Coadjuvant analgesics for cancer pain: using the clinical queries PubMed tool.

Coadjuvants for cancer pain are medications that, when added to opioids, can potentially decrease narcotic request and opioid-related side effects. Our goal was to review not only the evidence that supports the effectiveness, but also the mechanisms of action of these drugs. We performed a qualitative review using the PubMed database applying the clinical queries tool to identify therapeutic clinical trials or systematic reviews evaluating cancer pain--oral or transdermal--analgesia. We excluded studies using anti-inflammatories, steroids or narcotics as primary analgesia and studies focused on perioperative cancer pain. We supplemented the information describing the mechanisms of action and suggested dosage schemes. We found a qualitative systematic review evaluating ketamine, and randomized trials supporting the use of amitriptyline, gabapentin and transdermal nitroglycerin. We also found some negative trials using gabapentin and lamotrigine for neuropathic pain secondary to chemotherapy. Weak evidence supports intravenous magnesium and lidocaine for breakthrough cancer pain. Further primary research based on clinical trials is required to support some adjuvant analgesics for cancer pain.