CLINICAL PHARMACOLOGY and
THERAPEUTICS volume 21
number 2
February, 19n
Studies on digitalis VIII. Digitoxin metabolism on a maintenance regimen and after a single dose The metabolic pattern of cardioactive and inactive conjugated metabolites of digitoxin on maintenance (9 patients) and after a single 0.6-mg dose (5 patients) was studied in patients with normal renal and hepaticfunction. Serum sampies were obtained 24 hr after the last dose, and urine was collected over 24 hr. The extent or conjugation to glucuronic and sulfuric acid was 35.0% (SD, 17.4) in whole serum and 31.6o/c (SD, 19.3) in urine sampies. Unchanged digitoxin was the main cardioactive substance found bOlh in serum and in urine (89.7% and 87.0%) in the steady-state group. All known cardioactive metabolites were present; digoxin represented less than 1%. All active metabolites were conjugated to glucuronic /suifuric acid. Serum and urine patterns of metabolites were quite similar. Hydrolysis and conjugation appeared to be more important pathways than hydroxylation. Unchanged digitoxin was the most important cardioactive substance in serum and urine (80.4% and 56.5,)() in the single-dose group. Digoxin was the main cardioactive metabolite (/2.5% in serum and 25.5')( in urine). All active metabolites were conjugated. Hydroxylation, hydrolysis, and conjugation seemed to be equally important. The most important differences between the steady-state and single-dose groups were that in the steady-state group there was signijicantly more unchanged digitoxin, far less digoxin, and less hydroxylated metabolites than in the single-dose group. Caution is thus necessary when interpreting single-dose datafor a drug that is usedfor maintenance.
Liv Storstein, M.D. Oslo, Norway Medical Department B, University Clinic, Rikshospitalet
Supported by grants frorn The Norwegian Council on Cardiovascular Diseases, Astra LId., and The University of Oslo. Received for publication Feb. 7, 1976. Aeeepted for publieation July 12, 1976. Reprint requests to: Liv Storstein, M.D., Medieal Departrnent B, University Clinie, Pilestredet 32, Rikshospitalet, Oslo, Norway.
Digitoxin has a complex metabolism. The present concept of its biotransformation is presented in Fig. 1. A number of enzymatic proces ses are involved. The products of three of these, hydroxylation, hydrolysis, and conjuga125
126
Storstein
Clinical Pharmacology and Therapeutics
. . . [T_'.
OT-3 OT-2 OT-1
EpiOT-O
. . . ~[G_' . c> c> c>
c!njugates
:;> :;>
OG-3
OG-1
EpiOG-O
-
-
/>
c!njugates
0
,j>
® .. Hydrolysis
j>
f
3 O :-
~
c> fO~-2 ~ 7 0;-1~ c> fO~-l ~ ~ o+-o~ c> f o r o ~
OG-2
c> Hydroxylation
0+-3~ c> 0+-2~
Keto-
Keto- O o f .-
Epi-
Epi-
o+-o~ c> OT-O%
-
~
-
c> (OG-O ~
Conjugation
»RingOpening?
Oi hydroderivates ?
Fig. 1. Previous (A) and present (B) concept of digitoxin metabolism.
