Phenytoin interaction with enteral feedings administered through nasogastric tubes

Personalized antiseizure medication therapy in critically ill adult patients

Precision medicine has the potential to have a significant impact on both drug development and patient care. It is crucial to not only provide prompt effective antiseizure treatment for critically ill patients after seizures start but also have a proactive mindset and concentrate on epileptogenesis and the underlying cause of the seizures or seizure disorders. Critical illness presents different treatment issues compared with the ambulatory population, which makes it challenging to choose the best antiseizure medications and to administer them at the right time and at the right dose. Since there is a paucity of information available on antiseizure medication dosing in critically ill patients, therapeutic drug monitoring is a useful tool for defining each patient's personal therapeutic range and assisting clinicians in decision-making. Use of pharmacogenomic information relating to pharmacokinetics, hepatic metabolism, and seizure etiology may improve safety and efficacy by individualizing therapy. Studies evaluating the clinical implementation of pharmacogenomic information at the point-of-care and identification of biomarkers are also needed. These studies may make it possible to avoid adverse drug reactions, maximize drug efficacy, reduce drug-drug interactions, and optimize medications for each individual patient. This review will discuss the available literature and provide future insights on precision medicine use with antiseizure therapy in critically ill adult patients.

ESPEN practical guideline: Home enteral nutrition

This ESPEN practical guideline will inform physicians, nurses, dieticians, pharmacists, caregivers and other home enteral nutrition (HEN) providers in a concise way about the indications and contraindications for HEN, as well as its implementation and monitoring. This guideline will also inform interested patients requiring HEN. Home parenteral nutrition is not included but will be addressed in a separate ESPEN guideline. The guideline is based on the ESPEN scientific guideline published before, which consists of 61 recommendations that have been reproduced and renumbered, along with the associated commentaries that have been shorted compared to the scientific guideline. Evidence grades and consensus levels are indicated. The guideline was commissioned and financially supported by ESPEN and the members of the guideline group were selected by ESPEN.

Biopharmaceutical considerations in paediatrics with a view to the evaluation of orally administered drug products - a PEARRL review

OBJECTIVES

In this review, the current biopharmaceutical approaches for evaluation of oral formulation performance in paediatrics are discussed.

KEY FINDINGS

The paediatric gastrointestinal (GI) tract undergoes numerous morphological and physiological changes throughout its development and growth. Some physiological parameters are yet to be investigated, limiting the use of the existing in vitro biopharmaceutical tools to predict the in vivo performance of paediatric formulations. Meals and frequencies of their administration evolve during childhood and affect oral drug absorption. Furthermore, the establishment of a paediatric Biopharmaceutics Classification System (pBCS), based on the adult Biopharmaceutics Classification System (BCS), requires criteria adjustments. The usefulness of computational simulation and modeling for extrapolation of adult data to paediatrics has been confirmed as a tool for predicting drug formulation performance. Despite the great number of successful physiologically based pharmacokinetic models to simulate drug disposition, the simulation of drug absorption from the GI tract is a complicating issue in paediatric populations.

SUMMARY

The biopharmaceutics tools for investigation of oral drug absorption in paediatrics need further development, refinement and validation. A combination of in vitro and in silico methods could compensate for the uncertainties accompanying each method on its own.

Steady-state serum phenytoin concentrations after nasogastric tube administration of immediate-release phenytoin tablets and extended-release phenytoin capsules: an open-label, crossover, clinical trial

BACKGROUND

When phenytoin is prescribed for administration via nasogastric tube, immediate-release OR) phenytoin tablets are crushed before use and extended-release (ER) phenytoin capsules are opened and only the granules are used. However, it is unknown whether the same dose of these 2 different formulations will result in the same steady-state serum phenytoin concentration.

OBJECTIVE

The aim of this study was to determine whether ER phenytoin capsules can be used interchangeably with IR phenytoin tablets for prophylaxis of posttraumatic seizures.

METHODS

Inpatients at the neurosurgical ward at Prasat Neurological Institute, Bangkok, Thailand, between October 2004 and October 2005 were enrolled in the study. All patients were initially prescribed IR phenytoin tablets 300 mg/d as a maintenance dose for prophylaxis of posttraumatic seizures. The serum phenytoin concentration was measured after ≥5 days of treatment with IR phenytoin tablets 300 mg/d (two 50-mg tablets every 8 hours) that had been crushed before being administered concomitantly with a blenderized diet through the nasogastric tube. Without a washout period, the dosage form was changed to ER phenytoin capsules (three 100-mg capsules QD). The capsules were opened and the contents were administered concomitantly with the blenderized diet through the nasogastric tube for ≥5 days. The serum phenytoin concentration was again determined. The patients were closely monitored for seizures and adverse events (AEs).

RESULTS

Thirty-three patients enrolled in the study and 17 (10 women, 7 men; mean [SD] age, 62.94 [15.94] years [range, 18-89 years]) completed the study. The mean (SD) serum phenytoin concentrations after administration of phenytoin tablets and capsules were 6.03 (5.92) μg/mL and 3.80 (2.71) μg/mL, respectively (P = 0.019). The mean serum phenytoin concentrations, adjusted for low serum albumin concentrations after administration of tablets and capsules, were calculated and reported to be 10.33 (11.60) μg/mL and 6.28 (4.76) μg/mL, respectively (P = 0.035). The maximum phenytoin metabolic rate (Vmax) (assuming the substrate concentration at which the rate of metabolism is one half Vmax = 4 mg/L) after the administration of phenytoin tablets and capsules was 8.37 (2.42) mg/kg · d(-1) and 10.38 (6.48) mg/kg · d(-1), respectively. These values were not significantly different. All patients were seizure-free and no AEs were observed.

