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Hi All !
Can anyone tell me of their experience, or comments on an automated
adjustment of serum phenytoin concentrations based on the patient's
latest serum albumin level, and their level of renal dysfunction.
Our pharmacy staff presently make these adjustments on the ward,
however, this function may lend itself to computer automation at the
level of the biochemistry department (with assumptions stated). The
usual Sheiner-Tozer equations have been utilized where free
concentrations are not measured:
Cadj = Cobs/(0.02*alb(in g/L) + 0.1) for hypoalbuminemia
Cadj = Cobs/(0.01*alb(in g/L) + 0.1) for hypoalbuminemia & uremia
We presently use the EMIT monoclonal antibody assay for phenytoin.
Upon close examination, studies which have looked at uremia and
phenytoin have simply enrolled dialysis patients only. Now the tough
question, what should be the cutoff for defining a uremic patient?
Some would suggest a creatinine clearance value (ie. < 10 mL/min), &
others if they are on any form of dialysis. I feel that it should be
based on a urea value, however, I cannot find any references better
defining this issue from any of these perspectives.
Very best regards,
References that I have presently are: Slack Mauro et al. DICP,
1989;23:64-8; Roberts & Rainey, Clin Chem 1993;39:1872-77; and
Dager et al. Annals of Pharmacotherapy 1995;29:667-70.
Robert Ariano, Pharm.D.,BCPS
Clinical Pharmacist Critical Care
St.Boniface General Hospital
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