Which of the following blood tests will tell the nurse that an adequate amount of drug is present in the blood to prevent arrhythmias?
A. Serum chemistries
B. Complete blood counts
C. Drug levels
D. None of the above
Correct Answer: C. Drug levels
Knowing drug levels (peak and trough) is the only way to ensure there is enough drug in the body to work. Other choices do not demonstrate drug effect. Screening may have an important role in the epidemiological assessment of poisoning as it is a common finding that more substances are detected in urine than are recorded from history. Specific qualitative tests (e.g. amatoxins, paraquat) may be of clinical assistance in determining evidence of exposure. Clinicians are better served by relying on a careful interpretation of the history and clinical examination in conjunction with readily accessible investigations such as ECG, electrolytes and acid-base analysis.
Option A: The principal methods utilized to measure drug concentrations in clinical toxicology are the same as those used in therapeutic drug monitoring. These include fluorescent immunoassay, enzyme immunoassay, thin-layer chromatography, high performance liquid chromatography, gas chromatography, mass spectroscopy, flame photometry and simple colorimetric methods.
Option B: The use of drug concentrations for research in toxicology is both important and problematic. An understanding of the kinetics of drugs taken in overdose may contribute to the development of more rational treatment and improve clinical outcomes. The problems in assessing such data relate to the variables inherent in the clinical presentation. Such variables include ingested doses, times to presentation, gastrointestinal decontamination, and the likelihood that in most patients there is an opportunity to collect only very few samples.
Option D: To be useful clinically a drug concentration should assist in one or more of the following areas: diagnosis, prognosis, guiding therapy, or assessing the efficacy of current therapy. Even when these criteria are satisfied the drug concentration needs to be interpreted in the context of the individual patient’s clinical condition and other factors which may influence the pharmacodynamic response to any blood level (such as coexistent disease or age).