Study objective: Tricyclic antidepressants (TCAs) are a leading cause of death from intentional drug overdose. Available therapies are often unsatisfactory. In this study we evaluated the use of a high-affinity drug-specific polyclonal Fab fragment (TFab) as an antidote to desipramine toxicity. Design: We gave anesthetized rats under mechanical ventilation IV desipramine so that we might study the effect of TFab on survival or IP desipramine to facilitate study of the interaction of TFab and hypertonic sodium bicarbonate (NaHCO₃), the standard clinical treatment for TCA overdose. Interventions: For the study of the effects of TFab and NaHCO₃ on survival, each rat was given a constant IV infusion of desipramine until it died, together with TFab 2 g/kg, bovine serum albumin, or .9% NaCl starting 5 minutes after the desipramine infusion. In the study of the interaction of TFab and NaHCO₃, each rat received 30 mg/kg IP desipramine followed by TFab (molar TFab:desipramine ratio, .11), NaHCO₃, TFab+NaHCO₃, or NaCl at the time of maximal toxicity (15 minutes). Results: In the survival protocol, QRS-interval duration, systolic blood pressure, and heart rate were significantly improved by TFab, and survival was prolonged by 58% compared with that in the albumin and NaCl groups (P<.001). The molar ratio of TFab to administered desipramine was .21. The unbound fraction of desipramine in serum at the time of death was reduced by TFab, but the unbound desipramine concentration was not, suggesting that TFab prolonged survival by delaying the increase in the unbound serum desipramine concentration. In the interaction protocol, neither TFab nor NaHCO₃ was effective alone, but the combination significantly reduced QRS-interval prolongation (P =.001). Conclusion: These data demonstrate the efficacy of TFab in reducing desipramine-induced cardiovascular toxicity and prolonging survival. The pharmacokinetic effects of TFab in rats with severe desipramine toxicity were similar to those observed in sublethal desipramine toxicity. Therapeutic benefit is enhanced by the concurrent use of NaHCO₃ and may be achieved despite binding only a fraction of the desipramine dose. [Pentel PR, Scarlett W, Ross CA, Landon J, Sidki A, Keyler DE: Reduction of desipramine cardiotoxicity and prolongation of survival in rats with the use of polyclonal drug-specific antibody Fab fragments. Ann Emerg Med September 1995;26:334-340.]