Interaction between Heliopsis longipes extract and diclofenac on the thermal hyperalgesia test

Heliopsis longipes is an herbaceous plant found in Mexico, used traditionally for its analgesic and anesthetic activities. Plant extracts in combined use with synthetic drugs may represent a therapeutic advantage for the clinical treatment of pain, allowing the use of lower doses, and limiting side-effects. Therefore, the main objective of this study was to determine the possible pharmacological interaction between Heliopsis longipes ethanolic extract (HLEE) and diclofenac in the Hargreaves model of thermal hyperalgesia in the mouse. HLEE, diclofenac or fixed-dose ratio HLEE–diclofenac combinations were administered systemically to mice and the antihyperalgesic effect was evaluated using the thermal hyperalgesia test. All treatments produced a dose-dependent antihyperalgesic effect. ED 30 values were estimated for all the treatments and an isobologram was constructed. The derived theoretical ED 30 value for the HLEE–diclofenac combination was 54.4±9.4 mg/kg body wt, significantly higher than the actually observed experimental ED 30 value, 8.6±4.0 mg/kg body wt. This result corresponds to synergistic interaction between HLEE and diclofenac in the Hargreaves model of thermal hyperalgesia. Data suggest that low doses of the HLEE–diclofenac combination can interact synergistically at the systemic level and that this association may therefore represent a therapeutic advantage for the clinical treatment of inflammatory pain.