The stability and blanching efficacy of betamethasone-17-valerate in emulsifying ointment

Update on the advances and challenges in bioequivalence testing methods for complex topical generic products

Most of the government regulatory agencies, including the United States Food and Drug Administration and the European Medicine Agency, demand that the generic complex topical products prove pharmaceutical and bioequivalence. The evaluation of bioequivalence for complex topical dermatological formulations is a challenging task that requires careful consideration of several factors. Although comparative clinical studies are still considered the gold standard approach for establishing bioequivalence in most formulations, these studies can be costly and insensitive to detect formulation differences. Therefore, significant efforts have been made to develop and validate alternative approaches that demonstrate bioequivalence and expedite the availability of high-quality generic topical dermatological products. This article reviews the current methods for determining the bioequivalence of topical formulations in humans, with particular emphasis on recent advances in these methodologies. Most of the alternative methods are sensitive and reproducible, with the capability to ease the financial burden of comparative clinical studies within a short delivery time. The limitations associated with each technique are reviewed in detail.

The effect of dilution of fusidic acid cream and betamethasone dipropionate cream in complex extemporaneous mixes on formulation performance

The Aron regimen is an unconventional therapy which entails frequent applications of an extemporaneously prepared three component system (a topical antibiotic, a corticosteroid and an emollient), with the intention of decolonising the skin of S. aureus whilst treating atopic dermatitis. The impact of heavily diluting these topical medicinal products, to differing extents, on formulation performance is not well understood thus was investigated in this study. Following a single application of a range of compounded Aron mixes (fusidic acid and betamethasone dipropionate diluted to varying extents in an emollient base), significant reductions in the expected drug flux across silicone membrane, ex vivo percutaneous absorption and skin retention of both drugs relative to the marketed products were observed. This was attributed to a number of complex formulation effects making such changes difficult to predict in a clinical setting. Further investigations are required to evaluate the impact of frequent applications of the Aron mix to widespread areas on clinical efficacy, antimicrobial resistance and long term side effects.

Kinetics of thermal degradation of betamethasone valerate and betamethasone dipropionate in different media

The effect of pH, media, phosphate concentration and ionic strength on the kinetics of thermal degradation of betamethasone valerate and betamethasone dipropionate has been investigated. A validated HPLC method has been used to determine the parent compounds and their major thermal degradation products identified in the reaction. Betamethasone-17-valerate gave rise to two major products, namely, betamethasone-21-valerate and betamethasone alcohol, and betamethasone dipropionate degraded into three major products, namely, betamethasone-17-propionate, betamethasone-21-propionate and betamethasone alcohol, in different media. Betamethasone valerate showed maximum stability at pH 4-5 while betamethasone dipropionate was maximally stable at pH 3.5-4.5. The degradation of betamethasone valerate and betamethasone dipropionate was found to follow first-order kinetics and the apparent first-order rate constants (k_obs) for thermal degradation in different media range from 0.399-9.07×10^-3 h^-1 and 0.239-1.87×10^-3 h^-1, respectively. The values of the rate constants decrease with increasing solvent polarity, phosphate concentration and ionic strength. The second-order rate constants (k΄) for the phosphate ion inhibited reactions lie in the range of 3.02-1.30×10^-6 M^-1 s^-1.

The skin-blanching assay

The skin-blanching assay is used for the determination and bioequivalence of dermatologic glucocorticoids (GCs). The exact mechanism of the production of blanching is not fully understood, but it is considered that local vasoconstriction of the skin microvasculature and the consequent blood-flow reduction cause this phenomenon. Several factors influence skin blanching, including drug concentration, duration of application, nature of vehicle, occlusion, posture and location. The intensity of vasoconstriction can be measured in several ways: visual or quantitative methods, such as reflectance spectroscopy, thermography, laser Doppler velocimetry and chromametry. In literature, contradicting results in the correlation of the skin-blanching assay with different tests to determine GC sensitivity have been reported, limiting its clinical usefulness.

