Another necessary building block for a model of medications use is the concept of a drug therapy problem.* A drug therapy problem is any circumstance that a competent professional would judge to be inconsistent with achieving the objective of drug therapy. A DTP is overt, i.e., potentially detectable by a patient, caregiver, or professional, and is specific to a patient and time. In other words, DTPs are detectable in principle, although many may be undetected in fact.
A DTP is part of the process of care, in contrast to ADR, ADE, and DRM, which are outcomes of medications use. In systems terminology, a DTP is a state of an individual in a medications use system, an intermediate result of therapy.
A DTP is a possible precursor to a drug-related morbidity. The difference between a DRM and a DTP seems subtle at first, but maintaining a clear distinction between process and outcome is very important to understanding the model.
The notion of a DTP complements error and violation in three ways. First, DTPs are important and common latent injuries that can lead to DRM. Latent precursors include both latent injuries (a state of a patient in therapy) and latent failures (a state of a system's process or outcome) that result from human errors and violations, but which do not constitute or cause injury by themselves.** Latent injuries may continue indefinitely without causing injury until they are triggered, e.g., combined with other precursors. Reason called a latent error a resident pathogen. In this metaphor, a resident pathogen in a system is like a bacterial pathogen that can exist for a time in the body without causing disease. A latent injury, then, is like an impairment in a patient's immune system. The patient is susceptible to the pathogen. Then,
* The original term was drug-related problem.27,29 The term originally referred to the process of care. Unfortunately, some studies used DRP to denote an outcome, that is, as a kind of DRM. For example, suppose a patient were admitted to a hospital because of overdosage — too much of the correct drug. That confuses process with outcome. Drug overdose is a part of the process of care. Some people who receive excessive dosages show a toxic manifestation, and some do not. In all but exceptional cases, the toxic manifestation, the outcome, would have been the reason for admission, not the overdose. The distinction is important, so a new term was needed.
** Out of respect for clear terminology (and for James Reason), the original definition of latent precursor included only what we are calling latent failure. My usage somewhat expands the original. Understanding medications use requires a term for deficiencies (in the patient, so to speak) that were caused by the system, i.e., what I call latent injury.
when the pathogen finds the compromised host, the patient shows manifest infection, i.e., injury.
Second, DTP is useful in circumstances where error or violation would be ambiguous, as described in the preceding section. DTPs include events or states (circumstances in the process of therapy) that may not clearly result from a deviation; a slip, lapse, or mistake; or the violation of a social norm. This may avoid the tendency toward finger pointing and defensiveness that often result from ambiguous allegations of error. Some DTPs have unknown etiology. They may result from unrecognizable, possibly chance, events or from the intersection of multiple causes that would be innocuous in isolation but deleterious in combination.
To return to an earlier example, consider a patient who experiences gastric hemorrhage. Endoscopy reveals a number of oozing gastrointestinal lesions and one large one, which is the apparent source of the hemorrhage. A medication history reveals that the patient has been taking prescribed NSAID medicine for more than 2 years. Also, he (unwittingly) takes a proprietary over-the-counter medicine for heartburn, an effervescent powder containing aspirin. He denies black, tarry stools until 2 days before admission. His record does not include evidence that his physician monitors hematocrit or performs tests for occult blood. One could debate (endlessly) whether the prescriber or the patient had committed an error or violation. While voluntary guidelines for the use of NSAIDs certainly do exist, there is no official requirement for monitoring NSAID use. If there was an error, there is room for debate about whether it was inappropriate prescribing, inadequate patient information, patient nonadherence, the fault of the OTC manufacturer, etc. Or one could say that there are two DTPs — two potentially recognizable circumstances that are inconsistent with the therapeutic objective — duplicate therapy and long-term therapy with NSAIDs without monitoring.
In the story of Katherine LaStima, it is not necessary to find an error in order to understand what happened. Was her overuse of her rescue medication and underuse of her preventer medication an error? Perhaps it was her decision to go to the fair. The pharmacist in this case actually committed a clear violation of the insurance company's policy regarding frequency of refills. The absence of a medication use standard, and his failure to appreciate the clinical significance of the early refill, however, was a latent failure. The violation did not kill her, but the latent failure contributed to her death. Perhaps she or her parents were not well informed about the management of asthma or distracted by other concerns. Error does not help us to understand the system that killed her (or allowed her death). The pattern of prescription refills certainly indicates a DTP to be investigated further. DTP does move us closer to an understanding. The failure to recognize and resolve Katherine's DTP was the proximate cause of her death.
The third way that DTPs complement error is that DTP changes the focus from the details of process (who did what, when) to the management of process — anticipation of likely outcome (what is likely to result).
Despite the complexity of terms used in the literature and in Tables 3.2 and 3.3, there are relatively few types of DTPs. Bero et al. defined 14 types.19 Cipolle et al. have developed an exhaustive categorization of potential DTPs into eight types that are useful for practice and research.42 This will be described in more detail in Chapter 10. For purposes of modeling medications use and the genesis of DRM, we can think of DTPs as falling into three basic types. During the process of therapy, the patient, caregiver, or health professional could have observed one or more problems with:
1. Access: that the patient was not receiving necessary therapy for a valid indication
2. Effectiveness: that therapy was not having the intended effect within a reasonable time
3. Safety: that therapy was producing an undesired effect
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