A Prospective Population Pharmacokinetic Study on Morphine Metabolism in Cancer Patients

The Influence of Pharmacogenetic Factors on the Pharmacokinetics of Morphine and Its Metabolites in Pediatric Patients: A Systematic Review

Morphine is a potent analgesic used for treating surgical and cancer pain. Despite being the drug of choice for the management of severe pain in children, the high interindividual variability in morphine pharmacokinetics limits its clinical utility to effectively relieve pain without adverse effects. This review was conducted to identify and describe all studies that have assessed the effect of genetic factors on the pharmacokinetics of morphine and its main metabolites in children. Embase and Medline databases were used to conduct the literature search, and the systematic review was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Of the 188 articles screened and after the application of specific inclusion and exclusion criteria, the review identified 8 studies. These studies suggest that genetic variants of selected metabolic enzymes and transporters may play a role in the observed interindividual variability in morphine plasma concentrations. Variants of the genes SLC22A1 and ABCC3 had the most supporting evidence for genetic variants that influence morphine and morphine metabolites pharmacokinetics. Although the available evidence suggests a potential genetic contribution to the variability in morphine concentration, the heterogeneity of the included studies in terms of experimental design and small sample sizes in some studies makes it challenging to propose the use of genetic biomarkers to personalize morphine dosing. This underscores the need to conduct more comprehensive and large-scale pharmacokinetic-pharmacogenetic studies to determine how or if genetic testing can optimize morphine safety and effectiveness in children.

Implementing physics-based digital patient twins to tailor the switch of oral morphine to transdermal fentanyl patches based on patient physiology

Fentanyl transdermal patches are widely implemented for cancer-induced pain treatment due to the high potency of fentanyl and gradual drug release. However, transdermal fentanyl up-titration for opioid-naïve patients is difficult, which is why opioid treatment is often started with oral/iv morphine. Based on the daily dose of morphine, the initial dose of the fentanyl patch is decided upon. After reaching a stable level of pain, the switch is made from oral/iv morphine to transdermal fentanyl. There are standard calculation tools for transferring from oral/iv morphine to transdermal fentanyl, which is the same for all patients. By considering the variations in the physiology of the patients, a unique switching strategy cannot meet the needs of different patients. This study explores the outcome in terms of pain relief and minute ventilation during opioid therapy. For this, we used physics-based simulations on a virtually-generated population of patients, and we applied the same therapy to all patients. We could show that patients' physiology, such as gender, age, and weight, greatly impact the outcome of the therapy; as such, the correlation coefficient between pain intensity and age is 0.89, and the correlation coefficient between patient's weight and maximum plasma concentration of morphine and fentanyl is -0.98 and -0.97. Additionally, a different combination of the duration of overlap between morphine and fentanyl therapy with different doses of fentanyl was considered for the virtual patients to find the best opioid-switching strategy for each patient. We explored the impact of combining physiological features to determine the best-suited strategy for virtual patients. Our findings suggest that tailoring morphine and fentanyl therapy only based on a limited number of features is insufficient, and increasing the number of impactful physiological features positively influences the outcome of the therapy.

Analgesia and sedation strategies in neonates undergoing whole-body therapeutic hypothermia: A scoping review

BACKGROUND

Therapeutic hypothermia (TH) is a widely practiced neuroprotective strategy for neonates with hypoxic-ischemic encephalopathy. Induced hypothermia is associated with shivering, cold pain, agitation, and distress.

OBJECTIVE

This scoping review determines the breadth of research undertaken for pain and stress management in neonates undergoing hypothermia therapy, the pharmacokinetics of analgesic and sedative medications during hypothermia and the effect of such medication on short- and long-term neurological outcomes.

METHODS

We searched the following online databases namely, (i) MEDLINE, (ii) Web of Science, (iii) Cochrane Library, (iv) Scopus, (v) CINAHL, and (vi) EMBASE to identify published original articles between January 2005 and December 2022. We included only English full-text articles on neonates treated with TH and reported the sedation/analgesia strategy used. We excluded articles that reported TH on transport or extracorporeal membrane oxygenation, did not report the intervention strategies for sedation/analgesia, and reported hypoxic-ischemic encephalopathy in which hypothermia was not applied.

