Supplemental Digital Content is Available in the Text.This experimental highly controlled trial in 20 patients with fibromyalgia shows that the cannabinoid THC, but not CBD, is effective in the treatment of fibromyalgia pain.

The efficacy of the N-methyl-D-aspartate receptor antagonist ketamine as an analgesic agent is still under debate, especially for indications such as chronic pain. To understand the efficacy of ketamine for relief of pain, we performed a literature search for relevant narrative and systematic reviews and meta-analyses. We retrieved 189 unique articles, of which 29 were deemed appropriate for use in this review. Ketamine treatment is most effective for relief of postoperative pain, causing reduced opioid consumption. In contrast, for most other indications (that is, acute pain in the emergency department, prevention of persistent postoperative pain, cancer pain, and chronic non-cancer pain), the efficacy of ketamine is limited. Ketamine’s lack of analgesic effect was associated with an increase in side effects, including schizotypical effects.

Achieving successful treatment of postoperative pain remains a challenge. Recently, a sufentanil sublingual tablet system has been developed for treatment of moderate-to-severe postoperative pain. The phenylpiperidine sufentanil is a potent analgesic that rapidly crosses the blood-brain barrier and selectively activates central μ-opioid receptors. The system makes use of a hand-held dispenser system, which contains forty 15-μg sufentanil sublingual micro-tablets. The patient can release one tablet at 20-min intervals using a unique radiofrequency adhesive tag, which is wrapped around the patient's thumb. In this review, the authors discuss the pharmacology of sublingual sufentanil with reference to its suitability in the treatment of postoperative pain, the current evidence for the sublingual sufentanil system in postoperative pain treatment, and advantages and limitations of the sublingual system. We conclude that sufentanil is suited for the transmucosal route due to its pharmacokinetic profile, including rapid onset, absence of active metabolites and low tissue accumulation. The efficacy and safety of the sufentanil sublingual tablet system has been shown in over 600 patients in a limited set of studies; further independent studies are required to determine the position of the system among other forms of postoperative pain treatment. We conclude that the sublingual sufentanil tablet system allows effective pain relief, and allows patients to control their own pain relief and early postoperative mobility.

Ketamine is an N-methyl-D-aspartate receptor antagonist that at low-dose has effective analgesic properties. In cancer pain, ketamine is usually prescribed as adjuvant to opioid therapy when pain becomes opioid resistant or when neuropathic pain symptoms dominate the clinical picture. A literature search revealed four randomized controlled trials that examined the benefit of oral, subcutaneous or intravenous ketamine in opioid refractory cancer pain. None showed clinically relevant benefit in relieving pain or reducing opioid consumption. This suggests absence of evidence of benefit for ketamine as adjuvant analgesic in cancer pain. These findings contrast the benefit from ketamine observed in a large number of open-label studies and (retrospective) case series. We relate the opposite outcomes to methodological issues. The complete picture is such that there is still insufficient evidence to state with certainty that ketamine is not effective in cancer pain.

Background Tapentadol is a centrally acting analgesic with μ‐agonistic activity combined with noradrenaline reuptake inhibition. Its mechanism of action relies on improvement of descending pain inhibition. In the current study, tapentadol's ability to enhance conditioned pain modulation (CPM, an experimental measure of descending pain inhibition) was evaluated in fibromyalgia patients with absent or reduced CPM responses. Methods A total of 34 fibromyalgia patients completed this double‐blind trial. Patients were randomized to receive treatment with tapentadol sustained‐release or placebo for a 3‐month period with 1‐month follow‐up. At baseline, the cornea nerve fibre state (CNFS) was quantified to determine the presence of nerve fibre pathology and assess its value in the prediction of the analgesic response. Results Tapentadol significantly increased CPM responses during treatment with an average increase from baseline of 20.5 ± 12.5% (tapentadol) versus 3.0 ± 11.2% (placebo; p = 0.042). No treatment effect was observed for the absolute pain scores, however, analgesia responder rate analyses demonstrated a treatment effect in favour of tapentadol. Pain relief (a reduction in pain score ≥ 30%) was predicted by the presence of a normal CNFS (p = 0.035). Patients with an abnormal CNFS had no analgesic effect from tapentadol despite an increase in CPM. Conclusions In chronic pain patients with fibromyalgia, the increase in endogenous pain inhibition by tapentadol was translated into analgesia in patients with a normal CNFS. In those with abnormal CNFS, tapentadol treatment was without analgesic effect. Significance In this double‐blind randomized placebo‐controlled trial, we showed that tapentadol significantly enhanced the descending pain inhibition in fibromyalgia patients. Tapentadol‐induced pain relief was only present in patients with a normal CNFS.