Stability characteristics of cannabidiol for the design of pharmacological, biochemical and pharmaceutical studies.

Cannabidiol (CBD) is one of the most promising cannabinoids in therapeutics. Nevertheless, the reported stability testing has been carried out with plant extracts and not with CBD as a drug substance. The aim of this work was to evaluate the stability of CBD in solution. A High-Performance Liquid Chromatography (HPLC) analytical method, with CBD in ethanol, was previously validated for these stability studies. The resulting method was linear and proportional in a range of concentrations from 1 to 150 µg CBD/mL, as well as precise. It was also considered suitable to quantify CBD in aqueous medium as reported in accuracy studies. The stability of CBD was influenced by multiple factors. Temperature was one of the most critical parameters, with an activation energy of 92.19KJ/mol. At room temperature, CBD was highly unstable (t = 117.13 days). However, at 5 °C it was stable for at least 12 months. CBD was also sensitive to oxidation, with a short t of 1.77 days in oxidizing environments, as well as to light. The photolytic reaction seems to be oxidative. The solvent influences CBD stability, and the latter is more stable in ethanol than in aqueous medium. In fact, in simulated physiological conditions (pH 7.4 and 37 °C) 10% of CBD was degraded within 24 h. These studies indicate that CBD is highly unstable, and this should be taken into account in the development of in vitro and in vivo studies of CBD activity and in the pharmaceutical development of dosage forms.