tion, were studied for this report. Hydroxylation (phase Ireaction) transforms digitoxin (DT) derivatives to digoxin (DG) derivatives. Metabolites with less sugar (digitoxose) molecules are successively formed by hydrolysis (phase I reaction). All of the hydroxylated and hydrolyzed metabolites are cardioactive. Biologically inactive metabolites are synthesized by conjugation to glucuronic and sulfuric acids (phase 11 reaction). The main problems in the study of digitoxin metabolism are to establish methods which adequately separate the various metabolites and which are sensitive enough to allow determination of nano gram amounts of each. The methods used in this study make it possible to determine unchanged DT-3 and a maximum of 23 metabolites supposing a11 cardioactive substances are conjugated both to glucuronic and sulfuric acid. The cardioactive genins were epimerized to inactive metabolites 50 via keto intermediates 44 which were not measured in this investigation. Present knowledge of digitoxin metabolism originates from studies with tissue preparations,20-24, 29, 33, 44, 57 animal studies,5, 8, 9, 12-14, 16, 18, 25, 27, 28, 31, 41-43 and studies of the metabolic products found in human urine after a single dose of radioactive-labeled digitoxin.36-40, 56 Okita and associates 37 showed that only 6% to 10% of the original dose was excreted unchanged in the urine over aperiod of several
weeks. Studies in dogs 27 , 28 suggested that "digoxin-like" material was a main metabolite of digitoxin, and digoxin has also been proposed as a major metabolite in man. Data from single-dose studies are not necessarily applicable to steady-state studies. The aim of the present investigation was to study digitoxin metabolism in detail in patients on maintenance therapy and to compare these data with those obtained in patients given a single dose of digitoxin. Material and methods
The fo11owing abbreviations for glycosides will be used: DT-3 (digitoxin); DT-2 (digitoxigenin-bis-digitoxoside); DT-l (digitoxigenin-mono-digitoxoside); DT-O (digitoxigenin); DG-3 (digoxin); DG-2 (digoxigenin-bis-digitoxoside); DG-l (digoxigenin-mono-digitoxoside); and DG-O (digoxigenin). Steady-state study. Blood sampies of 150 ml were drawn 24 hr after the last dose in 9 patients on long-term maintenance therapy with digitoxin (Digitrin, O.l-mg tablets, Astra, Pharmacopoea Nordica standards, obtained from the same source as the intravenous preparation). Urine was collected during the same 24 hr. All patients had normal renal and hepatic function. None were in severe congestive heart failure. Cardioactive metabolites were studied in 9 serum and 9 urine sampies. Inactive, conjugated metabolites were studied in 4 serum and 9 urine sampies. The extent of conjugation was
Volume 2/ Number 2
studied in 16 serum and 13 urine sampies from patients on maintenance therapy. Single-dose study. Five patients with normal renal and hepatic function were given a single dose of 0.6 mg digitoxin (Norsk Medisinaldepot, Oslo, purity, 97%, 1.5% gitoxigeninglycosides, 1% water, and 0.5% inactive purities, in accordance with the Pharmacopoea Nordica) slowly intravenously , and serum and urine sampies were obtained after 24 hr, as described for the steady-state group. The sampies were analyzed for both active and inactive metabolites. Laboratory methods. 86Rb method. The modified Rb method described previously17, 48 was used for the determination of digitoxin and cardioactive metabolites in serum and urine. It was also used for the determination of the various metabolites after TLC separation. 50 Physiologie saline (1 ml) was added to the sampies scraped off the TLC plates before extraction with dichloromethane. Each metabolite was assayed with a standard curve of the corresponding authentie compound. Thin-layer chromatography (TLC). The method developed in our laboratory has been described in detail elsewhere. 