CBD in Dravet Syndrome: An Unchanged Clobazam Level Can Conceal a Metabolite Interaction
A stable clobazam concentration does not exclude an interaction with CBD. A small dose-ranging Dravet study found increased exposure to clobazam’s active metabolite even when parent clobazam exposure showed no relevant change.
A safety and pharmacokinetic study
Thirty-four children were randomized to placebo or CBD at target daily doses of 5, 10 or 20 mg/kg. The study measured plasma CBD, metabolites and selected concomitant antiseizure medicines, alongside safety assessments.
Many participants were taking clobazam or valproate. This was a short, small dose-ranging trial; it was not designed to supply a precise interaction estimate for every treatment combination.
Parent and metabolite results differed
Among participants with relevant end-of-treatment data, parent clobazam exposure did not show a relevant change, while mean N-desmethylclobazam concentrations increased substantially. That metabolite is pharmacologically active, making a parent-only measurement incomplete for the interaction question.
CBD and its metabolites also did not circulate at equal concentrations. The carboxy-CBD metabolite was particularly abundant. A laboratory report should identify each compound rather than treating all cannabinoid-related material as parent CBD.
Descriptive findings are not formal significance tests
The investigators summarized pharmacokinetic and safety data descriptively; no formal statistical comparisons were planned or performed. Reported concentration increases should therefore be described as observed changes, rather than assigned an invented p value.
Some liver-enzyme elevations and other adverse events occurred, including a withdrawal for marked transaminase elevation. Concomitant treatment and small group sizes constrain attribution. The study does not establish that every CBD recipient develops liver injury.
Implications for reviewing a medication case
Record the full regimen, titration, sampling time and both parent and relevant metabolite measurements. This evidence explains why “the other drug level did not rise” may be an incomplete answer. It does not provide a stand-alone dose adjustment or prove that a particular adverse event was caused by an interaction.
For context, see our discussion of THC concentrations and the separate question of impairment.
Primary research
Orrin Devinsky and colleagues. Randomized, dose-ranging safety trial of cannabidiol in Dravet syndrome. Neurology (2018). DOI: 10.1212/WNL.0000000000005254.
