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Bexarotene

Author: Anoma Ranaweera B.V. Sc; PhD (Clinical Biochemistry, University of Liverpool, UK), 2011.

Bexarotene is a medicine mainly used to treat cutaneous T-cell lymphoma (CTCL). It is not available in New Zealand.

Indications for treatment with bexarotene

Bexarotene (Targretin®; Ligand Pharmaceuticals Inc., San Diego, CA, U.S.A) is a member of a subclass of retinoids called rexinoids that selectively activate retinoid X receptors (RXRs), which have a biological activity distinct from retinoic acid receptors (RARs). Bexarotene capsules and bexarotene gel are used for the treatment of:

Mechanism of action of bexarotene

Bexarotene binds to, and activates RXRs which function as ligand-activated transcription factors that control gene expression. This leads to modulation of cell growth, apoptosis, and differentiation. Bexarotene inhibits the growth in vitro of some tumour cell lines of haematopoietic (blood) and squamous cell (skin) origin. It also induces tumour regression in vivo in some animal models. The exact mechanism of action of bexarotene in the treatment of cutaneous T-cell lymphoma (CTCL) is unknown.

Pharmacology of bexarotene

Dosage and administration of bexarotene

Bexarotene capsules

Each soft gelatin capsule for oral administration contains 75 mg of bexarotene. The recommended initial dose is 300 mg/m2/day.

Bexarotene gel 1%

Monitoring bexarotene

Adverse events due to bexarotene

The safety of bexarotene capsules has been evaluated in clinical studies. The most common adverse events reported with an incidence of at least 10% in patients with CTCL treated at an initial dose of 300 mg/m2/day are:

Adverse effects reported with topical bexarotene (incidence >10%) include:

Adverse events with topical bexarotene at an incidence of 1-10% have included:

Contraindications to bexarotene

Drug interactions

Use of bexarotene in specific populations

Pregnancy: Category X

Use in nursing mothers

It is not known whether bexarotene is excreted in human milk. Because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants, a decision should be made whether to discontinue nursing or to discontinue oral bexarotene, taking into account the importance of the drug to the mother.

Pediatric use

Safety and effectiveness in children have not been established.

Vitamin A supplementation

Because of the relationship of bexarotene to vitamin A, patients should be advised to limit vitamin A supplements to ≤15,000 IU/day to avoid potential additive toxic effects.

Patients with diabetes mellitus

Caution should be used when administering bexarotene capsules to patients using insulin, agents enhancing insulin secretion (e.g., sulfonylureas), or insulin-sensitizers (e.g., thiazolidinedione class). Based on its mechanism of action, bexarotene capsules could enhance the action of these agents, resulting in hypoglycaemia (low blood sugar).

Photosensitivity

Retinoids as a class have been associated with photosensitivity. Mild phototoxicity manifested as sunburn and skin sensitivity to sunlight has been observed in patients who are exposed to direct sunlight while receiving oral bexarotene. Patients should be advised to minimize exposure to sunlight and artificial ultraviolet light (including phototherapy and solaria) while receiving treatment with bexarotene.

Renal insufficiency

No formal studies have been conducted in patients with renal insufficiency (kidney disease). Urinary elimination of bexarotene and its known metabolites is a minor excretory pathway for bexarotene (<1% of administered dose), but because renal insufficiency can result in significant protein binding changes, and bexarotene is >99% protein bound, pharmacokinetics (drug concentrations) may be altered in patients with renal insufficiency.

Overdosage of bexarotene

There are no reports of clinical experience with an overdose. Any overdose with bexarotene capsules should be treated with supportive care for the signs and symptoms exhibited by the patient.

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