Does a sodium-free buffer affect QRS width in experimental amitriptyline overdose?
OBJECTIVE
We carried out this study to determine the effects of pH alteration on QRS width with administration of tromethamine, a non-sodium-containing buffering agent, in experimental amitriptyline overdose.


METHODS
Prospective, nonblinded trial.


METHODS
Adult mongrel dogs.


METHODS
Pentobarbital-anesthetized dogs were overdosed with amitriptyline 5 mg/kg followed by infusion at 1.0 mg/kg/minute until the QRS width doubled, then decreased to .5 mg/kg/minute until the end of the experiment. At two defined points of toxicity, the dose of tromethamine required to raise the pH to 7.50 +/- 4 was given. pH and QRS width at a speed of 100 mm/second were measured over a 30-minute period after each tromethamine dose. Data were analyzed with non-linear-regression analysis.


RESULTS
At toxicity 1 the mean pH was 7.32, with a QRS width of 11.6 mm. Two minutes after the tromethamine dose the pH rose to 7.51, with narrowing of the QRS width to 8.4 mm. At toxicity 2 the pH was 7.40, with QRS width of 10.6 mm. Two minutes after tromethamine, the pH rose to 7.49 and the QRS width decreased to 9.7 mm. Regression analysis showed a correlation between pH and QRS width; as pH increased, QRS width decreased (P = .0001).


CONCLUSIONS
Cardiac toxicity of amitriptyline overdose, as manifested by QRS widening, is reversible by pH changes alone.
Stone
C K
CK
Department of Emergency Medicine, East Carolina University School of Medicine, Greenville, North Carolina, USA.
Kraemer
C M
CM
Carroll
R
R
Low
R
R
D000639:Amitriptyline / Q000633:toxicity*; D000818:Animals; D004285:Dogs; D062787:Drug Overdose / Q000503:physiopathology; D004562:Electrocardiography / Q000187:drug effects*; D006863:Hydrogen-Ion Concentration; D011446:Prospective Studies; D014325:Tromethamine / Q000494:pharmacology*
D014325:Tromethamine; D000639:Amitriptyline