CLINICAL PHARMACOLOGY:
Danazol suppresses the pituitary-ovarian axis. This suppression is probably a combination of depressed hypothalamic-pituitary response to lowered estrogen production, the alteration of sex steroid metabolism, and interaction of danazol with sex hormone receptors. The only other demonstrable hormonal effect is weak androgenic activity. Danazol depresses the output of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
Recent evidence suggests a direct inhibitory effect at gonadal sites and a binding of danazol to receptors of gonadal steroids at target organs. In addition, danazol has been shown to significantly decrease IgG, IgM and IgA levels, as well as phospholipid and IgG isotope autoantibodies in patients with endometriosis and associated elevations of autoantibodies, suggesting this could be another mechanism by which it facilitates regression of the disease.
Bioavailability studies indicate that blood levels do not increase proportionally with increases in the administered dose. When the dose of danazol is doubled the increase in plasma levels is only about 35% to 40%.
Separate single dosing of 100 mg and 200 mg capsules of danazol to female volunteers showed that both the extent of availability and the maximum plasma concentration increased by three-to-four fold, respectively, following a meal (> 30 grams of fat), when compared to the fasted state. Further, food also delayed mean time to peak concentration of danazol by about 30 minutes.
In the treatment of endometriosis, danazol alters the normal and ectopic endometrial tissue so that it becomes inactive and atrophic. Complete resolution of endometrial lesions occurs in the majority of cases.
Changes in vaginal cytology and cervical mucus reflect the suppressive effect of danazol on the pituitary-ovarian axis.
In the treatment of fibrocystic breast disease, danazol usually produces partial to complete disappearance of nodularity and complete relief of pain and tenderness. Changes in the menstrual pattern may occur.
Generally, the pituitary-suppressive action of danazol is reversible. Ovulation and cyclic bleeding usually return within 60 to 90 days when therapy with danazol is discontinued.
In the treatment of hereditary angioedema, danazol at effective doses prevents attacks of the disease characterized by episodic edema of the abdominal viscera, extremities, face, and airway which may be disabling and, if the airway is involved, fatal. In addition, danazol corrects partially or completely the primary biochemical abnormality of hereditary angioedema by increasing the levels of the deficient C1 esterase inhibitor (C1EI). As a result of this action the serum levels of the C4 component of the complement system are also increased.
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