Experience with digoxin immune Fab (ovine) in patients with renal impairment. Digibind is a purified antigen binding fragment (Fab) of immunoglobulin G antibodies raised to bind digoxin. Studies in animals suggest renal excretion accounts for a substantial portion of Fab's elimination. Thus it is expected that elimination of antidigoxin Fab fragments would be prolonged in patients with renal impairment; it remains unclear whether digoxin might be released with possible recurrence of toxicity. To shed light on this potential for recrudescent digitalis toxicity following release of bound digoxin, the author scrutinized the records of patients with impaired renal function who were treated with Digibind. Data are available from three sources: the original multicenter investigation of Digibind in 150 patients with life-threatening digoxin or digitoxin toxicity, a postmarketing surveillance study of 745 patients treated with Digibind, and all other reports in the literature or to Burroughs Wellcome Co of physician experience with any antidigoxin Fab. Sixty percent of patients in the multicenter trial and 80% of patients in the postmarketing surveillance trial had some degree of renal impairment. Patients with poor renal function had no evidence of decreased effectiveness or safety either in terms of percent of patients responding, onset of effect or evidence of recrudescence. From all sources the authors identified 28 patients treated with Fab who were functionally anephric. Twenty-seven of these patients had no evidence of recrudescent toxicity. One patient was reported to have complete resolution of digoxin-induced third-degree atrioventricular (AV) block, but AV block recurred 10 days after Fab treatment and persisted for 10 days thereafter. Although this case offers the only clinical evidence suggesting recrudescence can occur, there were no likely alternative explanations for the clinical findings. 