> -----Original Message-----
> From: Warner, Maria
> Sent: 01 August 2008 12:48
> To: Cawood, Paul
> Subject:
>
> Hi,
> I have recently asked very similar questions and done a small audit to see how useful adjusting may be. The equation used commonly in the literature is the Sheiner Tozer equation. Several papers have adjusted around an albumin of 44g/L, although I have seen one paper that used 40g/L. The equation does not appear to be as useful in children. There is a considerable amount of intraindividual variation in phenytoin protein binding, and other factors such as renal function with have an impact on free phenytoin levels. However, other studies have shown adjusting to be a useful tool, whilst keeping these variances in mind (e.g. Int J Clin Pharmacol Ther 2004:42(10):550). In my audit 9% of all phenytoin concentrations reported over a one year period would have exceeded the therapeutic range only after adjustment using this equation. This included samples from GPs, inpatients and outpatients. We do not currently provide any comment or adjustment but are considering an approach to this at present. There were also a high number of phenytoin requests over the audit period where an albumin concentration was not available, meaning that potential hypoalbuminaemias may frequently be missed altogether.
> Regards,
> Maria
> Edinburgh Royal Infirmary
>
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