Formation of [20R]-dihydrodigoxin from digoxin in humans

The objective of this research was to determine the stereochemical identity of dihydrodigoxin (DHD3), a metabolite of digoxin excreted in urine after digoxin administration in man. Separation of the individual epimers in reference DHD3 was effected by a chemical derivatization-HPLC procedure. Comparison of individual derivatized epimers of DHD3 with the known 20R and 20S epimers of derivatized dihydrodigoxigenin using chromatographic data and NMR spectroscopy permitted identification of the 20R and 20S epimers in reference DHD3. Material corresponding chromatographically to R-DHD3 was isolated from urine of a volunteer taking oral digoxin daily. The NMR spectrum of the chromatographically pure, derivatized urinary isolate was identical to the NMR spectrum of derivatized R-DHD3. Urine samples from 20 patients on chronic digoxin therapy and from two volunteers were surveyed for chromatographic evidence of R- or S-DHD3 using HPLC of a fluorescent derivative as well as HPLC of a UV-absorbing derivative. The more sensitive fluorescence procedure yielded evidence for R-DHD3 in eight patients and both volunteers. There was a sufficient concentration in four patients and both volunteers for independent evidence of R-DHD3 using the UV-absorbing derivative. Chromatographic evidence (fluorescent derivative) for S-DHD3 was found in urine from three patients. However, this evidence for S-DHD3 was demonstrated to be an artifact by the absence of the peak expected for S-DHD3 in the chromatogram of the UV-absorbing derivative as well as by the inability of fecal incubates to convert digoxin to S-DHD3. The results of the investigation indicate that the DHD3 metabolite formed in humans is the 20R epimer.