RESULTS

The eligible publications (n = 97) included cohort studies (n = 72), non-randomized experimental studies (n = 2), pharmacokinetic studies (n = 4), dose escalation feasibility trial (n = 1), cross-sectional surveys (n = 5), and randomized control trials (n = 13). Neonatal Pain, Agitation, and Sedation Scale (NPASS) is the most frequently used pain assessment tool in this cohort. The most frequently used pharmacological agents are opioids (Morphine, Fentanyl), benzodiazepine (Midazolam) and Alpha2 agonists (Dexmedetomidine). The proportion of neonates receiving routine sedation-analgesia during TH is center-specific and varies from 40-100% worldwide. TH alters most drugs' metabolic rate and clearance, except for Midazolam. Dexmedetomidine has additional benefits of thermal tolerance, neuroprotection, faster recovery, and less likelihood of seizures. There is a wide inter-individual variability in serum drug levels due to the impact of temperature, end-organ dysfunction, postnatal age, and body weight on drug metabolism.

CONCLUSIONS

No multidimensional pain scale has been tested for reliability and construct validity in hypothermic encephalopathic neonates. There is an increasing trend towards using routine sedation/analgesia during TH worldwide. Wide variability in the type of medication used, administration (bolus versus infusion), and dose ranges used emphasizes the urgent need for standardized practice recommendations and guidelines. There is insufficient data on the long-term neurological outcomes of exposure to these medications, adjusted for underlying brain injury and severity of encephalopathy. Future studies will need to develop framework tools to enable precise control of sedation/analgesia drug exposure customized to individual patient needs.

Does nonlinear blood-brain barrier transport matter for (lower) morphine dosing strategies?

Morphine blood-brain barrier (BBB) transport is governed by passive diffusion, active efflux and saturable active influx. This may result in nonlinear plasma concentration-dependent brain extracellular fluid (brainECF) pharmacokinetics of morphine. In this study, we aim to evaluate the impact of nonlinear BBB transport on brainECF pharmacokinetics of morphine and its metabolites for different dosing strategies using a physiologically based pharmacokinetic simulation study. We extended the human physiologically based pharmacokinetic LeiCNS-PK3.0, model with equations for nonlinear BBB transport of morphine. Simulations for brainECF pharmacokinetics were performed for various dosing strategies: intravenous (IV), oral immediate (IR) and extended release (ER) with dose range of 0.25-150 mg and dosing frequencies of 1-6 times daily. The impact of nonlinear BBB transport on morphine CNS pharmacokinetics was evaluated by quantifying (i) the relative brainECF to plasma exposure (AUCu,brainECF/AUCu,plasma) and (ii) the impact on the peak-to-trough ratio (PTR) of concentration-time profiles in brainECF and plasma. We found that the relative morphine exposure and PTRs are dose dependent for the evaluated dose range. The highest relative morphine exposure value of 1.4 was found for once daily 0.25 mg ER and lowest of 0.1 for 6-daily 150 mg IV dosing. At lower doses the PTRs were smaller and increased with increasing dose and stabilized at higher doses independent of dosing frequency. Relative peak concentrations of morphine in relation to its metabolites changed with increasing dose. We conclude that nonlinearity of morphine BBB transport affects the relative brainECF exposure and the fluctuation of morphine and its metabolites mainly at lower dosing regimens.

No significant influence of OCT1 genotypes on the pharmacokinetics of morphine in adult surgical patients

We investigated the impact of genetic variants in OCT1 (SLC22A1) on morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) pharmacokinetics in adult patients scheduled for major surgery. Blood samples were taken before and 5, 10, 15, 30, 45, 60 and 90 min after a bolus of morphine (0.15 mg/kg). Patients were genotyped for the genetic variants (rs12208357, rs34059508, rs72552763 and rs34130495) in OCT1. Eighty-six patients completed the trial. The mean difference (95% confidence interval) for dose adjusted morphine, M3G and M6G AUC was 0.9 (-0.7-2.4), -5.9 (-11.8 to -0.03) and -1.1 (-2.5-0.4) h/L*10-6 , respectively, in patients with two reduced function alleles compared to patients with no reduced function alleles in OCT1. Accordingly, the (AUCM3G/Dose )/(AUCmorphine/Dose ) and (AUCM6G/Dose )/(AUCmorphine/Dose ) ratio was reduced, -1.8 (-3.2 to -0.4) and -0.4 (-0.7 to -0.03), respectively, when comparing the same groups. OCT1 variants had no influence on the experience of pain, adverse events or the number of PCA doses used. In conclusion, genetic variants in OCT1 had a small and clinically unimportant impact on the exposure of morphine after intravenous administration. Our results do not support pre-emptive genotyping for OCT1 prior to morphine administration in patients scheduled for major surgery.

