misoprostol
Prostaglandin E1 analog· Brands: Cytotec, Misotrol, MisoprostPOPRSL
Mechanism of action
Misoprostol is a synthetic prostaglandin E1 analogue. It binds to prostanoid receptors, particularly EP3 receptors, causing smooth muscle contraction in the uterus and gastrointestinal tract. In the stomach, it inhibits gastric acid secretion and enhances mucosal protection. The uterine contraction effect is used for induction of labour and management of postpartum haemorrhage. It also causes cervical ripening and softening, facilitating childbirth or abortion.
Pharmacokinetics
Misoprostol is rapidly absorbed after oral administration, with peak plasma concentrations within 30 minutes. It is metabolised in the liver to its active metabolite, misoprostol acid. The elimination half-life is about 20 to 40 minutes. It is excreted mainly in urine. When given sublingually or vaginally, absorption is variable and can be prolonged, leading to sustained uterine contractions. It crosses the placenta and may cause adverse effects on the fetus if used in pregnancy without proper indication.
Indications & dosing
Prevention of NSAID-induced gastric ulcers
Take with food; may cause diarrhoea.
- adult · PO: 200 mcg BID · Take with food; may cause diarrhoea.
Induction of labour (cervical ripening)off-label
Administered vaginally; maximum 6 doses. Off-label in some regions.
- adult · PR: 25 mcg q4-6h · Administered vaginally; maximum 6 doses. Off-label in some regions.
Medical termination of pregnancy (with mifepristone)
Given 24-48 hours after mifepristone.
- adult · SL: 800 mcg once · Given 24-48 hours after mifepristone.
Postpartum haemorrhage
May be repeated after 24 hours if needed.
- adult · PO: 600 mcg once · May be repeated after 24 hours if needed.
Contraindications & precautions
- Pregnancy (unless used for termination of pregnancy or under strict obstetric protocol) · Misoprostol can cause abortion, uterine rupture, and fetal harm.
- Hypersensitivity to misoprostol or other prostaglandins
- Exclude pregnancy before use in women of childbearing age and advise effective contraception.
- Use with caution in patients with cardiovascular disease, as misoprostol can cause hypotension.
- Use with caution in patients with inflammatory bowel disease, as it may worsen diarrhea.
- For obstetric indications, use only in accordance with local protocols and specialist supervision.
- Monitor for signs of uterine hyperstimulation in obstetric use.
Adverse effects
- Diarrhea
- Nausea
- Vomiting
- Abdominal pain
- Headache
- Dizziness
- Uterine ruptureserious
- Hypotensionserious
- Anaphylaxisserious
Renal & hepatic adjustment
- eGFR 0+: No dose adjustment required in renal impairment; use with caution in severe renal impairment due to increased risk of diarrhoea.
Monitoring, pregnancy & toxicity
- Uterine contractions · During labour induction or medical abortion
- Fetal heart rate · During labour induction
- Vaginal bleeding · Throughout treatment
- GI symptoms including diarrhoea · At each visit
- Pregnancy test · Before treatment in women of childbearing potential
- Signs of uterine rupture · In patients with prior uterine surgery
- Pregnancy: Contraindicated in pregnancy except for obstetric indications (induction of labour, medical abortion). Teratogenic; can cause uterine hyperstimulation and rupture. If used for NSAID-induced ulcer prevention in women of childbearing potential, ensure effective contraception before starting treatment.
- Toxicity: Diarrhoea and abdominal cramps · Supportive care; correction of fluid and electrolyte losses; consider antidiarrhoeal agents.
- Toxicity: Hypotension and bradycardia · Monitor vital signs; administer IV fluids and atropine if required.
- Toxicity: Uterine hyperstimulation in pregnant patients · Stop drug; monitor fetal heart rate; consider tocolysis; emergency obstetric care if necessary.
- Toxicity: Hyperthermia and seizures (rare) · Symptomatic treatment; cooling measures; anticonvulsants if required.
Clinical notes
Misoprostol is used for prevention and treatment of NSAID-induced gastric ulcers, for induction of labour, for medical abortion in combination with mifepristone, and for management of postpartum haemorrhage. It also has off-label uses, such as for cervical ripening. Doses vary by indication and route. It is contraindicated in pregnancy when used for ulcer protection, as it can induce abortion. Common side effects include nausea, vomiting, diarrhoea, abdominal pain, and fever. It should be used with caution in women of childbearing age, and appropriate counselling should be given. In many settings, misoprostol is listed as an essential medicine. Please refer to local guidelines and product information for specific dosing regimens.
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BNF; local formulary