Proceedings of The Physiological Society

University College Cork (2004) J Physiol 560P, PC7

Communications

REVERSAL OF DIGOXIN CARDIAC TOXICITY BY AN ANTICALIN (DIGICAL II) IN THE ANAESTHETIZED GUINEA PIG

Kelly,Roisin ; Peim,A ; Walz,A ; Caspari,T ; Schlehuber,S ; Skerra,A ; Snow,HM ;

1. Department of Physiology and Biological Services Unit, University College Cork, Cork, Ireland. 2. Pieris Proteolab AG, Freising-Weihenstephan, Germany. 3. Lehrstuhl fur Biologische Chimie, Technische Universitat Munchen, Freising-Weihenstephan, Germany.


Anticalins are a novel class of engineered receptor proteins with prescribed ligand specificity. Digical II is an Anticalin with high affinity (KD = 1.2± 0.2 nM ) for digoxin and as such has the potential to reverse digoxin toxicity in man (Schlehuber et al., 2000). We have tested the ability of Digical II to reverse digoxin toxicity in the guinea pig and described the pharmacokinetics of the interaction between digoxin and Digical II in the pig. Eleven guinea pigs (average wt 500g) were anaesthetized (ketamine 60mg/kg i.p. and xylazine 8mg/kg i.p., maintenance 1/10 induction dose every 30min), artificially ventilated, a jugular vein cannulated and the ECG lead II recorded. Atropine (0.8 mg/kg i.v.) and digoxin (500ug/kg i.v.) were given followed by an infusion of digoxin (1ug/min i.v.) for 20min. All guinea pigs showed ECG signs of digoxin toxicity by 13.9 min (mean: range 6-35min). In 6 guinea pigs, given saline placebo no reversal of toxicity took place and all animals were dead within 40.8±3.6 min (mean±S.E.M.). In 5 guinea pigs given Digical II (mean dose 12.8 mg i.v. range 9.5—16.4 mg) the mean survival time was significantly increased (p=0.006 unpaired t test) to 112.8±16.3 min (mean±S.E.M.). In these guinea pigs reversal of digoxin toxicity was observed within 29.2 min (mean: range 15—43 min) and all were alive at 60 min or longer and were then humanely killed. Preliminary experiments in anaesthetized pigs (induction pentobarbitone 30mg/kg i.v. maintenance 6mg/kg/h) were carried out to define the kinetics of the distribution (a) and elimination (b) phases of free digoxin, Digical II and protein bound digoxin. A jugular vein was cannulated for injection of drugs and withdrawal of blood samples. In the absence of Digical II, the t1/2(a) values of free digoxin were 12 and 18min and protein bound digoxin 10 and 20min (digoxin 12.5 ug/kg i.v.). When Digical II (450 ug/kg i.v.) was administered 90min after the initial dose of digoxin, the free plasma digoxin concentration fell below detection limit within 10 min and the elimination phase could not be measured. In contrast, protein bound digoxin increased and then declined with t1/2(a) values of 30 and 35min. These results show that Digical II is capable of rapidly clearing free digoxin from plasma and reversing digoxin cardiac toxicity. Experiments were carried out under licence from the Irish Government.

Where applicable, experiments conform with Society ethical requirements