Patients with severe hepatic impairment should remain under constant surveillance.
As letrozole is only used in postmenopausal patients, it is recommended to determine LH, FSH and/or oestradiol concentrations prior to treatment if the endocrine regulation status of the reproductive system is unclear.
Increased serum FSH concentrations lead to stimulation of ovarian follicle growth and may induce ovulation, therefore there is a potential possibility of pregnancy in peri-menopausal and early postmenopausal women during treatment with letrozole. In such cases, reliable methods of contraception should be used until stable postmenopausal hormone levels are established in this category of patients.
There are data on the development of osteoporosis and/or the incidence of bone fractures during the use of letrozole, therefore careful monitoring of bone status throughout the use of letrozole is recommended. It is recommended to avoid concomitant use of letrozole with tamoxifen, other anti-estrogen and estrogen-containing drugs, as these agents may attenuate the pharmacological effects of letrozole.
Letrozole is not indicated for the treatment of breast cancer without receptors for steroid hormones (oestrogen or progesterone).
Effects on the ability to drive and operate machinery
Some side effects of letrozole, such as general weakness, drowsiness and dizziness, may affect the ability to perform potentially hazardous activities requiring increased concentration and rapid psychomotor reactions. Consequently, caution should be exercised when driving and operating machinery. If these side effects occur, refrain from these activities.