Influence of gastric pH on digoxin biotransformation

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Abstract
3H-digoxin-12 .alpha. and unlabeled digoxin were administered down a nasogastric tube and digoxin, digoxigenin and its mono- and bis-digitoxosides, and pH were assayed in gastric fluid [GF] of 6 healthy subjects at intervals for 90 min each under 4 conditions: pentagastrin infusion 6 .mu.g/kg per h with the subjects ambulatory and supine, and saline infusion ambulatory and supine. Intragastric hydrolysis occurred at roughly the same rate as reported in vitro. At 90 min, an average of 12.5% of the radioactivity that remained in the GF was recovered as digoxin for the 2 conditions when pentagastrin was infused, compared with 52.5% for the 2 conditions when saline was infused. The main glycosidic metabolite was digoxigenin, and the amount correlated closely with the hydrogen ion activity in GF at 90 min (r = 0.83, P < 0.01). Only minor differences were found between the supine and ambulatory conditions. The clinical significance of these results is undetermined.