Drugs that may be used in or on the skin fall into several categories—antibiotics, antifungal drugs, antiparasitic drugs, nonsteroidal anti-inflammatory drugs, drugs that modulate the immune system, hormones, psychotropic agents, and vitamin and mineral supplements (see Drugs and Vaccines: Drugs Commonly Used to Treat Skin Disorders).
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Several factors may contribute to the signs associated with skin disorders. Each factor should be identified and addressed if treatment is to succeed. Successful treatment of skin diseases may require longterm or lifelong treatment and is frequently a matter of successful control rather than cure.
Certain bacteria commonly cause skin infections in animals. Until the particular bacteria can be identified, your veterinarian will probably treat your pet with an antibacterial drug from a class of drugs known to be effective against the most common bacteria. The duration of treatment varies with the type of infection present. In general, superficial infections should be treated for 7 days beyond surface healing; deep infections should be treated 7 to 21 days beyond apparent healing, which may require treatment durations of 8 to 12 weeks.
Several antifungal drugs are used to treat skin diseases in animals (see Drugs and Vaccines: Drugs Commonly Used to Treat Skin Disorders). Your veterinarian will make a determination, based on the fungus involved and your pet's species, which drug should be used for treatment. These drugs are usually given by mouth, although some may be given topically. The instructions should be followed carefully when these drugs are prescribed, as some may cause gastrointestinal upset or other adverse effects, and others may need to be taken with food or with another drug to increase the effectiveness of treatment.
Antiparasitic drugs are commonly used in all animals to combat infestation with parasites. This includes pests such as fleas and mites that can irritate the skin and cause disease, as well as parasites that live inside the animal's body.
One important class of drugs used to treat parasitic infestations is the macrocyclic lactones. Drugs from this class may be used to treat skin disorders caused by parasites, although their use is often off-label. (“Off-label” is a term that describes the use of an FDA-approved drug for a disorder other than that for which it was approved. It is a common practice in both human and veterinary medicine.) Depending on the drug, they may be given orally or topically.
Insect growth regulators halt or disrupt the development of the immature stages of some insects (larvae and/or eggs), leading to their death. These drugs are highly effective against insects such as fleas, flies, and mosquitoes that undergo complete metamorphosis, but they have little or no activity against ticks.
Chloronicotinyls (also known as neonicotinoids) kill fleas and lice, but have less activity against ticks. There are currently 2 drugs in this class, both of which have very different methods of action. One is administered topically and appears to paralyze fleas. The other is given orally and affects the nervous system of adult fleas, causing overstimulation and death.
Phenylpyrazoles have a broad spectrum of action and are effective against fleas, ticks, mites, and lice. Phenylpyrazoles are usually given topically.
Formamidines are effective against ticks. The one drug approved for veterinary use in this category is used as a dip or impregnated in a collar marketed to control ticks in dogs.
Other, older drugs are occasionally used, but many have been replaced by the drugs discussed above, which are often more effective, safer, and better for the environment.
Antihistamines work by blocking the receptors involved in the processes that cause itching and inflammation. Responses to antihistamines vary considerably, and several may need to be tried to find one that is effective for an animal (see Drugs and Vaccines: Drugs Commonly Used to Treat Skin Disorders). Antihistamines may enhance the effects of nonsteroidal anti-inflammatory drugs, corticosteroids, or fatty acid supplements and may allow dosages of these agents to be reduced in some cases. Some antihistamines can cause drowsiness and gastrointestinal signs. Overdoses can adversely affect the central nervous system and cause death.
Essential Fatty Acids
Fatty acids are important parts of cell membranes and play other important roles in the body, including maintaining healthy skin. They also have anti-inflammatory properties. Essential fatty acids cannot be made by the body and must be supplied in the diet. The essential fatty acids most important for balance in the skin of cats and dogs are linoleic acid and linolenic acid.
Essential fatty acids may be recommended to treat itching inflammatory diseases (such as allergies), conditions that cause crusting of the skin (such as discoid lupus erythematosus), and malformations of the nails or claws. Many commercial products are available. There are few side effects, but inflammation of the pancreas has been rarely reported. Large doses may also cause weight gain or diarrhea.
Hormonal treatment can be used to treat skin disorders. Glucocorticoids (a type of corticosteroids) may be used in either an anti-inflammatory or immunosuppressive capacity, depending on the dosage selected. Glucocorticoids are used for hypersensitivity skin conditions, contact dermatitis, immune-mediated diseases, and cancers. They are often prescribed to help curtail itching and inflammation.
Other hormones that may be prescribed to treat loss of hair or fur include thyroid hormone, progesterones, growth hormone, sex hormones, and melatonin.
Immunomodulators are drugs that help regulate the immune system's activity. Some drugs stimulate the immune system, while others suppress its actions. These drugs can be used to treat skin diseases and disorders. The most common use of immunostimulants in dogs is for chronic bacterial skin infections. Because the inflammatory process is directed by the immune system, immunosuppressants are often used to treat skin conditions involving inflammation and hypersensitivity (such as allergies), as well as various cancers and some types of arthritis.
Psychotropic drugs have been used off-label for treatment of feline psychogenic alopecia and canine acral lick dermatitis, syndromes that are characterized by excessive self-licking. Classes of drugs used include antidepressants, antipsychotics, opiate antagonists, anxiolytics, and mood stabilizers (see Drugs and Vaccines: Drugs Commonly Used to Treat Skin Disorders).
Vitamins and Minerals
Many vitamins and minerals play a role in maintaining skin health. Several can be used to treat skin diseases and disorders. Retinoids, which are naturally occurring and synthetic compounds with vitamin A activity, have been used for certain conditions involving the sebaceous (oil-producing) glands in the skin. The retinoids used most commonly are isotretinoin and acitretin.
Zinc is critical for the formation of keratin, the substance that forms the basis of skin, hair, and nails. Zinc supplementation can be given in cases of insufficient intestinal absorption, including deficiency syndrome I (Siberian Huskies, Alaskan Malamutes) and syndrome II (rapidly growing dogs on zinc-deficient diets). Diets high in phytates or minerals may inhibit zinc absorption. Supplementation is typically lifelong.
Last full review/revision July 2011 by Philip T. Reeves, BVSc (Hons), PhD, FANZCVS; Jörg M. Steiner, DrMedVet, PhD, DACVIM, DECVIM-CA; Dawn Merton Boothe, DVM, PhD, DACVIM, DACVCP; Maya M. Scott, BS, DVM; Ian Tizard, BVMS, PhD, DACVM; Jozef Vercruysse, DVM, DEVPC