Pharmacogenomic considerations in the opioid management of pain

Pharmacogenomic Biomarkers

Why does the usual dose of medication work for a person while another individual cannot give the expected response to the same drug? On the other hand, how come half of the usual dose of an analgesic relieves an individual’s pain immediately, as another man continue to suffer even after taking double dose? Although a treatment method has been successfully used in majority of the population for many years, why does the same therapy cause serious side effects in another region of the world? Most presently approved therapies are not effective in all patients. For example, 20-40% of patients with depression respond poorly or not at all to antidepressant drug therapy. Many patients are resistant to the effects of antiasthmatics and antiulcer drugs or drug treatment of hyperlipidemia and many other diseases. The reason for all those is basically interindividual differences in genomic structures of people, which are explained in this chapter in terms of the systems and the most frequently used drugs in clinical treatment.

Clinical Validation of a 106-SNV MALDI-ToF MS Pharmacogenomic Panel

BACKGROUND

Laboratorians have the opportunity to help minimize the frequency of adverse drug reactions by implementing pharmacogenomic testing and alerting care providers to possible patient/drug incompatibilities before drug treatment is initiated. Methods combining PCR with MALDI-ToF MS have allowed for sensitive, economical, and multiplexed pharmacogenomic testing results to be delivered in a timely fashion.

METHOD

This study evaluated the analytical performance of the Agena Biosciences iPLEX® PGx 74 panel and a custom iPLEX panel on a MassARRAY MALDI-TOF MS instrument in a clinical laboratory setting. Collectively, these panels evaluate 112 SNVs across 34 genes implicated in drug response. Using commercially available samples (Coriell Biorepository) and in-house extracted DNA, we determined ideal reaction conditions and assessed accuracy, precision, and robustness.

RESULTS

Following protocol optimization, the Agena PGx74 and custom panels demonstrated 100% concordance with the 1000 Genomes Project Database and clinically validated hydrolysis probe genotyping assays. 100% concordance was also observed in all assessments of assay precision when appropriate QC metrics were applied.

CONCLUSIONS

Significant development time was required to optimize sample preparation and instrumental analysis and 3 assays were removed due to inconsistent performance. Following modification of the manufacturer's protocol and instituting manual review of each assay plate, the Agena PGx74 and custom panel constitute a cost-effective, robust, and accurate method for clinical identification of 106 SNVs involved in drug response.

Pupillary unrest, opioid intensity, and the impact of environmental stimulation on respiratory depression

Opioid-induced respiratory depression (OIRD) confers significant morbidity, but its onset can be challenging to recognize. Pain or stimulation effects of conversation may mask or attenuate common clinical manifestations of OIRD. We asked whether pupillary unrest could provide an objective signal of opioid exposure, and whether this signal would be independent from the confounding influence of extrinsic stimulation. We conducted a cross-over trial of healthy volunteers using identical remifentanil infusions separated by a washout period; in both, pupillary unrest in ambient light (PUAL) was measured at 2.5-min intervals. During one infusion, investigators continuously engaged the subject in conversation, while in the other, a quiet environment was maintained; measures of respiratory depression were compared under each condition. We tested PUAL’s relationship to estimated opioid concentration under quiet conditions, measured PUAL’s discrimination of lower versus higher opioid exposure using receiver operating characteristic (ROC) analysis, and assessed the effect of stimulation on PUAL versus opioid using mixed effects regression. Respiratory depression occurred more frequently under quiet conditions (p < 0.0001). Under both conditions, PUAL declined significantly over the course of the remifentanil infusion and rose during recovery (p < 0.0001). PUAL showed excellent discrimination in distinguishing higher versus absent-moderate opioid exposure (AUROC = 0.957 [0.929 to 0.985]), but was unaffected by interactive versus quiet conditions (mean difference, interactive – quiet = − 0.007, 95% CI − 0.016 to 0.002). PUAL is a consistent indicator of opioid effect, and distinguishes higher opioid concentrations independently of the stimulating effects of conversational interaction. Under equivalent opioid exposure, conversational interaction delayed the onset and minimized the severity of OIRD.

Clinical trial registration: NCT 04301895

CYP2D6 Pharmacogenetics Testing and Post-Cesarean Section Pain Scores-a Preliminary Study

OBJECTIVE

Prospective observational study to analyze CYP2D6 pharmacogenetics in 55 Portuguese adult parturients undergoing elective cesarean section and to investigate the association between CYP2D6 alleles and pain score.

