Pharmacology & pharmacokinetics

This page includes information for health professionals about Mariprist's mechanism of action, drug interactions, and other important pharmacokinetic information.


  • Mariprist contains one 200mg tablet of mifepristone and four 200mcg tablets of misoprostol.

  • Mifepristone is a synthetic steroid with an antiprogestational action as a result of competition with progesterone at the progesterone receptors. It is almost exclusively used for termination of pregnancy.

  • Misoprostol is a synthetic prostaglandin E1 analogue. In comparison to other prostaglandin analogues, misoprostol is cheap, widely available, stable at room temperature, and has few side effects.

  • Misoprostol's clinical applications include: medical abortion; treatment of incomplete abortion and miscarriages; cervical priming prior to surgical procedures; induction of labour; and prevention and treatment management of postpartum haemorrhage.

  • As well as its obstetric and gynaecological indications, misoprostol is also used in the prevention and treatment of peptic ulcers.


  • The plasma elimination half-life for mifepristone is 30-40 hours, and for misoprostol is 20-40 minutes. After oral administration, mifepristone is rapidly and almost completely absorbed. Plasma concentrations peak at about 45 minutes.

  • Mifepristone is primarily metabolised by CYP3A4 enzyme.

  • After sublingual administration, misoprostol dissolves and is absorbed rapidly, with peak concentrations occurring at about 30 minutes. Bioavailability is very high.

Drug interactions

  • Few drug interactions studies have been performed with mifepristone. However, as a substrate and weak inhibitor of CYP3A4 enzyme, mifepristone may theoretically have clinically significant drug interactions with CYP3A4 inducers, inhibitors or substrates. Caution is advised in clients using any such medications.

  • Misoprostol has not been shown to have an effect on hepatic P450 enzyme systems.

  • Antacids may decrease the bioavailability of misoprostol, and antacids containing magnesium may aggravate diarrhoea caused by misoprostol. Otherwise, no clinically significant drug interactions have been identified with misoprostol.

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