Scot. med. J., 1976, 21: 93
SCOTTISH SOCIETY FOR EXPERIMENTAL MEDICINE-SELECTED ABSTRACTS
ANTICONVULSANT DRUG CONCENTRATIONS IN EPILEPTIC PATIENTS D. G. Lambie, J. W. Paxon, R. N. Nanda, R. H. Johnson, J. G. Ratcliffe I. D. Melville and G. D. Morrice Til-e University Department of Neurology, Institute of Neurological Sciences, Southern General Hospital, and The University Department of Materia Medica, Stobhill Hospital, Glasgow and Quarrier's Homes, Bridge of Weir. SAT I S F ACT 0 R Y seizure control in epileptic patients may be difficult to achieve when drug dosage is adjusted empirically. This may be due, in part, to indivudal variations in drug absorption or metabolism or differences in bioavailability of different drug preparations or non-compliance by the patient. We have measured total serum concentrations of anticonvulsant drugs in epileptic patients to assess their value in determining dosage schedules. In addition We have compared the non-protein bound drug fractions in serum with concentrations in cerebrospinal fluid (CSF) and mixed saliva. Blood samples were obtained from I I 6 epileptic patients (74 outpatients attending the epilepsy clinic, Institute of Neurological Sciences, Glasgow (Dr R. H. Johnson and Dr I. D. Melville) and 42 inpatients at Quarrier's Home for Epileptics, Bridge of Weir). CSF was also obtained from 40 of the inpatients. All patients were receiving phenytoin and in most cases, one or more other drugs. usually phenobarbitone or primidone. Phenytoin, phenobarbitone and primidone in serum and CSF were measured by gas liquid chromatography (Goudie & Burnett, 1973) and phenytoin in serum, CSF and saliva by a new radioimmunoassay technique (Paxton et al., 1976) which is more sensitive than existing methods and requires only 20 ,ul. of fluid. There was excellent correlation between the 2 methods for phenytoin (r=0.98). Only 39 of 1I6 patients receiving phenytoin had serum concentrations within the range of 10 to 20 Itg. per ml. (Fig. I) which has been generally proposed as the therapeutic range (Lancet, 1975). There was a poor correlation between total daily dose or weight related dose and serum phenytoin concentration. It is unlikely that the low concentrations were due solely to failure of compliance since drug intake was supervised in the inpatients and no significant differerences in mean serum phenytoin concentration was observed between in- and out-patients. Serum concentrations of phenobarbitone showed a better correlation with weight related dose of phenobarbitone and primidone (from which phenobarbitone may be derived in vivo). Almost all the patients had serum phenobarbitone concentrations within the likely therapeutic range 10 to 401'g. per ml. (Lancet, 1975). Phenobarbitone concentrations in patients receiving primidone were similar to those in patients on phenobarbitone alone. The non-protein bound (Tree') fraction of a drug in serum is generally considered to be the biologically active part. For phenytoin, the mean non-protein bound fraction measured by ultrafiltration was 0.1I (range 0.08-0.17) and was similar to the mean CSF to serum ratio ofO. 12 (range 0.09-0.25) in 40 patients,
indicating the CSF concentrations of drugs at equilibrium probably reflect serum 'free' concentrations. For phenobarbitone, the mean non-protein bound fraction in serum was 0.52 (lange 0.44-0.71) and the CSF to serum ratio 0.47 (range 0.32-0.78) in 17 patients. Primidone is not significantly bound in serum, and CSF and serum concentrations were approximately equal in I3 patients. However neither the standard techniques of ultrafiltration o~ equilibrium dialysis or measurement of CSF drug concentrations are suitable for routine use. We have therefore assessed whether the measurement of phenytoin by radioimmunoassay in saliva may have clinical applications since it has been suggested that salivary phenytoin concentration is dependent on the flee serum concentration (Bochner et al., 1974). Excellent correlations were found between saliva and serum phenytoin concentrations (r=0.97), saliva levels being approximately 10 per cent of total serum levels, and between saliva, and CSF concentrations (r=0.98), saliva levels being approximately 82 per cent of the CSF levels (Fig. 2). Measurement of salivary phenytoin levels by radioimmunoassay may therefore offer a simple m-ethod of determining biologically available phenytoin in epileptic patients. It is concluded that many patients on conventional phenytoin dosage regimes fail to achieve therapeutic concentrations. We are currently studying patients with low phenytoin concentrations whose seizures
SERUM DPH I >Jg/ml)
30
..
