Duangchit Panomvana1, Napanan Khummuenwai1, Supasil Sra-Ium2, Somchai Towanabut3. 1. Department of Pharmacy (Clinical), Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok, Thailand. 2. Department of Pharmacy, Ramathibodi Hospital, Bangkok, Thailand. 3. Department of Medicine, Neurological Institute, Bangkok, Thailand.
Abstract
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.
RCT Entities:
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.
Authors: K K Doak; C E Haas; K J Dunnigan; R A Reiss; J R Reiser; J Huntress; J L Altavela Journal: Pharmacotherapy Date: 1998 May-Jun Impact factor: 4.705