50 Five ml of serum or urine were extracted with 15 ml of dichloromethane (Merck) for 10 min; 10 ml of the extract were transferred to new tubes and evaporated to dryness at 50° C. on a water bath. Three ml of 70% ethanol were added to the residues and washed twice with 0.7 ml light petroleum (b.p., 400 to 60°) (AnalaR, BDR Chemical Ltd., and 2.5 ml of the ethanol extract were transferred to conical glass-stoppered tubes and evaporated in a stream of air (50° c., water bath). The extracts were dissolved in 25 J.d chloroform-methanol (50: 50), and 15 JLI were subsequently applied to precoated silica gel plates (Merck F 254) wh ich had been impregnated ovemight in 15% formamide solution in acetone. The test substances were applied directly after removal of the impregnated plates from the sealed glass jars. The standards were applied in 5-JLg amounts at both edges of each plate with 6 or 7 sampies in between. The plates were developed twice in the same direction (running distance, 18 cm) with ethyl methyl ketone-xylene (50:50) as solvents. Detection was performed with 20% sulfuric acid solution
Digitoxin metabolism
127
in ethanol and subsequent heating to 1200 C. Only the edges of the plates with the standards were cut off with a glass cutter; they were sprayed and heated because DT-3 and its cardioactive metabolites lose their biologie activity when heated above 500 c., and quantitation with the 86Rb method depends on biologie activity. The reproducibility of the method was good,50 and it showed no border-zone effect. Adequate separation of all 8 metabolites was verified. 50 Recovery was tested by adding known amounts of standards (50, 100, and 250 ng) to 5 ml serum and urine and determining each metabolite by the 86Rb method. No systematic differences in the recovery of the various metabolites were found, and recovery was the same, 59% for the different concentrations studied. The following standard deviations were found at different drug concentrations: mean value of 10 replicates with SD in parentheses: 3.2 (1.4), 7.5 (1.3), 13.4 (4.9), 25.6 (4.6),35.6 (9.4). Cleavage of conjugation bonds. Digitoxin metabolites are conjugated to glucuronic and sulfuric acids and thereby rendered watersoluble and inactive. An enzyme preparation (ß-glucuronidase from marine mollusca "Koch-Light") containing 2,000 Fishman units/mg of glucuronidase and 3,500 Fishman units/mg of sulfatase was used to split the conjugation bonds. The enzyme preparation was dissolved in acetic acid (0.1 mole/L) sodium acetate (0.1 mole/L) (82: 18) in a concentration of 1 mg/mI and pR was adjusted to 4.1, which was optimal for enzymatic cleavage. The method was used for two purposes: 1. To assess the extent of conjugation in whole serum and urine sampies. Buffer (0.3 ml) and enzyme (0.2 ml) solutions were added to serum/urine (0.5 ml) and the pR adjusted to 4.1. Duplicate sampies were left in a water bath at 37° C for 48 hr, which was the time necessary to complete cleavage of conjugation. The sampIes were then analyzed with the 86Rb method. The blank values for subjects not given digitoxin were zero. The patient sampies contained "total drug (100%), both digitoxin and cardioactive metabolites, and the cleaved conjugates, which thereby were rendered inactive. Digitoxin and cardioactive metabolites were determined in parallel sampies with the 86Rb
Storstein
128
Clinical Pharmacology and Therapeutics
M! fAtOlIC PATnRN IN URIN
METABOL Ie PATTERN IN SERUM
..
'1. 10
STIADY STAU GROUP
••
...
•"
DTt
..
.,
INACTlvlE
INACTlV(
ACTIV[
.f ..
01' II't't 01'1 . . .
T. DCO. DGI
..
~I
,oc,l~
•
1S".Gll DOSE GROUP
11
INACTlY[ • S
AcrlVE
•s
00
SI NGLE DOSE GROUP
ACT IV( • S
I NACT I V[
• S
00
..
.. so
.. DU
on
II"fl
.... MI ClG I 001
oe.
.~6
on on
Oft . , . " '
...... .l. oe. ",
M-
I
on ou
~1
.L * "1
OU OU
MI Mt
Fig. 2. Distribution between the cardioactive metabolites (100%) and between the inactive conjugated metabolites (100%) in serum and urine from patients on maintenance treatment and after a single dose.
Table I. Daily renal excretion of active and inactive metabolites in the steady-state and single-dose groups* Patient Steady -state I
2 3 4 5 6 7 8 9
Diuresis (ml/day)
Active metabolites ( p..g/day)
lnactive metabolites ( p..g/day)
Total (p..g/day)
500 1,000 850 1,250 400 1,350 2,100 950 650
23.85 20.70 13.18 40.38 7.56 57.51 45.15 17.81 10.73
1.35 6. 10 5.95 5.38 3.24 9.45 37 .71 10.07 8.45
25.20 26.80 19.13 45.76 10.80 66.96 76.86 27 .88 19.18
700 1,100 600 2,600 800
8.01 23.35 6.40 54 .29 41.20
17 .78 9.13 2.28 21.14 7.84
25.79 32.48 8.68 75.43 49.04
Single-dose
1 2 3 4 5
*The data were calculated by addi ng the amounts of metabolites found after TLC separation, correcting for analytic losses, and multiplying with urine volumes.
