Drugs for Behavior-Related Dermatoses

Chapter 117

Drugs for Behavior-Related Dermatoses

Common behavior problems that manifest with dermatologic disease include overgrooming (i.e., feline psychogenic alopecia), repetitive licking (i.e., lick granulomas), and self-mutilating behaviors. Differentiation between dermatologic and psychologic disease is a complex process. These behaviors can be a response to underlying pain or pruritus, or the symptoms of anxiety and compulsive disorders. Recent studies suggest that a behavioral cause for self-inflicted dermatologic disease may be overdiagnosed. Despite the repetitive and seemingly compulsive nature of self-injurious behavior disorders, often the initial trigger is pruritic disease, such as atopic dermatitis, cutaneous adverse food reactions, or flea allergy dermatitis.

Many patients have comorbidities, and special care should be taken to address the underlying medical conditions before or simultaneously with the treatment of behavior disorders. A thorough medical and behavioral history should be obtained and a full dermatologic workup performed before diagnosing and treating a patient for a behavior disorder. Psychotropic medications often are indicated for patients with primary behavior disorders or for those with behavior that may be complicating or caused by an underlying dermatologic disease. These medications can mitigate the behavioral aspects of primary dermatologic disease as well as allow medical treatment to be more effective when both dermatologic and behavioral conditions are suspected. This chapter offers an overview and clinical insight into the use of psychotropic medications to treat behavior-related dermatoses.

Psychotropic medications are used for their ability to mitigate anxiety and the animal’s response to external stressors. Several classes of drugs offer these benefits, some of which also have antipruritic properties, which makes them especially helpful when both dermatologic and behavioral problems are present. Before the patient begins treatment, baseline laboratory testing should be performed to ensure that it is safe to administer hepatically metabolized and renally excreted medications long term. Typically this includes a complete blood count, chemistry profile, total thyroxine level, and urinalysis. These tests should be performed every 6 to 12 months during treatment, depending on the age and health status of the pet. The initial goal should be to achieve therapeutic effects and to minimize adverse effects. This is best accomplished by starting the patient at the low end of the dosage range for the first 2 weeks of treatment, then titrating up to effect, while keeping in mind that therapeutic effects of some medications may take 4 to 6 weeks to appear. In mild to moderate cases, particularly those in which an instigating medical disease can be identified and treated, the patient can be weaned from medications by decreasing the dose by 25% every 2 weeks beginning 3 to 6 months after the cessation of clinical signs. In patients with severe compulsive disorders, however, treatment with psychotropic medications may be lifelong.

Classes of Psychotropic Medications

Tricyclic Antidepressants

The tricyclic antidepressants (TCAs) are named for their three-ringed molecular structure. Commonly used TCAs in veterinary medication include clomipramine (Clomicalm), doxepin, and amitriptyline (Elavil). Clomipramine, under the brand name Clomicalm, is approved by the U.S. Food and Drug Administration for use in dogs with separation anxiety and carries a veterinary label. The author recommends the use of the brand name drug Clomicalm, rather than the generic drug clomipramine, unless an allergy to the meat flavoring is suspected, because anecdotally many patients seem not to respond as well to the generic product. Each TCA has properties that block the reuptake pumps for the neurotransmitters serotonin, norepinephrine, and, to a lesser extent, dopamine. The blockade of neurotransmitter reuptake pumps results in greater neurotransmitter availability, which leads to receptor changes that allow for therapeutic anxiety relief within approximately 4 to 6 weeks. Specifically, activation of the serotonin 1A (5-HT1A) receptor because of the persisting increase in serotonin levels is responsible for the anxiety-relieving effects. Clomipramine has the greatest specificity for serotonin, which makes it more effective for anxiety relief. Amitriptyline tends to be heavily sedating and to have poorer anxiety-relieving effects and is therefore rarely used by the author. Furthermore, this class of drugs also exerts anticholinergic (muscarinic), antiadrenergic (α1), and antihistaminic (H1) properties and can block sodium channels in the brain and heart. These additional properties are responsible for adverse effects, such as sedation, dry mouth, constipation, urine retention, increased seizure potential, and arrhythmias. In cats the sedative effect can be profound and often leads to owner dissatisfaction and noncompliance. Preparing owners about the potential for these adverse effects may increase compliance and encourage communication about the pet’s response. In animals with a history of obstipation, seizures, or cardiovascular disease, this class of drugs should be avoided.

When a concurrent pruritic disease is being treated, the antihistamine properties of TCAs offer an additional benefit. Doxepin has the most potent antihistamine properties of any of the TCAs and, in fact, has 600 to 800 times the antihistamine effects of diphenhydramine. Unfortunately, the serotonin-enhancing effects of doxepin are the lowest in its class, which makes it a poor choice when anxiety or compulsion is the primary cause for the dermatosis. Each clinician should weigh the effects of both anxiety/compulsion and pruritus when choosing a TCA that will affect skin and behavior. See Table 117-1 for dosing recommendations.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Drugs for Behavior-Related Dermatoses

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