Disposition and metabolism of codeine after single and chronic doses in one poor and seven extensive metabolisers

Physiologically based pharmacokinetic modeling to predict the pharmacokinetics of codeine in different CYP2D6 phenotypes

Objectives

Codeine, a prodrug used as an opioid agonist, is metabolized to the active product morphine by CYP2D6. This study aimed to establish physiologically based pharmacokinetic (PBPK) models of codeine and morphine and explore the influence of CYP2D6 genetic polymorphisms on the pharmacokinetics of codeine and morphine.

Methods

An initial PBPK modeling of codeine in healthy adults was established using PK-Sim® software and subsequently extrapolated to CYP2D6 phenotype-related PBPK modeling based on the turnover frequency (Kcat) of CYP2D6 for different phenotype populations (UM, EM, IM, and PM). The mean fold error (MFE) and geometric mean fold error (GMFE) methods were used to compare the differences between the predicted and observed values of the pharmacokinetic parameters to evaluate the accuracy of PBPK modeling. The validated models were then used to support dose safety for different CYP2D6 phenotypes.

Results

The developed and validated CYP2D6 phenotype-related PBPK model successfully predicted codeine and morphine dispositions in different CYP2D6 phenotypes. Compared with EMs, the predicted AUC0-∞ value of morphine was 98.6% lower in PMs, 60.84% lower in IMs, and 73.43% higher in UMs. Morphine plasma exposure in IMs administered 80 mg of codeine was roughly comparable to that in EMs administered 30 mg of codeine. CYP2D6 UMs may start dose titration to achieve an optimal individual regimen and avoid a single dose of over 20 mg. Codeine should not be used in PMs for pain relief, considering its insufficient efficacy.

Conclusion

PBPK modeling can be applied to explore the dosing safety of codeine and can be helpful in predicting the effect of CYP2D6 genetic polymorphisms on drug-drug interactions (DDIs) with codeine in the future.

Perspectives from the Society for Pediatric Research: pharmacogenetics for pediatricians

This review evaluates the pediatric evidence for pharmacogenetic associations for drugs that are commonly prescribed by or encountered by pediatric clinicians across multiple subspecialties, organized from most to least pediatric evidence. We begin with the pharmacogenetic research that led to the warning of increased risk of death in certain pediatric populations ("ultrarapid metabolizers") who are prescribed codeine after tonsillectomy or adenoidectomy. We review the evidence for genetic testing for thiopurine metabolism, which has become routine in multiple pediatric subspecialties. We discuss the pharmacogenetic research in proton pump inhibitors, for which clinical guidelines have recently been made available. With an increase in the prevalence of behavioral health disorders including attention deficit hyperactivity disorder (ADHD), we review the pharmacogenetic literature on selective serotonin reuptake inhibitors, selective norepinephrine reuptake inhibitors, and ADHD medications. We will conclude this section on the current pharmacogenetic data on ondansetron. We also provide our perspective on how to integrate the current research on pharmacogenetics into clinical care and what further research is needed. We discuss how institutions are managing pharmacogenetic test results and implementing them clinically, and how the electronic health record can be leveraged to ensure testing results are available and taken into consideration when prescribing medications. IMPACT: While many reviews of pharmacogenetics literature are available, there are few focused on pediatrics. Pediatricians across subspecialties will become more comfortable with pharmacogenetics terminology, know resources they can use to help inform their prescribing habits for drugs with known pharmacogenetic associations, and understand the limitations of testing and where further research is needed.

Oral and intravenous pharmacokinetics of metformin with and without oral codeine intake in healthy subjects: A cross-over study

The aim of the study was to investigate if there is a clinically relevant drug interaction between metformin and codeine. Volunteers were randomized to receive on four separate occasions: (A) orally administered metformin (1 g), (B) intravenously administered metformin (0.5 g), (C) five doses of tablet codeine 25 mg; the last dose was administered together with oral metformin (1 g), and (D) five doses of tablet codeine 25 mg; the last dose was administered together with metformin (0.5 g) intravenously. Blood samples were drawn for 24 h after administration of metformin, and for 6 h after administration of codeine and analyzed using liquid chromatography and tandem mass spectrometry. Healthy volunteers genotyped as CYP2D6 normal metabolizers (*1/*1) without known reduced function variants in the OCT1 gene (rs12208357, rs34130495, rs34059508, and rs72552763) were invited. The median absorption fraction of metformin was 0.31 and was not influenced by codeine intake. The median time to maximum concentration (Tmax) after oral intake of metformin was 2 h without, and 3 h with codeine (p = 0.06). The geometric mean ratios of the areas under the plasma concentration time‐curve (AUCs) for morphine and its metabolites M3G and M6G for oral intake of metformin‐to‐no metformin were 1.21, 1.31, and 1.27, respectively, and for i.v. metformin‐to‐no metformin 1.28, 1.34, and 1.30, respectively. Concomitant oral and i.v. metformin increased the plasma levels of morphine, M3G and M6G. These small pharmacokinetic changes may well contribute to an increased risk of early discontinuation of metformin. Hence, a clinically relevant drug‐drug interaction between metformin and codeine seems plausible.

