Chapter 6: Toxicology

Learning Objectives

Introduction

Toxicology comprises several medical applications. The analysis of drugs in human specimens can be conducted for clinical or legal/forensic purposes. Clinical applications include the acute management of overdose and therapeutic monitoring of drug concentrations to achieve maximum efficacy while limiting the toxicity and side effects of medications. Forensic applications of toxicology include analysis of drugs to provide evidence for civil and criminal court cases, to investigate the cause of death, to deter the use of performance-enhancing drugs in athletic competitions, and to determine operator impairment related to traffic citations and vehicle accidents. Workplace drug testing assesses pre-employment drug abuse and on-the-job impairment. Given the number of therapeutic drugs, drugs of abuse, and environmental toxins, as well as the variety of diseases, signs, and symptoms associated with drug exposure and overdose, there is an array of laboratory testing strategies. For this reason, the discussion of toxicology in this chapter will be divided into 3 broad sections—therapeutic drug monitoring (TDM), drugs of abuse, and environmental toxins (Figure 6–1).

Therapeutic Drug Monitoring

Overview of Therapeutic Drug Monitoring

TDM is the practice of measuring the concentration of a drug or its metabolite in order to optimize the dosing of that drug to an individual patient and/or to assess patient compliance with a dosing schedule. The goal of TDM is to improve drug efficacy—the likelihood of a therapeutic effect while avoiding or minimizing adverse effects. Table 6–1 lists some commonly monitored drugs. Patients do not require monitoring for most drugs. However, for a limited group of agents or for patients with certain conditions (for instance, limited renal function, pregnancy, newborn or geriatric age groups), TDM plays an essential role in establishing the appropriate therapeutic dosing regimen.