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Advances in medical toxicology are achieved through the scientific method using observations, derived from cases of poisoning and nonpoisoning due to xenobiotic exposures, to generate hypotheses. Subsequent research questions are analyzed with epidemiological investigation, and preliminary studies are examined with methodological scrutiny. Initial analytical techniques are improved, and confirmatory studies are performed. Ultimately, models relating cause to effect are formulated.

To optimize patient care, it is useful to grade the quality of available scientific evidence used to justify treatment recommendations. Decisions about how strongly to recommend a medical action will be based upon the careful consideration of the risks of leaving a patient untreated, the potential benefits and harms of treatment, the quality of the guiding evidence, a balanced view of resource utilization, and the values of the person to be treated. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) Working Group has provided a framework for assessing and communicating levels of scientific evidence (Table 137–1).15 An understanding of basic principles of research design and epidemiology is required to interpret published studies and to lay the groundwork for future investigation in toxicology.

Table 137–1. GRADE System for Evaluating Clinical Recommendations15

Table 137–2 lists different study formats.

Table 137–2. Types of Epidemiologic Study Designsa

Observational Design: Descriptive

A staggering array of xenobiotics are able to injure people, necessitating reliance of toxicologists on good descriptive data regarding toxic outcomes. Through 2007, the National Poison Data System (NPDS) of the American Association of Poison Control Centers (AAPCC) has amassed a database of more than 45 million human exposures.5 Descriptive case reporting serves a valuable purpose in describing the characteristics of a medical condition or procedure and remains a fundamental tool of epidemiological investigation. A case report is a clinical description of a single patient or procedure with respect to a situation. Case reports are most useful for hypothesis generation. However, single case reports are not always generalizable, as the reported situation may be atypical. A number of case reports can be grouped, on the basis of similarities, into a case series. Case series can be used to characterize an illness or syndrome, but without a control group they are severely limited in proving cause and effect. In 1966, a case series of two patients with "acute liver ...

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