Corrected Phenytoin Calculator

The Sheiner-Tozer equation corrects a measured total phenytoin concentration for the reduced protein binding seen in hypoalbuminaemia. Phenytoin is highly protein-bound (about 90%), primarily to albumin; with low albumin the free (pharmacologically active) fraction rises while the measured total stays normal or low. The correction allows comparison against the standard therapeutic total range of about 10-20 µg/mL. It assumes normal renal function; in renal failure the correction is not as reliable because a structurally altered albumin binds phenytoin less well.