Pharmacogenetic Analysis Enables Optimization of Pain Therapy: A Case Report of Ineffective Oxycodone Therapy

Patients suffering from chronic pain may respond differently to analgesic medications. For some, pain relief is insufficient, while others experience side effects. Although pharmacogenetic testing is rarely performed in the context of analgesics, response to opiates, non-opioid analgesics, and antidepressants for the treatment of neuropathic pain can be affected by genetic variants. We describe a female patient who suffered from a complex chronic pain syndrome due to a disc hernia. Due to insufficient response to oxycodone, fentanyl, and morphine in addition to non-steroidal anti-inflammatory drug (NSAID)-induced side effects reported in the past, we performed panel-based pharmacogenotyping and compiled a medication recommendation. The ineffectiveness of opiates could be explained by a combined effect of the decreased activity in cytochrome P450 2D6 (CYP2D6), an increased activity in CYP3A, and an impaired drug response at the µ-opioid receptor. Decreased activity for CYP2C9 led to a slowed metabolism of ibuprofen and thus increased the risk for gastrointestinal side effects. Based on these findings we recommended hydromorphone and paracetamol, of which the metabolism was not affected by genetic variants. Our case report illustrates that an in-depth medication review including pharmacogenetic analysis can be helpful for patients with complex pain syndrome. Our approach highlights how genetic information could be applied to analyze a patient's history of medication ineffectiveness or poor tolerability and help to find better treatment options.

Steady-State Pharmacokinetics of Intravenous Hydromorphone in Japanese Patients with Renal Impairment and Cancer Pain

Background: The opioid analgesic hydromorphone has a low renal excretion ratio; however, exposure after oral administration is several times higher in those with moderate or severe renal impairment. Objectives: We evaluated the impact of renal impairment on the steady-state pharmacokinetics of intravenously administered hydromorphone in patients with cancer being treated for pain. Design: This was an open-label, prospective, parallel-comparison, interventional clinical pharmacology study. Setting/Subjects: This study was conducted at one hospital in Japan. Using creatinine clearance (CLcr) values, patients were grouped according to kidney function: CLcr ≥90 mL/min (normal), 60-<90 mL/min (mild impairment), 30-<60 mL/min (moderate impairment), or <30 mL/min (severe impairment). Measurements: Hydromorphone was administered by constant infusion to patients at the same constant dose rate as at the time of enrollment. Hydromorphone and its glucuronide metabolite concentrations in plasma and urine were measured by liquid chromatography-mass spectrometry. Pharmacokinetic parameters at steady state were assessed using noncompartmental analysis. Results: Thirty-two patients were enrolled (normal, n = 3; mild, n = 10; moderate, n = 15; and severe, n = 4). Adjusted geometric mean ratios for hydromorphone steady-state clearance (CLss) for patients with impaired versus normal renal function were 0.69 (90% confidence interval [CI], 0.41-1.14), 0.52 (90% CI, 0.31-0.84), and 0.55 (90% CI, 0.30-1.02) for mild, moderate, or severe impairment, respectively. Exposures to the metabolite hydromorphone-3-glucuronide generally increased with renal impairment. No adverse event was reported. Conclusion: Hydromorphone CLss in patients with impaired renal function (moderate and severe) was decreased ∼50% of that of normal renal function.

Reviewing pharmacogenetics to advance precision medicine for opioids

BACKGROUND

Adequate opioid prescribing is critical for therapeutic success of pain management. Despite the widespread use of opioids, optimized opioid therapy remains unresolved with risk of accidental lethal overdosing. With the emergence of accumulating evidence linking genetic variation to opioid response, pharmacogenetic based treatment recommendations have been proposed.

OBJECTIVE

The aim of this review is to evaluate pharmacogenetic evidence and provide an overview on genes involved in the pharmacokinetics and pharmacodynamics of opioids.

METHODS

For this review, a systematic literature search of published articles was used in PubMed®, with no language restriction and between the time period of January 2000 to December 2020. We reviewed randomized clinical studies, study cohorts and case reports that investigated the influence of genetic variants on selected opioid pharmacokinetics and pharmacodynamics. In addition, we reviewed current CPIC clinical recommendations for pharmacogenetic testing.