METHODS

DNA was extracted from peripheral blood by standard methods. Genetic analysis included allelic discrimination (CYP2D6*1, *2, *3, *4, *5, *6, *10, *17, and *41) and copy number determination with TaqMan probes by real-time polymerase chain reaction (PCR). Allele duplications were confirmed (long PCR and PCR-restriction fragment length polymorphism). Theoretical metabolic profiles prediction was based on genetic data and activity scores. Association was investigated between genotypes and predicted phenotypes with pain scores. Statistical analysis was performed by using a χ2 test, and significance was set at P < 0.05.

RESULTS

The percentage of poor, intermediate, extensive, and ultrarapid metabolizers found were 9%, 38%, 46%, and 7%, respectively. The results reveal a positive association between alleles *4, *10, and pain.

CONCLUSIONS

A positive association was found between predicted reduced or null activity of CYP2D6 and increased pain. It can be hypothesized that if CYP2D6 activity is reduced, tyramine metabolism will decrease, resulting in reduced formation of endogenous dopamine. Consequently, activation of the signal transduction pathways that controls pain and analgesic effect may be reduced, leading to an increase in pain. Therefore, we would recommend CYP2D6 genotyping to anticipate the needs for analgesia, which will help to adjust opioid dose and maximize clinical efficacy while reducing side effects.

Pupillary Unrest in Ambient Light and Prediction of Opioid Responsiveness: Case Report on Its Utility in the Management of 2 Patients With Challenging Acute Pain Conditions

Pupillary unrest in ambient light (PUAL), the normal pattern of pupil diameter fluctuation present in awake humans, has been proposed as a marker of central opioid effect. We report 2 cases in which PUAL identified the appropriate pain management for 2 patients, each with unique, challenging acute pain conditions. In both cases, PUAL accurately predicted opioid responsiveness, suggesting an effective, individualized analgesic approach for both patients.

Clinical pharmacogenomics testing in the era of next generation sequencing: challenges and opportunities for precision medicine

INTRODUCTION

The rapid development and dramatic decrease in cost of sequencing techniques have ushered the implementation of genomic testing in patient care. Next generation DNA sequencing (NGS) techniques have been used increasingly in clinical laboratories to scan the whole or part of the human genome in order to facilitate diagnosis and/or prognostics of genetic disease. Despite many hurdles and debates, pharmacogenomics (PGx) is believed to be an area of genomic medicine where precision medicine could have immediate impact in the near future. Areas covered: This review focuses on lessons learned through early attempts of clinically implementing PGx testing; the challenges and opportunities that PGx testing brings to precision medicine in the era of NGS. Expert commentary: Replacing targeted analysis approach with NGS for PGx testing is neither technically feasible nor necessary currently due to several technical limitations and uncertainty involved in interpreting variants of uncertain significance for PGx variants. However, reporting PGx variants out of clinical whole exome or whole genome sequencing (WES/WGS) might represent additional benefits for patients who are tested by WES/WGS.

The effects of food on opioid-induced nausea and vomiting and pharmacological parameters: a systematic review

Opioids remain the standard of care for treating moderate to severe pain resulting from surgery or injury in cases of acute pain, and are recommended for patients who have not responded to nonopioid analgesics. Effective management of pain has an impact on clinical course and often depends on achieving an acceptable balance between opioid efficacy, safety, and tolerability. Common opioid-related adverse events such as nausea and vomiting are associated with an overall lower achievement of effective pain management and patient satisfaction. However, in practice, clinicians employ various strategies to maximize efficacy, minimize these adverse effects, and ensure the careful, judicious, and evidence-based use of opioids for patients who require them. Typical strategies for management and minimization of these types of adverse events include dose reduction, dose titration, opioid rotation, prescription for an antiemetic, and recommending the patient take opioids with food. Overall, the most straightforward approach that clinicians tend to employ that does not require additional visits or adjustment of prescriptions, is to recommend patients take opioids with food. However, given the current climate with opioids, it is critical and imperative that decisions for use of opioids be grounded in a solid and thorough evidence-base. In fact, several opioids are recommended to be taken explicitly with or without food because of interactions with abuse-deterrent technologies that can cause increased adverse events or inadequate analgesia. Therefore, we sought to review, synthesize, and summarize the literature for randomized, controlled trials and other studies to support the hypothesis that taking opioids with food reduces opioid-related events such as nausea and vomiting. Based on the current evidence we surveyed, the recommendation to take opioids with food does not appear to consistently and unequivocally reduce nausea and vomiting and, in many cases, increases the frequency of these adverse events in the studies we examined.