Digitoxin metabolism
Vo/ume 21 Number 2
SERUM SINGLE DOSE GROUP
STEADY STATE GROUP
% 90 80 70
60
40 30 20 10
o OT3
OT2
OTI
OTO
DG3
DG2
lEID
DGI
OT3
OGO
OT2
OTI
OTO
DG3
OG2
DGI
DGO
~ INACTIVE
ACTIVE
URINE STEADY STATE GROUP
SINGLE DOSE GROUP
80
70
60 50
40 30 20 10
o OT 3
OT 2
OT 1
OT 0
DG 3
DG 2
DG 1
DG 0
OT 3
OT 2
OT 1
OT 0
oe 3
DG Z DG 1
DG 0
Fig. 3. Relationship between the active and conjugated forms of each metabolite in serum and urine from the steady-state and single-dose patients.
129
130
Storstein
Clinical Pharmacology and Therapeutics
Table II. Distribution oi cardioactive and inactive (conjugated) metabolites in serum and urine on steady-state maintenance treatment and after a single dose of digitoxin DT-3
I (SD) I
%
Steady-state A. Serum Active = 9) Inactive (n = 4) p< B. Urine Active (n = 9) Inactive (n = 9) p< Differences between serum and urine Active, p< Inactive, p< Single-dose A. Serum Active (n = 5) Inactive (n = 4) p< B. Urine Active (n = 5) Inactive (n = 5) p< Differences between serum and urine Active, p< Inactive, p< Differences between steady-state and single-dose I. Serum Active, p< Inactive, p< 11. Urine Active, p< Inactive, p
THERAPEUTICS volume 21
number 2
February, 19n
Studies on digitalis VIII. Digitoxin metabolism on a maintenance regimen and after a single dose The metabolic pattern of cardioactive and inactive conjugated metabolites of digitoxin on maintenance (9 patients) and after a single 0.6-mg dose (5 patients) was studied in patients with normal renal and hepaticfunction. Serum sampies were obtained 24 hr after the last dose, and urine was collected over 24 hr. The extent or conjugation to glucuronic and sulfuric acid was 35.0% (SD, 17.4) in whole serum and 31.6o/c (SD, 19.3) in urine sampies. Unchanged digitoxin was the main cardioactive substance found bOlh in serum and in urine (89.7% and 87.0%) in the steady-state group. All known cardioactive metabolites were present; digoxin represented less than 1%. All active metabolites were conjugated to glucuronic /suifuric acid. Serum and urine patterns of metabolites were quite similar. Hydrolysis and conjugation appeared to be more important pathways than hydroxylation. Unchanged digitoxin was the most important cardioactive substance in serum and urine (80.4% and 56.5,)() in the single-dose group. Digoxin was the main cardioactive metabolite (/2.5% in serum and 25.5')( in urine). All active metabolites were conjugated. Hydroxylation, hydrolysis, and conjugation seemed to be equally important. The most important differences between the steady-state and single-dose groups were that in the steady-state group there was signijicantly more unchanged digitoxin, far less digoxin, and less hydroxylated metabolites than in the single-dose group. Caution is thus necessary when interpreting single-dose datafor a drug that is usedfor maintenance.
Liv Storstein, M.D. Oslo, Norway Medical Department B, University Clinic, Rikshospitalet
Supported by grants frorn The Norwegian Council on Cardiovascular Diseases, Astra LId., and The University of Oslo. Received for publication Feb. 7, 1976. Aeeepted for publieation July 12, 1976. Reprint requests to: Liv Storstein, M.D., Medieal Departrnent B, University Clinie, Pilestredet 32, Rikshospitalet, Oslo, Norway.
