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The following message was posted to: PharmPK
Dear all,
A child (11 years old) with chronic renal failure
associated with uncontrolled epilepsy. He is
maintained on renal dialysis. He was given epanutin
(phenytoin) as a loading dose i.v. followed by a
maintenance dose every (i.v) 12 h. Depakine
(valproate) was added (orally given).
The following questions are raised:
1- What is the proper sampling time to measure drug
levels especially for phenytoin which is given i.v.?
2- Should this timing follow dialysis immediately?
3- Should we look for trough or peak levels or both of
them?.
4- Do some one has a clinical experience of which of
the AEDs (phenytoin, valproate or carbamazepine is of
choice to be used in dialyzable patients?.
Thank you for help
Dr Ehab EL Desoky M.D., PhD
Chairman,
Therapeutic drug monitoring lab
Assiut University hospital
Assiut. Egypt
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First off, phenytoin and other AEDs are not usually dialyzed. The
protein binding prohibits removal by the filter. If you are using
continuous renal replacement with a large bore filter, then perhaps
there will be some removal. Otherwise, the largest molecule removed
with dialysis is about 5000 daltons. The AEDs are much larger.
As far as peaks go, don't draw them. Draw the trough levels 18 - 24
hours post dose on a q day dosing and 12 hours post dose on a q 12 hr
dosing.
You will not be able to do standard or even non-standard kinetics while
the patient is on dialysis, because of multiple confounding variables
(third spacing, electrolyte shifts, and a small amount of drug removed
by dialysis)
All of that being said, I would check with the nephrologists to get the
specifics of the filters being used. You may be able to calculate
clearance based on sieving coefficients.
Please contact me off list if you need more information.
Thanks ..........Robert
Robert G. Aucoin, RPh
Clinical Pharmacist - Peds
Department of Pharmacy Office: 225-765-7652
Our Lady of the Lake RMC Pager: 225-237-6564
5000 Hennessy Blvd Toll Free: 888-765-7428
Baton Rouge, La 70808
RAucoin.-at-.ololrmc.com
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The following message was posted to: PharmPK
Dear Dr. Aucoin,
One more question is raised:
Do we take trough level irrespective it will be pre or post dialysis
level?
Ehab
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