Drug-Metabolizing Cytochrome P450 Enzymes Have Multifarious Influences on Treatment Outcomes

Drug metabolism is a critical process for the removal of unwanted substances from the body. In humans, approximately 80% of oxidative metabolism and almost 50% of the overall elimination of commonly used drugs can be attributed to one or more of various cytochrome P450 (CYP) enzymes from CYP families 1-3. In addition to the basic metabolic effects for elimination, CYP enzymes in vivo are capable of affecting the treatment outcomes in many cases. Drug-metabolizing CYP enzymes are mainly expressed in the liver and intestine, the two principal drug oxidation and elimination organs, where they can significantly influence the drug action, safety, and bioavailability by mediating phase I metabolism and first-pass metabolism. Furthermore, CYP-mediated local drug metabolism in the sites of action may also have the potential to impact drug response, according to the literature in recent years. This article underlines the ability of CYP enzymes to influence treatment outcomes by discussing CYP-mediated diversified drug metabolism in primary metabolic sites (liver and intestine) and typical action sites (brain and tumors) according to their expression levels and metabolic activity. Moreover, intrinsic and extrinsic factors of personal differential CYP phenotypes that contribute to interindividual variation of treatment outcomes are also reviewed to introduce the multifarious pivotal role of CYP-mediated metabolism and clearance in drug therapy.

Application of Model Informed Precision Dosing to Address the Impact of Pregnancy Stage and CYP2D6 Phenotype on Foetal Morphine Exposure

Guidance regarding the effect of codeine and its metabolites on foetal development is limited by small studies and inconsistent findings. The primary objective was to use physiologically based pharmacokinetic modelling to investigate the impact of gestational stage and maternal CYP2D6 phenotype on foetal morphine exposure following codeine administration. Full body physiologically based pharmacokinetic models were developed and verified for codeine and morphine using Simcyp (version 19.1). The impact of gestational age and maternal CYP2D6 phenotype on foetal and maternal morphine and codeine exposure following oral codeine administration was modelled in a cohort of 250 pregnant females and foetuses at gestational weeks 0 (mothers only), 6, 12, 24 and 36. Consistent with the known effect on codeine metabolism, a clinically meaningful (> 1.65-fold) increase in foetal morphine AUC was observed in the CYP2D6 UM phenotype cohort compared to the CYP2D6 EM and PM phenotype cohorts. The mean (95% CI) foetal morphine AUC in the CYP2D6 UM cohort of 0.988 (0.902 to 1.073) ng/mL.h was 1.8-fold higher than the CYP2D6 EM cohort of 0.546 (0.492 to 0.600) ng/mL.h (p < 0.001). Despite a 2.8-fold increase in maternal CYP2D6 protein abundance between gestational weeks 6 and 36, the mean foetal morphine AUC in the CYP2D6 EM and UM phenotype cohorts reduced by 1.55- and 1.75-fold, respectively, over this period. Maternal CYP2D6 phenotype is a significant determinant of foetal morphine AUC. Simulations suggest that the greatest risk with respect to foetal morphine exposure is during the first trimester of pregnancy, particularly in CYP2D6 UM phenotype mothers.

Role of opioid signaling in kidney damage during the development of salt-induced hypertension

Stimulation of kappa opioid receptors modulates calcium influx via TRPC6 channels in podocytes, which ultimately compromises the integrity of the glomerular filtration barrier and promotes a marked worsening of blood pressure control and renal damage.

Opioid use is associated with predictors of poor cardiorenal outcomes. However, little is known about the direct impact of opioids on podocytes and renal function, especially in the context of hypertension and CKD. We hypothesize that stimulation of opioid receptors (ORs) contributes to dysregulation of intracellular calcium ([Ca²⁺]_i) homeostasis in podocytes, thus aggravating the development of renal damage in hypertensive conditions. Herein, freshly isolated glomeruli from Dahl salt-sensitive (SS) rats and human kidneys, as well as immortalized human podocytes, were used to elucidate the contribution of specific ORs to calcium influx. Stimulation of κ-ORs, but not μ-ORs or δ-ORs, evoked a [Ca²⁺]_i transient in podocytes, potentially through the activation of TRPC6 channels. κ-OR agonist BRL52537 was used to assess the long-term effect in SS rats fed a high-salt diet. Hypertensive rats chronically treated with BRL52537 exhibited [Ca²⁺]_i overload in podocytes, nephrinuria, albuminuria, changes in electrolyte balance, and augmented blood pressure. These data demonstrate that the κ-OR/TRPC6 signaling directly influences podocyte calcium handling, provoking the development of kidney injury in the opioid-treated hypertensive cohort.

Options to manage postcraniotomy acute pain in neurosurgery: no protocol available

The physical processes of incision, traction and hemostasis used for craniotomy, stimulate nerve fibers and specific nociceptors, resulting in postoperative pain. During the first 24 h after craniotomy, 87% of patients have postoperatory pain. The rate of suffering pain after craniotomy falls 3% for every year of life. The objective of this study is to review the available therapeutic options to help physicians treating this pain, and discuss pain mechanisms, pathophysiology, plasticity, risk factors and psychological factors. This is a narrative review of the literature from 1970 to June 2019. Data were collected by doing a search in PubMed, EMBASE, Cochrane Reviews and a manual search of all relevant literature references. The literature includes some drugs treatment: Opioids, codeine, morphine, and tramadol, anti-inflammatory non-steroids such as cyclooxygenase-2 inhibitors, gabapentin. It discusses: side effects, pharmacodynamics and indications of each drug, anatomy and Inervation of Skull and its Linigs, pathogenesis of pain Post-craniotomy, scalp nerve block, surgical nerve injury, neuronal plasticity, surgical factors and chronic post-surgical pain.

