Variability of total phenytoin serum concentrations within elderly nursing home residents.
BACKGROUND
Approximately 6% of all elderly nursing home residents receive phenytoin. Phenytoin concentrations are often measured to guide therapy.


OBJECTIVE
To evaluate the intraresident variability among multiple measurements of total phenytoin serum concentrations in nursing home residents.


METHODS
This was an observational study of 56 elderly (>or=65 years) nursing home residents from 32 nursing homes who had at least 3 phenytoin concentrations measured while on the same dose of phenytoin for at least 4 weeks and who were not taking any interfering concomitant medications. These were a subset of 387 elderly nursing home residents from 112 nursing homes across the United States who had total phenytoin concentration measurements between June 1998 and December 2000.


RESULTS
The mean age was 80.1 years (range, 65 to 100 years) and 58.9% were women. The mean daily dose of phenytoin per resident was 4.9 +/- 1.5 mg/kg. Total phenytoin concentrations within an elderly nursing home resident varied as much as two- to threefold, even though there was no change in dose. The person with the smallest variability had a minimum concentration of 10.0 micro g/mL and a maximum of 10.4 micro g/mL. The person with the largest variability had a minimum concentration of 9.7 micro g/mL and a maximum of 28.8 micro g/mL.


CONCLUSIONS
There is considerable variability in the total phenytoin concentrations in the elderly nursing home resident and measurement of a single total phenytoin concentration should not be used to guide treatment.
Birnbaum
A
A
Experimental & Clinical Pharmacology, Epilepsy Research and Education Program, College of Pharmacy, University of Minnesota, MN 55455, USA. birnb002@umn.edu
Hardie
N A
NA
Leppik
I E
IE
Conway
J M
JM
Bowers
S E
SE
Lackner
T
T
Graves
N M
NM
D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D001835:Body Weight; D004304:Dosage Forms; D004333:Drug Administration Routes; D004827:Epilepsy / Q000188:drug therapy / Q000517:prevention & control; D005260:Female; D006801:Humans; D007297:Inpatients / Q000706:statistics & numerical data*; D008297:Male; D009735:Nursing Homes / Q000706:statistics & numerical data*; D010672:Phenytoin / Q000097:blood* / Q000627:therapeutic use; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D014481:United States
D004304:Dosage Forms; D010672:Phenytoin