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Cannabidiol (CBD), a phytocannabinoid compound of Cannabis sativa, shows limited oral bioavailability due to its lipophilicity and extensive first-pass metabolism. CBD is also known for its high intra- and inter-subject absorption variability in humans. To overcome these limitations a novel self-emulsifying drug delivery system (SEDDS) based on VESIsorb® formulation technology incorporating CBD, as Hemp-Extract, was developed (SEDDS-CBD). The study objective was to evaluate the pharmacokinetic profile of SEDDS-CBD in a randomized, double-blind, cross-over design in 16 healthy volunteers under fasted conditions. As reference formulation, the same Hemp-Extract diluted with medium-chain triglycerides (MCT-CBD) was used. CBD dose was standardized to 25 mg. Pharmacokinetic parameters were analyzed from individual concentration-time curves. Single oral administration of SEDDS-CBD led to a 4.4-fold higher Cmax and a 2.85-/1.70-fold higher AUC0–8h/AUC0–24h compared to the reference formulation. Tmax was substantially shorter for SEDDS-CBD (1.0 h) compared to MCT-CBD (3.0 h). Subgroup analysis demonstrated a higher bioavailability in women compared to men. This difference was seen for MCT-CBD while SEDDS-CBD mitigated this gender effect. Overall, SEDDS-CBD showed a significant improvement for all determined pharmacokinetic parameters: increased CBD plasma values (Cmax), favorably enhanced bioavailability (AUC) and fast absorption (Tmax). No safety concerns were noted following either administration.

PurposeCombination therapy of pregabalin and tramadol is used to treat chronic neuropathic pain; however, the pharmacokinetic (PK) interactions of these drugs has not been studied. This study aimed to evaluate PK interactions between pregabalin and tramadol and the safety of combination therapy.MethodsA randomized, open-label, multiple-dose, three-treatment, three-period, six-sequence cross-over study was conducted in healthy subjects. All subjects received the following three treatments for 4 days in each period: pregabalin 150 mg twice daily; tramadol extended-release (ER) 200 mg in the morning, and 100 mg in the evening; and co-administration of pregabalin 150 mg and tramadol ER 200 mg in the morning, and pregabalin 150 mg and tramadol ER 100 mg in the evening.ResultsA total of 21 subjects completed the study with no clinically significant safety issues. For pregabalin, the geometric mean ratio (GMR) (90% CI; confidence interval) of combination therapy to monotherapy for maximum concentration at steady state (Cmax,ss) and area under the concentration curve from 0 to dosing interval time at steady state (AUCτ,ss) were 0.8801 (0.8043–0.9632) and 1.0830 (1.0569–1.1098), respectively. The corresponding values for tramadol were 1.0177 (0.9839–1.0526) and 1.0152 (0.9896–1.0414), respectively. The GMR (90% CI) of combination therapy to monotherapy of O-desmethyl-tramadol for Cmax,ss and AUCτ,ss was 1.0465 (1.0095–1.0848) and 1.0361 (1.0001–1.0734), respectively.ConclusionsThere were no significant drug interactions between pregabalin and tramadol, considering that all of the 90% CI of PK measures were within the conventional bioequivalence range. Both drugs were well tolerated when administered concomitantly.

Background and Objective Several features favor paracetamol (acetaminophen) administration by the intravenous rather than the oral route in the postoperative setting. This study compared the pharmacokinetics and bioavailability of oral and intravenous paracetamol when given with or without an opioid, morphine. Methods In this randomized, single-blind, parallel, repeat-dose study in healthy adults, subjects received four repeat doses of oral or intravenous 1000 mg paracetamol at 6-h intervals, and morphine infusions (0.125 mg/kg) at the 2nd and 3rd intervals. Comparisons of plasma pharmacokinetic profiles were conducted before, during, and after opioid co-administrations. Results Twenty-two subjects were included in the pharmacokinetic analysis. Observed paracetamol peak concentration ( C max ) and area under the plasma concentration-time curve over the dosing interval (AUC 0–6 ) were reduced when oral paracetamol was co-administered with morphine (reduced from 11.6 to 7.25 µg/mL and from 31.00 to 25.51 µg·h/mL, respectively), followed by an abruptly increased C max and AUC 0–6 upon discontinuation of morphine (to 13.5 µg/mL and 52.38 µg·h/mL, respectively). There was also a significantly prolonged mean time to peak plasma concentration ( T max ) after the 4th dose of oral paracetamol (2.84 h) compared to the 1st dose (1.48 h). However, pharmacokinetic parameters of paracetamol were not impacted when intravenous paracetamol was co-administered with morphine. Conclusions Morphine co-administration significantly impacted the pharmacokinetics of oral but not intravenous paracetamol. The abrupt release of accumulated paracetamol at the end of morphine-mediated gastrointestinal inhibition following oral but not intravenous administration of paracetamol suggests that intravenous paracetamol provides a better option for the management of postoperative pain. ClinicalTrials.gov Identifier NCT02848729.

