How is dosage of anticonvulsants adjusted in CKD?
Phenytoin is a highly protein-bound drug. In patients receiving dialysis or in patients with CKD and significant proteinuria, the free fraction of phenytoin (free phenytoin) is elevated, although plasma phenytoin levels seem low. If not adjusted, total phenytoin levels are of little value.
In patients receiving dialysis, the monitoring of free concentration is recommended for a target plasma concentration of 1 to 2 mcg/mL.
If unable to obtain a free phenytoin level, the following equations can be used to adjust the serum concentrations based on either reduced albumin levels or presence of kidney failure (CrCl < 10 mL/min).
• Hypoproteinemia: C adjusted = C measured /[(0.2 × albumin) + 0.1]
• AKI and dialysis: C adjusted = C measured /[(0.1 × albumin) + 0.1]