Metabolism, pharmacokinetics and selected pharmacodynamic effects of codeine following a single oral administration to horses

OBJECTIVE

To describe the pharmacokinetics and selected pharmacodynamic variables of codeine and its metabolites in Thoroughbred horses following a single oral administration.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of 12 Thoroughbred horses, nine geldings and three mares, aged 4-8 years.

METHODS

Horses were administered codeine (0.6 mg kg-1) orally and blood was collected before administration and at various times until 120 hours post administration. Plasma and urine samples were collected and analyzed for codeine and its metabolites by liquid chromatography-mass spectrometry, and plasma pharmacokinetics were determined. Heart rate and rhythm, step counts, packed cell volume and total plasma protein were measured before and 4 hours after administration.

RESULTS

Codeine was rapidly converted to the metabolites norcodeine, codeine-6-glucuronide (C6G), morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). Plasma codeine concentrations were best represented using a two-compartment model. The Cmax, tmax and elimination t½ were 270.7 ± 136.0 ng mL-1, 0.438 ± 0.156 hours and 2.00 ± 0.534 hours, respectively. M3G was the main metabolite detected (Cmax 492.7 ± 35.5 ng mL-1), followed by C6G (Cmax 96.1 ± 33.8 ng mL-1) and M6G (Cmax 22.3 ± 4.96 ng mL-1). Morphine and norcodeine were the least abundant metabolites with Cmax of 3.17 ± 0.95 and 1.42 ± 0.79 ng mL-1, respectively. No significant adverse or excitatory effects were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Following oral administration, codeine is rapidly metabolized to morphine, M3G, M6G, C6G and norcodeine in horses. Plasma concentrations of M6G, a presumed active metabolite of morphine, were comparable to concentrations reported previously following administration of an analgesic dose of morphine to horses. Codeine was well tolerated based on pharmacodynamic variables and behavioral observations.

The Ontogeny of UDP-glucuronosyltransferase Enzymes, Recommendations for Future Profiling Studies and Application Through Physiologically Based Pharmacokinetic Modelling

Limited understanding of drug pharmacokinetics in children is one of the major challenges in paediatric drug development. This is most critical in neonates and infants owing to rapid changes in physiological functions, especially in the activity of drug-metabolising enzymes. Paediatric physiologically based pharmacokinetic models that integrate ontogeny functions for cytochrome P450 enzymes have aided our understanding of drug exposure in children, including those under the age of 2 years. Paediatric physiologically based pharmacokinetic models have consequently been recognised by the European Medicines Agency and the US Food and Drug Administration as innovative tools in paediatric drug development and regulatory decision making. However, little is currently known about age-related changes in UDP-glucuronosyltransferase-mediated metabolism, which represents the most important conjugation reaction for xenobiotics. Therefore, the objective of the review was to conduct a thorough literature survey to summarise our current understanding of age-related changes in UDP-glucuronosyltransferases as well as associated clinical and experimental sources of variance. Our findings indicate that there are distinct differences in UDP-glucuronosyltransferase expression and activity between isoforms for different age groups. In addition, there is substantial variability between individuals and laboratories reported for human liver microsomes, which results in part from a lack of standardised experimental conditions. Therefore, we provide a number of best practice recommendations for experimental conditions, which ultimately may help improve the quality of data used for quantitative clinical pharmacology approaches, and thus for safe and effective pharmacotherapy in children.

Guidelines for Monitoring and Management of Pediatric Patients Before, During, and After Sedation for Diagnostic and Therapeutic Procedures

The safe sedation of children for procedures requires a systematic approach that includes the following: no administration of sedating medication without the safety net of medical/dental supervision, careful presedation evaluation for underlying medical or surgical conditions that would place the child at increased risk from sedating medications, appropriate fasting for elective procedures and a balance between the depth of sedation and risk for those who are unable to fast because of the urgent nature of the procedure, a focused airway examination for large (kissing) tonsils or anatomic airway abnormalities that might increase the potential for airway obstruction, a clear understanding of the medication's pharmacokinetic and pharmacodynamic effects and drug interactions, appropriate training and skills in airway management to allow rescue of the patient, age- and size-appropriate equipment for airway management and venous access, appropriate medications and reversal agents, sufficient numbers of appropriately trained staff to both carry out the procedure and monitor the patient, appropriate physiologic monitoring during and after the procedure, a properly equipped and staffed recovery area, recovery to the presedation level of consciousness before discharge from medical/dental supervision, and appropriate discharge instructions. This report was developed through a collaborative effort of the American Academy of Pediatrics and the American Academy of Pediatric Dentistry to offer pediatric providers updated information and guidance in delivering safe sedation to children.