Purpose Low-dose ketamine is a lucrative therapeutic approach in cancer pain, perioperative treatment of pain, and management of treatment-resistant depression. The analgesic potency of its main metabolite norketamine is thought to be one third that of ketamine. However, few studies exist on the pharmacokinetics of orally administered S -ketamine. Methods In our study, 11 healthy volunteers received S -ketamine 0.25 mg/kg orally and 0.125 mg/kg intravenously. S -ketamine and norketamine concentrations were measured up to 23.5 h post-dose. A population pharmacokinetic model was built to describe S -ketamine and norketamine pharmacokinetics. Results A three-compartment model for both S -ketamine and norketamine best described the data. To accommodate for the extensive formation of norketamine after oral S -ketamine, a separate presystemic absorption-phase component was included in addition to its systemic formation. The oral bioavailability of S -ketamine was low, 8 % (11 % interindividual variability), and its clearance was high, 95 L/h/70 kg (13 % interindividual variability). Simulations suggested that after oral dosing, norketamine AUC at steady state is 16.5 times higher than that of S -ketamine. Conclusions Given that the analgesic effect of S -ketamine is due to both S -ketamine and norketamine, relatively small oral doses of S -ketamine can be assumed to be a feasible alternative to repeated intravenous dosing, for example in the setting of chronic pain.

The pharmacokinetics and pharmacodynamics of drugs are significantly altered in the burn patient, and the burn patient population shows wide inter- and intraindividual variation in drug handling. Burn injury evolves in two phases. The first phase corresponds to the burn shock, which occurs during the first 48 hours after thermal injury. In this phase, hypovolaemia, oedema, hypoalbuminaemia and a low glomerular filtration rate are observed, which result in a slower rate of drug distribution and lower renal clearance. The second phase (beyond 48 hours after injury) is a hyperdynamic state with high blood flow in the kidneys and liver, an increased α 1 -acid-glycoprotein level and loss of the drug with exudate leakage. As a result, protein binding, drug distribution and clearance may be altered. Because of the alteration in these variables, wide intraindividual variation of pharmacokinetic parameters occurs depending upon the time since thermal injury and fluid resuscitation. Interindividual variations may be correlated with the percentage of the body surface area that is burnt, creatinine clearance, albuminaemia or the α 1 -acid-glycoprotein level. A number of important variations in pharmacodynamic parameters have been described, but their mechanisms are poorly understood. From a practical point of view, for the subpopulation of burn patients who eliminate drugs extremely rapidly, higher doses and/or shorter dosing intervals are required to avoid treatment inefficacy. Drug concentration measurements help to take into account interindividual variability. However, adaptation of doses based on Bayesian methods is frequently not possible because the distribution of pharmacokinetic parameters is poorly characterized in this population. Methods based only on individual data or on a surrogate marker for efficacy may be used to optimize the dosing regimen in this population.

