Long-term contraception by steroid-releasing implants. II A preliminary report on long-term contraception by a single silastic implant containing norethindrone acetate (ENTA) in women

Abstract

This paper describes the long-term contraceptive effectiveness and acceptability of 4 different types of subdermal Silastic implants (A, B, C and D) containing norethindrone acetate in women. The four implants varied in their length, the wall-thickness, the amount of progestin contained in them and the average release rates. These were developed one after another to evolve a more effective, acceptable and longer acting implant. A single implant was administered to each of 213 women volunteers and followed for a total of 909 cycles. There were a total of 120 cycles in 13 women bearing implant A; 305 cycles in 39 women bearing implant B; 202 cycles in 76 women bearing implant C and 282 cycles in 85 women bearing an implant of type D. Pregnancies with implant A, B, C and D were 2, 2, 3 and 0, respectively. Menstrual irregularities were minimal with implant D; 80% of the cycles being normal. The use of the single implant D holds promise as a useful contraceptive method effective for almost a year.