Digitoxin has a complex metabolism. The present concept of its biotransformation is presented in Fig. 1. A number of enzymatic proces ses are involved. The products of three of these, hydroxylation, hydrolysis, and conjuga125
126
Storstein
Clinical Pharmacology and Therapeutics
. . . [T_'.
OT-3 OT-2 OT-1
EpiOT-O
. . . ~[G_' . c> c> c>
c!njugates
:;> :;>
OG-3
OG-1
EpiOG-O
-
-
/>
c!njugates
0
,j>
® .. Hydrolysis
j>
f
3 O :-
~
c> fO~-2 ~ 7 0;-1~ c> fO~-l ~ ~ o+-o~ c> f o r o ~
OG-2
c> Hydroxylation
0+-3~ c> 0+-2~
Keto-
Keto- O o f .-
Epi-
Epi-
o+-o~ c> OT-O%
-
~
-
c> (OG-O ~
Conjugation
»RingOpening?
Oi hydroderivates ?
Fig. 1. Previous (A) and present (B) concept of digitoxin metabolism.
tion, were studied for this report. Hydroxylation (phase Ireaction) transforms digitoxin (DT) derivatives to digoxin (DG) derivatives. Metabolites with less sugar (digitoxose) molecules are successively formed by hydrolysis (phase I reaction). All of the hydroxylated and hydrolyzed metabolites are cardioactive. Biologically inactive metabolites are synthesized by conjugation to glucuronic and sulfuric acids (phase 11 reaction). The main problems in the study of digitoxin metabolism are to establish methods which adequately separate the various metabolites and which are sensitive enough to allow determination of nano gram amounts of each. The methods used in this study make it possible to determine unchanged DT-3 and a maximum of 23 metabolites supposing a11 cardioactive substances are conjugated both to glucuronic and sulfuric acid. The cardioactive genins were epimerized to inactive metabolites 50 via keto intermediates 44 which were not measured in this investigation. Present knowledge of digitoxin metabolism originates from studies with tissue preparations,20-24, 29, 33, 44, 57 animal studies,5, 8, 9, 12-14, 16, 18, 25, 27, 28, 31, 41-43 and studies of the metabolic products found in human urine after a single dose of radioactive-labeled digitoxin.36-40, 56 Okita and associates 37 showed that only 6% to 10% of the original dose was excreted unchanged in the urine over aperiod of several
weeks. Studies in dogs 27 , 28 suggested that "digoxin-like" material was a main metabolite of digitoxin, and digoxin has also been proposed as a major metabolite in man. Data from single-dose studies are not necessarily applicable to steady-state studies. The aim of the present investigation was to study digitoxin metabolism in detail in patients on maintenance therapy and to compare these data with those obtained in patients given a single dose of digitoxin. Material and methods
The fo11owing abbreviations for glycosides will be used: DT-3 (digitoxin); DT-2 (digitoxigenin-bis-digitoxoside); DT-l (digitoxigenin-mono-digitoxoside); DT-O (digitoxigenin); DG-3 (digoxin); DG-2 (digoxigenin-bis-digitoxoside); DG-l (digoxigenin-mono-digitoxoside); and DG-O (digoxigenin). Steady-state study. Blood sampies of 150 ml were drawn 24 hr after the last dose in 9 patients on long-term maintenance therapy with digitoxin (Digitrin, O.l-mg tablets, Astra, Pharmacopoea Nordica standards, obtained from the same source as the intravenous preparation). Urine was collected during the same 24 hr. All patients had normal renal and hepatic function. None were in severe congestive heart failure. Cardioactive metabolites were studied in 9 serum and 9 urine sampies. Inactive, conjugated metabolites were studied in 4 serum and 9 urine sampies. The extent of conjugation was
Volume 2/ Number 2