The discovery that paracetamol is metabolized to the potent TRPV1 activator N-(4-hydroxyphenyl)-5Z,8Z,11Z,14Z-eicosatetraenamide (AM404) and that this metabolite contributes to paracetamol's antinociceptive effect in rodents via activation of TRPV1 in the central nervous system (CNS) has provided a potential strategy for developing novel analgesics. Here we validated this strategy by examining the metabolism and antinociceptive activity of the de-acetylated paracetamol metabolite 4-aminophenol and 4-hydroxy-3-methoxybenzylamine (HMBA), both of which may undergo a fatty acid amide hydrolase (FAAH)-dependent biotransformation to potent TRPV1 activators in the brain. Systemic administration of 4-aminophenol and HMBA led to a dose-dependent formation of AM404 plus N-(4-hydroxyphenyl)-9Z-octadecenamide (HPODA) and arvanil plus olvanil in the mouse brain, respectively. The order of potency of these lipid metabolites as TRPV1 activators was arvanil = olvanil>>AM404> HPODA. Both 4-aminophenol and HMBA displayed antinociceptive activity in various rodent pain tests. The formation of AM404, arvanil and olvanil, but not HPODA, and the antinociceptive effects of 4-aminophenol and HMBA were substantially reduced or disappeared in FAAH null mice. The activity of 4-aminophenol in the mouse formalin, von Frey and tail immersion tests was also lost in TRPV1 null mice. Intracerebroventricular injection of the TRPV1 blocker capsazepine eliminated the antinociceptive effects of 4-aminophenol and HMBA in the mouse formalin test. In the rat, pharmacological inhibition of FAAH, TRPV1, cannabinoid CB1 receptors and spinal 5-HT3 or 5-HT1A receptors, and chemical deletion of bulbospinal serotonergic pathways prevented the antinociceptive action of 4-aminophenol. Thus, the pharmacological profile of 4-aminophenol was identical to that previously reported for paracetamol, supporting our suggestion that this drug metabolite contributes to paracetamol's analgesic activity via activation of bulbospinal pathways. Our findings demonstrate that it is possible to construct novel antinociceptive drugs based on fatty acid conjugation as a metabolic pathway for the generation of TRPV1 modulators in the CNS.

Background Gabapentin has shown efficacy in the treatment of chronic neuropathic or mixed pain in adults. Although pediatric pain specialists have extensive experience with gabapentin for the treatment of neuropathic pain, its use is off-label. Its efficacy and safety in this context have never been shown. The aim of this trial is to compare gabapentin with placebo as add-on to morphine for the treatment of severe chronic mixed or neuropathic pain in children. This trial is part of the European Union Seventh Framework Programme project Gabapentin in Paediatric Pain (GAPP) to develop a pediatric use marketing authorization for a new gabapentin suspension. Methods/design The GAPP-2 study is a randomized, double-blind, placebo-controlled, multicenter superiority phase II study in children with severe chronic neuropathic or mixed pain. Its primary objective is to evaluate the efficacy of a gabapentin liquid formulation as adjunctive therapy to morphine. Sixty-six eligible children 3 months to 18 years of age with severe pain (pain scores ≥ 7), stratified in three age groups, will be randomized to receive gabapentin (to an accumulating dose of 45 to 63 mg/kg/day, dependent on age) or placebo, both in addition to morphine, for 12 weeks. Randomization will be preceded by a short washout period, and treatment will be initiated by a titration period of 3 weeks. After the treatment period, medication will be tapered during 4 weeks. The primary endpoint is the average pain scores in the two treatment groups (average of two measures each day for 3 days before the end-of-study visit [V10] assessed by age-appropriate pain scales (Face, Legs, Activity, Cry, Consolability scale; Faces Pain Scale–Revised; Numeric Rating Scale). Secondary outcomes include percentage responders to treatment (subjects with 30% reduction in pain scale), number of episodes of breakthrough pain, number of rescue interventions, number of pain-free days, participant dropouts, quality of life (Pediatric Quality of Life Inventory), and acceptability of treatment. Outcomes will be measured at the end-of-study visit after 12 weeks of treatment at the optimal gabapentin dose. Groups will be compared on an intention-to-treat basis. Discussion We hope to provide evidence that the combination of morphine and gabapentin will provide better analgesia than morphine alone and will be safe. We also aim to obtain confirmation of the recommended pediatric dose. Trial registration EudractCT, 2014-004897-40 . Registered on 7 September 2017. ClinicalTrials.gov, NCT03275012 . Registered on 7 September 2017.