-----.--._--Therapeutic Range
:: '. .... - - --..=t--
n~39
:: .;s
:. 100
..:.-.
1
200
, 300
!.DO
DPH TOTAL DAILY DOSE I mg I
Fig. 1. R-elationship of dose to serum concentrations of phenytoin (DPH) in 1I6 patients.
Lambie, Paxton, Nanda, Johnson, Ratcliffe, Melville and Morrice
are poorly controlled, to determine whether control is improved by raising phenytoin concentrations into the therapeutic range.
CSF DPH ( yg/mll
4 A C K NOW LED GEM E N T s. We wish to thank the Secretary of State for Scotland and the Radiochemical Centre, Amersham for financial support. We also thank Professors A. Goldberg and J. A. Simpson for encouragement.
3
REFERENCES Boclmer, F., Hooper, W. D., Sutherland, J. M., Eadie, M. J., Tyrer, J. H. (1974). Diphenylhydantoin concentrations in Saliva. Archives of Neurology, 31, 57
j'"
2
...
... ....
\\~
.10;·
,
/.
• r =0'98
y=1-21x-0'01
./
•
Lancet (1975). Editorial. Drug levels in epilepsy. Lancet, 1, 264
2
3
SALIVA DPH ( )Jg/ml l Fig. 2. Relationship of saliva to CSF concentrations of phenytoin (DPH) in 33 patients.
94
Goudie, J. H., Burnett, D. (1973). A gas chromatographic method for the simultaneous determination of phenobarbitone, primidone and phenytoin in serum using a nitrogen detector. Clinica Chimica Acta, 43, 423
Paxton, J. W., Rowell, F. J., Ratcliffe, J. G. (1976). Production and characterisation of antisera to diphenylhydantoin suitable for radioimmunoassay. Journal of Immunological Methods (in press)
SCOTTISH SOCIETY FOR EXPERIMENTAL MEDICINE-SELECTED ABSTRACTS
ANTICONVULSANT DRUG CONCENTRATIONS IN EPILEPTIC PATIENTS D. G. Lambie, J. W. Paxon, R. N. Nanda, R. H. Johnson, J. G. Ratcliffe I. D. Melville and G. D. Morrice Til-e University Department of Neurology, Institute of Neurological Sciences, Southern General Hospital, and The University Department of Materia Medica, Stobhill Hospital, Glasgow and Quarrier's Homes, Bridge of Weir. SAT I S F ACT 0 R Y seizure control in epileptic patients may be difficult to achieve when drug dosage is adjusted empirically. This may be due, in part, to indivudal variations in drug absorption or metabolism or differences in bioavailability of different drug preparations or non-compliance by the patient. We have measured total serum concentrations of anticonvulsant drugs in epileptic patients to assess their value in determining dosage schedules. In addition We have compared the non-protein bound drug fractions in serum with concentrations in cerebrospinal fluid (CSF) and mixed saliva. Blood samples were obtained from I I 6 epileptic patients (74 outpatients attending the epilepsy clinic, Institute of Neurological Sciences, Glasgow (Dr R. H. Johnson and Dr I. D. Melville) and 42 inpatients at Quarrier's Home for Epileptics, Bridge of Weir). CSF was also obtained from 40 of the inpatients. All patients were receiving phenytoin and in most cases, one or more other drugs. usually phenobarbitone or primidone. Phenytoin, phenobarbitone and primidone in serum and CSF were measured by gas liquid chromatography (Goudie & Burnett, 1973) and phenytoin in serum, CSF and saliva by a new radioimmunoassay technique (Paxton et al., 1976) which is more sensitive than existing methods and requires only 20 ,ul. of fluid. There was excellent correlation between the 2 methods for phenytoin (r=0.98). Only 39 of 1I6 patients receiving phenytoin had serum concentrations within the range of 10 to 20 Itg. per ml. (Fig. I) which has been generally proposed as the therapeutic range (Lancet, 1975). There was a poor correlation between total daily dose or weight related dose and serum phenytoin concentration. It is unlikely that the low concentrations were due solely to failure of compliance since drug intake was supervised in the inpatients and no significant differerences