Determining triage guidelines for unintentional overdoses with calcium channel antagonists.

Background: Calcium channel antagonists (CCAs) are known to cause significant toxicity in overdose. Determining triage guidelines for CCAs is an important but difficult task. This study was designed to determine if an unintentional overdose of a patient's CCA could result in clinically significant cardiovascular (CV) symptoms (hypotension, bradycardia, conduction disturbances).

Methods: Poison center records over a 3-year period were reviewed for adults ingesting at least double their prescribed dose of CCAs and who were evaluated in an emergency department (ED). Cases were reviewed for: patient age and gender, co-ingestants, CCA involved, dosage form, dose taken, usual dose, symptoms, available vital signs, and medical outcomes.

Results: 225 cases were identified; 161 cases met study criteria. There were 51 cases involving co-ingestants and 13 in which the usual dose was unknown. These were excluded. One hundred twenty-two patients (76%) were female and the mean age of all patients was 64 years. One hundred and four (65%) cases involved ingestions equal to double the usual dose (DD), 57 (35%) involved more than a DD. For DD cases, nine (9%) developed clinically significant CV signs or symptoms; while in cases with more than DD, eight (14%) did.

Conclusions: This retrospective review demonstrated that the toxicity of CCAs following a therapeutic overdose can be highly variable and that the dose producing a toxic effect on the cardiovascular system may be within the maximum range of therapeutic doses. This may be the result of a number of factors, including the broad range of therapeutic doses as well as the pre-existing conditions in patients taking these medications. This variability makes home management of these cases difficult and therefore, poison centers should be conservative in their evaluation of these cases.