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  • Title: Subdermal norethindrone pellets -- a method for contraception?
    Author: Odlind V, Moo-Young AJ, Gupta GN, Weiner E, Johansson ED.
    Journal: Contraception; 1979 Jun; 19(6):639-48. PubMed ID: 487813.
    Abstract:
    The mode of action of compressed pellets containing 85 per cent norethindrone (NET) and 15 per cent cholesterol was studied. Four pellets were inserted subcutaneously, in each of five healthy volunteers and left in place for 200--229 days. The NET content of the pellets varied between 23.9 mg and 25.6 mg; and the cholesterol content between 4.2 mg and 4.5 mg. Plasma levels of NET, estradiol and progesterone were determined by radioimmunoassays. Plasma levels of NET varied mostly between 1--2 ng/ml the first month after insertion. After two months plasma levels of NET ranged between 0.5 ng/ml and 1 ng/ml in all volunteers and there was a gradual decrease of the plasma NET levels throughout treatment. Pronounced day-to-day variations in plasma NET levels were recorded. The release rates of NET was calculated to be between 187 micrograms/day and 243 micrograms/day among the five volunteers. Ovulations occurred in four out of five subjects during treatment. This study indicates that the release of gestagen from four NET pellets was only initially high enough to completely inhibit ovulation and that to accomplish full contraceptive efficacy, a higher dose, i.e. more pellets, would have to be inserted. Pellets containing norethindrone (NET)-cholesterol (85%:15%, weight to weight) used for long-term subdermal implant for contraception were studied to elucidate their mode of action. Plasma levels of NET, estradiol, and progesterone were measured by radioimmunoassay; bleeding pattern was recorded; and daily release of NET was calculated after pellet removal from 5 healthy volunteers, each of whom had 4 subdermal pellets implanted for 200-229 days. NET content of pellets varied from 23.9 mg-25.6 mg; cholesterol content varied from 4.2-4.5 mg. Plasma levels of NET varied mostly between 1 and 2 ng/ml the 1st month after insertion. After 2 months, plasma levels of NET ranged from .5-1 ng/ml in all volunteers; there was a gradual decrease of the plasma NET levels throughout treatment. Pronounced day-to-day variations in plasma NET levels were recorded. Release rates of NET were calculated as between 187 and 243 mcg/day among the 5 volunteers. Ovulation occurred in 4/5 subjects, as determiend by hormonal profiles, during treatment. Overall, the release of NET was only high enough during the initial phase to completely inhibit ovulation, and therefore, to accomplish full contraceptive efficacy, a higher dose, i.e., more pellets, must be inserted subdermally.
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