Pharmacogenomics and pharmacogenetics for the intensive care unit: a narrative review

PURPOSE

Knowledge of how alterations in pharmacogenomics and pharmacogenetics may affect drug therapy in the intensive care unit (ICU) has received little study. We review the clinically relevant application of pharmacogenetics and pharmacogenomics to drugs and conditions encountered in the ICU.

SOURCE

We selected relevant literature to illustrate the important concepts contained within.

PRINCIPAL FINDINGS

Two main approaches have been used to identify genetic abnormalities - the candidate gene approach and the genome-wide approach. Genetic variability in response to drugs may occur as a result of alterations of drug-metabolizing (cytochrome P [CYP]) enzymes, receptors, and transport proteins leading to enhancement or delay in the therapeutic response. Of relevance to the ICU, genetic variation in CYP-450 isoenzymes results in altered effects of midazolam, fentanyl, morphine, codeine, phenytoin, clopidogrel, warfarin, carvedilol, metoprolol, HMG-CoA reductase inhibitors, calcineurin inhibitors, non-steroidal anti-inflammatory agents, proton pump inhibitors, and ondansetron. Changes in cholinesterase enzyme function may affect the disposition of succinylcholine, benzylisoquinoline muscle relaxants, remifentanil, and hydralazine. Genetic variation in transport proteins leads to differences in the response to opioids and clopidogrel. Polymorphisms in drug receptors result in altered effects of β-blockers, catecholamines, antipsychotic agents, and opioids. Genetic variation also contributes to the diversity and incidence of diseases and conditions such as sepsis, malignant hyperthermia, drug-induced hypersensitivity reactions, cardiac channelopathies, thromboembolic disease, and congestive heart failure.

CONCLUSION

Application of pharmacogenetics and pharmacogenomics has seen improvements in drug therapy. Ongoing study and incorporation of these concepts into clinical decision making in the ICU has the potential to affect patient outcomes.

Role of CYP2D6 Polymorphisms in the Outcome of Postoperative Pain Treatment

OBJECTIVE

To investigate the role of CYP2D6 phenotype in the outcome of postoperative (PO) pain (POP) treatment.

DESIGN

Longitudinal cohort study. Open-label trial with post hoc analysis.

SETTING

General Hospital Surgery and Recovery Units.

PATIENTS

Ninety unrelated Caucasians submitted to abdominal/thoracic surgery.

INTERVENTIONS

Standard multimodal POP treatment including opioids (tramadol) and nonsteroidal anti-inflammatory drugs (ketoprofen) at different dosages and infusion rates according to the predicted mild, moderate, or severe POP.

OUTCOME MEASURES

Pain (Numeric Rating Scale-NRS) and sedation (Ramsay Sedation Scale-RSS) up to 24 hours after surgery. By genotyping 16 CYP2D6 alleles, the four CYP2D6 phenotypes poor metabolizer (PM), intermediate metabolizers (IM), extensive metabolizers (EM) and ultrarapid metabolizers (UM) were predicted.

RESULTS

As compared with the CYP2D6-EM phenotype, in the early PO time (30 min) a higher RSS mean score in IM was observed (P = 0.035). A suggestion towards higher mean score in PM (P = 0.091) and a minor mean score in UM (P = 0.091) was also detected. No difference in the outcome of pain across the CYP2D6 phenotypes was observed.

CONCLUSIONS

In respect to the normal CYP2D6 phenotype, our results suggested that slowly metabolizers (IMs and PMs) might have a major sedation, whereas more rapid metabolizers (UM) a minor sedation, in the early time after surgery. A minor role of CYP2D6 phenotype in PO analgesia may be suggested.

Morphine glucuronidation increases its analgesic effect in guinea pigs

AIMS

Morphine is extensively metabolized to neurotoxic morphine-3-glucuronide (M3G) and opioid agonist morphine-6-glucuronide (M6G). Due to these different roles, interindividual variability and co-administration of drugs that interfere with metabolism may affect analgesia. The aim of the study was to investigate the repercussions of administration of an inducer (2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD) and an inhibitor (ranitidine) of glucuronidation in morphine metabolism and consequent analgesia, using the Guinea pig as a suitable model.

