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 A column in January's Psychiatric Services "Drug-Drug Interactions:The Silent Epidemic by Neil Sandson, MD of Sheppard Pratt Health System describes a recent report from the Institute of Medicine's committee on patient safety which published extensive recommendations for preventing medical errors. Drug-drug interactions (DDIs) represent a critically important and widely underrecognized source of medical errors.
A large number of pharmacodynamic interactions exist primarily from the interaction of different agents on brain receptors that can produce a synergy or cancellation of drug effects. In a similar fashion, a wide range of pharmacokinetic interactions exist, in which the blood levels of given agents may be raised or lowered. Dr. Sandson points out that "we have long grappled with the inherent complexity posed by our vast armamentarium of drugs and their numerous and varied effects. However, only in the past few years have we gained an appreciation for the prevalence, complexity, and clinical importance of two key systems that significantly influence drug levels, namely the cytochrome P-450 system and the P-glycoprotein transporter." In fact, DDIs have an enormous impact on patient care, and the pervasively poor recognition of DDIs is a major part of the problem.
Studies have found DDIs to be the main cause for roughly 2.8 percent of all admissions especially among persons older than 50 years who were taking medications. Recognition and detection of DDIs by physicians is generally poor. In one study of 263 physicians who practiced in the Southern California Department of Veterans Affairs system (21 percent of the physicians surveyed were psychiatrists), clinicians recognized only 53 percent of DDIs of moderate to severe intensity and only 54 percent of potentially fatal combinations. A number of these studies demonstrate how DDIs lead to increased rates of hospitalization, increased lengths of stay, and patient morbidity. It has been estimated, by using a cost-of-illness model, that this could represent a quarter of a million hospital admissions/year, costing the health care system over a billion dollars.
Recommendations
Preventing DDIs relies on two linked functions: detection and recognition. The most important developments in our ability to detect DDIs involve computer programs. Several medical systems have already demonstrated that the use of computers can lead to significant decreases in overall medical errors, including DDIs. Although computer systems can help prevent drug-drug interactions, they are far from perfect and the sensitivity of a DDI program is limited by the completeness of the database that is entered into it
Dr. Sandson concludes with the hope that continued advances in electronic medical records and order entry systems are the wave of the future and that "active" computer programs will grow more sophisticated with the ability to provide increased alert statuses with multileveled options for learning more about a potential DDI. He offers several pieces of advice for clinicians: 1) become familiar with the DDIs for the drugs you use most frequently; 2) pay special attention to potential DDIs when prescribing agents with a low therapeutic index; 3) use tables, charts, references, or computer programs that you like and trust and keep them handy; 4) encourage your patients to get all their medications at the same pharmacy and to enroll in that pharmacy's DDI monitoring program; 5) whenever possible, try to select agents with a low likelihood of producing DDIs within a given class of agents. Hopefully, these prudent measures will provide reasonable protection from the worst that DDIs have to offer until computer software is able to negotiate the delicate balance between completeness and utility.
Psychiatr Serv 56:22-24, January 2005
10:40:50 PM 
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