Regost

Uses

Adjuvant treatment of post-menopausal women with hormone receptor-positive early breast cancer, and also advanced breast cancer in post-menopausal women. First-line treatment of hormone receptor-positive post-menopausal women who have received 2 to 3 years of adjuvant tamoxifen.

Regost is also used to associated treatment for these conditions: Advanced Breast Cancer, Early Breast Cancer, Locally Advanced Breast Cancer (LABC), Metastatic Breast Cancer, Invasive, early Breast Cancer

How Regost works

Anastrazole exerts its anti-estrogenic effects via selective and competitive inhibition of the aromatase enzyme found predominantly in the adrenal glands, liver, and fatty tissues. Many breast cancers are hormone receptor-positive, meaning their growth is stimulated and/or maintained by the presence of hormones such as estrogen or progesterone. In postmenopausal women, estrogen is primarily derived from the conversion of adrenally-produced androgens into estrogens by the aromatase enzyme - by competitively inhibiting the biosynthesis of estrogen at these enzymes, anastrozole effectively suppresses circulating estrogen levels and, subsequently, the growth of hormone receptor-positive tumours.

Dosage

Regost dosage

Adults and elderly: 1 mg tablet to be taken orally once a day.

Side Effects

More common side effects are: Blurred vision chest pain or discomfort, dizziness, headache nervousness, pounding in the ears, shortness of breath, slow or fast heartbeat, swelling of the feet or lower legs

Toxicity

The reported oral TDLo in a human woman is 1.68 mg/kg given intermittently over the course of 12 weeks. Knowledge of the signs and symptoms of anastrozole overdose is incomplete as there are no documented descriptions of a patient receiving more than 60mg, a dose which was administered to a healthy male volunteer and was well-tolerated. There is no antidote for anastrozole and treatment should be supportive and symptomatic, including close monitoring of patient vital signs. As anastrozole exhibits relatively low protein binding, dialysis may be helpful and should be considered in select cases.

Precaution

There are no data to support the safe use of anastrozole in patients with moderate or severe hepatic impairment, or patients with severe impairment of renal function (creatinine clearance less than 20 mL/min). Women with osteoporosis or at risk of osteoporosis should have their bone mineral density at regular intervals monitored.

There are no data available for the use of anastrozole with LHRH analogues. This product contains lactose. Patients with rare hereditary problems of galactose intolerance, the lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.

Interaction

Antipyrine and cemetidine clinical interaction studies indicate that the co administration of anastrozole with other drugs is unlikely to result in clinically significant drug interactions mediated by cytochrome P450. Tamoxifen should not be co-administered with anastrozole as this may reduce its pharmacological action.

Food Interaction

• Take with or without food. Co-administration with food reduces the rate, but not the overall extent, of absorption.

Regost Cholesterol interaction

[Moderate] During a clinical trial, more patients receiving anastrozole were reported to have elevated serum cholesterol compared to patients receiving tamoxifen (9% versus 3.5%, respectively).

Caution should be taken when this agent is prescribed to these patients.

Regost Disease Interaction

Moderate: cardiovascular, cholesterol, hepatic dysfunction, osteoporosis

Volume of Distribution

The volume of distribution of anastrozole into brain tissue in mice is 3.19 mL/g. Distribution into the CNS is limited due to the activity of P-gp efflux pumps at the blood brain barrier, of which anastrozole is a substrate.

Elimination Route

Regost is rapidly absorbed and T_max is typically reached within 2 hours of dosing under fasted conditions. Coadministration with food reduces the rate but not the overall extent of absorption - mean C_max decreased by 16% and the median T_max was extended to 5 hours when anastrozole was administered 30 minutes after ingestion of food, though this relatively minor alteration in absorption kinetics is not expected to result in clinically significant effects.

Half Life

The elimination half-life of anastrozole is approximately 50 hours.

Clearance

Regost's clearance is mainly via hepatic metabolism and can therefore be altered in patients with hepatic impairment - patients with stable hepatic cirrhosis exhibit an apparent oral clearance approximately 30% lower compared with patients with normal liver function. Conversely, renal impairment has a negligible effect on total drug clearance as the renal route is a relatively minor clearance pathway for anastrozole. In volunteers with severe renal impairment, renal clearance was reduced by 50% while total clearance was only reduced by approximately 10%.

Elimination Route

Hepatic metabolism accounts for approximately 85% of anastrozole elimination. Approximately 10% of the administered dosage is eliminated unchanged in the urine.

Pregnancy & Breastfeeding use

Regost is contraindicated in pregnant and lactating women.

Contraindication

Patients with severe renal impairment (Creatinine clearance less than 20 mL/min), patients with moderate to severe hepatic disease and known hypersensitivity to anastrozole or to any of the excipients. Oestrozen-containing therapies should not be co-administered with anastrazole as they would negate its pharmacological action.

Special Warning

Renal impairment: No dose change is recommended in patients with mild or moderate renal impairment.

Hepatic impairment: No dose change is recommended in patients with mild hepatic impairment. For early disease, the recommended duration of treatment should be 5 years.

Acute Overdose

Clinical trials have been conducted with Regost tablets, up to 60 mg in a single dose given to healthy male volunteers and up to 10 mg daily given to postmenopausal women with advanced breast cancer; these dosages were tolerated. A single dose of Regost tablets that results in life-threatening symptoms has not been established. There is no specific antidote to overdosage and treatment must be symptomatic.

In the management of an overdose, consider that multiple agents may have been taken. Vomiting may be induced if the patient is alert. Dialysis may be helpful because Regost tablet is not highly protein bound. General supportive care, including frequent monitoring of vital signs and close observation of the patient, is indicated.

Storage Condition

Product should be stored within 30°C

Innovators Monograph

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