Phenobarbital is one of the most commonly used drugs for the treatment of grand mal, psychomotor epilepsy, and other forms of focal epilepsy. Monitoring of the serum level of the drug is essential in order to achieve maximal seizure control while maintaining minimal blood levels to avoid negative side effects. Measurements obtained by this device are used in the diagnosis and treatment of phenobarbital use or overdose and in monitoring levels of phenobarbital. As with other anti‑convulsant drugs, it is imperative that each patient’s dosage be individualized.
The therapeutic range of phenobarbital is correlated with seizure control as well as the absence of toxic effects, and is generally accepted to be between 10 and 30 μg/mL (43.1 and 129 μmol/L). Variation in metabolism and absorption of the drug may cause levels to rise above 40 μg/mL (172 μmol/L) or fall below 15 μg/mL (64.7 μmol/L). The most frequent dose‑related side effect is sedation, to which a tolerance usually develops. Phenobarbital serum levels above 40 μg/mL (172 μmol/L) are often associated with nystagmus, ataxia, and dysarthria. At high doses, phenobarbital can even cause an increase in seizure frequency.
| Micromole per liter | µmol/L = mcmol/L = umol/L = µM/L = mcM/L = uM/L = micromol/L |
| Milligram per liter | mg/L = millig/L = milligram/L = mg/liter |
| Milligram per deciliter | mg/dL = millig/dL = milligram/dL |
| Milligram per 100 milliliters | mg/100mL = millig/100mL = milligram/100mL |
| Milligram percent | mg% = millig% = milligram% |
| Microgram per milliliter | µg/mL = mcg/mL = ug/mL = microg/mL = microgram/mL |