Large-dose oral dextromethorphan as an adjunct to patient-controlled analgesia with morphine after knee surgery

Mechanisms of the antiplatelet and analgesic effects of dextromethorphan and its metabolites

Objective

In the present study, we investigated the effects of dextromethorphan (DM) and its metabolites, including dextrorphan (LK2), 3-methoxymorphinan (LK3), and 3-hydroxymorphinan (LK4), on platelet aggregation in vitro and the inflammatory pain caused by carrageenan in rats, and their underlying mechanisms.

Materials and Methods

Rabbit platelets were pretreated with DM or its metabolites to assess their effects on platelet aggregation and related target mediators. In addition, the analgesic activity and the underlying mechanisms of DM and LK3 were investigated in a carrageenan-evoked thermal hyperalgesia rat model.

Results

The inhibitory potency of DM and its metabolites on platelet aggregation induced by arachidonic acid or collagen was LK3> DM > LK4>> LK2 as demonstrated by the half-maximal inhibitory concentration values. Moreover, the mechanisms of the antiplatelet effect of DM and LK3 may involve the inhibition of intracellular calcium mobilization, expression of platelet surface glycoprotein IIb/IIIa, the formation of thromboxane B2, and elevation of platelet membrane fluidity. DM and LK3 also exhibited analgesic effects on carrageenan-evoked thermal hyperalgesia by suppressing the production of pro-inflammatory cytokines, nitric oxide, prostaglandin E2, and neutrophil infiltration in inflammatory sites.

Conclusion

DM and its metabolites, especially LK3, exhibit both antiplatelet and analgesic effects, and may, therefore, potentially ameliorate platelet hyperactivity and inflammatory-related diseases.

Perioperative Dextromethorphan as an Adjunct for Postoperative Pain: A Meta-analysis of Randomized Controlled Trials

BACKGROUND

N-methyl-D-aspartate receptor antagonists have been shown to reduce perioperative pain and opioid use. The authors performed a meta-analysis to determine whether the use of perioperative dextromethorphan lowers opioid consumption or pain scores.

METHODS

PubMed, Web of Science, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, Pubget, and EMBASE were searched. Studies were included if they were randomized, double-blinded, placebo-controlled trials written in English, and performed on patients 12 yr or older. For comparison of opioid use, included studies tracked total consumption of IV or intramuscular opioids over 24 to 48 h. Pain score comparisons were performed at 1, 4 to 6, and 24 h postoperatively. Difference in means (MD) was used for effect size.

RESULTS

Forty studies were identified and 21 were eligible for one or more comparisons. In 848 patients from 14 trials, opioid consumption favored dextromethorphan (MD, -10.51 mg IV morphine equivalents; 95% CI, -16.48 to -4.53 mg; P = 0.0006). In 884 patients from 13 trials, pain at 1 h favored dextromethorphan (MD, -1.60; 95% CI, -1.89 to -1.31; P < 0.00001). In 950 patients from 13 trials, pain at 4 to 6 h favored dextromethorphan (MD, -0.89; 95% CI, -1.11 to -0.66; P < 0.00001). In 797 patients from 12 trials, pain at 24 h favored dextromethorphan (MD, -0.92; 95% CI, -1.24 to -0.60; P < 0.00001).

CONCLUSION

This meta-analysis suggests that dextromethorphan use perioperatively reduces the postoperative opioid consumption at 24 to 48 h and pain scores at 1, 4 to 6, and 24 h.

Selective antinociceptive effects of a combination of the N-methyl-D-aspartate receptor peptide antagonist [Ser(1)]histogranin and morphine in rat models of pain

Numerous rather than a few analgesic endogenous neuropeptides are likely to work in concert in vivo in ameliorating pain. Identification of effective neuropeptide combinations would also facilitate the development of gene or cell-based analgesics. In this study, opioid peptides endomorphin-1 (EM-1) and endomorphin-2 (EM-2) and the peptide histogranin analogue [Ser¹]histogranin (SHG), which possess activity as an N-methyl-d-aspartate (NMDA) receptor antagonist, were intrathecally (i.t.) injected alone and in combination in rat models of acute and persistent pain. None of the peptides when injected alone altered hind paw responses of uninjured rats to acute noxious stimulation. EM-1 and EM-2 showed divergent efficacies in the persistent pain models. For example, EM-1 injected alone was antinociceptive in rats with neuropathic pain, whereas EM-2 demonstrated no efficacy. Demonstration of synergism was also divergent across the models. For example, while SHG combined with EM-1 did not alter the efficacy of EM-1 in rats with neuropathic pain, SHG significantly increased the efficacy of EM-1 in the formalin test. By contrast, the potency and efficacy of the peptides alone and combinations were much less than those of the reference analgesic morphine. Furthermore, morphine combined with the clinically used NMDA receptor antagonist ketamine showed synergism across a broad range of pain states. While the current set of neuropeptides could serve as a basis for analgesic therapeutics, there could be other neuropeptides with greater efficacy and potency and broader therapeutic application.

