Indometacin Other names: Indomethacin

Co-administration of indometacin and some antihypertensive agents may attenuate acutely the hypotensive effect of the latter, due partly to indometacin’s inhibition of prostaglandin synthesis. Therefore, caution should be exercised when considering the addition of indometacin to the regimen of a patient taking any of the following antihypertensive agents: alpha-adrenergic blocking agents, ACE inhibitors, beta-adrenergic blocking agents, diuretics, hydralazine, or losartan (an angiotensin II receptor antagonist).

The use of indometacin with aspirin or other salicylates is not recommended. Controlled clinical studies have shown no enhanced therapeutic effect, and one study showed a significant increase in the incidence of gastro-intestinal side effects. A study in normal volunteers showed that chronic administration of 3.6 g aspirin with indometacin lowered the indometacin blood levels by approximately 20%.

Concurrent administration of indomethacin and antacids may delay absorption of indomethacin and reduce blood levels by up to 50%.

Although clinical studies suggest that indometacin does not influence the hypoprothrombinaemia induced by anticoagulants, patients also receiving anticoagulants should be closely observed for alterations of the prothrombin time.

In some patients, the administration of indometacin can reduce the diuretic and antihypertensive effects of loop, potassium-sparing and thiazide diuretics. Therefore, when indometacin and diuretics are used concomitantly, the patient should be observed closely to determine if the desired effect of the diuretic is obtained.

Indometacin reduces basal plasma renin activity (PRA), as well as those elevations of PRA induced by frusemide administration, or salt or volume depletion. These facts should be considered when evaluating plasma renin activity in hypertensive patients.

Most of the above effects concerning diuretics have been attributed, at least in part, to mechanisms involving inhibition of prostaglandin synthesis by indometacin.

Indometacin and potassium-sparing diuretics each may be associated with increased plasma potassium levels. The potential effects of indometacin and potassium-sparing diuretics on potassium kinetics and renal function should be considered when these agents are administered concurrently.

Most of the above effects concerning diuretics have been attributed, at least in part, to mechanisms involving inhibition of prostaglandin synthesis by indometacin.

Concomitant administration of indomethacin and thyroid preparations may increase their cardiotoxicity.

There have been reports that 4-quinolones may induce convulsions in patients with or without a history of convulsions; taking NSAIDs at the same time may also induce them.

Concomitant administration of indomethacin and measles vaccine may increase the severity of the vaccine’s reactions until bleeding occurs.

The risk of gastro-intestinal bleeding and ulceration associated with NSAIDs is increased when used with corticosteroids.

The concomitant use of indometacin with other NSAIDs is not recommended due to the increased possibility of gastro-intestinal toxicity, with little or no increase in efficacy.

Indometacin may have a reversible inhibitory effect on women’s ovulation. The use of indometacin may impair female fertility and is not recommended in women attempting to conceive. In women who have difficulties conceiving or who are undergoing investigation of infertility, withdrawal of indometacin should be considered.

Administration of non-steroidal anti-inflammatory drugs concomitantly with cyclosporin has been associated with an increase in cyclosporin-induced toxicity, possibly due to decreased synthesis of renal prostacyclin. NSAIDs should be used with caution in patients taking cyclosporin, and renal function should be monitored carefully.

Co-administration of diflunisal with indometacin increases the plasma level of indometacin by about a third, with a concomitant decrease in renal clearance. Fatal gastro-intestinal haemorrhage has occurred. The combination should not be used.

Indometacin given concomitantly with digoxin has been reported to increase the serum concentration and prolong the half-life of digoxin. Therefore, when indometacin and digoxin are used concomitantly, serum digoxin levels should be closely monitored.

Indometacin 50 mg three times a day produced a clinically relevant elevation of plasma lithium and reduction in renal lithium clearance in psychiatric patients and normal subjects with steady-state plasma lithium concentrations. This effect has been attributed to inhibition of prostaglandin synthesis. As a consequence, when indometacin and lithium are given concomitantly, the patient should be observed carefully for signs of lithium toxicity. In addition, the frequency of monitoring serum lithium concentrations should be increased at the outset of such combination drug treatment.

