Letrozole

In vitro, letrozole inhibits the cytochrome P450 isoenzymes 2A6 and, moderately, 2C19 but the clinical relevance is unknown. Caution is therefore indicated when giving letrozole concomitantly with medicinal products whose elimination is mainly dependent on these isoenzymes and whose therapeutic index is narrow (e.g. phenytoin, clopidrogel).

Insufficient data are available for patients with severe hepatic impairment. Patients with severe hepatic impairment (Child-Pugh C) require close supervision.

The pharmacological action of letrozole is to reduce oestrogen production by aromatase inhibition. In premenopausal women, the inhibition of oestrogen synthesis leads to feedback increases in gonadotropin (LH, FSH) levels. Increased FSH levels in turn stimulate follicular growth, and can induce ovulation.

There is no clinical experience to date on the use of letrozole in combination with oestrogens or other anticancer agents, other than tamoxifen. Tamoxifen, other anti-oestrogens or oestrogen-containing therapies may diminish the pharmacological action of letrozole. In addition, co-administration of tamoxifen with letrozole has been shown to substantially decrease plasma concentrations of letrozole. Co-administration of letrozole with tamoxifen, other anti-oestrogens or oestrogens should be avoided.

Letrozole is a potent oestrogen-lowering agent. Women with a history of osteoporosis and/or fractures, or who are at increased risk of osteoporosis, should have their bone mineral density formally assessed prior to the commencement of adjuvant and extended adjuvant treatment and monitored during and following treatment with letrozole. Treatment or prophylaxis for osteoporosis should be initiated as appropriate and carefully monitored. In the adjuvant setting a sequential treatment schedule (letrozole 2 years followed by tamoxifen 3 years) could also be considered depending on the patient’s safety profile.

Based on human experience in which there have been isolated cases of birth defects (labial fusion, ambiguous genitalia), letrozole may cause congenital malformations when administered during pregnancy. Studies in animals have shown reproductive toxicity. Letrozole is contraindicated during pregnancy.

It is unknown whether letrozole and its metabolites are excreted in human milk. A risk to the newborns/infants cannot be excluded.

Letrozole is contraindicated during breast-feeding.

Women of perimenopausal status or child-bearing potential

Letrozole should only be used in women with a clearly established postmenopausal status. As there are reports of women regaining ovarian function during treatment with letrozole despite a clear postmenopausal status at start of therapy, the physician needs to discuss adequate contraception when necessary.

Fertility

The pharmacological action of letrozole is to reduce oestrogen production by aromatase inhibition. In premenopausal women, the inhibition of oestrogen synthesis leads to feedback increases in gonadotropin (LH, FSH) levels. Increased FSH levels in turn stimulate follicular growth, and can induce ovulation.

Letrozole has minor influence on the ability to drive and use machines. Since fatigue and dizziness have been observed with the use of letrozole and somnolence has been reported uncommonly, caution is advised when driving or using machines.

Summary of the safety profile

The frequencies of adverse reactions for letrozole are mainly based on data collected from clinical trials.

Up to approximately one third of the patients treated with letrozole in the metastatic setting and approximately 80% of the patients in the adjuvant setting as well as in the extended adjuvant setting experienced adverse reactions. The majority of the adverse reactions occurred during the first few weeks of treatment.

The most frequently reported adverse reactions in clinical studies were hot flushes, hypercholesterolaemia, arthralgia, fatigue, increased sweating and nausea.

Important additional adverse reactions that may occur with letrozole are: skeletal events such as osteoporosis and/or bone fractures and cardiovascular events (including cerebrovascular and thromboembolic events). The frequency category for these adverse reactions is described in following list.

List of adverse reactions

The frequencies of adverse reactions for letrozole are mainly based on data collected from clinical trials.

The following adverse drug reactions, listed below were reported from clinical studies and from post marketing experience with letrozole: Adverse reactions are ranked under headings of frequency, the most frequent first, using the following convention: very common ≥10%, common ≥1% to <10%, uncommon ≥0.1% to <1%, rare ≥0.01% to <0.1%, very rare <0.01%, not known (cannot be estimated from the available data).