A Randomized Controlled Trial Evaluating the Analgesic Effect of the Combination of Methadone With Morphine for Cancer Related Pain

CONTEXT AND OBJECTIVES

Although opioids play an indispensable role in the management of cancer-related pain, inadequate pain relief still occurs. The primary objective of this study was to evaluate whether the combination of a low dose of methadone with morphine promotes a reduction in opioid consumption; the secondary objectives were if the association promotes lower pain intensity, and adverse effects (AEs).

MATERIALS AND METHODS

A sample if 41 patients with cancer-related pain in palliative setting were included. Patients were starting the third step of the analgesic ladder, and 1 group (n=21) achieve methadone (2.5 mg/12 h) in combination with morphine/methadone, and another group (n=20) received morphine alone. Both groups could use morphine (5 mg) as needed to maintain pain intensity <4, and adjuvant in stable dose. The following outcomes were evaluated: total morphine dose, pain intensity, and AEs.

RESULTS

There was no difference in the number of adjuvants, and the dose of morphine used. Pain intensity was significantly lower in the morphine/methadone group after 2 weeks, with no statistically significant difference at other timepoints. There was no difference between groups in the AEs.

CONCLUSION

Low dose of methadone in combination with morphine provided faster pain control as compared with morphine alone, and although this study was not powered to show differences in AEs, we did not notice a difference.

Intravenous versus subcutaneous route pharmacokinetics of paracetamol (acetaminophen) in palliative care patients: study protocol for a randomized trial (ParaSCIVPallia)

BACKGROUND

Among palliative care (PC) patients who are administered paracetamol, the subcutaneous (SC) route is often an alternative to the intravenous (IV) route. Yet pharmacological and clinical data on whether these are equivalent pharmacokinetically are lacking. Many French palliative teams are now empirically using paracetamol by the SC route, but there are no data to support this practice. This trial aims to compare the pharmacokinetic (PK) parameters of paracetomol between the IV and SC routes in PC patients.

METHODS/DESIGN

This is a randomized, open, crossover study in two PC centers. The primary endpoints are AUC0-t, AUC0-∞, Cmax, Vd, and t1/2. All adverse events will be reported for a safety analysis. Twenty adult PC patients with an IV device having spontaneous pain not related to care, with a numeric pain rate scale > 3/10, or having a systematic prescription of paracetamol as the usual treatment will be included. All patients also have to meet all eligibility criteria.

CONCLUSION

This is the first study comparing PK parameters for IV paracetamol versus SC paracetamol in PC patients.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03944044. Registered on 4 June 2019. Committee for the protection of persons (CPP) 18.09.05.58206 approval 4 October 2018. National Drug Safety Agency (ANSM; Agence Nationale de Sécurité Médicament) MEDAECNAT-2018-09-00009 approval 29 November 2018.

Opioids as Substrates and Inhibitors of the Genetically Highly Variable Organic Cation Transporter OCT1

Genetic variants in the hepatic uptake transporter OCT1, observed in 9% of Europeans and white Americans, are known to affect pharmacokinetics and efficacy of tramadol, morphine, and codeine. Here, we report further opioids to be substrates and inhibitors of OCT1. Methylnaltrexone, hydromorphone, oxymorphone, and meptazinol were identified as OCT1 substrates. Methylnaltrexone is the strongest OCT1 substrate currently reported. It showed 86-fold higher accumulation in OCT1-overexpressing cells compared to control cells. We observed substantial differences in the inhibitory potency among structurally highly similar morphinan opioids (IC₅₀ ranged from 6.4 μM for dextrorphan to 2 mM for oxycodone). The ether linkage of C4-C5 in the morphinan ring leads to a strong reduction of inhibitory potency. In conclusion, although polyspecific, OCT1 possesses a strong selectivity for its ligands. In contrast to methylnaltrexone and hydromorphone, oxycodone and hydrocodone do not interact with OCT1 and may be safer for use in individuals with genetic OCT1 deficiency.