How does hypoalbuminemia affect phenytoin levels?

Phenytoin is 90% protein-bound; lower albumin increases free (active) fraction; use Sheiner-Tozer: adjusted level = measured level / (0.2 × albumin + 0.1) for ESRD or /(0.25 × albumin + 0.1) for normal renal function.

What adjusted total phenytoin level is therapeutic with hypoalbuminemia?

Normal total therapeutic range 10-20 mcg/mL assumes albumin 4 g/dL; with albumin 2 g/dL, a measured level of 5-10 mcg/mL may represent adequate free phenytoin; free phenytoin target 1-2 mcg/mL.

How is fosphenytoin dosed compared to phenytoin?

Fosphenytoin is dosed in phenytoin equivalents (PE); 1 PE = 1 mg phenytoin; loading dose 15-20 mg PE/kg IV; can infuse at up to 150 mg PE/min (3x faster than phenytoin, less cardiac risk).

What is Michaelis-Menten kinetics significance for phenytoin?

Phenytoin follows saturable (non-linear) pharmacokinetics; small dose increases near saturation can cause disproportionately large increases in levels; levels should be checked 5-7 days after any dose change.

What drug interactions increase phenytoin toxicity?

Inhibitors (fluconazole, isoniazid, amiodarone, sulfonamides) raise phenytoin levels; inducers (carbamazepine, rifampin) reduce levels; phenytoin itself induces CYP enzymes affecting many other drugs.

Phenytoin Free Fraction Adjustment Calculator

Adjusts phenytoin levels for hypoalbuminemia and renal failure using the Sheiner-Tozer equation, calculates phenytoin-equivalent doses for fosphenytoin conversion, and loading dose calculations.

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Frequently Asked Questions

How does hypoalbuminemia affect phenytoin levels?

What adjusted total phenytoin level is therapeutic with hypoalbuminemia?

How is fosphenytoin dosed compared to phenytoin?

What is Michaelis-Menten kinetics significance for phenytoin?

What drug interactions increase phenytoin toxicity?