Medroxyprogesterone Other names: Medroxyprogesterone acetate

Medroxyprogesterone acetate (MPA) is metabolized in-vitro primarily by hydroxylation via the CYP3A4. Specific drug-drug interaction studies evaluating the clinical effects with CYP3A4 inducers or inhibitors on MPA have not been conducted and therefore the clinical effects of CYP3A4 inducers or inhibitors are unknown.

Aminoglutethimide administered concurrently with medroxyprogesterone may significantly depress the bioavailability of medroxyprogesterone.

The metabolism of progestogens may be increased by concomitant use of substances known to induce drug-metabolising enzymes, specifically cytochrome P450 enzymes, such as anticonvulsants (e.g. phenobarbital, phenytoin, carbamazepine) and anti-infectives (e.g. rifampicin, rifabutin, nevirapine, efavirenz).

Medroxyprogesterone, especially in high doses, may cause weight gain and fluid retention. With this in mind, caution should be exercised in treating any patient with a pre-existing medical condition, such as epilepsy, migraine, asthma, cardiac or renal dysfunction, that might be adversely affected by weight gain or fluid retention.

Oral administration

Medroxyprogesterone acetate is not indicated during pregnancy. If pregnancy occurs during medication with medroxyprogesterone acetate, treatment should be withdrawn immediately.

The results of most epidemiological studies to date relevant to inadvertent foetal exposure to progestogens indicate no teratogenic or foetotoxic effect.

Intramuscular administration

Doctors should check that patients are not pregnant before initial injection of medroxyprogesterone acetate, and also if administration of any subsequent injection is delayed beyond 89 days (12 weeks and five days).

Infants from accidental pregnancies that occur 1-2 months after injection of medroxyprogesterone acetate may be at an increased risk of low birth weight, which in turn is associated with an increased risk of neonatal death. The attributable risk is low because such pregnancies are uncommon.

Medroxyprogesterone acetate is not indicated during lactation.

Medroxyprogesterone acetate and/or its metabolites are secreted in breast milk, but there is no evidence to suggest that this presents any hazard to the child. Infants exposed to medroxyprogesterone acetate via breast milk have been studied for developmental and behavioural effects to puberty. No adverse effects have been noted.

Children exposed to medroxyprogesterone acetate in utero and followed to adolescence, showed no evidence of any adverse effects on their health including their physical, intellectual, sexual or social development.

Medroxyprogesterone acetate may cause headaches and dizziness. Patients should be advised not to drive or operate machinery if affected.