Dravet Syndrome is a rare childhood epilepsy syndrome that is commonly associated with treatment-resistant epilepsy, despite best medical treatment. It is estimated that one in 15,700 children will be diagnosed with the condition, most of which will experience seizures in their first year of life. The focus for treatment is to reduce the frequency and severity of seizures and improve quality of life for both patients and their families.
Over the past decade, medical cannabis has gained increasing interest as a potential adjunct therapy for the treatment of certain forms of epilepsy. A number of patients have appeared in the media has seen an improvement in their condition following the addition of medical cannabis products to their treatment regime. In addition to anecdotal evidence, several studies have demonstrated the efficacy of medical cannabis products. However, these studies tended to involve short treatment periods and the long-term costs and outcomes of the therapy remain unclear.
A recent study by researchers in Canada aimed to assess the cost-effectiveness of a cannabinoid oil as an adjunct therapy in the treatment of treatment-resistant epilepsy in Dravet Syndrome. The study aimed to assess the cost vs. quality of life provided by a cannabinoid oil and stiripentol when administered alongside existing medications – clobazam and valproate. This is in addition to continuing clobazam and valproate on its own.
The Cost-Effectiveness of Medical Cannabis Products in the Treatment of Dravet Syndrome
On 1st November 2018, medical cannabis was rescheduled within the UK following a report from the then Chief Medical Officer, Dame Sally Davies. In 2019, the National Institute of Health and Care Excellence (NICE) subsequently recommended that a specific cannabinoid, called cannabidiol (CBD), be considered in conjunction with clobazam for treatment-resistant epilepsy for Dravet Syndrome and another childhood epilepsy syndrome (Lennox-Gastaut). Other cannabis-based medicinal products, including tetrahydrocannabinol (THC), are not recommended or licensed, for this use in the UK.
For their review, the researchers assessed the use of a mixed cannabinoid oil (20:1 CBD:THC) as adjunct therapy alongside clobazam and valproate. The study was based on the Canadian healthcare system and economic model, which permits the use of this cannabinoid formulation.
In order to determine the cost-effectiveness of the product, the cost was compared with Quality-Adjusted Life Years (QALYs) in patients aged between 5 and 18 years. QALYs are commonly used in economic assessments as a generic assessment of health status, where one QALY is equivalent to one year in perfect health. Background treatment of clobazam and valproate with an adjunct therapy of cannabinoid oil was compared with clobazam and valproate alone, and with adjunctive stiripentol.
The clinical effectiveness of each adjunct therapy was determined through the assessment of existing systematic reviews, however, only one study was available for this specific cannabis-based medicine. Reduction in seizures as well as prolongation of life was used to assess the QALYs gained through the treatment options.
The ability of the various treatment options to reduce the frequency of seizures was used to determine estimated QALYs expected to be experienced over a 13-year horizon period (when the cohort would be considered adults). Following the collection of this data, both costs and QALYs were discounted at a rate of 1.5% per year in line with Canadian guidelines.
The Results
The researchers determined that the cost of cannabinoid oil was significantly higher than the cost of clobazam and valproate alone ($275,434 CAD vs. $130,165 CAD). However, it proved to be less costly than adjunctive stiripentol (CA$292,487).
In addition, cannabinoid oil was found to be the most effective treatment in the provision of excess QALYs (15.12). In comparison, stiripentol was calculated to provide 13.37 QALYs and clobazam and valproate alone, 10.64 QALYs. In this study adding 20:1 CBD/THC oil to a clobazam and valproate regimen provided a greater improvement in health status in the average patient with Dravet and treatment-resistant epilepsy than either stiripentol or continuing on their present regime. The cost-effectiveness of this regimen was $32,399 CAD per QALY gained, which is equivalent to £19,018 per QALY gained. This is below the threshold used by NICE, however, the study is not directly translatable to the UK as the modeling was based on models used within the Canadian health system.
This is certainly promising research to support adjunctive therapy with a CBD/THC for treatment-resistant epilepsy, particularly in Dravet syndrome. However, it is important to note that this study has significant drawbacks. The modeling of outcomes was based on only one study for this particular oil and did not account for any adverse events between any group, where we know from studies that those on cannabis-based medicines suffer from increased adverse events when this is added on top of their other medications. There are also still unknowns about the long-term effects of THC on the developing brain. As such further research is necessary to really define the ultimate role cannabis-based medicines will have in childhood epilepsy.
