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Neuro4Nurses 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. www.neuro4nurses.com 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 1) 2) 3) 4) 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 Neuroscience Nursing, 30, 55-59. Bader, M.K. (1993). Case study of two methods for enteral phenytoin administration. Journal of Neuroscience Nursing, 25, 233-242. Kitchen, D., & Smith, D. (2001). Problem with phenytoin administration in neurology/neurosurgery ITU patients receiving enteral feedings. Seizure, 10, 265-268. 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) Gilbert, S., Hatton, J., & Magnuson, B. (1996). How to minimize interaction between phenytoin and enteral feeding: Two approaches. Nutrition in Clinical Practice, 11, 28-31. Sneed, R.C., & Morgan, W.T. (1988). Interference of oral phenytoin absorption by enteral tube feedings. Archives of Physical Medicine and Rehabilitation, 69, 682-684. Fleisher, D., Sheth, N., & Kou, J.H. (1990). Phenytoin interaction with enteral feeding administered through nasogastric tubes. Journal of Parenteral and Enteral Nutrition, 14, 513-516. Ozuna, J., & Friel, P. (1984). Effect of enteral tube feeding on serum phenytoin levels. Journal of Neurological Nursing, 16, 289-291. Crowder, K.M. (2000). An algorithm for monitoring phenytoin therapy. Journal of the American Academy of Nurse Practitioners, 12, 317-321. Hatton, J., & Magnuson, B. (1996). How to minimize interaction between phenytoin and enteral feeding: Two approaches-Therapeutic options. Nutrition in Clinical Practice, 11, 28-31. Cacek, A.T., DeVito, J.M., & Koonce, J.R. (1986). In vitro evaluation of nasogastric administration methods for phenytoin. American Journal of Hospital Pharmacy, 43, 689-692. Lubart, E., Berkovitch, M., Leibovitz, A. Orly, D. & Segal, R. (2010). Phenytoin blood concentration in hospitalized geriatric patients: Oral versus nasogastric feeding tube administration. Therapeutic Drug Monitoring, 32, 185-187. Au Yeung, S.C.S., & Ensom, M.H.H. (2000). Phenytoin and enteral feedings: Does evidence support an interaction? The Annals of Pharmacotherapy, 34, 896-905. Bauer, L.A. (1982). Interference of oral phenytoin absorption by continuous nasogastric feeding. Neurology, 32, 570-572. Saklad, J.J., Graves, R.H., & Sharp, W.P. (1986). Interaction of oral phenytoin with enteral feedings. Journal of Parenteral and Enteral Nutrition, 10, 322323. ©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.