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Urinary excretion of diphenylhydantoin metabolites in newborn infants
October 1974 The Journal.of P E D I A T R I C S
543
Urinary excretion of diphenylhydantoin metabolites in newborn infants The plasma half-life of diphenylhydantoin in newborn infants of epileptic mothers, treated with this drug, is in the same range as theplasma half-life in adults. The urinary excretion of diphenylhydantoin and its main metabolites has been investigated in six newborn infants. The results show that the rapMplasma disappearance of diphenylhydantoin is due to rapid metabolism of the drug.
A n d e r s R a n e , M . D . , Huddinge, S w e d e n
M ETABO LISM of most drugs is necessary for excretion, and little is known of drug-metabolizing capacity during the neonatal period. Some reports 1,2 suggest that it is poorly developed. The plasma half-life of transplacentally transferred DPH in newborn infants, however, is in the same range as the half-life observed in adults. 3 This suggests that the newborn infant metabolizes the drug as efficiently as the adult, since essentially no DPH is excreted unchanged.3 In order to test this hypothesis further, the urinary excretion of the main metabolites of DPH (conjugated and unconjugated p-OH-DPH) has been measured in newborn infants. In adults about 75% of an intramuscular dose of DPH is recovered in the urine as p-OH-DPH, 4 99% of which is conjugated. MATERIALS
AND METHODS
Six healthy newborn infants of epileptic mothers were included in this study. Clinical data relating to the mothers and their newborn infants have been described. 3 The maternal drug treatment during pregnancy is listed in Table I. The disappearance of DPH from the plasma was followed for the first 4 to 9 days of life; the results have been reported elsewhere. 3 Urine was collected quantitatively for varying time periods, depending
From the Dept of Clinical Pharmacology at the Karolinska Institutet, Huddinge University Hospital. Supported by "Expressen "s"Prenatal Research Fund, The Association of the Swedish Pharmaceutical lndustry, the Swedish Medical Research Council :(04X-4496).
on the individual tolerance to the plastic urine collection bag, which sometimes causes dermal irritation. If so, the urine collection was discontinued. If diapers were wet with urine, they were weighed and corrections were made in the calculations of the urinary excretion rate. Conjugated and unconjugated p-OH-DPH were measured by gas chromatography according to Karl6n and associates. 5 Unconjugated p-OH-DPH was extracted into toluene:ether (1:1). For the determination of conjugated p-OH-DPH aliquots of urine were subjected to acid byAbbreviations used: DPH: diphenylhydantoin Vd: volume of distribution drolysis after pre-extraction with isoamylalcohol which removes unconjugated p-OH-DPH and the dihydrodiol metabolite. The p-OH-DPH as well as the internal standard, p-CH3-DPH, were flash methylated 6 before chromatography. DPH was measured with a gas chromatographic method. 6 RESULTS The plasma half-lives of DPH in the investigated infants were in the same range as in adults. 3The mean excretion rates of conjugated and unconjugated p-OH-DPH during various time periods after birth are shown in Table II. In a semilog plot (not shown) the excretion rates of conjugated and unconjugated p-OH-DPH appeared to follow roughly the decay of plasma DPH in three of the infants (M. A., B. E., L. N.). A low initial excretion rate
Vol. 85, No. 4, pp. 543-545
544
Rane
The Journal of Pediatrics October 1974
T h e concentrations o f D P H in the urine w e r e negligible. In three investigated cases it was calculated that the excretion o f unchanged drug accounted for only 0.6, 2.7, and 7.5% respectively, o f the total body D P H , assuming a V d of 0.55 1/kg. If the Vd is greater, as indicated above, t h e estimated values would be even lower.
was observed in patients Y. Sg. and R. W., but thereafter it s e e m e d to decrease in parallel to the plasma concentration of DPH. In all infants m o r e than 91% of the excreted p-OHD P H was conjugated. In one case the total metabolite excretion between two t i m e points was compared to the disappearance of total body D P H , which was estimated f r o m the plasma c o n c e n t r a t i o n s at the s a m e time points, a s s u m i n g the s a m e apparent V a as in adults, i.e., 0.55 1/kg body weight. 7 This assumption, h o w e v e r , t u r n e d out not to be c o n s i s t e n t with the results, since these indicated a V a that was m o r e than twice as great as that in adults.
