Even though incorrect dosing occurs in about 5% of patients with heart attack who receive a certain blood clot-dissolving therapy, patient-related factors appear to be more responsible for adverse outcomes than the dosing errors, according to a recent study.
The findings could be important in defending malpractice lawsuits related to dosing errors, the authors suggest. Several studies have reported higher death, stroke, and major hemorrhagic event rates in patients who received incorrect doses of fibrinolytic (clot-busting) agents, according to background information in the article. However, several patient factors identified as related to risk of incorrect dosing are also markers of higher risk of death, thereby limiting inference about the cause-and-effect relationship of incorrect dosing and adverse outcomes.
It has been assumed that the adverse outcomes are caused by incorrect dosing. However, it also is possible that the adverse outcomes may be due to confounding factors such that sicker patients with an unstable early clinical course could be more likely to receive incorrect doses, says Rajendra H. Mehta, MD, MS, of Duke Clinical Research Institute and Duke University Medical Center in Durham, NC.
Mehta and colleagues conducted a study to determine how much of the association between incorrect dosing and adverse outcomes is cause and effect (JAMA 2005; 293:1,746-1,750). The researchers hypothesized that if the incorrect dose was causing adverse outcomes, the association between incorrect dosing of active fibrinolytic and adverse outcome would be much stronger than the association between incorrect dosing of fibrinolytic placebo.
The study included 16,949 patients with ST-segment elevation heart attack (STEMI; a certain measurement on an electrocardiogram) who were enrolled in the Assessment of the Safety and Efficacy of a New Thrombolytic (ASSENT-2) trial. Patients were assigned to either a bolus (injection of a specified dose) of tenecteplase (clot-dissolving agent; with alteplase [clot-dissolving agent] placebo bolus plus infusion) or a bolus of alteplase (with tenecteplase placebo plus infusion).
The researchers found that incorrect dosing occurred in 4.9% of patients who received active alteplase and in 4.6% of patients who received alteplase placebo. Patients receiving incorrect doses of alteplase or alteplase placebo were more likely to be older, female, black, shorter, have lower body weight and systolic blood pressure, and have a higher Killip class (heart failure measurement) at presentation.
Thirty-day mortality was higher in patients who received an overdose (9.8%) or underdose (19.5%) of alteplase compared with those who received a correct dose (5.4%). The same pattern was present in patients who received an alteplase placebo (10% for overdose, 23.5% for underdose, and 5.4% for correct dose). Similar patterns were seen for in- hospital intracranial hemorrhage and major bleeding. The higher rates of adverse outcomes with incorrect dosing were largely accounted for by adjusting for baseline characteristics.
“Medical errors due to incorrect dosing of fibrinolytic therapy have been shown to be associated with increased risk of adverse events in STEMI patients and with increased risk of litigation against caregivers,” the authors wrote. “When identifying an incorrect dose of a potentially toxic drug associated with an adverse outcome, the reflex and logical conclusion is to assume cause, particularly in malpractice litigation that is principally driven by adverse outcomes.”
However, this study raises the possibility that much of the adverse outcomes ascribed to dosing errors, at least in some situations, may be due to confounding rather than a direct effect of the error itself, they wrote.
“Thus, while medication errors need to be minimized, caution should be used in concluding that adverse outcomes associated with errors are primarily caused by the errors,” the authors conclude.
though incorrect dosing occurs in about 5% of patients with heart attack who receive a certain blood clot-dissolving therapy, patient-related factors appear to be more responsible for adverse outcomes than the dosing errors, according to a recent study.
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