A percentage expressed relative to baseline can be easy to misread. In a plasma-exchange case, a clobazam result of 75% of baseline describes a concentration about 25% below baseline.
The report followed a patient with refractory status epilepticus through two exchange sessions. In one session, total serum clobazam fell from 2.00 to 1.50 mg/L after the procedure. Levetiracetam and topiramate concentrations also fell relative to their pre-exchange samples. The laboratory measured total concentrations rather than free fractions.
A serum decrease does not establish the proportion of the body’s drug removed. Distribution, collection time and intervening doses can influence the result. The paper illustrates why a review needs the actual concentrations, sampling times and administration record alongside a reported percentage.
Effect of Plasmapheresis on Antiseizure Drug Levels, Epilepsy & Behavior Case Reports · Full text