Stratum Corneum Absorption Kinetics of 2 Potent Topical Corticosteroid Formulations: A Pilot Study

The active ingredient of any pharmaceutical product is responsible for the agent’s efficacy and safety profile. This ingredient is extensively studied in clinical trials and evaluated by the US Food and Drug Administration before the product is commercially available. In dermatologic products, especially those for treating dermatoses, the vehicle in which the active ingredient is formulated also plays a role in drug delivery and indirectly impacts therapeutic outcomes, unlike excipients in oral medications. Topical vehicles must be stable, provide a suitable environment that will not degrade the active ingredient or affect its efficacy, and be cosmetically acceptable.¹

Topical vehicles are formulated to maintain the stability of the active ingredient and allow it to readily penetrate the skin and reach its target area with minimal absorption into the bloodstream, thus avoiding systemic adverse events. A variety of vehicles can exist for a single active ingredient to accommodate different phases of disease and different anatomical sites where the disease may occur.² For example, alcohol-based vehicles, sprays, and foams are preferred for the scalp where evaporation of the vehicle is beneficial to prevent greasiness of the hair, while ointments may be preferred due to their occlusive nature for areas with xerotic or thick skin from dermatoses.

Cosmetic acceptability of the vehicle may influence patient adherence to therapy. Housman et al³ assessed a variety of products formulated in different vehicles (ie, solutions, foams, emollients, gels, creams, ointments) for the treatment of psoriasis. Patients with psoriasis applied each test product to a quarter-sized area of normal skin on the forearm using a cotton swab and completed a preference questionnaire. By far, respondents significantly preferred solutions and foams over creams, gels, and ointments (P<.01). Side effects were rated to be the most important characteristics of topical therapy, followed by time needed for application, ease of application, and messiness.³ Presumably, if patients are frustrated with the topical product that they are using, adherence to the prescribed dosage and application instructions will diminish over time, leading to suboptimal steady-state levels of the product. If appropriate levels of the drug are not present at the target site, treatment will not be successful.

Steady-state levels of a topical drug at the site of action also are maintained via appropriate application frequency, most commonly once to 4 times daily for dermatologic products. Fluocinonide and halcinonide are class II (potent) corticosteroids indicated for the relief of inflammatory and pruritic manifestations of corticosteroid-responsive dermatoses and usually are administered at least twice daily. In double-blind clinical studies comparing both products in the treatment of psoriasis, halcinonide resulted in more improved outcomes than fluocinonide.^4-6 Sudilovsky and Clewe⁴ studied 140 patients with moderate to severe psoriasis. After 3 weeks of treatment, 44% showed superior results with halcinonide, 27% showed superior results with fluocinonide, 26% showed equal results with both products, and 3% showed no relief.⁴ Similarly, Close⁵ reported that 61% of patients showed superior results with halcinonide, 25% showed superior results with fluocinonide, 10% showed equal results with both products, and 4% showed no relief (N=50). Lynfield and Watsky⁶ reported that 56% of patients with severe psoriasis who were treated with halcinonide for 2 weeks showed improvement to normal or slight inflammation compared to 44% of patients treated with fluocinonide (N=59). All 3 studies used cream formulations of halcinonide and fluocinonide.

Recently, halcinonide cream was shown to have an immediate release into the stratum corneum that peaked within 1 hour of application and remained elevated for 6 hours before beginning to decline.⁷ These results support a biphasic release of halcinonide, which is in agreement with its formulation—that halcinonide exists in both a solution phase for immediate release into the skin and in a suspension phase that allows a sustained release after equilibrium is reached between the solution and suspension phases.⁸ Fluocinonide is not known to be formulated in a similar way. Its vehicle composition and penetration into the skin could explain the superior efficacy of halcinonide versus fluocinonide.

The current pilot study was conducted to compare the release pattern of fluocinonide cream versus halcinonide cream into the stratum corneum using an in vivo, noninvasive method. Results for halcin-onide have been previously published.⁷

Methods

Participants were sequestered in a controlled environment for the entire day to allow the skin to equilibrate prior to product application. The methodology for the application and quantification of halcinonide cream 0.1% into the stratum corneum of 5 participants using a tape-stripping protocol has been described elsewhere.⁷ Concordia Clinical Research institutional review board (Cedar Knolls, New Jersey) approved this study, which was conducted at Dermatology Consulting Services (High Point, North Carolina).

A 0.1-g dose of generic fluocinonide cream 0.05% was applied to four 2.5-cm circular sites on the forearm in 5 participants with normal skin until completely absorbed. Circular tape strips were subsequently placed on the application site at 1, 3, 6, and 9 hours posttreatment and were held for 10 seconds with a controlled pressure plunger to ensure adequate and consistent contact between the tape strip and the skin. The tape strip was removed with forceps, rolled with the skin scale inside, and placed in a glass vial. This procedure was repeated 6 times at 1 of 4 sites with a new tape strip at each time point to obtain samples from deeper skin layers. A total of 24 tape strips were collected from each participant.

All vials were frozen at -20°C and were shipped overnight to Robert Kellar, PhD, at the Center for Bioengineering Innovation at Northern Arizona University (Flagstaff, Arizona) for mass spectroscopy evaluation. Once received at the outside facility, the vials were stored at -20°C until analysis. Each sample was spiked with a known quantity of an appropriate reference standard and extracted with 1 mL acetonitrile at room temperature for 1 minute with agitation. New unused tape strips were spiked with a small amount of fluocinonide reference standard for extraction efficiency.

Extracts were evaporated to dryness under nitrogen gas, resuspended in 200 µL chromatography solvent, and quantified using liquid chromatography–mass spectrometry. To remove the skin scale from the tape strips, 10 mL of a solvent solution of 0.1 mg/mL fludrocortisone acetate in acetonitrile was dispensed into a 4 dram vial containing the tape strip. The vials were ultrasonicated and shaken for 10 to 15 minutes, and the samples were further diluted to 100-fold and were inverted several times to ensure complete dissolution of fluocinonide before liquid chromatography–mass spectrometry.

A standard curve ranging from the lower limit of quantification to the upper limit of quantification for the fluocinonide reference was used to determine the quantity of fluocinonide in each of the tape strips. Once the lower limit of quantification was reached in a given set of tape strip samples (1-, 3-, 6-, and 9-hour samples), the next 2 sequential tape strips in that set were analyzed to confirm fluocinonide was not detectable in deeper layers. Standard quality controls were analyzed to ensure run-to-run and sample-to-sample accuracy.

Each sample was analyzed in duplicate; 10 mg fluocinonide was used as a reference standard. The minimum detectable concentration of fluocinonide was 1 ng/mL.