Human Mitragynine and 7-Hydroxymitragynine Pharmacokinetics after Single and Multiple Daily Doses of Oral Encapsulated Dried Kratom Leaf Powder.

Kratom leaves, consumed by millions worldwide as tea or ground leaf powder, contain multiple alkaloids, with mitragynine being the most abundant and responsible for most effects. Mitragynine is a partial µ-opioid receptor agonist and competitive antagonist at κ- and δ-opioid receptors; however, unlike morphine, it does not activate the ß-arrestin-2 respiratory depression pathway. Due to few human mitragynine data, the largest randomized, between-subject, double-blind, placebo-controlled, dose-escalation study of 500-4000 mg dried kratom leaf powder (6.65-53.2 mg mitragynine) was conducted. LC-MS/MS mitragynine and 7-hydroxymitragynine plasma concentrations were obtained after single and 15 daily doses. Mitragynine and 7-hydroxymitragynine Cmax increased dose proportionally, and AUC was slightly more than dose proportional. The median mitragynine Tmax was 1.0-1.3 h after single and 1.0-1.7 h after multiple doses; for 7-hydroxymitragynine Tmax, it was 1.2-1.8 h and 1.3-2.0 h. Steady-state mitragynine concentrations were reached in 8-9 days and 7-hydroxymitragynine within 7 days. The highest mean mitragynine T1/2 was 43.4 h after one and 67.9 h after multiple doses, and, for 7-hydroxymitragynine, it was 4.7 and 24.7 h. The mean 7-hydroxy-mitragynine/mitragynine concentration ratios were 0.20-0.31 after a single dose and decreased (0.15-0.21) after multiple doses. These mitragynine and 7-hydroxymitragynine data provide guidance for future clinical kratom dosing studies and an interpretation of clinical and forensic mitragynine and 7-hydroxymitragynine concentrations.

Genome-wide association study of pain sensitivity assessed by questionnaire and the cold pressor test.

ABSTRACT: We deployed an online pain sensitivity questionnaire (PSQ) and an at-home version of the cold pressor test (CPT) in a large genotyped cohort. We performed genome-wide association studies on the PSQ score (25,321 participants) and CPT duration (6853). We identified one new genome-wide significant locus associated with the PSQ score, which was located in the TSSC1 (also known as EIPR1 ) gene (rs58194899, OR = 0.950 [0.933-0.967], P -value = 1.9 × 10 -8 ). Although high pain sensitivity measured by both PSQ and CPT was associated with individual history of chronic and acute pains, genetic correlation analyses surprisingly suggested an opposite direction: PSQ score was inversely genetically correlated with neck and shoulder pain ( rg = -0.71), rheumatoid arthritis (-0.68), and osteoarthritis (-0.38), and with known risk factors, such as the length of working week (-0.65), smoking (-0.36), or extreme BMI (-0.23). Gene-based analysis followed by pathway analysis showed that genome-wide association studies results were enriched for genes expressed in the brain and involved in neuronal development and glutamatergic synapse signaling pathways. Finally, we confirmed that females with red hair were more sensitive to pain and found that genetic variation in the MC1R gene was associated with an increase in self-perceived pain sensitivity as assessed by the PSQ.

Cebranopadol: A Novel, First-in-Class, Strong Analgesic: Results from a Randomized Phase IIa Clinical Trial in Postoperative Acute Pain.

BACKGROUND: Cebranopadol is a potent, first-in-class analgesic with a novel mechanistic approach combining nociceptin/orphanin FQ peptide (NOP) and opioid peptide receptor agonism. OBJECTIVE: We aim to evaluate, for the first time, the analgesic efficacy, safety, and tolerability of cebranopadol in patients suffering from moderate to severe acute pain following bunionectomy. STUDY DESIGN: We conducted a phase IIa, randomized, multi-center, double-blind, double-dummy, placebo- and active-controlled, parallel group clinical trial. METHODS: A total of 258 patients who underwent a primary bunionectomy were randomly assigned to receive a single oral administration of cebranopadol 200 µg, 400 µg, or 600 µg, morphine controlled-release (CR) 60 mg, or placebo. The primary efficacy end-point was the sum of pain intensity (SPI) 2 to 10 hours (SPI2-10) after the first investigational medicinal product (IMP) intake time-point. RESULTS: Cebranopadol doses of 400 µg and 600 µg were more effective in reducing postoperative acute pain compared to placebo, from 2 hours until approximately 22 hours after the first IMP intake time-point. No difference was observed between cebranopadol 200 µg and placebo. Per the subject global impression of the IMP assessment, patients who received cebranopadol 400 µg and 600 µg were more satisfied with the ability of the medication to treat their pain compared to those who received morphine CR 60 mg. On the primary end-point, the effect of morphine CR 60 mg was smaller than that of cebranopadol 400 µg and 600 µg. However, the analgesic effect of morphine CR 60 mg emerged later relative to IMP intake, as shown by the fact that similar SPI results as seen for cebranopadol 400 µg and 600 µg were obtained for later time windows. Cebranopadol treatment was safe, and single-dose administrations of 400 µg were better tolerated than morphine CR 60 mg. The relative frequency of patients with at least one treatment-emergent adverse event (TEAE) increased with increasing cebranopadol doses and was highest in the morphine CR 60 mg group. LIMITATION: Although a double-dummy design was used to ensure blinding, a limitation of this trial was that cebranopadol and morphine CR were administered at 2 different time-points post-surgery, given the anticipated difference in the time to reach the maximum plasma concentration between the 2 treatments. CONCLUSION: Administration of single cebranopadol doses of 400 µg and 600 µg induced more effective analgesia following bunionectomy surgery compared to the traditional opioid morphine on the primary end-point (SPI2-10), while both cebranopadol doses and morphine ensured adequate 24-hour pain relief. Moreover, cebranopadol was better tolerated and received a better overall rating by the patients. KEY WORDS: Opioids, morphine, µ-opioid receptor, nociceptin/orphanin FQ peptide receptor, analgesic, bunionectomy, surgery, post-operative pain, single hallux valgus repair.

