Progestins
Progestins
Progestins are hormones used to treat various forms of cancer. These drugs include:
- hydroxyprogesterone caproate
- medroxyprogesterone acetate
- megestrol acetate.
Pharmacokinetics
When taken orally, megestrol acetate is well absorbed. After I.M. injection in an aqueous or oil suspension, hydroxyprogesterone caproate and medroxyprogesterone are absorbed slowly from their deposit sites.
Warning!
Adverse reactions to antiandrogens
When antiandrogens are used with gonadotropin-releasing hormone analogues, the most common adverse reactions are:
- hot flashes
- decreased sexual desire
- impotence
- diarrhea
- nausea
- vomiting
- breast enlargement.
Pharmacodynamics
The mechanism of action of progestins in treating tumors isn’t completely understood. Researchers believe the drugs bind to a specific receptor to act on hormonally sensitive cells.
They aren’t exhibitionists
Because progestins don’t exhibit a cytotoxic activity (destroying or poisoning cells), they’re considered cytostatic (they keep the cells from multiplying).
Pharmacotherapeutics
Progestins are used for the palliative treatment of advanced endometrial, breast, prostate, and renal cancers. Of these drugs, megestrol is used most commonly.
Drug interactions
No drug interactions have been identified for megestrol. However, other progestins do have significant interactions with other drugs.
- Barbiturates, carbamazepine, and rifampin reduce the progestin effects of hydroxyprogesterone.
- Hydroxyprogesterone and medroxyprogesterone may interfere with bromocriptine’s effects, causing menstruation to stop.
- Hydroxyprogesterone taken with dantrolene and other liver-toxic drugs increases the risk of liver toxicity.
- Dose adjustments in oral anticoagulants may be needed when they’re taken with hydroxyprogesterone.
- Aminoglutethimide and rifampin may reduce the progestin effects of medroxyprogesterone. (See Adverse reactions to progestins.)
Warning!
Adverse reactions to progestins
Mild fluid retention is probably the most common reaction to progestins. Other adverse reactions include:
- thromboemboli
- breakthrough bleeding, spotting, and changes in menstrual flow
- breast tenderness
- liver function abnormalities.
Oil issues
Patients who are hypersensitive to the oil carrier used for injection (usually sesame or castor oil) may experience a local or systemic hypersensitivity reaction.
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