Phenytoin and albumin

Q: Phenytoin level needs to be corrected with serum albumin level?

A) Yes

B) No

Answer: A

Phenytoin is protein-bound, and clinical symptoms correlate well with its level. Although not very precise, hypoalbuminemia needs to be corrected using the Sheiner-Tozer formula.

Corrected total phenytoin concentration = Observed total phenytoin concentration/([0.2 x Albumin]+0.1)

A major criticism of the Sheiner-Tozer equation is that it depends on various factors, such as temperature, timing of concentration sampling, steady-state dosing conditions, renal function, age, concomitant medications, and patient type. 

Other option is to use free phenytoin level, but usually it's not widely available in all hospitals' laboratories.

#pharmacology

References:

1. Kiang TK, Ensom MH. A Comprehensive Review on the Predictive Performance of the Sheiner-Tozer and Derivative Equations for the Correction of Phenytoin Concentrations. Ann Pharmacother. 2016 Apr;50(4):311-25. doi: 10.1177/1060028016628166. Epub 2016 Jan 29. PMID: 26825643.

2. Dager WE, Inciardi JF, Howe TL. Estimating phenytoin concentrations by the Sheiner-Tozer method in adults with pronounced hypoalbuminemia. Ann Pharmacother. 1995 Jul-Aug;29(7-8):667-70. doi: 10.1177/106002809502907-802. PMID: 8520077.

3. Bolt J, Gorman SK. Precision, bias, and clinical utility of the Sheiner-Tozer equation to guide phenytoin dosing in critically ill adults. J Clin Pharmacol. 2013 Apr;53(4):451-5. doi: 10.1002/jcph.27. Epub 2013 Feb 22. PMID: 23436385.