Progesterone Receptor Antagonist
Examples
Mifepristone (given with prostaglandin - misoprostol)
Indications
Medical termination of pregnancy
Contraindications
Contraindications
- Severe uncontrolled asthma
- Suspicion of ectopic pregnancy
- Adrenal failure
- Acute porphyria
- Hepatic impairment
- Renal impairment
Cautions
- Asthma
- Haemorrhagic disorders or anti-coagulant therapy
- Endocarditis
- Presence of prosthetic heart valve
- Cardiovascular disease - existing or presence of risk factors
- Adrenal suppression
Mechanism
Mifepristone binds the progesterone receptor with high affinity, thus preventing the binding of progesterone. Progesterone is essential for the maintenance of pregnancy.
Further its action as a partial agonist to prostaglandins sensitises the myometrium and when given in combination with prostaglandins (e.g. misoprostol) contractions are induced.
The combined action results in the termination of pregnancy.
Administration
Oral or Vaginal
Adverse Reactions
- Nausea, vomiting and gastro-intestinal cramps
- Uterine contractions
- Vaginal bleeding
- Malaise and faintness
- Skin rash
Interactions
Corticosteroids - mifepristone may reduce the effects
Education
Seek medical attention if heavy bleeding occurs.
Pharmacokinetics
Following oral administration the drug is rapidly absorbed. It is metabolised by the cytochrome P450 pathway in the liver and is excreted in the faeces (90%) and in the urine (10%).