Rat brain CYP2D activity alters in vivo central oxycodone metabolism, levels and resulting analgesia

Oxycodone is metabolized by CYP2D to oxymorphone. Despite oxymorphone being a more potent opioid-receptor agonist, its contribution to oxycodone analgesia may be minor because of low peripheral production, low blood-brain barrier permeability and central nervous system efflux. CYP2D metabolism within the brain may contribute to variation in central oxycodone and oxymorphone levels, thereby affecting analgesia. Brain CYP2D expression and activity are subject to exogenous regulation; nicotine induces rat brain, but not liver, CYP2D consistent with higher brain CYP2D in smokers. We assessed the role of rat brain CYP2D in orally administered oxycodone metabolism (in vivo brain microdialysis) and analgesia (tail-flick test) by inhibiting brain CYP2D selectively with intracerebroventricular propranolol (mechanism-based inhibitor) and inducing brain CYP2D with nicotine. Inhibiting brain CYP2D increased brain oxycodone levels (1.8-fold; P < 0.03) and analgesia (1.5-fold AUC_0-60 ; P < 0.001) after oxycodone, while inducing brain CYP2D increased brain oxymorphone levels (4.6-fold; P < 0.001) and decreased analgesia (0.8-fold; P < 0.02). Inhibiting the induced brain CYP2D reversed the change in oxycodone levels (1.2-fold; P > 0.1) and analgesia (1.1-fold; P > 0.3). Brain, but not plasma, metabolic ratios were affected by pre-treatments. Peak analgesia was inversely correlated with ex vivo brain (P < 0.003), but not hepatic (P > 0.9), CYP2D activity. Altering brain CYP2D did not affect analgesia from oral oxymorphone (P > 0.9 for AUC_0-60 across all groups), which is not a CYP2D substrate. Thus, brain CYP2D metabolism alters local oxycodone levels and response, suggesting that people with increased brain CYP2D activity may have reduced oxycodone response. Factors that alter individual oxycodone response may be useful for optimizing treatment and minimizing abuse liability.

The Pharmacokinetics of Morphine and Codeine in Human Plasma and Urine after Oral Administration of Qiangli Pipa Syrup

Papaveris pericarpium, a natural source of morphine and codeine, is the principal active component in many antitussive traditional Chinese medicines. We herein report the first PK study of papaveris pericarpium in human plasma and urine following oral administration of single (15, 30, 60 mL) and multiple dose (15 mL) of Qiangli Pipa Syrup (MOR 0.1 mg/mL, COD 0.028 mg/mL) by monitoring morphine and codeine using a HPLC-MS/MS method. Their T_max and t_1/2 values are independent of dosages, while the AUC_0-t linearly increased with higher dosages, indicating linear PK characteristics. AUC_0-t increased obviously after multiple doses, indicating possible risk of accumulative toxicity. Urine studies suggested risks of positive opiate drug tests with a cutoff of 300 ng/mL, which lasted 6-14 h at different doses. These results provide important information for clinical safety, efficacy and rational drug use of Qiangli Pipa Syrup and also guide the related judicial expertise of its administration.

Guidelines for Monitoring and Management of Pediatric Patients Before, During, and After Sedation for Diagnostic and Therapeutic Procedures: Update 2016

The safe sedation of children for procedures requires a systematic approach that includes the following: no administration of sedating medication without the safety net of medical/dental supervision, careful presedation evaluation for underlying medical or surgical conditions that would place the child at increased risk from sedating medications, appropriate fasting for elective procedures and a balance between the depth of sedation and risk for those who are unable to fast because of the urgent nature of the procedure, a focused airway examination for large (kissing) tonsils or anatomic airway abnormalities that might increase the potential for airway obstruction, a clear understanding of the medication's pharmacokinetic and pharmacodynamic effects and drug interactions, appropriate training and skills in airway management to allow rescue of the patient, age- and size-appropriate equipment for airway management and venous access, appropriate medications and reversal agents, sufficient numbers of staff to both carry out the procedure and monitor the patient, appropriate physiologic monitoring during and after the procedure, a properly equipped and staffed recovery area, recovery to the presedation level of consciousness before discharge from medical/dental supervision, and appropriate discharge instructions. This report was developed through a collaborative effort of the American Academy of Pediatrics and the American Academy of Pediatric Dentistry to offer pediatric providers updated information and guidance in delivering safe sedation to children.

Pharmacogenetics of Agents Acting on the Central Nervous System

This article will review the various agents affecting the central nervous system (CNS) such as the analgesics, antidepressants, anticonvulsants, antipsychotics, and benzodiazepines. Most of the research in pharmacogenetics with the CNS agents have been conducted in the antidepressants. The cytochrome 450 IID6 isozyme system has been shown to influence the disposition of the antidepressants and antipsychotics. Amitriptyline metabolism to nortriptyline and nortriptyline conversion to its 10-OH metabolite were shown to be influenced by the IID6 isozyme. Interestingly, imipramine metabolism to desipramine is only partially related to the IID6 isozyme. Biotransformation of imipramine to its 2-OH metabolite was shown to be affected by the IID6 isozyme, but its metabolism to the 10-OH remains to be investigated. Of the antipsychotic drugs, haloperidol and thioridazine are two agents most studied. Haloperidol is converted to a reduced metabolite via a ketone reductase enzyme. The reduced metabolite is oxidized back to Haloperidol. This oxidation pathway was reported to be affected by the IID6 isozyme. Thioridazine metabolism to mesoridazine and conversion of codeine to morphine appear to be also influenced by CP-450 IID6. Other 450 isozymes are reported to be involved with other CNS agents.

