General Information

Panretin (alitretinoin) Gel, 0.1% is a naturally-occurring endogenous retinoid.

Panretin is specifically indicated for topical treatment of cutaneous lesions in patients with AIDS-related Kaposi’s sarcoma.

Panretin is supplied as a gel. Panretin gel should initially be applied two (2) times a day to cutaneous KS lesions. The application frequency can be gradually increased to three (3) or four (4) times a day according to individual lesion tolerance. If application site toxicity occurs, the application frequency can be reduced. Should severe irritation occur, application of drug can be temporarily discontinued for a few days until the symptoms subside.

Sufficient gel should be applied to cover the lesion with a generous coating. The gel should be allowed to dry for three to five minutes before covering with clothing. Because unaffected skin may become irritated, application of the gel to normal skin surrounding the lesions should be avoided. In addition, do not apply the gel on or near mucosal surfaces of the body.

A response of KS lesions may be seen as soon as two weeks after initiation of therapy but most patients require longer application. With continued application, further benefit may be attained. Some patients have required over 14 weeks to respond. In clinical trials, Panretin gel was applied for up to 96 weeks. Panretin gel should be continued as long as the patient is deriving benefit.

Mechanism of Action

Alitretinoin (9-cis-retinoic acid) is a naturally-occurring endogenous retinoid that binds to and activates all known intracellular retinoid receptor subtypes (RARa, RARb, RARg, RXRa, RXRb and RXRg). Once activated these receptors function as transcription factors that regulate the expression of genes that control the process of cellular differentiation and proliferation in both normal and neoplastic cells. Alitretinoin inhibits the growth of Kaposi’s sarcoma (KS) cells in vitro.

Side Effects

The most common adverse effect associated with the use of Panretin was local skin reactions.

Clinical Trial Results

Panretin gel was evaluated in two multicenter, prospective, randomized, double-blind, vehicle-controlled studies in patients with cutaneous lesions of AIDS-related KS. In both studies the primary efficacy endpoint was the patients’ cutaneous KS tumor response rate through 12 weeks of study drug treatment which was assessed by evaluating from 3 to 8 KS index lesions according to the modified AIDS Clinical Trials Group (ACTG) response criteria as applied to topical therapy (i.e., evaluation of height and area reductions of the index lesions only; progressive disease in non-index lesions and new lesions were not considered progressive disease; progressive disease was scored only in the treated index lesions). A global evaluation by physicians was also carried out. It considered all of the patient’s treated lesions (index and other) compared to baseline. In this evaluation, patients with at least a 50% improvement in the KS lesions were considered responders. In addition, photographs of lesions in patients considered responders by the modified ACTG criteria were examined by the FDA for a cosmetically beneficial response, defined as at least a 50% improvement in appearance compared to baseline, considering both the KS lesions and dermal toxicity at the lesion site, in at least 50% of the index lesions and maintained for at least 3 weeks. Patients were also asked about their satisfaction with the treatment.

In Study 1, a total of 268 patients were entered from centers in the U.S. and Canada. Patients were treated topically three to four times a day with either Panretin gel or a matching vehicle gel for a minimum of 12 weeks, followed by an open-label phase in patients who had not yet progressed on Panretin gel. Responses to Panretin gel were seen in both previously untreated patients and in patients with prior systemic and/or topical KS treatment. A total of 72 patients responded to Panretin gel during the randomized or crossover portions of the study. At a median duration of monitoring of 16 weeks, only 15% of the 72 patients had relapsed. Panretin gel would not be expected to affect development of new lesions in untreated areas and these were seen in about 50% of patients, at similar rates in treated and untreated patients, responders and non-responders. The patients’ assessment of their overall satisfaction with the drug effect on all treated lesions significantly favored Panretin gel.

Study 2 was an international study with a planned enrollment of 270 patients. Patients were treated topically twice a day with Panretin gel or a matching vehicle for 12 weeks. The study was stopped early because of positive interim results in the initial 82 patient data set. Responses to Panretin gel were seen both in previously untreated patients and in patients with prior systemic and/or topical KS treatment.

In the clinical trials, responses were seen as early as two (2) weeks; most patients, however, required four (4) to eight (8) weeks of treatment, and some patients did not experience significant improvement until 14 or more weeks of treatment. The cumulative percentage of patients who achieved a response was less than 1% at 2 weeks, 10% at 4 weeks, and 28% at 8 weeks.