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Recovery of phenytoin from an enteral nutrient formula
Insights
Phenytoin recovery from enteral formula was significantly lower than from water. Recovery rates varied with formula concentration and volume, indicating potential clinical implications for patients receiving both medications.
Area of Science:
- Pharmacokinetics
- Drug Interactions
- Clinical Pharmacy
Background:
- Phenytoin is an antiepileptic drug often administered orally.
- Enteral nutrient formulas are used for patients requiring nutritional support.
- Interactions between oral medications and enteral formulas can affect drug bioavailability.
Purpose of the Study:
- To determine the recovery of phenytoin oral suspension when mixed with an enteral nutrient formula.
- To investigate the impact of formula concentration and volume on phenytoin recovery.
- To assess the potential clinical significance of phenytoin-enteral formula interactions.
Main Methods:
- Two-phase study involving in vitro mixing of phenytoin oral suspension with Osmolite (enteral formula) and a control solution.
- Samples were filtered using ultrafiltration and assayed for phenytoin concentration via homogeneous enzyme-multiplied immunoassay technique.
- Phase 1 assessed recovery at a theoretical concentration; Phase 2 evaluated effects of varying phenytoin concentration and solvent volume.
Main Results:
- Mean phenytoin recovery from Osmolite was significantly lower (3.70 µg/mL) compared to the control solution (9.87 µg/mL).
- Phenytoin recovery from Osmolite increased with higher phenytoin concentrations.
- Phenytoin recovery from Osmolite decreased as the volume of the formula increased.
Conclusions:
- Significant reduction in phenytoin recovery occurs when mixed with the tested enteral nutrient formula.
- The observed in vitro interactions suggest potential clinical implications for patients on both phenytoin and enteral nutrition.
- Further in vivo studies in humans are necessary to confirm these findings and guide clinical practice.
Abstract:
The recovery of phenytoin from phenytoin oral suspension dispersed in an enteral nutrient formula was determined. The study was conducted in two phases. In phase 1, diluted phenytoin oral suspension was added to 10 1-mL samples of full-strength Osmolite and 10 1-mL samples of a distilled water control solution to produce a theoretical concentration of 10 micrograms/mL. The samples were filtered through an ultrafiltration membrane and assayed for phenytoin concentration by a homogeneous enzyme-multiplied immunoassay technique. In phase 2, varying amounts of diluted phenytoin oral suspension were added to 30-mL quantities of half-strength Osmolite or control solution to determine the effect of phenytoin concentration on recovery of phenytoin; also, a constant amount of diluted phenytoin oral suspension was added to 30-, 60-, and 90-mL quantities of half-strength Osmolite or control solution to determine the effect of solvent volume on recovery of phenytoin. Duplicate samples of each phase 2 mixture were filtered and assayed in the same manner as phase 1 samples. The mean concentration of phenytoin in phase 1 samples was 3.70 +/- 0.28 microgram/mL for Osmolite and 9.87 +/- 0.27 microgram/mL for control solution; this difference was significant. The percentage of phenytoin recovered from phase 2 samples of Osmolite increased with increasing phenytoin concentration and decreased with increasing volumes of Osmolite. The decreased recovery of phenytoin from the enteral nutrient formula used in this study has potential clinical importance, but further research in humans is needed to substantiate these in vitro observations.