hepatitis), hepatomegaly, cholestatic jaundice,

Frequency not reported: Clinical hepatotoxicity, liver failure

Liver failure was reported in less than 1% of patients.

Common (1% to 10%): Diarrhea, nausea, vomiting

Rare (less than 0.1%): Intermittent abdominal pain, gastritis, dyspepsia

Very rare (less than 0.01%): Steatorrhea, recurrent hematemesis, stomatitis, changed bowel habit

Frequency not reported: Hemorrhagic pancreatitis, gastrointestinal bleeding, salivary gland swelling, tongue edema, anorexia, flatulence

Hemorrhagic pancreatitis, gastrointestinal bleeding, salivary gland swelling, tongue edema, flatulence, and anorexia were reported in less than 1% of patients.

Eosinophilic fibrohistiocytic lesion of bone marrow, pancytopenia, anemia, hemolytic anemia, reticulocytosis, lymphadenopathy, disseminated intravascular coagulation, and lymphocytosis were reported in less than 1% of patients.

Very rare (less than 0.01%): Leukocytosis, leukopenia, eosinophilia, thrombocytopenia, granulocytopenia, agranulocytosis, aplastic anemia

Frequency not reported: Bone marrow depression, eosinophilic fibrohistiocytic lesion of bone marrow, pancytopenia, anemia, hemolytic anemia, reticulocytosis, lymphadenopathy, lymphocytosis, disseminated intravascular coagulation

Common (1% to 10%): Renal failure/insufficiency

Very rare (less than 0.01%): Xanthine crystalluria, azotemia

Xanthine crystalluria has been reported in 3 patients; 2 patients with Lesch-Nyhan syndrome and 1 patient with lymphosarcoma who produced an extremely large amount of uric acid during chemotherapy.

Increased serum creatinine and kidney function abnormality has been reported in less than 1% of patients.

Uncommon (0.1% to 1%): Headache

Very rare (less than 0.01%): Ataxia, somnolence, coma, paralysis, paresthesia, neuropathy, taste perversion, neuritis

Frequency not reported: Drowsiness, confusion, foot drop, seizure, status epilepticus, myoclonus, twitching, cerebral infarction, stroke, tremor

Confusion, foot drop, seizure, status epilepticus, myoclonus, twitching, cerebral infarction, stroke, and tremor were reported in less than 1% of patients.

Very rare (less than 0.01%): Visual disorder, cataract, macular changes

Frequency not reported: Optic neuritis

Very rare (less than 0.01%): Furunculosis, angioimmunoblastic lymphadenopathy

Uncommon (0.1% to 1%): Increase in acute gout attacks

Very rare (less than 0.01%): Diabetes mellitus, hyperlipidemia

Frequency not reported: Hypercalcemia, hypocalcemia, hyperphosphatemia, hypokalemia, hyperuricemia, electrolyte abnormality, hyperglycemia, hypernatremia, metabolic acidosis, glycosuria, hyperkalemia, lactic acidosis, water intoxication, hypomagnesemia

Early clinical experience with this drug found acute gouty attacks on therapy initiation to be one of the more commonly observed adverse reactions; however, current use analyses suggests this incidence is now less than 1%. The reason for this change has not been determined, but it may be due to patients initiating therapy more gradually.

Hypercalcemia, hypocalcemia, hyperphosphatemia, hypokalemia, hyperuricemia, electrolyte abnormality, hyperglycemia, hypernatremia, metabolic acidosis, glycosuria, hyperkalemia, lactic acidosis, water intoxication, and hypomagnesemia have been reported in less than 1% of patients.

Rare (less than 0.1%): Myopathy, arthralgias

Uncommon (0.1% to 1%): Necrotizing angiitis, vasculitis, edema

Very rare (less than 0.01%): Angina, bradycardia, hypertension

Frequency not reported: Pericarditis, peripheral vascular disease thrombophlebitis, vasodilation, heart failure, cardiorespiratory arrest, decreased venous pressure, flushing, cardiovascular disorder, ECG abnormality, hemorrhage, ventricular fibrillation

Pericarditis, peripheral vascular disease thrombophlebitis, vasodilation, heart failure, cardiorespiratory arrest, decreased venous pressure, flushing, cardiovascular disorder, ECG abnormality, hemorrhage, and ventricular fibrillation were reported in less than 1% of patients.

Uncommon (0.1% to 1%): Gynecomastia

Uncommon (0.1% to 1%): Infertility, impotence, nocturnal emission

Very rare (less than 0.01%): Uremia, hematuria, male infertility, impotence, erectile dysfunction

Frequency not reported: Urinary tract infection

Injection site reactions have been reported with the parenteral product in less than 1% of patients.

Frequency not reported: Injection site reactions

Uncommon (0.1% to 1%): Fever, general malaise, asthenia

Very rare (less than 0.01%): Vertigo

Frequency not reported: Tinnitus

Very rare (less than 0.01%): Depression

Frequency not reported: Amnesia, insomnia, agitation

Amnesia, agitation, and insomnia were reported in less than 1% of patients.

Rare (less than 0.1%): Epistaxis

Frequency not reported: Bronchospasm, asthma, pharyngitis, rhinitis, respiratory failure/insufficiency, ARDS, increased respiration rate, apnea

Bronchospasm, asthma, pharyngitis, respiratory failure/insufficiency, ARDS, increased respiration rate, apnea, and rhinitis were reported in less than 1% of patients.