Antinociceptive effects of Ca²⁺ channel blockers

The antinociceptive action of four Ca²⁺ channel blockers, nifedipine, nimodipine, verapamil and diltiazem, was evaluated and compared to that of morphine using three algesiometric tests in mice and rats, namely, formalin, writhing and modified hot-plate test. Dose-response curves for all the drugs tested were similar and a significant dose-dependent antinociceptive action was evident in the formalin and writhing tests. However, in the hot-plate test, only nimodipine exhibited a significant analgesic effect, confirming the misleading results previously reported for this test. The findings suggest a pharmacological role of Ca²⁺ channel blockers in the modulation of antinociception under acute conditions. The analgesic action of Ca²⁺ channel blockers could be mediated by an increase in the nociceptive threshold resulting from interference with Ca²⁺ influx at opioid receptors, because Ca²⁺ influx is critical for the release of neurotransmitters and other substances implicated in nociception and inflammation. It is suggested that if a substance has a Ca²⁺ channel blocking effect, it should probably have some antinociceptive properties.