are the ones responsible for administering, storing, and monitoring the use of medications. Support systems for the patient are minimal in the ambulatory setting, and in some instances the medication container label may be the only source of information for the patient.

Although medication injuries often result from a complex interaction of agent, host, and environment, the most appropriate basis for identifying safety interventions may be patient-focused approaches such as those used in the injury-prevention field. The first step in an injury-prevention approach uses a heuristic called a phase–factor matrix (originally developed by Haddon) (Figure 2-1) to identify plausible interventions.

In this matrix the three phases of the injury process appear in the left-hand column: pre-event, event (or the injury), and post-event. Across the top of the matrix are the three entities among which the interactions traditionally occur to cause an injury or disease: the host or patient, the agent or drug, and the environment. When the phase–factor matrix was used to identify interventions for ADEs from Warfarin, the first two environmental changes identified were standardized naming and dosing conventions and improved medication label readability for patients (Budnitz and Layde, 2007).

Once interventions are identified, the second step in the injury-prevention approach is to consider implementation strategies since different strategies require different actions on the part of individuals, stakeholders, and society, and each strategy has different strengths, weaknesses, costs, and feasibility. Strategies include education, enforcement (e.g., laws mandating use of seat belts), and engineering (e.g., better medication label design). Injury-prevention strategies are typically classified as

FIGURE 2-1 Phase–factor matrix for identifying plausible intervention.

SOURCE: Budnitz (2007).