DISCUSSION T h e roughly parallel decline of drug concentration in plasma and in the rate of urinary metabolite excretion indicates that the rate o f excretion reflects the rate o f f o r m a t i o n o f metabolites. Glazko and associates 4 also obs e r v e d a parallel decay o f these s a m e parameters during t h e last part of the plasma disappearance c u r v e in adults w h o had received a single intravenous dose of DPH. The initially slow rate of metabolite excretion in two o f the babies m i g h t be caused by a physiologically impaired renal excretory capacity, only noted in these newb o r n infants. In order to verify this theory, the plasma c o n c e n t r a t i o n s o f t h e m e t a b o l i t e s w o u l d h a v e to be d e t e r m i n e d . M e t h o d s for t h e d e t e r m i n a t i o n o f D P H metabolites in plasma are not available. Such determinations have been done with amylobarbitone. 8 A n initial rise of the plasma concentration o f the hydroxylated metabolite of amylobarbitone was observed in n e w b o r n infants w h o r e c e i v e d t h e drug in utero via the m o t h e r . A possible maternal origin o f the metabolites m u s t be
Table I. Maternal drug t r e a t m e n t during pregnancy
Daily dose (rag) Mother of
I
Diphenylhydantoin
[ Nitra] zepam
Carbamazepine
Phenobarbital
M. A.
400
5
--
--
B.E. L.N. Y. Sb.*
500 200 500
7.5 -10
1,000 ---
---
Y. Sg.
300
--
--
--
R.W.
500
--
--
50
--
*Also treated with 25 mg hydrochlorthiazide (last 7 weeks) and 40 mg furosemide (last 2 weeks).
Table II. T h e rate of urinary excretion of conjugated and u n c o n j u g a t e d p - O H - D P H at different times after birth
Infants I
p-OH-DPH (ug metabolite excreted/min)*
|
M.A.
Conjugated Unconjugated
B.E.
Conjugated Unconjugated
L.N.
Conjugated Unconjugated
Y. Sb.
Conjugated Unconjugated
Y. Sg.
Conjugated Unconjugated
R.W.
Conjugated Unconjugated
2.93 0.11 (17.5, 21.3) 19.47 1.34 (40.6, 3 . 9 ) 1.52 0.15 (23.8, 11.7) 1.69 0.03 (26.3, 12.0) 0.61 0.04 ( 9.9, 12.0) 2.37 0.05 (25.8, 7.8)
1.47 0.03 ( 40.3, 24.3) 11.92 0.61 (65.6, 3 . 3 ) 0.79 0.03 (45.4, 6 . 8 ) 0.19 $ (111.0, 6.0) 5.09 0.09 ( 21.9, 12.0) 2.57 0.08 ( 35.9, 12.0)
. .
. .
. .
. .
1.17 0.03 (91.8, 0.5) 0.64 0.03 (93.5, 3 . 0 ) . .
---
---
---
0.38 I" (115.1, 3.2) . . . .
---
---
4.01 0.07 (45.9, 12.0) 8.99 0.41 (55.4, 17.5)
3.60 0.11 ( 57.9, 12.0) 7.84 $ ( 68.2, 9.0)
1.76 t" (106.0, 12.0) 3.01 0.08 ( 91.7, 8.0)
0.54 t (118.0. 12.0) ---
. .
*The first and second figures within the parentheses indicate midpoint (hours after birth) and duration (hours), respectively, of the urine collection periods. tUnmeasurable concentration. SNot determined because of insufficient amount of urine.
Volume 85 Number 4
considered. The possible transfer of unconjugated p-OHDPH across the h u m a n placenta cannot be ruled out despite the fact that it does not occur in rodents. 9 However, in all cases more than 91% of the excreted p-OHDPH was conjugated. This figure agrees well with the 88-89% recently reported in h u m a n newborn infants.9 The conjugate of p-OH-DPH is tess likely than the unconjugated metabolite to pass the placenta. The conjugated p-OH-DPH does not pass the placenta of rodents. 9 In summary the present data show that the rapid plasma disappearance of DPH in newborn infants of mothers, treated with this drug is due to rapid metabolism of the drug. However, it is possible that the drug metabolizing capacity has been induced in utero by DPH itself and/or the other drugs that the mothers were receiving. The expert technical assistance of Miss Gerd Lundqvist is gratefully acknowledged. REFERENCES 1. Gladtke, E.: Pharmocokinetic studies on phenylbutazone in children, I1 Farmaco 23: 897, 1968. 2. Weiss, C. F., Glazko, A. L, and Weston, J. K.: Chloramfenicol in the newborn infant, N. Engl. J. Med. 262: 787, 1960.