RESULTS

Results of this review indicate consistent evidence supporting the association between selected genetic variants of CYP2D6 for opioid metabolism. CPIC guidelines include recommendations that indicate the avoidance of tramadol use, in addition to codeine, in CYP2D6 poor metabolizers and ultrarapid metabolizers, and to monitor intermediate metabolizers for less-than-optimal response. While there is consistent evidence for OPRM1 suggesting increased postoperative morphine dosing requirements in A118G G-allele carriers, the clinical relevance remains limited.

CONCLUSION

There is emerging evidence of clinical relevance of CYP2D6 and, to a lesser extent, OPRM1 polymorphism in personalized opioid drug dosing. As a result, first clinics have started to implement pharmacogenetic guidelines for CYP2D6 and codeine.

Hydromorphone population pharmacokinetics in pediatric surgical patients

BACKGROUND

Hydromorphone is an opioid agonist used for pediatric analgesia. Due to lack of data, pediatric dosing (based on adult pharmacokinetic models) is not optimal.

AIM

This study characterizes hydromorphone population pharmacokinetics in pediatric surgical patients.

METHODS

In this prospective observational study, 34 children (4-18 years, bodyweight 23-89.6 kg) received multiple intravenous hydromorphone boluses followed by postoperative hydromorphone patient-controlled analgesia. Arterial blood samples were collected before and at 3, 10, 30, and 90 (and few samples at 1350) minutes after the first dose. Hydromorphone concentrations were measured by validated LC-MS/MS assay. Nonlinear mixed-effects modeling was used for pharmacokinetic model development. The final population pharmacokinetic model was evaluated by visual predictive check and bootstrap analysis. Monte Carlo simulations based on the final pharmacokinetic model determined optimal patient-controlled analgesia parameters to achieve a target of 20 ng/mL (as the median effective analgesic concentration), using minimum effective analgesic concentration of 4 ng/mL as a proxy for patient-controlled analgesia dose demand, and not exceeding the defined safe upper threshold of 40 ng/mL.

RESULTS

Hydromorphone pharmacokinetic profiles were adequately described by a two-compartmental model with first-order elimination. Bodyweight was found to be a significant covariate for hydromorphone clearance. Allometrically scaledpharmacokinetic parameter estimates (per 70 kg), systemic clearance (0.748 L/min), volume of distribution (33 L), peripheral clearance (1.57 L/min), and peripheral volume of distribution (146 L) were similar to reported adult parameter estimates. Sex, race, age, and type of surgery were not identified as significant covariates. To identify optimal patient-controlled analgesia dosing parameters, we simulated several initial loading doses, demand doses, and lockout intervals. Our simulations support an initial patient-controlled analgesia loading dose of 15 µg/kg followed by a demand dose of 6 µg/kg with lockout intervals of 20 minutes.

CONCLUSIONS

After intravenous hydromorphone, plasma pharmacokinetic profiles in children undergoing different surgeries were well described by a two-compartment population allometric pharmacokinetic model using bodyweight as the size descriptor. Model informed simulations identified patient-controlled analgesia parameters to inform initial settings, with adjustments as needed based on observed individual effects.

Pharmacogenomics of Pain Management: The Impact of Specific Biological Polymorphisms on Drugs and Metabolism

PURPOSE OF REVIEW

Pain is multifactorial and complex, often with a genetic component. Pharmacogenomics is a relative new field, which allows for the development of a truly unique and personalized therapeutic approach in the treatment of pain.

RECENT FINDINGS

Until recently, drug mechanisms in humans were determined by testing that drug in a population and calculating response averages. However, some patients will inevitably fall outside of those averages, and it is nearly impossible to predict who those outliers might be. Pharmacogenetics considers a patient's unique genetic information and allows for anticipation of that individual's response to medication. Pharmacogenomic testing is steadily making progress in the management of pain by being able to identify individual differences in the perception of pain and susceptibility and sensitivity to drugs based on genetic markers. This has a huge potential to increase efficacy and reduce the incidence of iatrogenic drug dependence and addiction. The streamlining of relevant polymorphisms of genes encoding receptors, transporters, and drug-metabolizing enzymes influencing the pain phenotype can be an important guide to develop safe new strategies and approaches to personalized pain management. Additionally, some challenges still prevail and preclude adoption of pharmacogenomic testing universally. These include lack of knowledge about pharmacogenomic testing, inadequate standardization of the process of data handling, questionable benefits about the clinical and financial aspects of pharmacogenomic testing-guided therapy, discrepancies in clinical evidence supporting these tests, and doubtful reimbursement of the tests by health insurance agencies.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).