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Phenytoin Unit Converter
Phenytoin (commonly known as Dilantin) is an anticonvulsant medication used to treat tonic-clonic and complex partial seizures. It exhibits non-linear (Michaelis-Menten) kinetics, making therapeutic drug monitoring (TDM) critical.
Because small dose increases can lead to disproportionately large increases in serum concentration, regular monitoring is required. This converter facilitates switching between standard mass units (μg/mL, mg/L) and SI molar units (μmol/L).
Mass Units
StandardMicrograms per milliliter (Numerically equivalent to mg/L).
SI / Molar Units
Clinical Context
Therapeutic Range (Total Phenytoin): Generally 10 – 20 μg/mL (40 – 80 μmol/L).
Toxic Levels:
• > 20 μg/mL: Nystagmus (involuntary eye movement).
• > 30 μg/mL: Ataxia (loss of coordination).
• > 40 μg/mL: Lethargy and confusion.
Conversion Logic:
Molecular Weight of Phenytoin: ~252.27 g/mol.
1 μg/mL ≈ 3.964 μmol/L.
1 μmol/L ≈ 0.252 μg/mL.
Clinical References
How to Use This Converter
Follow these steps to normalize Phenytoin levels.
Enter Values
Input your laboratory results into the corresponding unit field (e.g., μg/mL).
Automatic Conversion
The calculator converts between mass units and the SI molar unit (μmol/L).
Reset
Use the Clear button to reset all fields.
Frequently Asked Questions
Phenytoin is highly protein-bound (~90%). If a patient has low albumin (hypoalbuminemia), the Total Phenytoin level may appear artificially low even if the Free (active) drug is adequate. In these cases, a “Corrected Phenytoin” calculation is often required.
Yes. 10 μg/mL = 10 mg/L.