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Uptake of drugs from topically applied anti-inflammatory preparations applied to racing animals
A D Thomas1, I C Bowater, J H Vine
1School of Engineering and Science, Swinburne University of Technology, Hawthorn, Victoria.
Objective:
To determine whether a drug detected in the blood or urine of a racing animal could have penetrated through the skin from a topically applied preparation.
Design:
Blood and urine of dogs and horses were analysed after topical administration of three common nonsteroidal anti-inflammatory preparations.
Experimental Method:
Dimethylsulphoxide was analysed using a gas chromatograph with a flame photometric detector. Phenylbutazone, its metabolites and lignocaine were analysed using a gas chromatograph with a mass selective detector.
Results:
Dimethylsulphoxide, phenylbutazone and lignocaine were detected in dog urine after multiple applications of the preparations. The maximum concentration of dimethylsulphoxide in dog urine correlated with the concentration of dimethylsulphoxide in the preparation. Phenylbutazone penetrated the skin more effectively from the cream than from the solution or gel preparations. This penetration was independent of the concentration of dimethylsulphoxide.
Conclusion:
The superior penetration of phenylbutazone from the cream can be explained by it being present as a neutral molecule in an hydrophobic medium. It is proposed that phenylbutazone penetrates the skin of greyhounds most effectively by a hydrophobic lipid route which is likely to be different from the path by which dimethylsulphoxide penetrates the skin.