"Scientists at the National Institutes of Health report they have discovered in mouse studies that a small molecule released in the spinal cord triggers a process that is later experienced in the brain as the sensation of itch.
The mechanism of action of diclofenac sodium in the treatment of actinic keratoses (AK) is unknown. The contribution to efficacy of individual components of the vehicle has not been established.
When Solaraze® is applied topically, diclofenac is absorbed into the epidermis. In a study in patients with compromised skin (mainly atopic dermatitis and other dermatitic conditions) of the hands, arms or face, approximately 10% of the applied dose (2 grams of 3% gel over 100 cm2) of diclofenac was absorbed systemically in both normal and compromised epidermis after seven days, with four times daily applications.
After topical application of 2 g Solaraze® three times daily for six days to the calf of the leg in healthy subjects, diclofenac could be detected in plasma. Mean bioavailability parameters were AUC0-t 9±19 ng/hr/mL (mean±SD) with a Cmax of 4±5 ng/mL and a Tmax of 4.5±8 hours. In comparison, a single oral 75 mg dose of diclofenac (Voltaren®)† produced an AUC of 1600 ng/hr/mL. Therefore, the systemic bioavailability after topical application of Solaraze® is lower than after oral dosing.
Comparative bioavailability studies have not been conducted between available diclofenac topical products (gels containing 1 - 3% diclofenac) which have different dosing regimens. A cross-study evaluation of the data indicates that diclofenac is more bioavailable when applied to diseased skin and less bioavailable when applied to intact skin.
Blood drawn at the end of treatment from 60 patients with AK lesions treated with Solaraze® in three adequate and well-controlled clinical trials was assayed for diclofenac levels. Each patient was administered 0.5 g of Solaraze® Gel twice a day for up to 105 days. There were up to three 5 cm X 5 cm treatment sites per patient on the face, forehead, hands, forearm, and scalp. Serum concentrations of diclofenac were, on average, at or below 20 ng/mL. These data indicate that systemic absorption of diclofenac in patients treated topically with Solaraze® is much lower than that occurring after oral daily dosing of diclofenac sodium.
No information is available on the absorption of diclofenac when Solaraze® is used under occlusion.
Diclofenac binds tightly to serum albumin. The volume of distribution of diclofenac following oral administration is approximately 550 mL/kg.
Biotransformation of diclofenac following oral administration involves conjugation at the carboxyl group of the side chain or single or multiple hydroxylations resulting in several phenolic metabolites, most of which are converted to glucuronide conjugates. Two of these phenolic metabolites are biologically active, however to a much smaller extent than diclofenac. Metabolism of diclofenac following topical administration is thought to be similar to that after oral administration. The small amounts of diclofenac and its metabolites appearing in the plasma following topical administration makes the quantification of specific metabolites imprecise.
Diclofenac and its metabolites are excreted mainly in the urine after oral dosing. Systemic clearance of diclofenac from plasma is 263±56 mL/min (mean±SD). The terminal plasma half-life is 1-2 hours. Four of the metabolites also have short terminal half-lives of 1-3 hours.
Clinical trials were conducted involving a total of 427 patients (213 treated with Solaraze® and 214 with a gel vehicle). Each patient had no fewer than five AK lesions in a major body area, which was defined as one of five 5 cm X 5 cm regions: scalp, forehead, face, forearm and hand. Up to three major body areas were studied in any patient. All patients were 18 years of age or older (male and female) with no clinically significant medical problems outside of the AK lesions and had undergone a 60-day washout period from disallowed medications (masoprocol, 5-fluorouracil, cyclosporine, retinoids, trichloroacetic acid/lactic acid/peel, 50% glycolic acid peel) and hyaluronan-containing cosmetics. Patients were excluded from participation for reasons of known or suspected hypersensitivity to any Solaraze® ingredient, pregnancy, allergies to aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs), or other dermatological conditions which might affect the absorption of the study medication. Application of dermatologic products such as sunscreens, cosmetics, and other drug products was not permitted. Patients were instructed to apply a small amount of Solaraze® Gel (approximately 0.5 g) onto the affected skin, using their fingers, and gently smoothing the gel over the lesion. In addition, all patients were instructed to avoid sun exposure. Complete clearing of the AK lesions 30 days after completion of treatment was the primary efficacy variable. No long-term patient follow-ups, after the 30-day assessments, were performed for the detection of recurrence.
|Complete Clearance of Actinic Keratosis Lesions 30 Days Post-Treatment (all locations)|
|Study 1 90 days treatment||27/58 (47%)||11/59 (19%)||< 0.001|
|Study 2 90 days treatment||18/53 (34%)||10/55 (18%)||0.061|
|Study 3 60 days treatment||15/48 (31%)||5/49 (10%)||0.021|
|30 days treatment||7/49 (14%)||2/49 ( 4%)||0.221|
|Complete Clearance of Actinic Keratosis Lesions 30 Days Post- Treatment (by location)|
|Scalp||Forehead||Face||Arm/Forearm||Back of Hand|
|Study 1 - 90 days treatment|
|Solaraze®||1/4 (25%)||17/30 (57%)||9/17 (53%)||4/12 (33%)||6/16 (38%)|
|Vehicle||3/9 (33%)||8/24 (33%)||5/17 (29%)||4/12 (33%)||0/14 (0)|
|Study 2 - 90 days treatment|
|Solaraze®||2/6 (33%)||9/19 (47%)||4/5 (80%)||5/8 (63%)||1/17 (6%)|
|Vehicle||0/4 (0)||6/22 (27%)||2/8 (25%)||0/5 (0)||3/16 (19%)|
|Study 3 - 60 days treatment|
|Solaraze®||3/7 (43%)||13/31 (42%)||10/19 (53%)||0/1 (0)||2/8 (25%)|
|Vehicle||0/6 (0)||5/36 (14%)||2/13 (15%)||0/2 (0)||1/9(11%)|
|30 days treatment|
|Solaraze®||2/5 (40%)||4/29 (14%)||3/14 (21%)||0/0 (0)||0/9 (0)|
|Vehicle||0/5 (0)||2/29 (7%)||2/18(11%)||0/1 (0)||1/9(11%)|
|All data combined|
|Solaraze®||8/22 (36%)||43/109 (39%)||26/55 (47%)||9/21 (43%)||9/50 (18%)|
|Vehicle||3/24 (13%)||21/111 (19%)||11/56(20%)||4/20 (20%)||5/48 (10%)|
Last reviewed on RxList: 1/4/2012
This monograph has been modified to include the generic and brand name in many instances.
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