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Phenytoin

SI UNITS (recommended)

CONVENTIONAL UNITS

Synonym

Dilantin

Units of measurement

µmol/L, mg/L, mg/dL, mg/100mL, mg%, µg/mL

Phenytoin (diphenylhydantoin) has been used extensively for seizure control in patients having both grand mal epilepsy (major motor), cortical focal seizures, and temporal lobe epilepsy. Serum level monitoring of the drug is essential in order to achieve maximal seizure control while maintaining minimal blood levels. Because of individual variation in absorption and metabolism, optimum levels may vary.

Expected values

The therapeutic range of phenytoin is correlated with seizure control as well as the absence of toxic effects, and is generally accepted to be between 10 and 20 μg/mL (39.6 and 79.2 μmol/L). Because of individual variation in absorption and metabolism of the drug, optimum levels may vary and reach higher than 20 μg/mL (79.2 μmol/L) or they may fall below 10 μg/mL (39.6 μmol/L). Toxic signs are seldom seen below 15 μg/mL (59.4 μmol/L), while nystagmus often appears when serum levels rise above 20 μg/mL (79.2 μmol/L). Ataxia is observed most often when serum levels reach 25 to 30 μg/mL (99 to 119 μmol/L) and somnolence and dysarthria above 40 μg/mL (158 μmol/L). At high doses, phenytoin can even cause an increase in the frequency of seizures.

Units description

Micromole per literµmol/L = mcmol/L = umol/L = µM/L = mcM/L = uM/L = micromol/L
Milligram per litermg/L = millig/L = milligram/L = mg/liter
Milligram per decilitermg/dL = millig/dL = milligram/dL
Milligram per 100 millilitersmg/100mL = millig/100mL = milligram/100mL
Milligram percentmg% = millig% = milligram%
Microgram per milliliterµg/mL = mcg/mL = ug/mL= microg/mL = microgram/mL

Lab units Conversion Calculator. Convert Phenytoin level to µmol/L, mg/L, mg/dL, mg/100mL, mg%, µg/mL. Clinical laboratory units online conversion from conventional or traditional units to Si units. Table of conversion factors for Phenytoin.

Last updated: February 17, 2025

Created by: Dr. Rajesh Moganti

Reviewed by : Medical Review Board

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