Although opioids have known antidepressant activity, their use in major depressive disorder (MDD) has been greatly limited by risk of abuse and addiction. Our aim was to determine whether opioid modulation achieved through a combination of a μ-opioid partial agonist, buprenorphine (BUP), and a potent μ-opioid antagonist, samidorphan (SAM), would demonstrate antidepressant activity without addictive potential. A placebo-controlled crossover study assessed the opioid pharmacodynamic profile following escalating doses of SAM co-administered with BUP in opioid-experienced adults. A subsequent 1-week, placebo-controlled, parallel-group study was conducted in subjects with MDD and an inadequate response to standard antidepressant therapy. This second study evaluated safety and efficacy of ratios of BUP/SAM that were associated with partial and with maximal blockade of opioid responses in the initial study. Pupillometry, visual analog scale assessments, and self-reported questionnaires demonstrated that increasing amounts of SAM added to a fixed dose of BUP resulted in dose-dependent reductions in objective and subjective opioid effects, including euphoria and drug liking, in opioid-experienced adults. Following 7 days of treatment in subjects with MDD, a 1 : 1 ratio of BUP and SAM, the ratio associated with maximal antagonism of opioid effects, exhibited statistically significant improvement vs placebo in HAM-D17 total score (p=0.032) and nearly significant improvement in Montgomery-Åsberg Depression Rating Scale (MADRS) total score (p=0.054). Overall, BUP/SAM therapy was well tolerated. A combination of BUP and SAM showed antidepressant activity in subjects with MDD. Balanced agonist-antagonist opioid modulation represents a novel and potentially clinically important approach to the treatment of MDD and other psychiatric disorders.

Buprenorphine is used to treat opioid use disorder (OUD). Weekly and monthly subcutaneous long-acting buprenorphine injections (CAM2038) provide more stable buprenorphine plasma levels and reduce the treatment burden, misuse, and diversion associated with sublingual transmucosal buprenorphine formulations. To characterize the pharmacokinetic/pharmacodynamic (PK/PD) relationship, a maximum inhibition (I max ) model was developed relating CAM2038 buprenorphine plasma concentration to drug liking maximum effect (E max ) visual analog scale (VAS; bipolar) score after intramuscular hydromorphone administration. Data included time-matched observations of buprenorphine plasma concentration and drug liking E max VAS score after hydromorphone 18 mg administration in 47 non-treatment-seeking adults with moderate to severe OUD in a phase 2 study. Analysis used non-‍linear mixed-effects modeling (NONMEM ® ). The final I max model adequately described the PK/PD relationship between buprenorphine plasma concentration and drug liking E max VAS score. Simulations showed drug liking was effectively blocked at low buprenorphine plasma concentrations (0.4 ng/mL) where the upper 95% confidence interval of the drug liking E max VAS score was below the pre-defined 11-point complete blockade threshold. The buprenorphine plasma concentration required to achieve 90% of the maximal effect (IC 90 ) of drug liking was 0.675 ng/mL. Interindividual variability in responses to buprenorphine was observed; some participants experienced fluctuating responses, and a few did not achieve drug liking blockade even with higher buprenorphine plasma concentrations. This affirms the need to individualize treatment and titrate doses for optimal treatment outcomes. PK/PD models were also developed for desire to use VAS and Clinical Opiate Withdrawal Scale (COWS) scores, with results aligned to those for drug liking.

To provide consistent pain relief and improve convenient sustained release (SR), a fixed-dose combination tramadol/acetaminophen tablet was formulated. This study aimed to evaluate the pharmacokinetic profiles of an SR 75-mg tramadol/650-mg acetaminophen formulation after a single dose compared with an immediate release (IR) 37.5-mg tramadol/325-mg acetaminophen formulation after 2 doses and at steady state and to assess the effect of food on the pharmacokinetic SR formulation profile after a single dose. Two clinical trials were conducted: (1) an open-label, randomized, 3-period, 3-treatment, crossover study to assess the pharmacokinetic SR (one 75-mg tramadol/650-mg acetaminophen combination tablet) formulation profiles after a single dose and IR (one 37.5-mg tramadol/325-mg acetaminophen combination tablet q6h for 2 doses) formulation profiles after 2 doses and the effect of food intake on healthy male subjects and (2) an open, randomized, 2-period, 2-treatment multiple dose crossover study to evaluate the steady-state pharmacokinetic SR and IR formulation profiles. Safety assessments were performed. Forty-three subjects completed each study protocol. The SR combination tramadol/acetaminophen formulation was clinically and statistically equivalent to the IR combination formulation in the fasting state. When tramadol and acetaminophen tablets were administered with food, the time to peak plasma concentrations and the tramadol/acetaminophen absorption were unaffected. There was no serious adverse event reported. The SR combination tramadol/acetaminophen tablet exhibited similar exposure and absorption rates compared with those of the IR formulation of tramadol, O-desmethyltramadol, and acetaminophen. The SR formulation may be more convenient for patients and has the potential to enhance compliance and pain control. ClinicalTrials.gov identifier: NCT01880125