Urinary excretion o f diphenylhydantoin metabolites
545
3. Rane, A., Garle, M., Borga, O., and Sjbqvist, F.: Plasma disappearance of transplacentally transferred phenytoin in the newborn studied with mass fragmentography, Clin. Pharmacol. Ther. 15: 39, 1974. 4. Glazko, A. J., Chang, R., Baukema, J., Bill, W. A., Goulet, J. R., and Buchanan, R. A.: Metabolic disposition of diphenylhydantoin in normal human subjects following intravenous administration, Clin. Pharmacol. Ther. 10: 498, 1969. 5. Karl~n, B., Garle, M., Rane, A., Gutovh, M., and Lindborg, B.: Assay of the major (4-hydroxylated) metabolites of diphenythydantoin in human urine, submitted to Europ. J. Clin. Pharmacol. 6. Berlin, A., Agurell, S., Borg~, O., Lund, L., and Sjbqvist, F.: Micromethod for the determination of diphenylhydantoin in plasma and cerebrospinal fluid: A comparison between a gas chromatographic and a spectrophotometric method, Scand. J. Clin. Lab. Invest. 29: 281, 1972. 7. Lund, L., Alvin, G., Berlin. A., and Alexanderson, B.: Single and multiple oral dose kinetics of phenytoin in man, Europ. J. Clin. Pharmacol. (in press), 1974. 8. Krauer, B., Draffan, G. H., Williams, F. M., Clare, R. A., Dollery, C. T., and Hawkins, D. F.: Eliminationkinetics of amobarbital in mothers and their newborn infants, Clin. Pharmacol. Ther. 14: 442, 1973. 9. Reynolds, J. W., and Mirkin, B. L.: Urinary corticosteriod and diphenylhydantoin metabolite patterns in neonates exposed to anticonvulsantdrugs in utero, Clin. Pharmacol. Ther. 14: 891, 1973.
543
Urinary excretion of diphenylhydantoin metabolites in newborn infants The plasma half-life of diphenylhydantoin in newborn infants of epileptic mothers, treated with this drug, is in the same range as theplasma half-life in adults. The urinary excretion of diphenylhydantoin and its main metabolites has been investigated in six newborn infants. The results show that the rapMplasma disappearance of diphenylhydantoin is due to rapid metabolism of the drug.
A n d e r s R a n e , M . D . , Huddinge, S w e d e n
M ETABO LISM of most drugs is necessary for excretion, and little is known of drug-metabolizing capacity during the neonatal period. Some reports 1,2 suggest that it is poorly developed. The plasma half-life of transplacentally transferred DPH in newborn infants, however, is in the same range as the half-life observed in adults. 3 This suggests that the newborn infant metabolizes the drug as efficiently as the adult, since essentially no DPH is excreted unchanged.3 In order to test this hypothesis further, the urinary excretion of the main metabolites of DPH (conjugated and unconjugated p-OH-DPH) has been measured in newborn infants. In adults about 75% of an intramuscular dose of DPH is recovered in the urine as p-OH-DPH, 4 99% of which is conjugated. MATERIALS
AND METHODS
Six healthy newborn infants of epileptic mothers were included in this study. Clinical data relating to the mothers and their newborn infants have been described. 3 The maternal drug treatment during pregnancy is listed in Table I. The disappearance of DPH from the plasma was followed for the first 4 to 9 days of life; the results have been reported elsewhere. 3 Urine was collected quantitatively for varying time periods, depending
From the Dept of Clinical Pharmacology at the Karolinska Institutet, Huddinge University Hospital. Supported by "Expressen "s"Prenatal Research Fund, The Association of the Swedish Pharmaceutical lndustry, the Swedish Medical Research Council :(04X-4496).
