Indometacin

Indometacin

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Systematic (IUPAC) name
2-{1-[(4-chlorophenyl)carbonyl]-5-methoxy-2-methyl-1H-indol-3-yl}acetic acid
Clinical data
Pregnancy category	C (Au), C/D (US)
Routes of administration	Oral, rectal, IV, topical
Legal status
Legal status	℞ (Prescription only)
Pharmacokinetic data
Bioavailability	~100% (oral), 80–90% (rectal)
Protein binding	99%
Metabolism	Hepatic
Biological half-life	4.5 hours
Excretion	Renal 60%, faecal 33%
Identifiers
CAS Number	53-86-1
ATC code	C01EB03 (WHO) M01AB01, M02AA23, S01BC01
PubChem	CID 3715
IUPHAR/BPS	1909
DrugBank	APRD00109
ChemSpider	3584
Chemical data
Formula	C19H16ClNO4
Molar mass	357.787 g.mol-1[[]]
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Indometacin (INN) or indomethacin (USAN and former BAN) is a non-steroidal anti-inflammatory drug commonly used to reduce fever, pain, stiffness, and swelling. It works by inhibiting the production of prostaglandins, molecules known to cause these symptoms. It is marketed under many trade names, including Indocin, Indocid, Indochron E-R, and Indocin-SR.

Indications

Clinical indications for indometacin include:

• Patent ductus arteriosus
• retinopathy of prematurity
• ankylosing spondylitis
• rheumatoid arthritis
• arthritic gout
• osteoarthritis
• juvenile arthritis
• psoriatic arthritis
• Reactive arthritis (ReA)
• Paget's disease of bone
• Bartter syndrome
• Exertion headaches
• pseudogout
• dysmenorrhea (menstrual cramps)
• pericarditis
• bursitis
• tendinitis
• nephrogenic diabetes insipidus (prostaglandin inhibits vasopressin's action in the kidney)
• fever and pain associated with malignant diseases (tumors, bony metastases, lymphogranulomatosis)
• paroxysmal hemicrania, hemicrania continua and migraine
• renal colic (pain due to kidney stones)
• cryoglobulinemia

Indomethacin has also been used clinically to delay premature labor, reduce amniotic fluid in polyhydramnios, and to close patent ductus arteriosus.

Indomethacin is a potent drug with many serious side effects and should not be considered an analgesic for minor aches and pains or fever. The drug is more potent than aspirin, but is not a better analgesic. In mild to moderate pain a standard oral dose of indomethacin proved as effective as 600 mg aspirin.

Contraindications

• concurrent peptic ulcer, or history of ulcer disease
• allergy to indomethacin, aspirin, or other NSAIDs
• patients with nasal polyps reacting with an angioedema to other NSAIDs

• children under 2 years of age (with the exception of neonates with patent ductus arteriosus)
• severe pre-existing renal and liver damage
• caution: pre-existing bone marrow damage (frequent blood cell counts are indicated)
• caution: bleeding tendencies of unknown origin (indomethacin inhibits platelet aggregation)
• caution: Parkinson's disease, epilepsy, psychotic disorders (indomethacin may worsen these conditions)
• concurrent with potassium sparing diuretics
• patients who have a patent ductus arteriosus dependent heart defect (such as Transposition of the great vessels)

Mechanism of action

Main article: Non-steroidal anti-inflammatory drug

Indomethacin is a nonselective inhibitor of cyclooxygenase (COX) 1 and 2, enzymes that participate in prostaglandin synthesis from arachidonic acid. Prostaglandins are hormone-like molecules normally found in the body, where they have a wide variety of effects, some of which lead to pain, fever, and inflammation.

Prostaglandins also cause uterine contractions in pregnant women. Indomethacin is an effective tocolytic agent, able to delay premature labor by reducing uterine contractions through inhibition of PG synthesis in the uterus and possibly through calcium channel blockade.

Indomethacin has two additional modes of actions with clinical importance:

• It inhibits motility of polymorphonuclear leukocytes, similar to colchicine.
• It uncouples oxidative phosphorylation in cartilaginous (and hepatic) mitochondria, like salicylates.

These additional effects account as well for the analgesic and the anti-inflammatory properties.

Indomethacin readily crosses the placenta and can reduce fetal urine production to treat polyhydramnios. It does so by reducing renal blood flow and increasing renal vascular resistance, possibly by enhancing the effects of vasopressin on the fetal kidneys.

Adverse effects

Since indomethacin inhibits both COX-1 and COX-2, it inhibits the production of prostaglandins in the stomach and intestines, which maintain the mucous lining of the gastrointestinal tract. Indomethacin, 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.

To reduce the possibility of peptic ulcers, indomethacin should be prescribed at the lowest dosage needed to achieve a therapeutic effect, usually between 50–200 mg/day. It should always be taken with food. Nearly all patients benefit from an ulcer protective drug (e.g. highly dosed antacids, ranitidine 150 mg at bedtime, or omeprazole 20 mg at bedtime). Other common gastrointestinal complaints, including dyspepsia, heartburn and mild diarrhea are less serious and rarely require discontinuation of indomethacin.

Many NSAIDs, but particularly indomethacin, cause lithium retention by reducing its excretion by the kidneys. Thus indomethacin 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.

Indomethacin also reduces plasma renin activity and aldosterone levels, and increases sodium and potassium retention. It also enhances the effects of vasopressin. Together these may lead to:

• edema (swelling due to fluid retention)
• hyperkalemia (high potassium levels)
• hypernatremia (high sodium levels)
• hypertension (high blood pressure)

The drug may also cause elevations of serum creatinine and more serious renal damage such as acute renal failure, chronic nephritis and nephrotic syndrome. These conditions also often begin with edema and hyperkalemia.

Additionally, indomethacin quite often causes headache (10 to 20%), sometimes with vertigo and dizziness, hearing loss, tinnitus, blurred vision (with or without retinal damage) and worsens 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.

Due to its strong antipyretic activity indomethacin may obscure the clinical course of serious infections.

Psychosis has also been reported with prolonged use.

The frequency and severity of side effects and the availability of better tolerated alternatives make indomethacin today a drug of second choice. Its use in acute gout attacks and in dysmenorrhea is well-established because in these indications the duration of treatment is limited to a few days only, therefore serious side effects are not likely to occur.

Necessary examinations during longterm treatment

Patients 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 indomethacin 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.

Animal toxicity and human overdose

Indomethacin has a high acute toxicity both for animals (12 mg/kg in rats and 50 mg/kg in mice) and for humans. Exact human data does not exist, but some fatal human cases, particularly in children and adolescents, have been seen.

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.

The treatment is symptomatic and largely the same as with diclofenac. However, the possibility of severe GI tract symptoms should be particularly noted.

The risk of overdose after exaggerated local treatment with gel or spray is very limited.

Usual dosage forms

• tablets or capsules 25 and 50 mg
• suppositories 50 and 100 mg
• modified-release Capsules 75 mg
• syrup (25 mg/5ml)
• injectable concentrate 50 mg for i.m. injection
• spray or gel
• patches containing 0.5% by weight
• 1% topical liquid

History

Indomethacin was discovered in 1963 and it was first approved for use in the U.S. by the Food and Drug Administration in 1965. Its mechanism of action, along with several other NSAIDs that inhibit COX, was described in 1971.

External links

• Effects of Perinatal Indomethacin Treatment on Preterm Infants, academic dissertation (PDF)
• Indomethacin, from MedicineNet
• Indomethacin, from Drugs.com
• Indocin: Description, chemistry, ingredients, from RxList.com

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