Quantitative Skin Blanching Assay of Corticosteroid Creams Using Tristimulus Colour Analysis

The potencies of four proprietary corticosteroid creams were ranked using blanching measured by a tristimulus colour analyser as an index. Intra-subject variation was measured in a trial using a single subject while in a second study inter-subject variation was quantified using six volunteers. Discriminative parameters were derived from the extended multiple-point chromaticity coordinates L* and a* recorded after application of the steroid creams under occlusion. Analysis of variance of the data using the linear regression model was followed by Tukey's multiple comparison tests. Ranking of the creams using parameters of the pharmacodynamic response corresponded with the generally accepted rank order of the potencies of the corticosteroid creams. It is proposed that this multiple-point skin blanching assay of topical corticosteroids using an internationally accepted clear measurement standard and the subsequent data analysis be adopted as a standard protocol.

Skin irritation in man: a comparative bioengineering study using improved reflectance spectroscopy

Variable types of skin irritation were induced in 8 human female volunteers, ranging from subclinical to visible erythema with slight oedema. Skin reactions were graded clinically and objectively using transepidermal water loss (TEWL), laser Doppler flowmetry (LDF) and improved reflectance spectroscopy. This last technique enables separation of in vivo erythemas into relatively deoxygenated (venous--deoxy hem) and oxygenated (arterial--oxy hem) haemoglobin components. Compared to uninvolved skin, an empty patch increased oxy hem by 197% +/- 121% (p < 0.05). Exposure to vehicles also changes skin biophysics. At sodium lauryl sulfate (SLS) and hydrochloric acid (HCl) exposed sites, a linear correlation between concentration and oxy hem, LDF and TEWL was found. These chemicals predominantly increased TEWL values. Nonanoic acid (NON) and imipramine (IMI) also raised oxy hem, LDF and TEWL values linearly at increasing concentrations. Although IMI 2.5% clinically was graded as a type ++ response, no significant increase in TEWL was found. The improved reflectance spectroscopic technique proved valid in skin irritation studies, with a higher sensitivity than laser Doppler flowmetry, and allowed irritant vascular reactions to be discriminated into arterial and venous components. Furthermore, our observations clearly demonstrate that clinically indistinguishable skin irritation reactions induce significantly different changes in barrier function (disruption) and vascular status.

Therapy with topical corticosteroids

Therapy with topical corticosteroids has improved greatly in recent years due to both advanced understanding of their mode of action and awareness of their side effects, as well as newly developed derivatives with specifically designed pharmacological properties. Paradoxically, the fear of using corticosteroids has increased on the part of the public during the same period. Treatment of inflammatory or neoplastic skin disorders with topical corticosteroids can be both successful and safe only if certain points are clarified before it is begun. These include (a) specific diagnosis, (b) choice of strength of the compound needed for control of the disease, (c) time schedule for length of therapy and planned patient visits, and (d) choice of vehicle adequate to the skin lesion. Topical corticosteroids of different potency are available today; one can classify these into four groups (weak, medium, strong, very strong) and use them in a patient-tailored treatment. When large areas are to be treated, systemic side effects must be taken into consideration, and compounds that are degraded quickly after absorption are recommended. Finally, the corticophobia of many patients must be addressed by careful information to ensure compliance. Using these guidelines, treatment with corticosteroids is highly effective, easy to use by the patient, and allows a maximum of safety.

Stability of steroid ointments diluted with Compound Zinc Paste B.P

The chemical stability of a range of corticosteroid ointments diluted with Compound Zinc Paste B.P. was studied by high-performance liquid chromatography (HPLC). Betamethasone dipropionate degraded by first-order kinetics at both 25 degrees C and 32 degrees C. At 25 degrees C the mean first-order reaction rate constant was 9.58 x 10(-3)/day, with a t90 (time to reach 90% of the original concentration) of 11.0 days. At 32 degrees C the mean first-order reaction rate constant was 2.42 x 10(-2)/day, with a t90 of 4.4 days. Of the other steroids studied, Fluocinolone acetonide was the least stable, with 33.8% remaining after a 7-day storage period at 25 degrees C. Betamethasone-17-valerate and fluocinonide were of intermediate stability between betamethasone dipropionate and fluocinolone acetonide. None of the steroid ointments studied had adequate stability in Compound Zinc Paste B.P. to allow extemporaneous dilution with this base.

