A Guide To Drug-Drug Interactions In Podiatry

Robert G. Smith, DPM, MSc, RPh, CPed

Given the likelihood that one of your patients is already taking a prescription drug, it is critical to be aware of potential interactions between medications. In addition to reviewing pertinent pharmacology principles, this author offers insights on azole antifungals, NSAIDs and a variety of other medications, and how to reduce the risk of harmful interactions.

   Prescription medications are vital to preventing and treating illness, and can help avoid more costly medical problems.1 The use of prescription medications to treat chronic medical conditions is particularly prevalent among older individuals. Almost 40 percent of older Americans take five or more therapeutic agents monthly.2 Moreover, the most recent data from a sample population survey of United States civilian households reveals 50 percent of the population consumes at least one or more prescription drugs a month while one out of 10 Americans use five or more prescription drugs each month.2

   The term “drug misadventure” is used to define the phenomena associated with negative drug experiences.3 Further, Mannasse simplifies drug misadventures to mean: “when something goes wrong with drug therapy and is unexpected.”4 Kelly reports that one category of drug misadventures is drug interactions.5 Given the aforementioned statistics, a potential for drug-drug interactions exists for at least 10 percent of Americans.

   Some drugs interact with other prescription medications, over-the-counter medications, food or drink, tobacco products, alcohol consumption, and botanical or herbal products. The literature has not well defined the ability of the clinician to accurately identify and manage potential drug-drug interactions. Many healthcare providers may overlook or are unaware of specific potential drug interactions.

   Given that a large number of drugs are introduced every year and new interactions between medications are increasingly reported, it is important that clinicians be knowledgeable of the existence of pharmacological interactions that are either beneficial or harmful within a patient’s medication regimen. While it is not possible for the healthcare provider to recognize all clinically significant drug interactions, it is possible to understand the scientific principles and mechanisms involved.

   Accordingly, let us take a closer look at drug-drug interactions in the context of frequently prescribed medications and their possible altered effects within the scope of the lower extremity.

What You Should Know About Pharmacology Principles And Drug Interactions

Understanding observed physiological effects specific to both pharmacodynamic and pharmacokinetic principles is essential when discussing drug-drug interactions. Patients need to maintain drug concentrations within the appropriate target range for efficacy. When it comes to drug interactions, the drug affected by the interaction is the “object drug” and the drug causing the interaction is the “precipitant drug.”

   The science of pharmacology encompasses both pharmacokinetics, which is the science that describes the body’s action on a medicinal agent, and pharmacodynamics, which is the scientific description of the medicinal agent’s action on the body’s systems.

   Pharmacokinetics involves four major body functions: absorption, distribution, metabolism and excretion. Drug absorption occurs at different sites along the gastrointestinal tract, including the stomach and the small and large intestines. Factors affecting absorption include: change in gastrointestinal pH, drug binding in the gastrointestinal tract, change in gastrointestinal flora, change in gastrointestinal motility and malabsorption caused by other drugs. Most interactions result in a reduced absorption rather than increased absorption from the gut.

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