Caution should be exercised with simultaneous use of indometacin with methotrexate. Indometacin has been reported to decrease the tubular secretion of methotrexate and to potentiate toxicity.

NSAIDs and aspirin should be avoided until at least 8 to 12 days after administration of mifepristone.

The concomitant administration of indomethacin and phenylbutazone derivatives and pyrazolone enhances the action of indomethacin due to binding sites to plasma proteins. There is an increased risk of toxic effects, especially from the gastrointestinal tract.

Hypertensive crises have been reported due to oral phenylpropanolamine alone and, rarely, to phenylpropanolamine given with indometacin. This additive effect is probably due partly to indometacin’s inhibition of prostaglandin synthesis. Caution should be exercised when indometacin and phenylpropanolamine are administered concomitantly.

Co-administration of probenecid may increase plasma levels of indometacin.

Indomethacin may reduce the clearance of tamoxifen.

Co-administration of telmisartan and indomethacin can lead to acute renal failure and hyperkalaemia.

It has been reported that the addition of triamterene to a maintenance schedule of indometacin resulted in reversible acute renal failure in two of four healthy volunteers. Indometacin and triamterene should not be administered together.

Indometacin should be used cautiously in patients with a history of bronchial asthma and in patients with psychiatric disorders, epilepsy, or parkinsonism, as indometacin may tend to aggravate these disorders.

Headache, sometimes accompanied by dizziness and light-headedness, may occur, usually early in treatment. Starting therapy with a low dosage and increasing it gradually will usually minimise the incidence of headache. These symptoms frequently disappear on continuing therapy or reducing the dosage, but if headache persists despite dosage reduction, indometacin should be withdrawn. Patients should be warned that they may experience dizziness and, if they do, should not drive a car or undertake potentially dangerous activities needing alertness.

Fluid retention and peripheral oedema have been observed in some patients taking indometacin. Indometacin should therefore be used with caution in patients with cardiac dysfunction, hypertension or other conditions predisposing to fluid retention.

Inhibition of prostaglandin synthesis may adversely affect the pregnancy and/or the embryo/foetal development.

Data from epidemiological studies suggest an increased risk of miscarriage and of cardiac malformation and gastroschisis after use of a prostaglandin synthesis inhibitor in early pregnancy. The absolute risk for cardiovascular malformation was increased from less than 1%, up to approximately 1.5%. The risk is believed to increase with dose and duration of therapy.

In animals, administration of a prostaglandin synthesis inhibitor has been shown to result in increased pre- and post-implantation loss and embryo-foetal lethality. In addition, increased incidences of various malformations, including cardiovascular, have been reported in animals given a prostaglandin synthesis inhibitor during the organogenetic period.

During the first and second trimester of pregnancy, indometacin should not be given unless clearly necessary. If indometacin is used by a woman attempting to conceive, or during the first and second trimester of pregnancy, the dose should be kept as low and duration of treatment as short as possible.

During the third trimester of pregnancy, all prostaglandin synthesis inhibitors may expose:

The foetus to:

• Cardiopulmonary toxicity (with premature closure of the ductus arteriosus and pulmonary hypertension).
• Renal dysfunction, which may progress to renal failure with oligo-hydroamniosis.

The mother and the neonate, at the end of pregnancy, to:

• Possible prolongation of bleeding time, an anti-aggregating effect which may occur even at very low doses.
• Inhibition of uterine contractions resulting in delayed or prolonged labour.

Consequently, indometacin is contraindicated during the third trimester of pregnancy.

Studies in animals have shown reproductive toxicity.

Administration of indometacin is not recommended in breast-feeding mothers. Indometacin is excreted in breast milk.

Patients should be warned that they may experience dizziness, drowsiness, visual disturbances or headaches and if they do, should not drive or undertake activities requiring alertness.