A portable scanning reflectance spectrophotometer using visible wavelengths for the rapid measurement of skin pigments

A portable rapid scan reflectance spectrometer (400-700 nm in 2.8 s) has been developed for the measurement of cutaneous pigments. The instrument incorporates a tungsten halogen lamp light source, light transmission by fibre optics and wavelength selection by a circular variable wavelength interference filter. A microcomputer controls the instrument and processes the data. The performance of the instrument was evaluated by undertaking in vitro measurements of the reflectance spectra of blood. An index of the haemoglobin content of the sample based on the gradients of the log inverse reflectance spectrum between isobestic points at 527.5, 544 and 573 nm was devised and shown to be independent of the oxygenation of the haemoglobin. The haemoglobin index was combined with measurements at 558.5 nm, a wavelength at which absorbance is sensitive to the oxygenation of haemoglobin, to give a measure of oxygen saturation. The parameter was validated by determining the oxygen dissociation curve of red cells in plasma in vitro at pH 7.33, 37 degrees C and under a partial pressure of 40 mmHg of CO2.

A portable reflectometer for the rapid quantification of cutaneous haemoglobin and melanin

A portable reflectance instrument for the rapid quantification of cutaneous haemoglobin and melanin is presented. Light emitting diodes (LEDS) are used to illuminate the skin and a silicon photodiode to detect the light diffusely reflected from the surface. Reflectance measurements are made at only three wavelengths and the problems of pigment quantification consequent upon this are discussed. In addition to quantification of haemoglobin and melanin, qualitative information on the redox state of the blood may also be obtained. Measurements made on a port wine stain, which had been treated with 576 nm CW laser radiation at times between 1 and 6 months previously, provided information on the vascular response to this thermal injury. Despite the treated area visually appearing normal at 6 months post-treatment the measured levels of deoxygenated and total haemoglobin were still markedly higher than those in the adjacent uninvolved skin. The cutaneous pigment indices are insensitive to skin movement and almost all body sites are suitable for measurement.

Bioengineering and the patch test

Several non-invasive techniques based on different physical principles have been developed to investigate skin function and have been used for patch test assessment. In the present paper, the advantages and the defects of these methods are described in the light of the more recent data available in literature. Meanwhile, the eye and the fingers still remain the simplest method to assess skin irritancy. Bioengineering techniques could provide efficient recording systems for monitoring skin color, skin blood flow and barrier function damage, useful to the investigator rather than to the clinician.

The bioavailability of dermatological and other topically administered drugs

The literature addressing determination of the bioavailability of dermatological and other topically administered drugs has been reviewed. The various methods employed, their advantages and drawbacks, have been identified and evaluated. The state of the art and the success of topical bioavailability assessment are discussed in the light of the information presented. It is concluded that, although current methodology ensures the responsible use of topical medicaments, the techniques are, on the whole, quantitatively inadequate. A number of recommendations are proposed as possible improvements to the approaches now undertaken, and specific measurements for drugs in different therapeutic categories are suggested. The ultimate objective of this survey is to catalyze the establishment of straightforward, objective, quantitative, and reproducible methods to evaluate topical bioavailability and to reduce significantly, thereby, the incidence of bioinequivalence and pharmacological inactivity observed following drug dosing to the skin.

Skin reflectance measurements of patch test responses

Skin reflectance values were used as an objective measure of skin haemoglobin content at patch test sites to facilitate quantification of the erythematous response to contact allergens in patients with allergic contact dermatitis. Reflectance measurements of patch test responses correlated well with the clinical scoring and provided a numerical measure of reaction severity. Experimental contact allergen formulations were also evaluated by this method.

The stability and blanching efficiency of some Betnelan-V cream dilutions

In this study Betnelan-V cream was diluted with Beeler's basis and Cold cream. Cold Cream reduced the skin-blanching activity of the original cream more than Beeler's base. The stability of betamethasone-17-valerate was better in a Beeler's basis dilution than in a Cold cream dilution.

The effect of serial dilution of betamethasone-17-valerate on blanching potential and chemical stability

The effect of serial dilution of betamethasone-17-valerate (Betnovate ointment) in Unguentum Merck was investigated using a single application blanching assay in 10 subjects and high performance liquid chromatography. There was no statistically significant difference between any of the diluted formulations with regard to blanching potential. Chemical stability was maintained following a 1:32 dilution for 2 months and 1:4 dilution for 5 months at least, after storage at room temperature.