on the individual tolerance to the plastic urine collection bag, which sometimes causes dermal irritation. If so, the urine collection was discontinued. If diapers were wet with urine, they were weighed and corrections were made in the calculations of the urinary excretion rate. Conjugated and unconjugated p-OH-DPH were measured by gas chromatography according to Karl6n and associates. 5 Unconjugated p-OH-DPH was extracted into toluene:ether (1:1). For the determination of conjugated p-OH-DPH aliquots of urine were subjected to acid byAbbreviations used: DPH: diphenylhydantoin Vd: volume of distribution drolysis after pre-extraction with isoamylalcohol which removes unconjugated p-OH-DPH and the dihydrodiol metabolite. The p-OH-DPH as well as the internal standard, p-CH3-DPH, were flash methylated 6 before chromatography. DPH was measured with a gas chromatographic method. 6 RESULTS The plasma half-lives of DPH in the investigated infants were in the same range as in adults. 3The mean excretion rates of conjugated and unconjugated p-OH-DPH during various time periods after birth are shown in Table II. In a semilog plot (not shown) the excretion rates of conjugated and unconjugated p-OH-DPH appeared to follow roughly the decay of plasma DPH in three of the infants (M. A., B. E., L. N.). A low initial excretion rate
Vol. 85, No. 4, pp. 543-545
544
Rane
The Journal of Pediatrics October 1974
T h e concentrations o f D P H in the urine w e r e negligible. In three investigated cases it was calculated that the excretion o f unchanged drug accounted for only 0.6, 2.7, and 7.5% respectively, o f the total body D P H , assuming a V d of 0.55 1/kg. If the Vd is greater, as indicated above, t h e estimated values would be even lower.
was observed in patients Y. Sg. and R. W., but thereafter it s e e m e d to decrease in parallel to the plasma concentration of DPH. In all infants m o r e than 91% of the excreted p-OHD P H was conjugated. In one case the total metabolite excretion between two t i m e points was compared to the disappearance of total body D P H , which was estimated f r o m the plasma c o n c e n t r a t i o n s at the s a m e time points, a s s u m i n g the s a m e apparent V a as in adults, i.e., 0.55 1/kg body weight. 7 This assumption, h o w e v e r , t u r n e d out not to be c o n s i s t e n t with the results, since these indicated a V a that was m o r e than twice as great as that in adults.
DISCUSSION T h e roughly parallel decline of drug concentration in plasma and in the rate of urinary metabolite excretion indicates that the rate o f excretion reflects the rate o f f o r m a t i o n o f metabolites. Glazko and associates 4 also obs e r v e d a parallel decay o f these s a m e parameters during t h e last part of the plasma disappearance c u r v e in adults w h o had received a single intravenous dose of DPH. The initially slow rate of metabolite excretion in two o f the babies m i g h t be caused by a physiologically impaired renal excretory capacity, only noted in these newb o r n infants. In order to verify this theory, the plasma c o n c e n t r a t i o n s o f t h e m e t a b o l i t e s w o u l d h a v e to be d e t e r m i n e d . M e t h o d s for t h e d e t e r m i n a t i o n o f D P H metabolites in plasma are not available. Such determinations have been done with amylobarbitone. 8 A n initial rise of the plasma concentration o f the hydroxylated metabolite of amylobarbitone was observed in n e w b o r n infants w h o r e c e i v e d t h e drug in utero via the m o t h e r . A possible maternal origin o f the metabolites m u s t be
Table I. Maternal drug t r e a t m e n t during pregnancy
Daily dose (rag) Mother of
I
Diphenylhydantoin
[ Nitra] zepam
Carbamazepine
Phenobarbital
M. A.
400
5
--
--
B.E. L.N. Y. Sb.*
500 200 500
7.5 -10
1,000 ---
---
Y. Sg.
300
--
--
--
R.W.
500
--
--
50
--
*Also treated with 25 mg hydrochlorthiazide (last 7 weeks) and 40 mg furosemide (last 2 weeks).
Table II. T h e rate of urinary excretion of conjugated and u n c o n j u g a t e d p - O H - D P H at different times after birth
Infants I
p-OH-DPH (ug metabolite excreted/min)*
|
M.A.
Conjugated Unconjugated
B.E.
Conjugated Unconjugated
L.N.
Conjugated Unconjugated
Y. Sb.
Conjugated Unconjugated
Y. Sg.
Conjugated Unconjugated
R.W.