in mean serum phenytoin concentration was observed between in- and out-patients. Serum concentrations of phenobarbitone showed a better correlation with weight related dose of phenobarbitone and primidone (from which phenobarbitone may be derived in vivo). Almost all the patients had serum phenobarbitone concentrations within the likely therapeutic range 10 to 401'g. per ml. (Lancet, 1975). Phenobarbitone concentrations in patients receiving primidone were similar to those in patients on phenobarbitone alone. The non-protein bound (Tree') fraction of a drug in serum is generally considered to be the biologically active part. For phenytoin, the mean non-protein bound fraction measured by ultrafiltration was 0.1I (range 0.08-0.17) and was similar to the mean CSF to serum ratio ofO. 12 (range 0.09-0.25) in 40 patients,
indicating the CSF concentrations of drugs at equilibrium probably reflect serum 'free' concentrations. For phenobarbitone, the mean non-protein bound fraction in serum was 0.52 (lange 0.44-0.71) and the CSF to serum ratio 0.47 (range 0.32-0.78) in 17 patients. Primidone is not significantly bound in serum, and CSF and serum concentrations were approximately equal in I3 patients. However neither the standard techniques of ultrafiltration o~ equilibrium dialysis or measurement of CSF drug concentrations are suitable for routine use. We have therefore assessed whether the measurement of phenytoin by radioimmunoassay in saliva may have clinical applications since it has been suggested that salivary phenytoin concentration is dependent on the flee serum concentration (Bochner et al., 1974). Excellent correlations were found between saliva and serum phenytoin concentrations (r=0.97), saliva levels being approximately 10 per cent of total serum levels, and between saliva, and CSF concentrations (r=0.98), saliva levels being approximately 82 per cent of the CSF levels (Fig. 2). Measurement of salivary phenytoin levels by radioimmunoassay may therefore offer a simple m-ethod of determining biologically available phenytoin in epileptic patients. It is concluded that many patients on conventional phenytoin dosage regimes fail to achieve therapeutic concentrations. We are currently studying patients with low phenytoin concentrations whose seizures
SERUM DPH I >Jg/ml)
30
..
-----.--._--Therapeutic Range
:: '. .... - - --..=t--
n~39
:: .;s
:. 100
..:.-.
1
200
, 300
!.DO
DPH TOTAL DAILY DOSE I mg I
Fig. 1. R-elationship of dose to serum concentrations of phenytoin (DPH) in 1I6 patients.
Lambie, Paxton, Nanda, Johnson, Ratcliffe, Melville and Morrice
are poorly controlled, to determine whether control is improved by raising phenytoin concentrations into the therapeutic range.
CSF DPH ( yg/mll
4 A C K NOW LED GEM E N T s. We wish to thank the Secretary of State for Scotland and the Radiochemical Centre, Amersham for financial support. We also thank Professors A. Goldberg and J. A. Simpson for encouragement.
3
REFERENCES Boclmer, F., Hooper, W. D., Sutherland, J. M., Eadie, M. J., Tyrer, J. H. (1974). Diphenylhydantoin concentrations in Saliva. Archives of Neurology, 31, 57
j'"
2
...
... ....
\\~
.10;·
,
/.
• r =0'98
y=1-21x-0'01
./
•
Lancet (1975). Editorial. Drug levels in epilepsy. Lancet, 1, 264
2
3
SALIVA DPH ( )Jg/ml l Fig. 2. Relationship of saliva to CSF concentrations of phenytoin (DPH) in 33 patients.
94
Goudie, J. H., Burnett, D. (1973). A gas chromatographic method for the simultaneous determination of phenobarbitone, primidone and phenytoin in serum using a nitrogen detector. Clinica Chimica Acta, 43, 423
Paxton, J. W., Rowell, F. J., Ratcliffe, J. G. (1976). Production and characterisation of antisera to diphenylhydantoin suitable for radioimmunoassay. Journal of Immunological Methods (in press)