Infections and infestations

Uncommon: Urinary tract infection

Neoplasms, benign, malignant and unspecified (including cysts and polyps)

Uncommon: Tumour pain¹

Blood and the lymphatic system disorders

Uncommon: Leukopenia

Immune system disorders

Not known: Anaphylactic reaction

Metabolism and nutrition disorders

Very common: Hypercholesterolaemia

Common: Anorexia, appetite increase

Psychiatric disorders

Common: Depression

Uncommon: Anxiety (including nervousness), irritability

Nervous system disorders

Common: Headache, dizziness

Uncommon: Somnolence, insomnia, memory impairment, dysaesthesia (including paresthesia, hypoesthesia), taste disturbance, cerebrovascular accident, carpal tunnel syndrome

Eye disorders

Uncommon: Cataract, eye irritation, blurred vision

Cardiac disorders

Uncommon: Tachycardia, ischaemic cardiac events (including new or worsening angina, angina requiring surgery, myocardial infarction and myocardial ischaemia)

Common: Palpitations¹

Vascular disorders

Very common: Hot flushes

Common: Hypertension

Uncommon: Thrombophlebitis (including superficial and deep vein thrombophlebitis)

Rare: Pulmonary embolism, arterial thrombosis, cerebrovascular infarction

Respiratory, thoracic and mediastinal disorders

Uncommon: Dyspnoea, cough

Gastrointestinal disorders

Common: Nausea, dyspepsia¹, constipation, abdominal pain, diarrhoea, vomiting

Uncommon: Dry mouth, stomatitis¹

Hepatobiliary disorders

Uncommon: Increased hepatic enzymes, hyperbilirubinemia, jaundice

Not known: Hepatitis

Skin and subcutaneous tissue disorders

Very common: Increased sweating

Common: Alopecia, rash (including erythematous, maculopapular, psoriaform, and vesicular rash), dry skin

Uncommon: Pruritus, urticaria

Not known: Angioedema, toxic epidermal necrolysis, erythema multiforme

Musculoskeletal and connective tissue disorders

Very common: Arthralgia

Common: Myalgia, bone pain¹, osteoporosis, bone fractures, arthritis

Not known: Trigger finger

Renal and urinary disorders

Uncommon: Increased urinary frequency

Reproductive system and breast disorders

Common: Vaginal bleeding

Uncommon: Vaginal discharge, vaginal dryness, breast pain

General disorders and administration site conditions

Very common: Fatigue (including asthenia, malaise)

Common: Peripheral oedema, chest pain

Uncommon: General oedema, mucosal dryness, thirst, pyrexia

Investigations

Common: Weight increase

Uncommon: Weight loss

¹ Adverse drug reactions reported only in the metastatic setting

Some adverse reactions have been reported with notably different frequencies in the adjuvant treatment setting. The following tables provide information on significant differences in letrozole versus tamoxifen monotherapy and in the letrozole-tamoxifen sequential treatment therapy:

Adjuvant letrozole monotherapy versus tamoxifen monotherapy – adverse events with significant differences:

Note: “During treatment” includes 30 days after last dose. “Any time” includes follow-up period after completion or discontinuation of study treatment.

Differences were based on risk ratios and 95% confidence intervals.

Sequential treatment versus letrozole monotherapy – adverse events with significant differences:

* Significantly less than with letrozole monotherapy
** Significantly more than with letrozole monotherapy
Note: Reporting period is during treatment or within 30 days of stopping treatment.

Description of selected adverse reactions

Cardiac adverse reactions

In the adjuvant setting, in addition to the data presented in the table above, the following adverse events were reported for letrozole and tamoxifen, respectively (at median treatment duration of 60 months plus 30 days): angina requiring surgery (1.0% vs. 1.0%); cardiac failure (1.1% vs. 0.6%); hypertension (5.6% vs. 5.7%); cerebrovascular accident/transient ischaemic attack (2.1% vs. 1.9%).

In the extended adjuvant setting for letrozole (median duration of treatment 5 years) and placebo (median duration of treatment 3 years), respectively: angina requiring surgery (0.8% vs. 0.6%); new or worsening angina (1.4% vs. 1.0%); myocardial infarction (1.0% vs. 0.7%); thromboembolic event* (0.9% vs. 0.3%); stroke/transient ischaemic attack* (1.5% vs. 0.8%) were reported.

Events marked * were statistically significantly different in the two treatment arms.

Skeletal adverse reactions

For skeletal safety data from the adjuvant setting, please refer to the table above.

In the extended adjuvant setting, significantly more patients treated with letrozole experienced bone fractures or osteoporosis (bone fractures, 10.4% and osteoporosis, 12.2%) than patients in the placebo arm (5.8% and 6.4%, respectively). Median duration of treatment was 5 years for letrozole, compared with 3 years for placebo.