Annals of Long Term Care

Therapeutic drug monitoring (TDM) provides valuable data about the safety and efficacy of drug therapy. A lack of TDM has been associated with a significant proportion of preventable adverse drug events among elderly patients. A number of barriers to the performance of optimal monitoring exist in the long-term care (LTC) setting. When faced with a lack of desired TDM, the clinician must attribute this to one of three scenarios: monitoring is feasible but has not been performed; monitoring is only feasible with the use of creative strategies; or monitoring is not feasible, and decisions about whether to continue drug therapy must be considered. This article describes common barriers to optimal monitoring using specific drug therapy examples and discusses options for overcoming these barriers. The pharmacist’s role in TDM in the LTC setting is also highlighted. (Annals of Long-Term Care: Clinical Care and Aging 2010;18[10]:33-38).

Introduction
Therapeutic drug monitoring (TDM) begins when a medication is first prescribed and involves determining an appropriate initial and maintenance dosage regimen for the patient.¹ There are generally two sources that provide guidance to the clinician about optimal TDM. The first is medication-specific and comes from published product data. The second is environment-specific and derived from long-term care (LTC) regulations and guidelines for drug regimen review. Successful medication monitoring enables team members to: (1) track progress toward therapeutic end points and ensure maintenance once achieved; and (2) detect the emergence or presence of adverse drug events (ADEs). Unfortunately, in the LTC setting, medication monitoring presents a challenge. A variety of considerations either pose barriers to the performance of monitoring activities or affect the interpretation of the findings. This article discusses some of the most commonly encountered challenges in the LTC setting and suggests some strategies for overcoming them.

Consequences Associated with Lack of Monitoring
Consequences of inadequate monitoring can include emergence of ADEs as a result of the failure to detect problems associated with the drug therapy. Prevalence rates of ADEs associated with lack of monitoring vary based on the clinical setting. One study in the LTC setting suggested that 80% of ADEs occurring among LTC residents occurred at the monitoring stage,² and the literature has shown that a high proportion of monitoring-related ADEs result in hospitalization or are found to be preventable.³

Consequences may also include therapeutic failure, a term employed when drug therapy does not achieve the therapeutic goal for which it was prescribed. Therapeutic failures can result in unnecessary exposure to ineffective drug therapy or exacerbation of the underlying condition. Data describing the prevalence and health outcomes of therapeutic failure are not LTC-specific, but studies suggest that 6.8% to 28% of emergency department or hospital admissions associated with ADEs are due to therapeutic failure.^4-6

Ideally, optimal practice of TDM should be able to detect, or prevent, these scenarios by identifying new symptoms suggestive of adverse effects, identifying under- or overadherence, or evaluating the therapeutic response of the underlying condition. Lack of ability to do this has consequences for the provider as well, because failure to supervise or monitor care has been ranked as the third most common reason for a malpractice claim to be brought against a physician.⁷

Barriers to Appropriate Monitoring
The most common barriers to the performance of monitoring activity can be grouped into three categories: logistical; provider-related; and patient-related.