"Target-Site" Drug Metabolism and Transport

The recent symposium on "Target-Site" Drug Metabolism and Transport that was sponsored by the American Society for Pharmacology and Experimental Therapeutics at the 2014 Experimental Biology meeting in San Diego is summarized in this report. Emerging evidence has demonstrated that drug-metabolizing enzyme and transporter activity at the site of therapeutic action can affect the efficacy, safety, and metabolic properties of a given drug, with potential outcomes including altered dosing regimens, stricter exclusion criteria, or even the failure of a new chemical entity in clinical trials. Drug metabolism within the brain, for example, can contribute to metabolic activation of therapeutic drugs such as codeine as well as the elimination of potential neurotoxins in the brain. Similarly, the activity of oxidative and conjugative drug-metabolizing enzymes in the lung can have an effect on the efficacy of compounds such as resveratrol. In addition to metabolism, the active transport of compounds into or away from the site of action can also influence the outcome of a given therapeutic regimen or disease progression. For example, organic anion transporter 3 is involved in the initiation of pancreatic β-cell dysfunction and may have a role in how uremic toxins enter pancreatic β-cells and ultimately contribute to the pathogenesis of gestational diabetes. Finally, it is likely that a combination of target-specific metabolism and cellular internalization may have a significant role in determining the pharmacokinetics and efficacy of antibody-drug conjugates, a finding which has resulted in the development of a host of new analytical methods that are now used for characterizing the metabolism and disposition of antibody-drug conjugates. Taken together, the research summarized herein can provide for an increased understanding of potential barriers to drug efficacy and allow for a more rational approach for developing safe and effective therapeutics.

Nicotine Increases Codeine Analgesia Through the Induction of Brain CYP2D and Central Activation of Codeine to Morphine

CYP2D metabolically activates codeine to morphine, which is required for codeine analgesia. Permeability across the blood-brain barrier, and active efflux, suggests that initial morphine in the brain after codeine is due to brain CYP2D metabolism. Human CYP2D is higher in the brains, but not in the livers, of smokers and 7-day nicotine treatment induces rat brain, but not hepatic, CYP2D. The role of nicotine-induced rat brain CYP2D in the central metabolic activation of peripherally administered codeine and resulting analgesia was investigated. Rats received 7-day nicotine (1 mg/kg subcutaneously) and/or a single propranolol (CYP2D mechanism-based inhibitor; 20 μg intracerebroventricularly) pretreatment, and then were tested for analgesia and drug levels following codeine (20 mg/kg intraperitoneally) or morphine (3.5 mg/kg intraperitoneally), matched for peak analgesia. Nicotine increased codeine analgesia (1.59X AUC(0-30 min) vs vehicle; p<0.001), while propranolol decreased analgesia (0.56X; p<0.05); co-pretreatment was similar to vehicle controls (1.23X; p>0.1). Nicotine increased, while propranolol decreased, brain, but not plasma, morphine levels, and analgesia correlated with brain (p<0.02), but not plasma (p>0.4), morphine levels after codeine. Pretreatments did not alter baseline or morphine analgesia. Here we show that brain CYP2D alters drug response despite the presence of substantial first-pass metabolism of codeine and further that nicotine induction of brain CYP2D increases codeine response in vivo. Thus variation in brain CYP2D activity, due to genetics or environment, may contribute to individual differences in response to centrally acting substrates. Exposure to nicotine may increase central drug metabolism, not detected peripherally, contributing to altered drug efficacy, onset time, and/or abuse liability.

Transporter-Mediated Disposition of Opioids: Implications for Clinical Drug Interactions

Opioid-related deaths, abuse, and drug interactions are growing epidemic problems that have medical, social, and economic implications. Drug transporters play a major role in the disposition of many drugs, including opioids; hence they can modulate their pharmacokinetics, pharmacodynamics and their associated drug-drug interactions (DDIs). Our understanding of the interaction of transporters with many therapeutic agents is improving; however, investigating such interactions with opioids is progressing relatively slowly despite the alarming number of opioids-mediated DDIs that may be related to transporters. This review presents a comprehensive report of the current literature relating to opioids and their drug transporter interactions. Additionally, it highlights the emergence of transporters that are yet to be fully identified but may play prominent roles in the disposition of opioids, the growing interest in transporter genomics for opioids, and the potential implications of opioid-drug transporter interactions for cancer treatments. A better understanding of drug transporters interactions with opioids will provide greater insight into potential clinical DDIs and could help improve opioids safety and efficacy.

Death or neurologic injury after tonsillectomy in children with a focus on obstructive sleep apnea: houston, we have a problem!

BACKGROUND

Obesity is epidemic in the United States and with it comes an increased incidence of obstructive sleep apnea (OSA). Evidence regarding opioid sensitivity as well as recent descriptions of deaths after tonsillectomy prompted a survey of all members of the Society for Pediatric Anesthesia regarding adverse events in children undergoing tonsillectomy.