studied in 16 serum and 13 urine sampies from patients on maintenance therapy. Single-dose study. Five patients with normal renal and hepatic function were given a single dose of 0.6 mg digitoxin (Norsk Medisinaldepot, Oslo, purity, 97%, 1.5% gitoxigeninglycosides, 1% water, and 0.5% inactive purities, in accordance with the Pharmacopoea Nordica) slowly intravenously , and serum and urine sampies were obtained after 24 hr, as described for the steady-state group. The sampies were analyzed for both active and inactive metabolites. Laboratory methods. 86Rb method. The modified Rb method described previously17, 48 was used for the determination of digitoxin and cardioactive metabolites in serum and urine. It was also used for the determination of the various metabolites after TLC separation. 50 Physiologie saline (1 ml) was added to the sampies scraped off the TLC plates before extraction with dichloromethane. Each metabolite was assayed with a standard curve of the corresponding authentie compound. Thin-layer chromatography (TLC). The method developed in our laboratory has been described in detail elsewhere. 50 Five ml of serum or urine were extracted with 15 ml of dichloromethane (Merck) for 10 min; 10 ml of the extract were transferred to new tubes and evaporated to dryness at 50° C. on a water bath. Three ml of 70% ethanol were added to the residues and washed twice with 0.7 ml light petroleum (b.p., 400 to 60°) (AnalaR, BDR Chemical Ltd., and 2.5 ml of the ethanol extract were transferred to conical glass-stoppered tubes and evaporated in a stream of air (50° c., water bath). The extracts were dissolved in 25 J.d chloroform-methanol (50: 50), and 15 JLI were subsequently applied to precoated silica gel plates (Merck F 254) wh ich had been impregnated ovemight in 15% formamide solution in acetone. The test substances were applied directly after removal of the impregnated plates from the sealed glass jars. The standards were applied in 5-JLg amounts at both edges of each plate with 6 or 7 sampies in between. The plates were developed twice in the same direction (running distance, 18 cm) with ethyl methyl ketone-xylene (50:50) as solvents. Detection was performed with 20% sulfuric acid solution
Digitoxin metabolism
127
in ethanol and subsequent heating to 1200 C. Only the edges of the plates with the standards were cut off with a glass cutter; they were sprayed and heated because DT-3 and its cardioactive metabolites lose their biologie activity when heated above 500 c., and quantitation with the 86Rb method depends on biologie activity. The reproducibility of the method was good,50 and it showed no border-zone effect. Adequate separation of all 8 metabolites was verified. 50 Recovery was tested by adding known amounts of standards (50, 100, and 250 ng) to 5 ml serum and urine and determining each metabolite by the 86Rb method. No systematic differences in the recovery of the various metabolites were found, and recovery was the same, 59% for the different concentrations studied. The following standard deviations were found at different drug concentrations: mean value of 10 replicates with SD in parentheses: 3.2 (1.4), 7.5 (1.3), 13.4 (4.9), 25.6 (4.6),35.6 (9.4). Cleavage of conjugation bonds. Digitoxin metabolites are conjugated to glucuronic and sulfuric acids and thereby rendered watersoluble and inactive. An enzyme preparation (ß-glucuronidase from marine mollusca "Koch-Light") containing 2,000 Fishman units/mg of glucuronidase and 3,500 Fishman units/mg of sulfatase was used to split the conjugation bonds. The enzyme preparation was dissolved in acetic acid (0.1 mole/L) sodium acetate (0.1 mole/L) (82: 18) in a concentration of 1 mg/mI and pR was adjusted to 4.1, which was optimal for enzymatic cleavage. The method was used for two purposes: 1. To assess the extent of conjugation in whole serum and urine sampies. Buffer (0.3 ml) and enzyme (0.2 ml) solutions were added to serum/urine (0.5 ml) and the pR adjusted to 4.1. Duplicate sampies were left in a water bath at 37° C for 48 hr, which was the time necessary to complete cleavage of conjugation. The sampIes were then analyzed with the 86Rb method. The blank values for subjects not given digitoxin were zero. The patient sampies contained "total drug (100%), both digitoxin and cardioactive metabolites, and the cleaved conjugates, which thereby were rendered inactive. Digitoxin and cardioactive metabolites were determined in parallel sampies with the 86Rb
Storstein
128
Clinical Pharmacology and Therapeutics
M! fAtOlIC PATnRN IN URIN
METABOL Ie PATTERN IN SERUM
..
