Challenges obtaining a biowaiver for topical veterinary dosage forms

Obtaining a biowaiver for topical drugs used in veterinary species faces many of the same challenges associated with human topicals. However, the skin of domestic animals varies anatomically and biochemically and experimental approaches to assess bioequivalence (BE) in veterinary species have challenges that are not often encountered with human skin. This is especially the situation with locally acting drugs. The focus of this paper is to address several of the challenges associated with (i) determining the BE of these locally acting drugs and (ii) critically examine the current technological advances that can act as a surrogate for clinical trials.

Effects of short-term high-dose and low-dose dermal exposure to Jet A, JP-8 and JP-8 + 100 jet fuels

Occupational and environmental exposures to jet fuel recently have become a source of public and regulatory concern. This study investigates the cutaneous toxicity of three fuels used in both civilian and military aircraft. Pigs, an accepted animal model for human skin, were exposed to low-dose (25 microl or 7.96 microl cm(-2)) or high-dose (335 microl or 67 microl cm(-2)) Jet A, JP-8 and JP-8 + 100 under occluded (Hill Top) chamber or cotton fabric) and non-occluded conditions for 5 h, 24 h and 5 days. To mimic occupational exposure, fuel-soaked fabric (high dose) was used. Erythema, edema, transepidermal water loss (TEWL) and epidermal thickness were quantified. High-dose fabric occluded sites had slight erythema at 5 h with increased erythema at 5 days. No erythema was noted in any of the occluded (Hill Top) or non-occluded sites at any of the time points. Morphological assessments depicted slight intracellular epidermal edema at all time points. An increase in change in TEWL (DeltaTEWL) was observed at the 5-h and 24-h fabric and Hill Top occluded treatments and a decrease at the 5-day fabric and Hill Top occluded sites. In all 5-day JP-8 + 100 fabric sites, intracorneal microabscesses filled with inflammatory cells were observed. Epidermal thickening was significant (P < 0.05) in all three jet fuels at the high-dose fabric sites, with JP-8 + 100 being the thickest. The epidermal rete peg depth increased significantly (P < 0.05) at 24 h and 5 days with Jet A, JP-8, and JP-8 + 100 in the fabric sites. No significant differences were noted in the 5-day non-occluded fabric and Hill Top occluded and non-occluded sites. Jet fuel JP-8 + 100 tended to have the greatest proliferative response. In conclusion, the high-dose fabric-soaked exposure at 5 days to Jet A, JP-8 and JP-8 + 100 fuels caused the greatest increase in cutaneous erythema, edema, epidermal thickness and rete peg depth compared with high-dose non-occluded or low-dose exposure under Hill Top occluded and non-occluded conditions.

Topical L-ascorbic acid: percutaneous absorption studies

BACKGROUND

Reactive oxygen species generated by ultraviolet light result in photocarcinogenic and photoaging changes in the skin. Antioxidants protect skin from these insults.

OBJECTIVE

This study defines formulation characteristics for delivering L-ascorbic acid into the skin to supplement the skin's natural antioxidant reservoir.

METHODS

L-ascorbic acid or its derivatives were applied to pig skin. Skin levels of L-ascorbic acid were measured to determine percutaneous delivery.

RESULTS

L-ascorbic acid must be formulated at pH levels less than 3.5 to enter the skin. Maximal concentration for optimal percutaneous absorption was 20%. Tissue levels were saturated after three daily applications; the half-life of tissue disappearance was about 4 days. Derivatives of ascorbic acid including magnesium ascorbyl phosphate, ascorbyl-6-palmitate, and dehydroascorbic acid did not increase skin levels of L-ascorbic acid.

CONCLUSIONS

Delivery of topical L-ascorbic acid into the skin is critically dependent on formulation characteristics.

The use of mechanistically defined chemical mixtures (MDCM) to assess mixture component effects on the percutaneous absorption and cutaneous disposition of topically exposed chemicals. II. Development of a general dermatopharmacokinetic model for use in risk assessment

We present a conceptual approach to a general comprehensive mathematical model to quantify percutaneous absorption of topically applied chemicals in complex mixtures on the basis of biophysical parameters estimated or measured using in vitro and ex vivo perfused skin preparations. This model addresses mechanistically defined chemical mixtures (MDCM) which consist of components selected because of their potential to modulate by various mechanisms the absorption of a marker toxic penetrant. This model accounts for observed toxicodynamic general and specific effects of chemicals, acting single or in concert, on the absorption of any or all components in a defined mixture. We have also included experimental data from an isolated perfused porcine skin flap study with topically applied parathion as the marker penetrant and acetone or DMSO as solvent, with methyl nicotinate as a potential rubefacient, sodium laurel sulfate as a surfactant, and stannous chloride as a reducing agent in order to provide an illustration of the application and performance of the model. This model supports the MDCM concept that defining and then simulating those components of a complex mixture that could have a significant impact on the absorption of a marker toxic compound would be a useful screening approach in the risk assessment of topical chemical mixtures. It may also be used to identify critical pathways where chemical mixture component interactions significantly modify the absorption of the penetrant of interest.