METHODS

An electronic survey was sent to 2377 members of the Society for Pediatric Anesthesia. Additionally, data from the American Society of Anesthesiologists Closed Claims Project were obtained. Adverse events during or after tonsillectomy with or without adenoidectomy in children were included. Children at risk for OSA were identified as either having a positive history for OSA or a post hoc application of the American Society of Anesthesiologists OSA practice guidelines. These children were compared with all other children by Fisher exact test for proportions and t test for continuous variables.

RESULTS

A total of 129 cases were identified from the 731 replies to the survey, with 92 meeting inclusion criteria for having adequate data. Another 19 cases with adequate data were identified from the 45 from the American Society of Anesthesiologists Closed Claims Project. A total of 111 cases were included in the final analysis. Death and permanent neurologic injury occurred in 86 (77%) cases and were reported in the operating room, postanesthesia care unit, on the ward, and at home. Sixty-three (57%) children fulfilled American Society of Anesthesiologists criteria to be at risk for OSA. Children categorized as at risk for OSA were more likely than other children to be obese and to have comorbidities (P < 0.0001). A larger proportion of at risk children had the event attributed to apnea (P = 0.016), whereas all others had a larger proportion of events attributed to hemorrhage (P = 0.006).

CONCLUSIONS

Deaths or neurologic injury after tonsillectomy due to apparent apnea in children suggest that at least 16 children could have been rescued had respiratory monitoring been continued throughout first- and second-stage recovery, as well as on the ward during the first postoperative night. A validated pediatric-specific risk assessment scoring system is needed to assist with identifying children at risk for OSA who are not appropriate to be cared for on an outpatient basis.

Lack of impairment due to confirmed codeine use prior to a motor vehicle accident: role of pharmacogenomics

BACKGROUND

We examined forensic serum toxicology and pharmacogenomics data from a woman on codeine shortly before she caused a motor vehicle accident.

METHODS

A woman driving erratically collided with a parked car of a highway seriously injuring 2 men working to repair the parked vehicle. The woman tested positive for codeine, acetaminophen and barbital. She had been taking these medications for 20 years due to migraine headache. Serum toxicology and genotype analysis for cytochrome P450, UDP glucuronosyltransferase, and other metabolizing enzymes were measured.

RESULTS

The woman was tried and convicted of driving under the influence resulting in bodily harm and was sentenced to 6 years. Toxicology results on peripheral blood showed a total and free codeine of 840 and 348 μg/L, respectively, and total morphine of 20 μg/L (17, 3, and 0 μg/L for morphine-3-glucuronide, morphine-6-glucuronide, and free morphine, respectively). She was heterozygous for CYP 2D6 *2/*4 (extensive/poor metabolism) and heterozygous for UGT 2B7 *1/*2 (extensive/ultra-rapid metabolism). The woman was also taking fluoxetine and bupropion which are strong inhibitors of CYP 2D6.

CONCLUSIONS

Based on her genotype and phenotype and reports by the arresting officer, we suggest that the subject in question was not intoxicated by opiates at the time of her motor vehicle accident and may have been falsely incarcerated.

Morphine is a substrate of the organic cation transporter OCT1 and polymorphisms in OCT1 gene affect morphine pharmacokinetics after codeine administration

We investigated whether morphine and its pro-drug codeine are substrates of the highly genetically polymorphic organic cation transporter OCT1 and whether OCT1 polymorphisms may affect morphine and codeine pharmacokinetics in humans. Morphine showed low transporter-independent membrane permeability (0.5 × 10⁻⁶ cm/s). Morphine uptake was increased up to 4-fold in HEK293 cells overexpressing human OCT1. The increase was concentration-dependent and followed Michaelis-Menten kinetics (KM = 3.4 μM, VMAX = 27 pmol/min/mg protein). OCT1-mediated morphine uptake was abolished by common loss-of-function polymorphisms in the OCT1 gene and was strongly inhibited by drug-drug interactions with irinotecan, verapamil and ondansetron. Morphine uptake in primary human hepatocytes was strongly reduced by MPP⁺, an inhibitor of organic cation transporters, and morphine was not a substrate of OCT3, the other organic cation transporter expressed in human hepatocytes. In concordance with the in vitro data, morphine plasma concentrations in healthy volunteers were significantly dependent on OCT1 polymorphisms. After codeine administration, the mean AUC of morphine was 56% higher in carriers of loss-of-function OCT1 polymorphisms compared to non-carriers (P = 0.005). The difference remained significant after adjustment for CYP2D6 genotype (P = 0.03). Codeine itself had high transporter-independent membrane permeability (8.2 × 10⁻⁶ cm/s). Codeine uptake in HEK293 cells was not affected by OCT1 overexpression and OCT1 polymorphisms did not affect codeine AUCs. In conclusion, OCT1 plays an important role in the hepatocellular uptake of morphine. Carriers of loss-of-function OCT1 polymorphisms may be at higher risk of adverse effects after codeine administration, especially if they are also ultra-rapid CYP2D6 metabolizers.