'1. 10
STIADY STAU GROUP
••
...
•"
DTt
..
.,
INACTlvlE
INACTlV(
ACTIV[
.f ..
01' II't't 01'1 . . .
T. DCO. DGI
..
~I
,oc,l~
•
1S".Gll DOSE GROUP
11
INACTlY[ • S
AcrlVE
•s
00
SI NGLE DOSE GROUP
ACT IV( • S
I NACT I V[
• S
00
..
.. so
.. DU
on
II"fl
.... MI ClG I 001
oe.
.~6
on on
Oft . , . " '
...... .l. oe. ",
M-
I
on ou
~1
.L * "1
OU OU
MI Mt
Fig. 2. Distribution between the cardioactive metabolites (100%) and between the inactive conjugated metabolites (100%) in serum and urine from patients on maintenance treatment and after a single dose.
Table I. Daily renal excretion of active and inactive metabolites in the steady-state and single-dose groups* Patient Steady -state I
2 3 4 5 6 7 8 9
Diuresis (ml/day)
Active metabolites ( p..g/day)
lnactive metabolites ( p..g/day)
Total (p..g/day)
500 1,000 850 1,250 400 1,350 2,100 950 650
23.85 20.70 13.18 40.38 7.56 57.51 45.15 17.81 10.73
1.35 6. 10 5.95 5.38 3.24 9.45 37 .71 10.07 8.45
25.20 26.80 19.13 45.76 10.80 66.96 76.86 27 .88 19.18
700 1,100 600 2,600 800
8.01 23.35 6.40 54 .29 41.20
17 .78 9.13 2.28 21.14 7.84
25.79 32.48 8.68 75.43 49.04
Single-dose
1 2 3 4 5
*The data were calculated by addi ng the amounts of metabolites found after TLC separation, correcting for analytic losses, and multiplying with urine volumes.
Digitoxin metabolism
Vo/ume 21 Number 2
SERUM SINGLE DOSE GROUP
STEADY STATE GROUP
% 90 80 70
60
40 30 20 10
o OT3
OT2
OTI
OTO
DG3
DG2
lEID
DGI
OT3
OGO
OT2
OTI
OTO
DG3
OG2
DGI
DGO
~ INACTIVE
ACTIVE
URINE STEADY STATE GROUP
SINGLE DOSE GROUP
80
70
60 50
40 30 20 10
o OT 3
OT 2
OT 1
OT 0
DG 3
DG 2
DG 1
DG 0
OT 3
OT 2
OT 1
OT 0
oe 3
DG Z DG 1
DG 0
Fig. 3. Relationship between the active and conjugated forms of each metabolite in serum and urine from the steady-state and single-dose patients.
129
130
Storstein
Clinical Pharmacology and Therapeutics
Table II. Distribution oi cardioactive and inactive (conjugated) metabolites in serum and urine on steady-state maintenance treatment and after a single dose of digitoxin DT-3
I (SD) I
%
Steady-state A. Serum Active = 9) Inactive (n = 4) p< B. Urine Active (n = 9) Inactive (n = 9) p< Differences between serum and urine Active, p< Inactive, p< Single-dose A. Serum Active (n = 5) Inactive (n = 4) p< B. Urine Active (n = 5) Inactive (n = 5) p< Differences between serum and urine Active, p< Inactive, p< Differences between steady-state and single-dose I. Serum Active, p< Inactive, p< 11. Urine Active, p< Inactive, p
