A CBD–Clobazam Trial Could Not Clear Every Other Antiseizure Drug Interaction
A trial designed around CBD and clobazam did not establish that CBD lacks interactions with every other antiseizure medicine. The authors explicitly considered several additional drug comparisons too sparse for a reliable conclusion.
Twenty enrolled patients were not twenty complete PK comparisons
Adults with uncontrolled epilepsy who were already taking stable clobazam were randomized 4:1 to pharmaceutical CBD or placebo. CBD was titrated to 20 mg/kg/day, followed by a maintenance period. Plasma drug profiles were measured before CBD and near the end of treatment.
Seven of the twenty enrolled patients were excluded from the pharmacokinetic analysis for reasons including dosing problems, withdrawal or medication changes. The number contributing to a particular drug analysis was therefore smaller than the enrollment headline and depended on which medications were taken.
One informative comparison does not validate the entire regimen
The study found increased exposure to N-desmethylclobazam, clobazam’s active metabolite, while parent clobazam exposure was largely unchanged. It reported no effect on levetiracetam, but insufficient data for firm conclusions about other investigated antiseizure medicines, including valproate, stiripentol and topiramate.
An inadequately populated comparison is different from a demonstrated absence of interaction. A null result also needs to be interpreted within the tested dose, timing, population and confidence interval; it does not certify all combinations or all clinically relevant effects.
The direction of the experiment matters
Patients were already taking clobazam before CBD was introduced. The authors stated that this trial did not assess the effect of clobazam on CBD and its metabolites. Measuring both compounds during co-treatment does not, by itself, establish the reverse causal comparison.
The short trial was not designed to establish seizure efficacy or exposure-response relationships. Its pharmacokinetic contribution should be used within that scope. When reviewing a medication case, identify which interaction was actually tested, the relevant parent and metabolite measurements, the analyzable subgroup and the direction of treatment change. Absence of adequate data should remain visible in the opinion.
Related: the separate parent-clobazam and active-metabolite findings.
Primary research
A Phase 2, Double‐Blind, Placebo‐Controlled Trial to Investigate Potential Drug‐Drug Interactions Between Cannabidiol and Clobazam. DOI: 10.1002/jcph.1634.
