Brand Name Drug: Targretin
Active Ingredient Drug: bexarotene
Indication: Treatment of cutaneous manifestations of early and advanced cutaneous T-cell lymphoma in patients refractory to at least one prior systemic therapy
Company Name: Ligand Pharmaceuticals Incorporated
Availability: Approved by FDA December 29, 1999
Introduction
Cutaneous T-cell lymphoma (CTCL) is a cancer of the T lymphocytes and afflicts between 16,000 and 20,000 people in the U.S. The cancer ordinarily manifests itself in the skin, but over time may progress to involve other organs. Skin lesions in CTCL patients can become deforming and culminate in ulceration, with secondary infection. Many treatments for cutaneous T-cell lymphoma have been external, such as UV light therapy and electron beam therapy.
Now a new drug manufactured by Ligand Pharmaceuticals Incorporated offers CTCL patients a more convenient form of treatment: Targretin (bexarotene). Targretin is an oral retinoid drug that can be taken once daily and has been shown to help some patients by reducing the severity of skin lesions. It is available in gelatin capsule form, with a recommended dosage of 300 mg/day per square meter of body surface area, to be taken with food. A gel form of Targretin is currently under review by the FDA.
How It Works
Targretin selectively binds to and activates retinoid X receptors (RXRs), which play an important role in cellular differentiation and proliferation. Targretin inhibits the growth in vitro of some tumor cell lines of hematopoietic and squamous cell origin, and has also induced tumor regression in animal studies. The exact mechanism of action of Targretin in the treatment of cutaneous T-cell lymphoma is unknown.
Targretin: Clinical Study Results
Two multicenter, open-label clinical studies were conducted in the U.S., Canada, Europe, and Australia to evaluate Targretin in 152 patients with advanced and early stage cutaneous T-cell lymphoma. Of this group, 102 were found to have been refractory to at least two prior therapies – one of them systemic – including 90 patients with advanced disease and 12 with early disease. Patients had an
Patients were treated with 300 mg/m(2)/day, a dosage that could be increased to 400 mg if no response was seen after 8 or more weeks of therapy and the patient could tolerate the drug. Tumor response was assessed using a Composite Assessment of Index Lesion Disease Severity, with a partial response defined as an improvement of at least 50% of the index lesions without worsening of lesions or development of new ones. A complete clinical response required complete disappearance of all manifestations of disease.
At the 300 mg dose, 1.6% of patients had a complete tumor response and 30% had a partial response. The rate of relapse in the patients who had a tumor response was 30% over a median observation period of 21 weeks. Responses were observed as early as 4 weeks and new responses continued to be seen at later visits.
What the Patient Should Know
Several mild to moderate events were observed in association with Targretin, and were essentially reversible. These included elevated blood triglycerides and cholesterol and decreased HDL cholesterol, acute pancreatitis associated with the triglyceride increase, leukopenia and neutropenia, hypothyroidism, headache, asthenia, rash, anemia, nausea, infection, peripheral edema, abdominal pain, diarrhea, fatigue/lethargy, and dry skin. Adverse events were dose-dependent, being most common in patients treated at a dose higher than 300 mg/m(2)/day.
Because Targretin is a retinoid – a class of drugs that has been associated with birth defects – Targretin must not be taken by women who are pregnant or intend to become pregnant. Targretin should be used with caution in patients with renal or hepatic impairment. Ketoconazole, itraconazole, erythromycin, gemfibrozil, grapefruit juice, and other inhibitors of cytochrome P450 may cause increased plasma Targretin levels, while rifampin, phenytoin, phenobarbital, and cytochrome p450 inducers may decrease plasma Targretin levels; patients taking these drugs should inform their physicians. Targretin should also be used with caution in patients taking antidiabetic medication, since Targretin may enhance their effects and result in hypoglycemia.
Patients are also advised to limit vitamin A intake to no more than 15,000 IU/day, and to provide themselves with adequate sun protection, since Targretin and other retinoids may increase photosensitivity.
Jennifer is a clinical pharmacologist. She helps doctors of all medical specialties choose medications. Jennifer consults about drug dosage, interactions, and side effects.