MAIN METHODS

Thirty male Dunkin-Hartley guinea pigs were divided in six groups: control, morphine, ranitidine, ranitidine+morphine, TCDD and TCDD+morphine. After previous exposure to TCDD and ranitidine, morphine effect was assessed by an increasing temperature hotplate (35-52.5°C), during 60min after morphine administration. Then, blood was collected and plasma morphine and metabolites were quantified.

KEY FINDINGS

Animals treated with TCDD presented faster analgesic effect and 75% reached the cut-off temperature of 52.5°C, comparing with only 25% in morphine group. Animals treated with ranitidine presented a significantly lower analgesic effect, compared with morphine group (p<0.05). Moreover, significant differences between groups were found in M3G levels and M3G/morphine ratio (p<0.001 and p<0.0001), with TCDD animals presenting the highest values for M3G, M6G, M3G/morphine and M6G/morphine, and the lowest value for morphine. The opposite was observed in the animals treated with ranitidine.

SIGNIFICANCE

Our results indicate that modulation of morphine metabolism may result in variations in metabolite concentrations, leading to different analgesic responses to morphine, in an animal model that may be used to improve morphine effect in clinical practice.

A new model for using quantitative urine testing as a diagnostic tool for oxycodone treatment and compliance

We conducted a prospective, randomized, cross-sectional study to develop and validate a new model to predict oxycodone in urine that can be used to help evaluate whether patients are complying with their oxycodone dosing regimens. We studied 20 patients: eight black women, two white women, six black men, and four white men; ages 48 ± 10 years (mean ± SD); weight 97 ± 32 kg. Pain levels before treatment averaged 9.5 ± 0.9 out of 10. We prescribed oral oxycodone for each patient, tailoring the dosing regimen using clinical pharmacokinetics and measured the oxycodone concentration in each patient's urine 10 to 14 days after starting the dosing regimen. For each patient, we predicted oxycodone in their urine using our model, checked the actual concentration, and compared predicted with actual concentrations. For 18 of 20 patients (90%), actual results fell within ±10% of our model's prediction. One patient was 35% below the prediction; the other was 51% above. Our model accurately predicts oxycodone in urine (±10% for 90% of the patients). The model appears clinically useful for evaluating the results of a quantitative urine test, since it objectively discriminates between (1) a "normal" patient complying with their oxycodone dosing regimen, and (2) a patient who may require genetic testing to distinguish between unusual metabolism or abuse.

Recent Non-Interventional Advances in Cancer Pain Among Singapore Patients

Introduction: Pain is a common symptom in cancer patients, but very little information about the prevalence, severity, and treatment of pain in cancer patients in Singapore is available. Therefore, our prospective survey in the National Cancer Centre (NCC) outpatients is incorporated in this report. In addition, a review concerning the recent advances on non-interventional pain management in cancer treatment, which is relevant in the context, is discussed. Materials and Methods: For the prospective survey, a questionnaire was distributed for self-administration by patients while waiting for consultation at the NCC outpatient departments. Literature searches on advances in pain management were conducted, reviewed and discussed. Results: In the last decade, there have been advances in pain pharmacology ranging from wider therapeutic options and management approaches to novel delivery techniques. Acupuncture and massage therapy became increasingly popular among cancer patients. Some clinical trials of acupuncture show benefits in palliation of cancer pain. From the prospective survey, 41.2% of the responders reported pain in the past week, and only 70.8% talked to their doctors about their pain. One third of the patients received analgesics. Of these, 86.5% said that they were taking the prescribed medications, however, 37.4% admitted to having difficulties taking them. Non-drug methods were used by 25.4% of the patients. Medicated oil, cream or gel was used by 49.3%; only 2.6% reported use of Chinese herbs. Conclusion: Pain is a significant symptom in outpatients attending a cancer centre, affecting 41.2% of the patients. Although majority of patients who suffered from pain reported this to doctors, much more medical effort is needed to help patients to relieve their pain and proper complementary therapy could be considered. Key words: Cancer outpatients, Complementary therapies, Non-pharmacological pain treatments, Pain prevalence