First demonstration that brain CYP2D-mediated opiate metabolic activation alters analgesia in vivo

The response to centrally acting drugs is highly variable between individuals and does not always correlate with plasma drug levels. Drug-metabolizing CYP enzymes in the brain may contribute to this variability by affecting local drug and metabolite concentrations. CYP2D metabolizes codeine to the active morphine metabolite. We investigated the effect of inhibiting brain, and not liver, CYP2D activity on codeine-induced analgesia. Rats received intracerebroventricular injections of CYP2D inhibitors (20 μg propranolol or 40 μg propafenone) or vehicle controls. Compared to vehicle-pretreated rats, inhibitor-pretreated rats had: (a) lower analgesia in the tail-flick test (p<0.05) and lower areas under the analgesia-time curve (p<0.02) within the first hour after 30 mg/kg subcutaneous codeine, (b) lower morphine concentrations and morphine to codeine ratios in the brain (p<0.02 and p<0.05, respectively), but not in plasma (p>0.6 and p>0.7, respectively), tested at 30 min after 30 mg/kg subcutaneous codeine, and (c) lower morphine formation from codeine ex vivo by brain membranes (p<0.04), but not by liver microsomes (p>0.9). Analgesia trended toward a correlation with brain morphine concentrations (p=0.07) and correlated with brain morphine to codeine ratios (p<0.005), but not with plasma morphine concentrations (p>0.8) or plasma morphine to codeine ratios (p>0.8). Our findings suggest that brain CYP2D affects brain morphine levels after peripheral codeine administration, and may thereby alter codeine's therapeutic efficacy, side-effect profile and abuse liability. Brain CYPs are highly variable due to genetics, environmental factors and age, and may therefore contribute to interindividual variation in the response to centrally acting drugs.

Methadone inhibits CYP2D6 and UGT2B7/2B4 in vivo: a study using codeine in methadone- and buprenorphine-maintained subjects

AIMS

To compare the O-demethylation (CYP2D6-mediated), N-demethylation (CYP3A4-mediated) and 6-glucuronidation (UGT2B4/7-mediated) metabolism of codeine between methadone- and buprenorphine-maintained CYP2D6 extensive metabolizer subjects.

METHODS

Ten methadone- and eight buprenorphine-maintained subjects received a single 60 mg dose of codeine phosphate. Blood was collected at 3 h and urine over 6 h and assayed for codeine, norcodeine, morphine, morphine-3- and -6-glucuronides and codeine-6-glucuronide.

RESULTS

The urinary metabolic ratio for O-demethylation was significantly higher (P= 0.0044) in the subjects taking methadone (mean ± SD, 2.8 ± 3.1) compared with those taking buprenorphine (0.60 ± 0.43), likewise for 6-glucuronide formation (0.31 ± 0.24 vs. 0.053 ± 0.027; P < 0.0002), but there was no significant difference (P= 0.36) in N-demethylation. Similar changes in plasma metabolic ratios were also found. In plasma, compared with those maintained on buprenorphine, the methadone-maintained subjects had increased codeine and norcodeine concentrations (P < 0.004), similar morphine (P= 0.72) and lower morphine-3- and -6- and codeine-6-glucuronide concentrations (P < 0.008).

CONCLUSION

Methadone is associated with inhibition of CYP2D6 and UGTs 2B4 and 2B7 reactions in vivo, even though it is not a substrate for these enzymes. Plasma morphine was not altered, owing to the opposing effects of inhibition of both formation and elimination; however, morphine-6-glucuronide (analgesically active) concentrations were substantially reduced. Drug interactions with methadone are likely to include drugs metabolized by various UGTs and CYP2D6.

Analgesic effects of codeine-6-glucuronide after intravenous administration

Centrally administered codeine glucuronide has been shown to exhibit antinociceptive properties with decreased immunosuppressive effects compared to codeine. In this study, codeine-6-glucuronide was administered to rats, and its analgesic effect was compared to that of codeine. The concentrations of codeine and its metabolites in plasma and brain were also determined at the peak response time after administration of each compound. Receptor-binding studies with rat brain homogenates and affinity profiles were also determined. Intravenous administration of codeine-6-glucuronide resulted in approximately 60% of the analgesic response elicited by codeine itself. Analysis of plasma and brain showed that codeine-6-glucuronide is relatively stable in vivo, with only small amounts of morphine-6-glucuronide being detected in addition to unchanged codeine-6-glucuronide. The receptor affinity of codeine-6-glucuronide was similar to that of codeine. It is concluded that intravenously administered codeine-6-glucuronide possesses analgesic activity similar to that of codeine, and may have clinical benefit in the treatment of pain

CYP2D6 polymorphisms and codeine analgesia in postpartum pain management: a pilot study

BACKGROUND

Codeine, a common opiate prescribed for pain postcesarean section (c-section), is biotransformed by the highly polymorphic Cytochrome P450 enzyme 2D6 (CYP2D6). Ultrarapid metabolizers (UMs), individuals with multiple active copies of CYP2D6, can biotranform up to 50% more codeine into morphine than normal individuals can. In contrast, poor metabolizers (PMs), individuals who have no active CYP2D6 genes, convert almost no codeine into morphine and as a result may take multiple doses of codeine without attaining analgesia.

OBJECTIVE

The aim was to study the relationship between CYP2D6 genotype and codeine analgesia among women recovering from c-section.

METHODS

Forty-five mothers prescribed codeine provided a blood sample for CYP2D6 genotyping and recorded their pain level 4 times a day for 3 days immediately after a c-section. Codeine was used on an as-needed basis; doses and times were recorded. The relationship between CYP2D6 genotype, pain scores, need for codeine, and adverse events was studied. Theoretical morphine dose, based on CYP2D6 genotype, was estimated.