Morphine and MK-801 administration leads to alternative N-methyl-D-aspartate receptor 1 splicing and associated changes in reward seeking behavior and nociception on an operant orofacial assay

The NMDA receptor plays a large role in opioid-induced plastic changes in the nervous system. The expression levels of its NR1 subunit are altered dramatically by morphine but no changes in its alternative splicing have been reported. Changes in the splicing of the N1, C1, C2, and C2' cassettes can alter the pharmacology and regulation of this receptor. Western Blots run on brain tissue from rats made tolerant to morphine revealed altered splicing of the N1 cassettes in the accumbens and amygdala (AMY), and the C1 cassette in the AMY and the dorsal hippocampus (HIPP). After 3days of withdrawal C2'-containing NR1 subunits were down-regulated in each of these areas. These were not due to acute doses of morphine and may represent long-term alterations in drug-induced neuroplasticity. We also examined the effects of morphine tolerance on an operant orofacial nociception assay which forces an animal to endure an aversive heat stimulus in order to receive a sweet milk reward. Morphine decreased pain sensitivity as expected but also increased motivational reward seeking in this task. NMDAR antagonism potentiated this reward seeking behavior suggesting that instead of attenuating tolerance, MK-801 may actually alter the rewarding and/or motivational properties of morphine. When combined, MK-801 and morphine had an additive effect which led to altered splicing in the accumbens, AMY, and the HIPP. In conclusion, NR1 splicing may play a major role in the cognitive behavioral aspects especially in motivational reward-seeking behaviors.

Preoperative oral dextromethorphan does not reduce pain or morphine consumption after open cholecystectomy

BACKGROUND

Dextromethorphan, the D-isomer of the codeine analog levorphanol, is a weak, noncompetitive N-Methyl-D-Aspartate (NMDA) receptor antagonist. It has been suggested that NMDA receptor antagonists induce preemptive analgesia when administered before tissue injury occurs, thus decreasing the subsequent sensation of pain.

MATERIALS AND METHODS

The study was conducted in the Dr. Ali Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran, between February 2005 and December 2006. In this study, 72 patients scheduled for elective cholesyctectomy were randomized into three groups to receive either oral dextromethorphan 45 mg (Group D45 = 24), dextromethorphan 90 mg (Group D90 = 24), or placebo (Group C, n = 24), as premedication, 120 minutes before surgery. A visual analog scale (VAS) for pain of each patient was measured at arrival in the ward and six and 24 hours after surgery.

RESULTS

The demographic characteristics of patients, ASA physical status class, duration of surgery, and the basal VAS pain score were similar in the two groups. There was no significant difference in the mean of the VAS pain scores measured over time or morphine consumption among the three groups.

CONCLUSION

Dextromethorphan 45 mg and 90 mg, administrated orally, two hours before surgery, had no effect on postoperative morphine requirement and pain intensity.

Translational pain research: achievements and challenges

The achievements in both preclinical and clinical pain research over the past 4 decades have led to significant progress in clinical pain management. However, pain research still faces enormous challenges and there remain many obstacles in the treatment of clinical pain, particularly chronic pain. Translational pain research needs to involve a number of important areas including: 1) bridging the gap between pain research and clinical pain management; 2) developing objective pain-assessment tools; 3) analyzing current theories of pain mechanisms and their relevance to clinical pain; 4) exploring new tools for both preclinical and clinical pain research; and 5) coordinating research efforts among basic scientists, clinical investigators, and pain-medicine practitioners. These issues are discussed in this article in light of the achievements and challenges of translational pain research.

PERSPECTIVE

The subjective nature of clinical pain calls for innovative research approaches. As translational pain research emerges as an important field in pain medicine, it will play a unique role in improving clinical pain management through coordinated bidirectional research approaches between bedside and bench.

