Transdermal Medications in Dogs
Animals are often prescribed medication to be administered at home. Medications are usually given by mouth, though some are given by injection (e.g. insulin). Many pets can be medicated without much difficulty but some dogs are resistant to being handled by their owners so alternative methods of drug administration must be sought. For such refractory pets, transdermal medication may be the way to go.
Transdermal delivery is a process that involves administering medications through the skin. The drug is placed on the skin using some form of a gel or patch and then is absorbed through the skin into the blood stream. This system of drug delivery has been used in people for years but only recently has it become popular in animals. The most significant advantage of transdermal medications is the ability to administer a drug to a dog that cannot or will not take medication orally.
There are some disadvantages associated with transdermal drug delivery. Although transdermal medications have been employed in human medicine for decades, little research on the subject has been performed in animals, so we don't have much idea about whether drugs are actually getting through the skin or indeed having any beneficial effect. The amount of a drug absorbed through a dog's relatively thick skin is unpredictable and absorption may be erratic. Some drugs cannot be made into transdermal formulations because the dose of the medication is too high. Other drugs are too potent and carry a high risk of toxicity. With regard to antibiotics, a steady low concentration of the antibiotic is not recommended in the treatment of infectious disease. Low concentrations of antibiotic increase the risk of the bacteria developing a resistance to the medication and then overwhelming the animal.
Other potential complications associated with transdermal drug delivery include skin reactions and allergy to the medication. The base used for many intradermal medications is soy lecithin, which has been linked to food allergies. Also, as dogs groom themselves, there is a risk of them ingesting the medication.
There are various drugs manufactured for transdermal delivery. The most well known is fentanyl, a medication used to control pain. Fentanyl is available as a "patch." Other drugs, like methimazole, ketoprofen, thyroid supplements, phenobarbital, insulin and metoclopramide, are often dissolved in a transdermal gel. Many other drugs can be compounded in gels for application to the skin. Small particles within the gel disrupt the skin surface, allowing the drug to penetrate through the skin and enter the blood stream.
Use of Transdermal Drugs
When all attempts at administering drugs at home, either orally or by injectable, have failed, transdermal medication can be considered. The patch or gel should be applied in an area not easily accessible to the pet, and in a hairless area. The most common site of application is the skin on the inside of the ear, which may, or may not, be the site for optimal absorption. When employing a transdermal medication, it is helpful to measure serum levels of the drug to monitor the efficacy of the drug delivery system. This is particularly important with phenobarbital. Other blood tests may also be helpful to monitor the efficacy of treatment, including blood glucose measurements with insulin and thyroxine levels with methimazole or thyroid supplementation.
Pet owners must be thoroughly educated on the care and use of the medication patch. The animal must be watched closely and the patch periodically changed to maintain a steady systemic concentration of the drug. Since this system has not been extensively studied, dogs receiving transdermal medications should be monitored carefully and any irregularities noted should immediately be reported to the attending veterinarian.