Last Review: August 2005
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Transdermal medication delivery for veterinary patients (especially cats) is an answer to an age-old prayer from both veterinarians and pet owners. Delivering medication to cats noninvasively and without "kitty rodeos" and owner guilt is truly a landmark in veterinary pharmacotherapy. The transdermal delivery of medications has been well documented in veterinary medicine for ivermectin, selamectin, fipronil, nitroglycerin, imidacloprid, and fentanyl. Many medications can be administered transdermally to veterinary patients and there is a great desire to use that form of delivery for many others, but not every veterinary drug is suitable for transdermal use.
Before any drug is compounded in a transdermal dosage form, the veterinarian and the compounding pharmacist must carefully consider the pharmacologic characteristics of the drug with respect to the target species. They must also identify specific objective assessment parameters for determining the safety and efficacy of the treatment, as well as whether the risk of drug exposure to the client during administration precludes use of a transdermal dosage form.
Transdermally delivered drugs bypass hepatic portal first-pass metabolism, and extrapolating oral doses to transdermal doses can result in toxicity. To date there have been limited published studies of the pharmacokinetics, safety, or efficacy of compounded transdermal medications in veterinary patients. Until controlled studies provide evidence of safety and efficacy, the compounding pharmacist and veterinarian must use their best scientific judgment to predict whether a particular drug is suitable for transdermal delivery in a given patient. When transdermal agents are used, comprehensive data should be catalogued to determine clinical success or toxicity.
Diagnostic information (eg, the blood glucose level, blood pressure, serum T4 levels, and results of urine cultures) should also be catalogued to indicate a response to transdermal therapy. Ideally, transdermal dosage forms should be used only when traditional oral and injectable routes have not been effective.
In this database, considerations for the transdermal use of several veterinary medications (including pharmacokinetic factors and assessment parameters for determining toxicity and efficacy) are presented.
This information is meant only as a catalyst for thought; it in no way endorses the safety or efficacy of any of the listed drugs that are administered transdermally.
Disclaimer: Information in this electronic database is presented based on limited published information regarding single dose pharmacokinetic studies of transdermally administered drugs. Where studies were not found, pharmacokinetic parameters for oral drug use in the target species were used to potentially predict maximum safe transdermal doses for those drugs. This information is purely based on hypothesis as none of the drugs in the chart have undergone scientific safety and efficacy studies for chronic dosing in animals, with the exception of methimazole. The information in this chart also replaces that published originally in the International Journal of Pharmaceutical Compounding Mar/Apr 2003 p. 106.