CNS reactions: headaches, dizziness, light-headedness, depression, vertigo, and fatigue (including malaise and listlessness). Reactions reported infrequently include mental confusion, anxiety, syncope, drowsiness, convulsions, coma, peripheral neuropathy, muscle weakness, involuntary muscle movements, insomnia, psychiatric disturbances such as hallucinations, depersonalisation; and, rarely, paraesthesia, dysarthria, aggravation of epilepsy and Parkinsonism. These are often transient and disappear frequently with continued treatment or with reduced dosage. However, occasionally, severe reactions require stopping therapy.

Gastro-intestinal: the more frequent reactions are nausea, anorexia, vomiting, epigastric distress, abdominal pain, constipation, and diarrhoea. Others which may develop are ulceration – single or multiple – of oesophagus, stomach, duodenum or small or large intestine, including perforation and haemorrhage with a few fatalities having been reported; gastro-intestinal tract bleeding without obvious ulcer formation; and increased abdominal pain when used in patients with pre-existing ulcerative colitis. Reactions occurring infrequently are stomatitis; gastritis; flatulence; bleeding from the sigmoid colon – occult or from a diverticulum – and perforation of pre-existing sigmoid lesions (diverticula, carcinoma). Rarely, intestinal strictures (diaphragms) and intestinal ulceration followed by stenosis and obstruction has been reported. With suppositories, tenesmus and irritation of the rectal mucosa have occasionally been reported. Pancreatitis has been reported with an unknown frequency. Other gastro-intestinal side effects which may or may not be caused by indometacin include: ulcerative colitis and regional ileitis.

Hepatic: rarely, hepatitis and jaundice. (Some fatalities reported.)

Cardiovascular/Renal: oedema, increased blood pressure, tachycardia, chest pain, arrhythmia, palpitation, hypotension, congestive heart failure, blood urea elevation, and haematuria (all infrequent).

Dermatological/Hypersensitivity: pruritus, urticaria, angioneurotic oedema, angiitis, erythema nodosum, skin rash and photosensitivity, exfoliative dermatitis, Stevens-Johnson syndrome, erythema multiforme, toxic epidermal necrolysis, loss of hair, rapid fall in blood pressure resembling a shock-like state, acute anaphylaxis, acute respiratory distress including sudden dyspnoea, asthma and pulmonary oedema (all infrequent). Bronchospasm may be precipitated in patients suffering from, or with a history of, bronchial asthma or allergic disease.

Haematological: infrequently, blood dyscrasias may occur, including leucopenia, petechiae or ecchymosis, purpura, aplastic and haemolytic anaemia, agranulocytosis, bone-marrow depression, disseminated intravascular coagulation, and particularly thrombocytopenia. Because some patients may develop anaemia secondary to obvious or occult gastro-intestinal bleeding, appropriate blood determinations are recommended.

Ocular: infrequently, blurred vision, diplopia, and orbital and peri-orbital pain. Corneal deposits and retinal disturbances, including those of the macula, have been reported in patients with rheumatoid arthritis on prolonged therapy, but similar changes may also be expected in patients with rheumatoid arthritis who have not received indometacin.

Aural: tinnitus, hearing disturbances (rarely deafness).

Genito-urinary: proteinuria, nephrotic syndrome, interstitial nephritis, and renal insufficiency including renal failure (all rare).

Miscellaneous: vaginal bleeding, hyperglycaemia, glycosuria, hyperkalaemia, flushing and sweating, epistaxis, breast changes including enlargement and tenderness, gynaecomastia, and ulcerative stomatitis (all rare).

The following adverse reactions have been associated with use of indometacin suppositories: tenesmus; proctitis; rectal bleeding, burning, pain, discomfort, and itching.

Laboratory tests

Borderline elevations of one or more liver tests may occur, and significant elevations of ALT (SGPT) or AST (SGOT) have been seen in less than 1% of patients receiving therapy with non-steroidal anti-inflammatory drugs in controlled clinical trials. If abnormal liver tests persist or worsen, if clinical signs and symptoms consistent with liver disease develop, or if systemic manifestations such as rash or eosinophilia occur, indometacin should be stopped.

False-negative results in the dexamethasone suppression test (DST) in patients being treated with indometacin have been reported. Thus, results of this test should be used with caution in these patients.