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Evaluating the efficacy and safety of calcium channel blockers as adjunctive analgesics to opioid therapy: a literature review

Calcium channel blockers have been postulated as opioid adjuncts, due to their complementary mechanism of action, which may reduce pain signal transduction. The purpose of this study was to conduct a literature review regarding the safety and efficacy of calcium channel blockers alongside opioids in pain management. From August 2020 to January 2021, PubMed, Scopus, and ProQuest were searched using the following terminology: calcium channel blocker OR verapamil OR diltiazem OR amlodipine OR nicardipine OR nimodipine OR nifedipine AND analgesia. Studies included were those with adult human subjects that had reported efficacy and safety outcomes for calcium channel blocker use as opioid adjuncts. Exclusion criteria for the analysis were articles including pregnant patients, those not readily translatable to English and those detailing the use of calcium channel blockers for an alternative diagnosis or indication. Ten studies were included in this review. Five were randomised controlled trials, one involving verapamil, one addressing diltiazem, one including nifedipine and three examining nimodipine. A sixth clinical trial involving verapamil, diltiazem and nimodipine was reviewed. The seventh and final clinical trial included nimodipine or nifedipine use during aorto‐coronary bypass surgery. One conclusive study addressed nimodipine’s use in cancer patients treated with morphine and the other nifedipine’s morphine adjunct potential postoperatively. Currently, there is insufficient data to support the use of calcium channel blockers as adjuncts to opioid therapy in pain management. When compared, the studies came to varying conclusions and demonstrated conflicting data indicating the need for more research regarding this topic.