Accurate pain reporting training diminishes the placebo response: Results from a randomised, double-blind, crossover trial.

Analgesic trials frequently fail to demonstrate efficacy of drugs known to be efficacious. Poor pain reporting accuracy is a possible source for this low essay-sensitivity. We report the effects of Accurate-Pain-Reporting-Training (APRT) on the placebo response in a trial of Pregabalin for painful-diabetic-neuropathy. The study was a two-stage randomized, double-blind trial: In Stage-1 (Training) subjects were randomized to APRT or No-Training. The APRT participants received feedback on the accuracy of their pain reports in response to mechanical stimuli, measured by R-square score. In Stage-2 (Evaluation) all subjects entered a placebo-controlled, cross-over trial. Primary (24-h average pain intensity) and secondary (current, 24-h worst, and 24-h walking pain intensity) outcome measures were reported. Fifty-one participants completed the study. APRT patients (n = 28) demonstrated significant (p = 0.036) increases in R-square scores. The APRT group demonstrated significantly (p = 0.018) lower placebo response (0.29 ± 1.21 vs. 1.48 ± 2.21, mean difference ± SD = -1.19±1.73). No relationships were found between the R-square scores and changes in pain intensity in the treatment arm. In summary, our training successfully increased pain reporting accuracy and resulted in a diminished placebo response. Theoretical and practical implications are discussed.

Respiratory Effects of the Nociceptin/Orphanin FQ Peptide and Opioid Receptor Agonist, Cebranopadol, in Healthy Human Volunteers.

BACKGROUND: Cebranopadol is a novel strong analgesic that coactivates the nociceptin/orphanin FQ receptor and classical opioid receptors. There are indications that activation of the nociceptin/orphanin FQ receptor is related to ceiling in respiratory depression. In this phase 1 clinical trial, we performed a pharmacokinetic-pharmacodynamic study to quantify cebranopadol's respiratory effects. METHODS: Twelve healthy male volunteers received 600 µg oral cebranopadol as a single dose. The following main endpoints were obtained at regular time intervals for 10 to 11 h after drug intake: ventilation at an elevated clamped end-tidal pressure of carbon dioxide, pain threshold and tolerance to a transcutaneous electrical stimulus train, and plasma cebranopadol concentrations. The data were analyzed using sigmoid Emax (respiration) and power (antinociception) models. RESULTS: Cebranopadol displayed typical opioid-like effects including miosis, analgesia, and respiratory depression. The blood-effect-site equilibration half-life for respiratory depression and analgesia was 1.2 ± 0.4 h (median ± standard error of the estimate) and 8.1 ± 2.5 h, respectively. The effect-site concentration causing 50% respiratory depression was 62 ± 4 pg/ml; the effect-site concentration causing 25% increase in currents to obtain pain threshold and tolerance was 97 ± 29 pg/ml. The model estimate for minimum ventilation was greater than zero at 4.9 ± 0.7 l/min (95% CI, 3.5 to 6.6 l/min). CONCLUSIONS: At the dose tested, cebranopadol produced respiratory depression with an estimate for minimum ventilation greater than 0 l/min. This is a major advantage over full µ-opioid receptor agonists that will produce apnea at high concentrations. Further clinical studies are needed to assess whether such behavior persists at higher doses.

Actual driving performance and psychomotor function in healthy subjects after acute and subchronic treatment with escitalopram, mirtazapine, and placebo: a crossover trial.

OBJECTIVE: The effects of escitalopram 10 to 20 mg/day and mirtazapine 30 to 45 mg/day on actual driving and psychomotor performance of 18 healthy subjects were determined in a randomized, double-blind, placebo-controlled, multiple-dose, 3-way crossover trial. METHOD: Each treatment period lasted for 15 days and was separated from the next period by a washout period of at least 13 days. Subjects received an evening dose of escitalopram 10 mg, mirtazapine 30 mg, or placebo from days 1 to 7 and an evening dose of escitalopram 20 mg, mirtazapine 45 mg, or placebo from days 8 to 15. On days 2, 9, and 16, reflecting acute period, dose increase, and steady state, respectively, the Road Tracking Test was performed. The main parameter was standard deviation of lateral position. Psychomotor performance was also assessed on days 2, 9, and 16 by laboratory computer tasks. Subjective sleep quality was measured with the Groninger Sleep Quality Scale, and mood was measured by visual analogue scales. RESULTS: Treatment differences were apparent during the acute treatment period, in which subjects treated with mirtazapine 30 mg performed less well on the driving test as compared to placebo. The Divided Attention Task results also revealed a significant increase in tracking error after a single dose of mirtazapine 30 mg as compared to placebo. Mirtazapine decreased feelings of alertness and contentedness. Mirtazapine did not affect performance on days 9 and 16 of treatment. Escitalopram did not affect driving, psychomotor performance, or subjective mood throughout treatment. CONCLUSION: Driving performance, as well as psychomotor functioning, was not affected by escitalopram treatment in healthy subjects. Driving performance was significantly impaired after ingestion of mirtazapine 30 mg during the acute treatment period.