Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2018 Publisher: Bayer plc, 400 South Oak Way, Reading, RG2 6AD
Pharmacotherapeutic group: sex hormones and modulators of the genital system, progestogens; Estren derivatives
ATC Code: G03DC02
Norethisterone has progestational actions similar to those of progesterone, but is a more potent inhibitor of ovulation and has weak oestrogenic and androgenic properties. It is used to treat a number of disorders of the menstrual cycle.
Norethisterone is absorbed from the gastro-intestinal tract and its effects last for at least 24 hours. It is excreted in the urine.
Norethisterone is partly metabolised to ethinylestradiol after oral administration of norethisterone or norethisterone acetate in humans. This conversion results in an equivalent dose of about 4-6 µg ethinylestradiol per 1 mg orally administered norethisterone/norethisterone acetate.
Non-clinical data on norethisterone or its esters reveal no special risk for humans based on conventional studies of repeated dose toxicity, genotoxicity and carcinogenic potential which is not already included in other relevant sections. However, it should be kept in mind that sexual steroids might stimulate the growth of hormone-dependent tissues and tumours.
Reproduction toxicity studies showed the risk of masculinisation in female fetuses when administered at high doses at the time of the development of the external genitalia. Since epidemiological studies show that this effect is relevant in humans after high doses, it must be stated that Primolut N may provoke signs of virilisation in female fetuses if administered during the hormone-sensitive stage of somatic sexual differentiation (from day 45 of pregnancy onwards). Apart from this, no indications of teratogenic effects were obtained from the studies.
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