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Phenytoin (Dilantin) Administration when
Patient is on Continuous Tube Feeding.
Phenytoin is the most commonly used
antiepileptic agent in the treatment of seizure
disorders. The therapeutic range of phenytoin is very
narrow (40-80 micromol/L or 10-20 microgram/mL)
and the serum drug level is affected by varies factors
such as serum albumin level, drugs concurrently
used, and enteral feeding1.
Corrected phenytoin level
Phenytoin has a high affinity with plasma protein;
approximately 90% of phenytoin in the blood is
bound with albumin and 10% is free or unbound.
Only the free or unbound phenytoin is
pharmacologically effective2. Due to the high affinity
of phenytoin to albumin, lower serum albumin level
will significantly affect the free phenytoin level.
Several methods such as the Sheiner-Tozer
equation have been used to calculate the “corrected
serum phenytoin concentration” to assess the free
phenytoin level.
Phenytoin-nutrition interaction
In 1982, Bauer had noticed that serum phenytoin
was decreased when it was given with enteral
feeding formulas. Numerous research has been
performed and most of the research results suggest
that phenytoin binds with the feeding formula protein
or adheres to the feeding tube which affects the
serum phenytoin level1,3,4,5,6.
When phenytoin is administered via the
nasogastric (NG) tube, part of the drug adheres to
the feeding tube. Fleisher, Sheth, & Kou7 indicated
that significant amount of phenytoin was bound to
the NG tubing when the solution form of the drug
was administered. However, Ozuna & Friel8 argued
that only a small amount (7%) of phenytoin was lost
in the NG tube if the drug was in suspension form.
Drug-drug interaction of phenytoin
Majority of the phenytoin is bound with albumin.
Some drugs that are concurrently used for patients
with seizures may also bind with protein and
compete with phenytoin for the albumin binding site.
When these drugs are used, phenytoin is displaced
from the albumin which results in a higher free
phenytoin level. The drugs that may affect serum
phenytoin level include anticoagulants, nonsteroidal
anti-inflammatory drugs, phenobarbital, cimetidine,
folate, sulfonamidews, ceftriaxone, and nafcillin 9.
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Discussion
At present, no research has concluded the “best”
method for administration of phenytoin via NG tube
when a patient is on continuous tube feeds. Some
researchers suggested that a phenytoin suspension
is the preferred form for NG tube administration10.
Some suggested that capsules should be used for
the NG route because the phenytoin concentration
varies between the top and bottom of the drug
bottle7. However, Hatton and Magnuson10 argued
that the sustained release form of phenytoin
capsules (Dilantin Kapseals) should not be open
because of the long acting characteristic of the drug.
Evidence has showed that there is a binding
interaction of phenytoin and the plastic NG tube;
some of the phenytoin is lost when given via NG
tube11. In order to minimize drug lost in the NG tube,
some researchers recommended flushing the NG
tube with 30-50mL of water before and after drug
administration3,7,12.
Because of the drug and nutrition interaction,
some researchers suggested stopping tube feeds
one to two hours before and after phenytoin
administration2,3,10,13,14.
Nursing Implication
Concluding with the recommendations from the
researchers, a phenytoin suspension is preferred
when given via NG tube. Drug bottles should be
shaken well before pouring the drug. Nasogastric
tube should be flushed with a minimum 30 milliliters
of water before and after phenytoin administration.
Tube feeding should also be held 2 hours before and
two hours after phenytoin administration.
Review by Kelsey Echlin, RD
Clinical Dietitian
Foothill Medical Center
Reference
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Hennessy, 2003). Recovery of phenytoin from
feeding formulas and protein mixtures. American
Journal of Health System Pharmacy, 60,
Faraji, B., & Yu, P.P. (1998). Serum phenytoin levels
of patients on gastrostomy tube feeding. Journal of
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Bader, M.K. (1993). Case study of two methods for
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Kitchen, D., & Smith, D. (2001). Problem with
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Crowder, K.M. (2000). An algorithm for monitoring
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Cacek, A.T., DeVito, J.M., & Koonce, J.R. (1986). In
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Lubart, E., Berkovitch, M., Leibovitz, A. Orly, D. &
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Au Yeung, S.C.S., & Ensom, M.H.H. (2000).
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Saklad, J.J., Graves, R.H., & Sharp, W.P. (1986).
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©2013
Disclaimer: The author of this article neither represents nor guarantees that the
practices described herein, if followed, ensure safe and effective patient care. The
author further assumes no responsibility or liability in connection with any
information or recommendations contained in this article. The recommendations and
instructions in this article are based on the knowledge and practice in neuroscience
as of the date of publication. These recommendation and instructions are subject to
change based on the availability of new scientific information.