CONCLUSION

The steady-state serum phenytoin concentration was significantly lower with ER phenytoin capsules 300 mg/d than IR phenytoin tablets 300 mg/d administered via nasogastric feeding tube concomitantly administered with a blenderized diet in these neurosurgical patients. Key words: phenytoin nasogastric tube feeding extended-release capsule immediate-release tablet.

Oral absorption kinetics of levetiracetam: the effect of mixing with food or enteral nutrition formulas

BACKGROUND

Levetiracetam (LEV) is an antiepileptic drug with a favorable pharmacokinetic profile, including negligible protein binding and linear elimination kinetics. Because LEV is likely to be used in populations that include children and the elderly, alternative techniques of administration, such as crushing the tablet and mixing its contents with semisolid food or enteral nutrition formulas (ENFs), may be required in some clinical settings. Although previous studies have suggested that administration with food does not affect the overall absorption of LEV, there is a lack of data regarding concomitant administration with ENFs.

OBJECTIVE

The objective of this study was to evaluate the oral absorption of LEV after concomitant administration with food or ENFs.

METHODS

This was an unblinded, 3-way crossover study. After an overnight fast, subjects received a single dose of LEV 500 mg administered either as an intact tablet with 120 mL water (control, treatment A) or crushed and mixed with 4 oz applesauce (treatment B) or 120 mL of a common ENF (treatment C). All subjects received each treatment in a randomized sequence; there was a 7-day washout period between treatments. Serial blood samples were obtained over 24 hours for determination of the LEV serum concentration-time profile using gas chromatography with nitrogen phosphorus detection. AUC(0-24), C(max), and T(max) were calculated using noncompartmental methods and analyzed using analysis of variance.

RESULTS

Ten healthy adult volunteers (6 men, 4 women) participated in the study (mean [SD] age, 28.9 [6.5] years; mean body weight, 78.6 [12.9] kg). No significant differences were noted between control and any other study treatment. Mean AUC values were 191.9 (50.2), 165.7 (43.4), and 168.3 (43.9) microg/mL . h for treatments A, B, and C, respectively. Mean T(max) values were 1.08 (0.65), 1.32 (0.75), and 1.62 (0.73) hours, respectively. Mean C(max) values were 14.8 (5.6), 12.1 (2.8), and 10.8 (2.0) microg/mL for the respective treatments. Mean LEV serum concentrations at 12 hours after dosing were similar for all study treatments (3.9, 4.1, and 4.0 microg/mL). The long-term stability of LEV in the various combinations was not assessed.

CONCLUSIONS

In these healthy volunteers, the overall rate and extent of absorption of oral LEV were not significantly impaired after crushing and mixing of the tablet with either a food vehicle or a typical ENF product. The data suggest that peak serum concentrations of LEV may be slightly reduced after mixing with ENFs, although the difference was not significant compared with control values.

Phenytoin and enteral feedings: does evidence support an interaction?

OBJECTIVE

To systematically review the reported interaction between oral dosage forms of phenytoin and enteral feeding formulations with respect to the evidence supporting or refuting its existence, proposed mechanism(s) underlying the interaction, and recommended interventions.

DATA SOURCES

We conducted a MEDLINE search (1966-April 2000) for English-language articles on phenytoin-enteral feeding interactions; the search terms used were phenytoin, enteral feeding, and/or interaction, and/or in vitro. This search was supplemented by a bibliographic review of all relevant articles.

STUDY SELECTION

Prospective, randomized, controlled studies; prospective, nonrandomized, controlled studies; prospective, nonrandomized, uncontrolled studies; retrospective studies; clinical experience reports; case reports; in vitro studies; and letters were evaluated for relevant information.

DATA EXTRACTION

Data elements abstracted from these articles were study design, type (patients or healthy volunteers) and number of subjects involved, method of administration of phenytoin and enteral feeding, formulation of phenytoin, type of feeding (and whether it was continuous or interrupted), major findings, and proposed mechanisms of the interaction.

DATA SYNTHESIS

Although four prospective, randomized, controlled trials in healthy human volunteers refute the existence of the interaction, there are numerous reports and studies showing dramatic decreases of serum phenytoin concentrations in patients when it is coadministered with enteral feeding formulations. Therefore, evidence supports the existence of this interaction in patients and in vitro studies, but not in healthy volunteers. Unfortunately, the exact mechanisms underlying this interaction remain unknown. Many methods have been devised to prevent and treat the interaction once it has occurred; however, a single, generally accepted, and practical intervention strategy is still lacking.

CONCLUSIONS

The exact role of enteral feeding in this interaction is unclear due to the lack of prospective, randomized, controlled trials performed in patients. However, decreased serum phenytoin concentrations associated with enteral feeding may increase the risk of seizures. Clinicians should be aware of this potential drug-nutrient interaction and design a patient-specific care plan that includes consideration of the enteral feeding formulation and method of administration, as well as the phenytoin dosage form, schedule of administration, and monitoring.

Nutrition support in the critically ill patient

Despite an absence of well-controlled studies demonstrating a clear mortality benefit, providing nutrition support in the critically ill patient has become routine in most ICU settings. Unless clearly contraindicated, patients should be fed enterally, using conventional isotonic feedings employing gastric or postpyloric access. When to begin nutrition support varies, depending on baseline nutritional status, anticipated time until oral feedings are resumed, and the degree of stress. Energy and protein requirements should be assessed routinely with minimum goals of avoiding overfeeding and minimizing any net negative nitrogen balance. All patients receiving feedings require close surveillance to identify predictable complications and to tailor therapy to achieve nutritional goals. Adjunctive therapies should be employed as needed to help achieve nutritional goals, eg, insulin infusions to control serum glucose and prokinetic agents to improve gastric emptying. When feasible and safe, parenterally fed patients should be transitioned to enteral or oral feedings when appropriate.