Indometacin, also known as indomethacin, is a nonsteroidal anti-inflammatory drug (NSAID) commonly used as a prescription medication to reduce fever, pain, stiffness, and swelling from inflammation. It works by inhibiting the production of prostaglandins, endogenous signaling molecules known to cause these symptoms. It does this by inhibiting cyclooxygenase, an enzyme that catalyzes the production of prostaglandins.
Indometacin is a potent drug with many serious side effects and should not be considered an analgesic for minor aches and pains or fever. The medication is better described as an anti-inflammatory, rather than an analgesic. Indometacin can also affect warfarin and subsequently raise INR.
In general, adverse effects seen with indometacin are similar to all other NSAIDs. For instance, indometacin inhibits both cyclooxygenase-1 and cyclooxygenase-2, which then inhibits the production of prostaglandins in the stomach and intestines responsible for maintaining the mucous lining of the gastrointestinal tract. Indometacin, therefore, like other non-selective COX inhibitors can cause peptic ulcers. These ulcers can result in serious bleeding and/or perforation requiring hospitalization of the patient.
Many NSAIDs, but particularly indometacin, cause lithium retention by reducing its excretion by the kidneys. Thus indometacin users have an elevated risk of lithium toxicity. For patients taking lithium (e.g. for treatment of depression or bipolar disorder), less toxic NSAIDs such as sulindac or aspirin are preferred.
Paradoxically yet uncommonly, indometacin can cause headache (10 to 20%), sometimes with vertigo and dizziness, hearing loss, tinnitus, blurred vision (with or without retinal damage). There are unsubstantiated reports of worsening Parkinson's disease, epilepsy, and psychiatric disorders. Cases of life-threatening shock (including angioedema, sweating, severe hypotension and tachycardia as well as acute bronchospasm), severe or lethal hepatitis and severe bone marrow damage have all been reported. Skin reactions and photosensitivity are also possible side effects.
People should undergo regular physical examination to detect edema and signs of central nervous side effects. Blood pressure checks will reveal development of hypertension. Periodic serum electrolyte (sodium, potassium, chloride) measurements, complete blood cell counts and assessment of liver enzymes as well as of creatinine (renal function) should be performed. This is particularly important if Indometacin is given together with an ACE inhibitor or with potassium-sparing diuretics, because these combinations can lead to hyperkalemia and/or serious kidney failure. No examinations are necessary if only the topical preparations (spray or gel) are applied.
Generally, overdose in humans causes drowsiness, dizziness, severe headache, mental confusion, paresthesia, numbness of limbs, nausea and vomiting. Severe gastrointestinal bleeding is also possible. Cerebral edema, and cardiac arrest with fatal outcome have been seen in children.
Indometacin's role in treating certain headaches is unique compared to other NSAIDs. In addition to the class effect of COX inhibition, there is evidence that indometacin has the ability to reduce cerebral blood flow not only through modulation of nitric oxide pathways but also via intracranial precapillary vasoconstriction. Indometacin property of reducing cerebral blood flow is useful in treating raised intracranial pressure. A case report has shown that an intravenous bolus dose of indometacin given with 2 hours of continuous infusion is able to reduce intracranial pressure by 37% in 10 to 15 minutes and increases cerebral perfusion pressure by 30% at the same time. This reduction in cerebral pressure may be responsible for the remarkable efficacy in a group of headaches that is referred to as "indometacin-responsive headaches", such as idiopathic stabbing headache, chronic paroxysmal hemicranial, and exertional headaches. On the other hand, the activation of superior salivary nucleus in the brainstem is used to stimulate the trigeminal autonomic reflex arc, causing a type of headache called trigeminal autonomic cephalgia. Indometacin inhibits the superior salivatory nucleus, thus relieving this type of headache.