How Do Xanthine Oxidase Inhibitors Work?

Xanthine oxidase inhibitors are medications prescribed for the treatment of gout, a painful condition caused by excessive uric acid levels in the blood (hyperuricemia). Uric acid is a waste product from the metabolization of purine, an essential chemical compound in the body, also found in many foods. Cells use purine to make the building blocks of DNA and RNA.

Excess uric acid gets deposited as monosodium urate crystals in joints, bones, and soft tissues, inducing an immune reaction that results in inflammation and associated symptoms. Gout most commonly affects the big toes, but can also affect other joints such as ankles, knees, elbows, wrists, and fingers.

Xanthine oxidase inhibitors reduce uric acid production by inhibiting the activity of xanthine oxidase, an enzyme that synthesizes uric acid from hypoxanthine, a purine derivative. Xanthine oxidase inhibitors specifically inhibit xanthine oxidase, without affecting the purines vital for DNA and RNA synthesis.

Xanthine oxidase inhibitors may be administered as oral tablets or intravenous (IV) injections, and are approved by FDA to prevent and treat the following conditions:

• Gout and gout flares
• Chronic gout
• Hyperuricemia
• Antineoplastic-induced hyperuricemia, a condition caused by chemotherapy

Side effects of xanthine oxidase inhibitors may include the following:

• Liver function abnormalities
• Rash
• Renal failure
• Arthralgia (joint pain)
• Amblyopia (lazy eye)
• Blurred vision
• Deafness
• Tinnitus (ringing in the ears)
• Vertigo
• Blood dyscrasias (disorders) such as:
  • Neutropenia (low levels of neutrophil, a type of immune cell)
  • Increase or decrease in levels of leukocytes
  • Agranulocytosis (low granulocytes, immune cells with granules)
  • Anemia (low red blood cell count)
  • Pancytopenia (decrease in all types of blood cells)
  • Eosinophilia (high level of eosinophils, a type of immune cells)
  • Thrombocytopenia (decrease in platelet count)
  • Idiopathic thrombocytopenic purpura (easy bruising and bleeding due to thrombocytopenia)
• Splenomegaly (spleen enlargement)
• Electrolyte abnormalities
• Dehydration
• Thirst
• Skin and subcutaneous reactions such as:
  • Generalized rash
  • Urticaria (hives)
  • Pruritus (itching)
  • Dermatitis
  • Dermographism (a skin condition that causes welts to develop with scratching or stroking the skin)
  • Eczema
  • Peeling skin
  • Photosensitivity
  • Ecchymosis (bruising)
  • Petechiae (skin discoloration)
  • Skin lesions
  • Skin edema
  • Abnormal skin odor
  • Purpura (purple spots on the skin caused by small blood vessels bursting)
  • Angioedema (swelling in the tissue under the skin or mucous membranes)
  • Drug rash with eosinophilia and systemic symptoms (DRESS)
  • Toxic epidermal necrolysis (a severe skin condition with widespread redness, skin cell death, and exfoliation which can lead to sepsis)
  • Stevens-Johnson syndrome (a rare medical emergency with flu-like symptoms and a painful rash)
• Anaphylaxis (severe allergic reaction)
• Alopecia (hair loss)
• Abnormal hair growth
• Hair color changes
• Hot flush
• Hyperhidrosis (excessive sweating)
• Cardiac disorders such as:
  • Angina pectoris (chest pain due to coronary heart disease)
  • Atrial fibrillation/flutter
  • Cardiac murmur
  • Abnormal ECG
  • Palpitations
  • Sinus bradycardia (slow heartbeat)
  • Tachycardia (rapid heartbeat)
• Cardiovascular abnormalities
• Hypertension (high blood pressure)
• Hypotension (low blood pressure)
• Bronchospasm
• Dyspnea (shortness of breath)
• Respiratory tract congestion
• Cough
• Sneezing
• Bronchitis (inflammation of the bronchial passage)
• Pharyngitis (throat inflammation)
• Pharyngeal edema
• Throat irritation
• Nasal dryness
• Epistaxis (nasal bleeding)
• Paranasal sinus hypersecretion
• Upper respiratory tract infection
• Gastrointestinal (GI) effects such as:
  • Abdominal distention
  • Abdominal pain and discomfort
  • Nausea
  • Vomiting
  • Diarrhea
  • Constipation
  • Dyspepsia (indigestion)
  • Flatulence
  • Frequent stools
  • Gastritis
  • Gastroesophageal reflux disease (GERD)
  • Hematemesis (blood in vomit)
  • Hyperchlorhydria (high hydrochloric acid secretion in the stomach)
  • Hematochezia (blood in stools)
  • Peptic ulcer
• Dry mouth
• Mouth ulceration
• Gingival pain (gum pain)
• Increase or decrease in appetite
• Weight gain or loss
• Anorexia (loss of appetite)
• Diabetes mellitus
• Hyperglycemia (high blood glucose levels)
• Hyperlipidemia (high levels of blood fats)
• Hypercholesterolemia (high blood cholesterol)
• Hypertriglyceridemia (high level of triglycerides in the blood)
• Hypokalemia (low potassium in the blood)
• Hepatotoxicity (toxicity to the liver)
• Abnormal liver function results
• Liver disorders
• Jaundice
• Hepatic steatosis (fatty liver)
• Hepatitis (liver inflammation)
• Hepatomegaly (liver enlargement)
• Liver failure
• Cholelithiasis (gallstones)
• Cholecystitis (gallbladder inflammation)
• Pancreatitis (inflammation of the pancreas)
• Kidney function abnormality
• Tubulointerstitial nephritis (inflammation of the tubules and surrounding tissue in the kidney)
• Nephrolithiasis (kidney stones)
• Renal damage
• Renal insufficiency
• Hematuria (blood in the urine)
• Proteinuria (excessive protein excretion in the urine)
• Pollakiuria (frequent urination)
• Urinary urgency
• Incontinence
• Chest pain and discomfort
• Edema
• Feeling abnormal
• Fatigue
• Lethargy
• Malaise
• Asthenia (weakness)
• Pain
• Influenza-like symptoms
• Arthritis
• Joint stiffness
• Joint swelling
• Muscle spasms and twitching
• Muscle tightness
• Muscle weakness
• Musculoskeletal stiffness and pain
• Hypotonia (decreased muscle tone)
• Rhabdomyolysis (breakdown of skeletal muscle cells)
• Foot drop
• Gait disturbance
• Balance disorder
• Peripheral neuritis (nerve inflammation)
• Sensory-motor neuropathy (nerve damage)
• Guillain-Barre syndrome (a rare neurological disorder)
• Tremor
• Hemiparesis (muscle weakness on one side of the body)
• Hypoesthesia (reduced skin sensation)
• Paresthesia (abnormal skin sensation)
• Lacunar infarction (a type of stroke caused by a block in a small blood vessel deep in the brain)
• Cerebrovascular accident
• Transient ischemic attack (stroke caused by reduced blood flow to the brain)
• Altered taste
• Hyposmia (reduced sense of smell)
• Iritis (inflammation of the iris)
• Macular retinitis (inflammation in macula, the central portion of the retina)
• Cataracts
• Headache
• Migraine
• Somnolence (drowsiness)
• Dizziness
• Mental impairment
• Confusion
• Agitation
• Aggression
• Anxiety
• Depression
• Insomnia
• Irritability
• Nervousness
• Panic attack
• Personality change
• Decrease in libido
• Erectile dysfunction
• Gynecomastia (breast tissue growth in males)
• Breast pain
• Herpes zoster infection
• Abnormal blood and urine test results

Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.

Generic and brand names of xanthine oxidase inhibitor drugs include:

• allopurinol
• Aloprim
• febuxostat
• Uloric
• Zyloprim