[Increased sensitivity to pain in long-term opioid treatment]

Recent years have seen a rise in the prescription of strong opioids for chronic and even subthreshold forms of pain. Animal and human experiments and clinical observations have shown that, compared to placebos, chronic opioid administration results in not only tolerance to its analgesic effects but also in heightened pain sensitivity. Therefore chronic, especially high-dose, opioid treatment can not be recommended for chronic pain but is instead contraindicated. Patients on long-term opioids will often reject proposals to withdraw the drug. Important elements of treatment are patient education, empathy and unconditional acceptance by the patient, motivation enhancement and psychological support, collaboration with other prescribers and therapists, detoxification, measures to increase pain tolerance, encouragement of general health behavior and salutotherapy, treatment of the primary illness, and prescription of participation oriented alternative analgesics.

Efficacy of pre- and postoperative oral dextromethorphan for reduction of intra- and 24-hour postoperative morphine consumption for transabdominal hysterectomy

OBJECTIVE

We studied the effect of dextromethorphan (DEX), an N-methyl-D-aspartate receptor antagonist, on analgesic consumption and pain scores after abdominal hysterectomy. We aimed to compare the analgesic effectiveness and incidence of adverse side effects of oral DEX with placebo (P).

DESIGN

This was a double-blinded, randomized, placebo-controlled study.

SETTING AND PATIENTS

One hundred patients were randomized to two groups. Group DEX was given 30-mg tablets of oral DEX with their premedication and three more times in the first 24 hours after surgery. Group P received the placebo following the same schedule. Postoperative analgesic requirements were assessed using a patient-controlled analgesia system. Pain was assessed at rest using a visual analogue scale in the post-anesthetic care unit (PACU), 6 and 24 hours after surgery.

RESULTS

Mean pain scores were significantly lower at the PACU (62.6 vs 75.7) as was the mean sum of all resting pain scores (144.5 vs 173.1). Mean morphine consumption was greatest in the DEX group (35.1 vs 33.0 mg; P < 0.05). The sedation scores, postoperative analgesic requirements, and incidence of side effects were similar between the P and DEX groups as were the mean pain scores.

CONCLUSIONS

During PACU, however, there were two differences between the DEX and placebo groups: 1) a lower pain score at PACU; and 2) a prolonged time to the first use of morphine at PACU in the DEX group as compared with the placebo group. A low-dose DEX had a weaker though still measurable effect in this clinical trial compared with trials using higher doses.

Dextromethorphan potentiates the antinociceptive effects of morphine and the delta-opioid agonist SNC80 in squirrel monkeys

Dextromethorphan (DXM) is a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist shown to prevent the development of tolerance to the antinociceptive effects of morphine in rodents. DXM also potentiates the antinociceptive effects of the mu-opioid receptor agonist morphine under some conditions; however, the effect of DXM in combination with opioids other than morphine has not been well characterized. This study determined the antinociceptive effects of DXM administered alone or in combination with morphine or the delta-opioid receptor (DOR) agonist SNC80 using a squirrel monkey titration procedure. In this procedure, shock (delivered to the tail) increases in intensity every 15 s (0.01-2.0 mA) in 30 increments. Five lever presses during any given 15-s shock period produces a 15-s shock-free period after which shock resumes at the next lower intensity. This assay provides a measure of antinociception that is separable from motor effects [response rate (RR)]. Morphine (0.3-3.0 mg/kg i.m.) and SNC80 (1.0-10 mg/kg i.m.), but not DXM (1.0-10 mg/kg i.m.) dose- and time-dependently increased the intensity below which monkeys (n = 4) maintained shock 50% of the time [median shock level (MSL)]. Doses of morphine and SNC80 that alone did not increase MSL were potentiated by DXM. Importantly, these combinations did not significantly alter RR. These data support previous findings with other NMDA receptor antagonists and morphine using this procedure and also extend those findings to a DOR agonist.

Pain management in the opioid-dependent patient

The opioid-dependent patient presents great challenges for pain management. These challenges are not limited to potential addictive behaviors. In contrast to the profound pain relieving effects of acute opioid intake, chronic opioid intake can promote a counterintuitive state of enhanced pain sensitivity. Multiple biologic mechanisms inducing opioid tolerance and hyperalgesia have recently been elucidated. The potential hyperalgesic state accompanying opioid dependence complicates pain management somewhat for acute pain and cancer pain, but it especially does so for chronic pain. Guidelines for treatment of opioid dependence in the pain patient are proposed. Treatment oriented toward the long term requires limit setting and psychologic support that go beyond simple medication management.