Comparative contraceptive efficacy and mechanism of action of the norgestimate-containing triphasic oral contraceptive
London, R.S.; Chapdelaine, A.; Upmalis, D.; Olson, W.; Smith, J.
Acta Obstetricia et Gynecologica Scandinavica. Suppl 156: 9-14
1992
ISSN/ISBN: 0300-8835 PMID: 1324557 DOI: 10.3109/00016349209156509Document Number: 419012
Norgestimate (NGM), a derivative of 19-nortestosterone with very specific affinity for the progesterone receptor, has been used in combination with ethinyl estradiol (EE) in low doses in both monophasic and triphasic oral contraceptives (OCs). An open-label comparative clinical trial was conducted with 4234 healthy women using triphasic levonorgestrel (LNG)/EE and NGM/EE through a total of 22,312 menstrual cycles. Contraceptive efficacy was excellent with both preparations with no statistically significant between-regimen differences in pregnancy rates. The theoretical Pearl index was 0.12 for the NGM/EE triphasic, and 0.34 for the LNG/EE triphasic. Adverse experiences in both groups were typical of those which could occur among women taking low-dose OCs. The % of subjects who discontinued treatment due to use-related adverse experiences was similar among the 2 preparations; 8.6% for the NGM/EE triphasic and 6.8% for the LNG/EE triphasic. In a separate mechanism of action study, specific endocrine parameters were investigated in 20 subjects who used the NGM/EE triphasic for 4 cycles. Ovulation suppression was demonstrated in statistically significant decreases from pretreatment values in serum levels of luteinizing hormone, follicle stimulating hormone, progesterone, and estradiol. Significant on-treatment increases in serum levels of sex hormone binding globulin evidenced minimal androgenicity. All hormonal values returned to or toward normal in the posttreatment cycle. The study results support those obtained in large noncomparative studies of the NGM/EE triphasic. This phased-dose combination suppresses ovulation and is a very effective, minimally androgenic contraceptive with good safety profile.