A drug concentration can fall during plasma exchange, but the clinical consequence requires separate evidence.
The case involved a twenty-seven-year-old man with new-onset refractory status epilepticus receiving several antiseizure drugs. Concentrations were monitored around two plasma-exchange sessions. Clobazam fell to approximately eighty-five percent of baseline during treatment and seventy-five percent afterward; levetiracetam and topiramate also decreased.
This was one patient with severe illness and concurrent medicines. The observations do not establish a universal removal fraction or an automatic need for replacement dosing. A fall to seventy-five percent of baseline is a twenty-five-percent reduction, not removal of seventy-five percent of the drug.
For reconstructing exposure, preserve the timing of sampling, exchange, fluid replacement and drug administration. Consider redistribution and metabolite measurements. The report supports attention to extracorporeal treatment as a changing pharmacokinetic condition, while leaving the relationship between that concentration change and any individual seizure to clinical and EEG evidence.
Source reviewed: Effect of plasmapheresis on serum levels of clobazam levetiracetam and topiramate (PMC5607118). Forensic applications above are interpretive analysis of the supplied publication.
Related reading: A Synthetic Cannabinoid Enhanced Clonazepam but Not Clobazam in One Mouse Seizure Model.