Risks and errors in prescribing Flashcards
what is a therapeutic index?
• If given in sufficient dose, all drugs can cause harm. Hopefully, however, there will be a reasonable ‘safety margin’ between the dose that achieves the desired effect, and the dose that is harmful. The therapeutic index seeks quantify this. Historically, the therapeutic index was derived from animal studies, and described the ratio between the dose that was ‘effective’ in 50% of the animals, and the dose that was lethal in 50% of the animals. In modern use, however, the term is applied in a broader sense. It is better thought of as a concept rather than a number, which refers not just to lethality, but any harmful effect.
what steps need to be taken when prescribing drugs with a narrow therapeutic index
o Calculation of the dose based on the patient’s weight (e.g. gentamicin), or body surface area (e.g. cytotoxic chemotherapeutic agents), and carefully accounting for the effects of renal or hepatic impairment and drug interactions.
o Careful monitoring for adverse drug reactions: for example, by continuously monitoring the cardiac rhythm when giving phenytoin or aminophylline by intravenous infusion.
o Measurement of the blood concentration of the drug (therapeutic drug monitoring, e.g. gentamicin), or its effect on a surrogate endpoint (e.g. warfarin and INR), then adjusting the dose accordingly.
human factors involved in prescribing
o Dangers often exist where drugs are prescribed in an unusual, unfamiliar or complex way. These may include unusual doses (loading doses, calculated doses, variable doses), dosage units (e.g. ‘micrograms’, ‘units), and intervals (e.g. alternate daily, weekly). Intravenous infusions are particularly risky as they often combine several of these factors, often with high-risk drugs and sick patients.
o Contextual factors: The context in which a task is performed (the environment, people, other pressures, etc) may have various effects that increase the risk of error and harm. These include ambiguity (which we may erroneously suppress), distraction, time pressures and disengagement.
o Cognitive biases: These may be defined as systematic errors of thinking. Many biases are described (see the table, below, for selected examples; and for more examples and detail, The Decision Lab (Links to an external site.) is an excellent resource)
strategies to help de-bias thinking
o Bias specific teaching/learning: to increase awareness of biases
o Slowing down: forcing yourself to ‘stop and think’
o Metacognition: ‘thinking about thinking’ e.g. forcing yourself to ask ‘what else could this be?’
o Checklists: these may be used as ‘cognitive forcing tools’
