Again, the most accurate assessment can be made by obtaining the actual unbound (free) level. Liponi DF, Winter ME, Tozer TN. 1982 Mar;31(3):301-4.4. I. Michaelis-Menten model: routine clinical pharmacokinetic data. 22. Allen JP, Ludden TM, Burrow SR, Clementi WA, Stavchansky SA. The elderly (defined as age>60) on the other hand, exhibit a saturation of metabolism at dosages that are usually 20 % lower than in younger patients. Phenytoin cumulation kinetics. Tozer TN, Winter ME. Bachmann KA, Belloto RJ Jr. Factors which may decrease the affinity of phenytoin to albumin or cause displacement include: interacting drugs, increased bilirubin, renal failure …). Phenytoin. 3rd Ed. Pryka RD, Rodvold KA, Erdman SM. Hayes MJ, Langman MJ, Short AH. Ann Pharmacother. If the phenytoin concentration is >16 ug/mL, any change may result in a significant increase in … Phenytoin sodium 100 mg oral capsules / tablets = phenytoin sodium 100mg IV injection Phenytoin sodium 100mg capsules/ tablets/ injection = phenytoin 90mg suspension Phenytoin safety and monitoring requirements Check drug is prescribed correctly on drug cardex Check dru g dose is appropriate Check drug is being administered Age and phenytoin kinetics in adult epileptics. The program uses a maintenance dose of 4 to 6 mg/kg for all adults < 60 years old. 1988;48(4): 310-4. For this reason, the program recommends initial dosages of 3-4 mg/kg in this age group. Equation used to estimate the dose required to increase current level to normal range if subtherapeutic: = [0.7 x IBW x (15 – current level) ] / 0.92* * (if capsules/injection used) This is especially important in obese patients where the utilization of total body weight would result in an over-estimation of dosage. 1975 Feb;2(1):73-9. J Clin Pharm Ther. Steady-state pharmacokinetics of phenytoin from routinely collected patient data10. CPG objective: The objective of this guideline is to improve the use of phenytoin and fosphenytoin through improved dosing, administration, and monitoring to improve patient safety, tolerance and efficacy. The final equation is:It is important to remember that since phenytoin’s elimination is a saturable process, and clearance decreases with increasing concentrations, the steady state concentration is NOT proportional to the maintenance dose (e.g. Peterson GM, Khoo BH, von Witt RJ. Sample prescription – example 70kg patient: 3.1. Ther Drug Monit. The dose is the same for all phenytoin products when initiating therapy. Am J Clin Pathol. Vancouver, WA: Applied Therapeutics; 1992: 25.1 – 25.44 Applied Pharmacokinetics: Principles of Therapeutic Drug Monitoring. Clin Pharmacol Ther. Also, the half-life has little value in estimating the time to steady state. 1, – 5 However, phenytoin dosing can pose a challenge to clinicians because of its narrow therapeutic range and nonlinear pharmacokinetic profile. J Pharmacokinet Biopharm. Target Population: Br J Clin Pharmacol. Sample serum levels 7 to 10 days following each dosage change to assess the trend. Steady-state plasma concentrations as a function of the absorption rate and dosing interval for drugs exhibiting concentration-dependent clearance: consequences for phenytoin therapy. All factors must be considered: addition of interacting drugs, changes in absorption (eg enteral feeding + oral administration of phenytoin), concomitant disease state(s) which may alter phenytoin kinetics, etc. Related ArticlesComparison of eight phenytoin dosing methods in institutionalized patients.9. Initial loading dose of phenytoin for status epilepticus'Top-up' loading dose of phenytoin for status epilepticusDecision making algorithm for the administration of phenytoin formulations 19. Phenytoin is a commonly used medication for the treatment of status epilepticus and acute seizure control in the emergency department (ED). 21. Grasela TH, Sheiner LB, Rambeck B, Boenigk HE, Dunlop A, Mullen PW, Wadsworth J, Richens A, Ishizaki T, Chiba K, et al. The following equations can be used to adjust the serum concentrations based on either reduced albumin levels or presence of renal failure (crcl < 10 ml/min). Clinical response in epilepsy in relation to total and free serum levels of phenytoin. 1996 Mar;30(3): 219-23. Evaluation of methods for estimating population pharmacokinetics parameters. Gugler R, Manion CV, Azarnoff DL. (3) Changes in the daily maintenance dose should be made in small increments (30-100mg maximum). Phenytoin: pharmacokinetics and bioavailability. Renal function and therapeutic concentrations of phenytoin. Efficacy of individualized phenytoin sodium loading doses administered by intravenous infusion. JAMA. 1991 Sep;13(5):415-9. Factors which may reduce albumin levels include: hepatic cirrhosis, cachexia, burns, malnutrition, and nephrotic syndrome. Sheiner LB, Beal SL. Administration of phenytoin via enteral feeding tubes is not recommended due to variable absorption of phenytoin. 4 to 6 mg/kg for all phenytoin products when initiating therapy DL, Thompson D, RG... Assessment can be made in small increments ( 30-100mg maximum ):253-6.Dela Cruz FG, Kanter MZ, JH... Dose is the same daily maintenance dose is the same daily maintenance dose with! Days, However, it may be increased by 50 mg/day dosing the! Oct 17 ; 238 ( 16 ):1750-3.17 equations in some patients C. 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