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Compendium May 2008 (Vol 30, No 5)

Editorial: Polypharmacy and Geriatric Patients

by Katrina L. Mealey, DVM, PhD, DACVIM, DACVCP

    Treating geriatric patients with multiple diseases or disorders is challenging. These patients often require multiple drugs (polypharmacy) to achieve the desired therapeutic objective. However, with each new drug a patient receives, the risk for an adverse drug interaction increases exponentially. To complicate matters further, geriatric patients are more likely than younger patients to experience drug interactions because they receive more medications on average, often have more coexisting diseases, and may have an inadequate nutrition status. Poor nutrition status not only affects a patient's ability to withstand a toxic pharmacologic insult but also contributes to low plasma protein levels, which can exacerbate interactions between highly protein-bound drugs. The key, then, is preventing serious drug interactions from occurring in these patients.

    Many serious adverse drug interactions can be avoided by taking the following approach to drug therapy in all patients:

    • First, since it is impossible to remember all potential drug interactions, concentrate on common drug-drug interactions that involve drugs with a narrow margin of safety. Examples of these types of drugs that are used in veterinary medicine include digoxin, some behavior-modifying drugs (i.e., clomipramine, fluoxetine, selegiline), α2-adrenergic agonists (e.g., detomidine, medetomidine), and theophylline. Drug interactions among the behavior-modifying drugs, for example, can result in serotonin syndrome, an excess of serotonin in the central nervous system that has a high morbidity and mortality rate.
    • Second, be aware of the patient's pharmacologic and physiologic limits. As a general rule, if a geriatric patient is already receiving four or more drugs or has three or more comorbidities (coexisting medical conditions), conduct a thorough investigation into potential adverse drug interactions before prescribing a new drug.
    • Third, be on the lookout for adverse consequences of drug-drug interactions. If a patient develops a new medical disorder, make sure to rule out an adverse drug reaction or interaction before treating the patient with a new drug for the new signs. For example, geriatric dogs with mitral regurgitation are often treated with furosemide. The potential clinical effects of furosemide include a number of signs that could be misinterpreted as signs of canine cognitive dysfunction (e.g., loss of housetraining due to diuresis, decreased activity level or disorientation due to hypotension). Before treating this patient with a drug such as selegiline, which has a high potential for drug-drug interactions, the best course of action would be to modify the dose of furosemide.

    Fortunately, many resources are available to help veterinarians determine whether two drugs are likely to interact adversely. Many cost nothing and are already available at any veterinary hospital. For example, product package inserts contain useful information about both adverse drug reactions and potential drug-drug interactions. As veterinarians, sometimes we have to take the time to read the fine print. Pharmaceutical companies are also usually great resources for this type of information for the drugs that they market; often, such information is either provided on the company's Web site or available by telephone. Also, in most—if not all—states, pharmacies are required to have drug-interaction resources (either software programs or reference texts). In my experience, pharmacists are almost always willing to consult with veterinarians on this kind of information free of charge.

    Polypharmacy may be necessary for the optimal medical care of many geriatric patients. However, the practice of polypharmacy is one of the critical areas in which we must consider the precept Primum non nocere (First, do no harm).

    Downloadable PDF

    Dr. Mealey discloses that she has received financial support from the American Kennel Club Canine Health Foundation, Bayer Animal Health, IDEXX, and Morris Animal Foundation.

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