Conjugated Unconjugated
2.93 0.11 (17.5, 21.3) 19.47 1.34 (40.6, 3 . 9 ) 1.52 0.15 (23.8, 11.7) 1.69 0.03 (26.3, 12.0) 0.61 0.04 ( 9.9, 12.0) 2.37 0.05 (25.8, 7.8)
1.47 0.03 ( 40.3, 24.3) 11.92 0.61 (65.6, 3 . 3 ) 0.79 0.03 (45.4, 6 . 8 ) 0.19 $ (111.0, 6.0) 5.09 0.09 ( 21.9, 12.0) 2.57 0.08 ( 35.9, 12.0)
. .
. .
. .
. .
1.17 0.03 (91.8, 0.5) 0.64 0.03 (93.5, 3 . 0 ) . .
---
---
---
0.38 I" (115.1, 3.2) . . . .
---
---
4.01 0.07 (45.9, 12.0) 8.99 0.41 (55.4, 17.5)
3.60 0.11 ( 57.9, 12.0) 7.84 $ ( 68.2, 9.0)
1.76 t" (106.0, 12.0) 3.01 0.08 ( 91.7, 8.0)
0.54 t (118.0. 12.0) ---
. .
*The first and second figures within the parentheses indicate midpoint (hours after birth) and duration (hours), respectively, of the urine collection periods. tUnmeasurable concentration. SNot determined because of insufficient amount of urine.
Volume 85 Number 4
considered. The possible transfer of unconjugated p-OHDPH across the h u m a n placenta cannot be ruled out despite the fact that it does not occur in rodents. 9 However, in all cases more than 91% of the excreted p-OHDPH was conjugated. This figure agrees well with the 88-89% recently reported in h u m a n newborn infants.9 The conjugate of p-OH-DPH is tess likely than the unconjugated metabolite to pass the placenta. The conjugated p-OH-DPH does not pass the placenta of rodents. 9 In summary the present data show that the rapid plasma disappearance of DPH in newborn infants of mothers, treated with this drug is due to rapid metabolism of the drug. However, it is possible that the drug metabolizing capacity has been induced in utero by DPH itself and/or the other drugs that the mothers were receiving. The expert technical assistance of Miss Gerd Lundqvist is gratefully acknowledged. REFERENCES 1. Gladtke, E.: Pharmocokinetic studies on phenylbutazone in children, I1 Farmaco 23: 897, 1968. 2. Weiss, C. F., Glazko, A. L, and Weston, J. K.: Chloramfenicol in the newborn infant, N. Engl. J. Med. 262: 787, 1960.
Urinary excretion o f diphenylhydantoin metabolites
545
3. Rane, A., Garle, M., Borga, O., and Sjbqvist, F.: Plasma disappearance of transplacentally transferred phenytoin in the newborn studied with mass fragmentography, Clin. Pharmacol. Ther. 15: 39, 1974. 4. Glazko, A. J., Chang, R., Baukema, J., Bill, W. A., Goulet, J. R., and Buchanan, R. A.: Metabolic disposition of diphenylhydantoin in normal human subjects following intravenous administration, Clin. Pharmacol. Ther. 10: 498, 1969. 5. Karl~n, B., Garle, M., Rane, A., Gutovh, M., and Lindborg, B.: Assay of the major (4-hydroxylated) metabolites of diphenythydantoin in human urine, submitted to Europ. J. Clin. Pharmacol. 6. Berlin, A., Agurell, S., Borg~, O., Lund, L., and Sjbqvist, F.: Micromethod for the determination of diphenylhydantoin in plasma and cerebrospinal fluid: A comparison between a gas chromatographic and a spectrophotometric method, Scand. J. Clin. Lab. Invest. 29: 281, 1972. 7. Lund, L., Alvin, G., Berlin. A., and Alexanderson, B.: Single and multiple oral dose kinetics of phenytoin in man, Europ. J. Clin. Pharmacol. (in press), 1974. 8. Krauer, B., Draffan, G. H., Williams, F. M., Clare, R. A., Dollery, C. T., and Hawkins, D. F.: Eliminationkinetics of amobarbital in mothers and their newborn infants, Clin. Pharmacol. Ther. 14: 442, 1973. 9. Reynolds, J. W., and Mirkin, B. L.: Urinary corticosteriod and diphenylhydantoin metabolite patterns in neonates exposed to anticonvulsantdrugs in utero, Clin. Pharmacol. Ther. 14: 891, 1973.