Animals are often prescribed medication to be administered at home. Medications are usually given by mouth, though some are injected (e.g. insulin). Many pets can be medicated without much difficulty, but some pets, particularly cats, are resistant to handling by their owners so alternative methods of drug delivery 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, dissolved or suspended in some gel or patch, is absorbed through the skin and into the blood stream. This system of drug delivery is often used in people but has only recently has become popular in animals. The most significant advantage of transdermal medications is the ability to administer drugs to pets that cannot or will not take oral medications.
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 done in animals, so we don't have much idea about whether drugs are actually getting through the skin or indeed having any measurable effect. The amount of a drug absorbed through cats' 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. Others 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 and feline asthma. Also, since cats constantly 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 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 administration is the skin on the inside the ear, which may, or may not, be the most site of 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, animals receiving transdermal medications should be carefully monitored and irregularities should be immediately reported