Adverse Drug Events

The use of medications (pharmaceutical drugs consisting of prescription and over-the-counter drugs, biologics, vaccines, and/or dietary supplements) generally results in beneficial, defined therapeutic outcomes when these drugs and related medications are taken properly and appropriately monitored. Nevertheless, there are inherent risks in using any medications. Adverse drug events are frequent and costly consequences of medication use. They are widely reported to be a significant cause of patient morbidity and mortality, and they cost billions of dollars in annual healthcare expenditures.

There is no universally accepted definition for an adverse drug event, and numerous definitions exist. Most definitions are similar to those put forth by the World Health Organization (WHO) and/or the U.S. Food and Drug Administration (FDA). The WHO defines an adverse drug event as any response to a drug that is noxious and unintended in doses normally used in people for diagnosis, prevention, and treatment. The FDA describes serious adverse drug events as events that result in patient death, life-threatening outcomes, hospitalization, disability, congenital anomaly, and outcomes requiring healthcare interventions.

Adverse drug events include both preventable and unavoidable events, the latter of which are also known as adverse drug reactions. An adverse drug reaction is an unintended, undesired, and unexpected response to a drug that negatively affects a patient. It may result in the need to change drug therapies and/or other treatments; hospitalization or other institutional admission or prolonged stay; and patient complications, including disability or death. Common side effects of pharmaceutical drugs are not generally considered to be adverse drug reactions.

Adverse drug events include the following: unexpected, injurious adverse drug reactions experienced during use of the medicine; and harmful outcomes secondary to preventable medication errors, including errors of omission or commission. The causes of medication errors (i.e., preventable adverse drug reactions) are multifactorial and can be related to drug prescribing, order communication, dispensing, administration, monitoring, product packaging and labeling, product nomenclature, education, monitoring, and other product use. Medication errors result from failed systems, lack of knowledge, and lapses in performance or mental processes—regardless of whether the medication is under the control of the patient, caregiver, or healthcare practitioner. Medication errors may be caused by defective systems involving patients and caregivers, healthcare practitioners, regulators, manufacturers, healthcare organizations, and other entities.

In addition to physical afflictions, adverse drug events impose a significant economic burden on society. The number of people who reportedly died from medication errors increased 2.5-fold from 1983 to 1993. The national Institute of Medicine (IOM) estimated that approximately 106,000 individuals died from an adverse drug event in 1994, and an estimated 2.2 million individuals were hospitalized with a serious adverse drug event. In [Page 33]2006, the IOM concluded that at least 1.5 million preventable adverse drug events occur in the United States annually, and the true number might be much higher. The IOM conservatively estimates the 2006 national hospital costs associated with adverse drug events at $3.5 billion.

In 1995, Johnson and Bootman developed a probability pathway model to estimate the direct cost of managing drug-related morbidity and mortality in the ambulatory-care setting in the United States. Their results showed that drug-related mortality and morbidity cost $76.6 billion per year. An updated analysis based on that 1995 model showed that the cost of drug-related problems among ambulatory Americans more than doubled in 2000 to an estimated $177.4 billion, with hospital admissions accounting for $121.5 billion or 69% of the total costs. These costs are borne by patients, families, health insurers, government, healthcare providers, employers, and others.

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