RESULTS

Women at the genotypic extremes reported codeine effects consistent with their genotype: the 2 PMs of codeine reported no analgesia as a result of taking codeine, whereas 2 of the 3 UMs reported immediate pain relief from codeine but stopped taking it due to dizziness and constipation. Much larger numbers are needed to study similar correlations among extensive and intermediate metabolizers.

CONCLUSIONS

In this pilot study, the extreme CYP2D6 genotypes (PMs and UMs) seemed to predict pain response and adverse events. Larger sample sizes are needed to correlate the range of genotypes with pain response.

A systematic review of the use of opioid medication for those with moderate to severe cancer pain and renal impairment: a European Palliative Care Research Collaborative opioid guidelines project

BACKGROUND

Opioid use in patients with renal impairment can lead to increased adverse effects. Opioids differ in their effect in renal impairment in both efficacy and tolerability. This systematic literature review forms the basis of guidelines for opioid use in renal impairment and cancer pain as part of the European Palliative Care Research Collaborative's opioid guidelines project.

OBJECTIVE

The objective of this study was to identify and assess the quality of evidence for the safe and effective use of opioids for the relief of cancer pain in patients with renal impairment and to produce guidelines.

SEARCH STRATEGY

The Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, MedLine, EMBASE and CINAHL were systematically searched in addition to hand searching of relevant journals.

SELECTION CRITERIA

Studies were included if they reported a clinical outcome relevant to the use of selected opioids in cancer-related pain and renal impairment. The selected opioids were morphine, diamorphine, codeine, dextropropoxyphene, dihydrocodeine, oxycodone, hydromorphone, buprenorphine, tramadol, alfentanil, fentanyl, sufentanil, remifentanil, pethidine and methadone. No direct comparator was required for inclusion. Studies assessing the long-term efficacy of opioids during dialysis were excluded.

DATA COLLECTION AND ANALYSIS

This is a narrative systematic review and no meta-analysis was performed. The Grading of RECOMMENDATIONS Assessment, Development and Evaluation (GRADE) approach was used to assess the quality of the studies and to formulate guidelines.

MAIN RESULTS

Fifteen original articles were identified. Eight prospective and seven retrospective clinical studies were identified but no randomized controlled trials. No results were found for diamorphine, codeine, dihydrocodeine, buprenorphine, tramadol, dextropropoxyphene, methadone or remifentanil.

CONCLUSIONS

All of the studies identified have a significant risk of bias inherent in the study methodology and there is additional significant risk of publication bias. Overall evidence is of very low quality. The direct clinical evidence in cancer-related pain and renal impairment is insufficient to allow formulation of guidelines but is suggestive of significant differences in risk between opioids.

RECOMMENDATIONS

RECOMMENDATIONS regarding opioid use in renal impairment and cancer pain are made on the basis of pharmacokinetic data, extrapolation from non-cancer pain studies and from clinical experience. The risk of opioid use in renal impairment is stratified according to the activity of opioid metabolites, potential for accumulation and reports of successful or harmful use. Fentanyl, alfentanil and methadone are identified, with caveats, as the least likely to cause harm when used appropriately. Morphine may be associated with toxicity in patients with renal impairment. Unwanted side effects with morphine may be satisfactorily dealt with by either increasing the dosing interval or reducing the 24 hour dose or by switching to an alternative opioid.

Acute and chronic pain following craniotomy

PURPOSE OF REVIEW

The purpose of the review is to describe what is currently known about the mechanisms, incidence and risk factors for acute and chronic postcraniotomy pain. The review will also summarize the evidence supporting the prevention and management of acute and chronic postcraniotomy pain.

RECENT FINDINGS

Current studies suggest acute and chronic pain is common in patients after craniotomy. Surgical and patient factors may influence the incidence and severity of pain and a multimodal approach to acute postcraniotomy pain is recommended. Although codeine and tramadol are frequently used in the postoperative period, research suggests morphine provides superior efficacy with a good safety profile. Local anesthesia with nerve blocks has not been shown to consistently reduce acute postoperative pain, though it has recently been demonstrated to dramatically reduce the incidence of chronic pain. Despite this, little is known about the mechanisms, prevention and treatment of chronic postcraniotomy pain.

SUMMARY

Acute and chronic pain following craniotomy is frequent and underrecognized. Several surgical and patient risk factors predispose patients to pain following neurosurgery. Further research is needed to determine the mechanisms, predictors, prevention and optimal treatment of acute and chronic pain following craniotomy.

Communicating pharmacogenetic research results to breastfeeding mothers taking codeine: a pilot study of perceptions and benefits

Sixty-two codeine-prescribed breastfeeding mothers from a pharmacogenetic study were interviewed regarding the communication of individual CYP2D6 genotype results and overall research findings. All participants wanted to receive the results of their individual genetic tests; however, individuals placed different values on the usefulness of this information toward future medical decisions. Receiving one's pharmacogenetic test results was not associated with a negative psychosocial impact. Thirty-three percent of the participants wished to withhold these results from their physicians. Participants' expectations seem to dictate the extent of transparency of pharmacogenetic research results.

Pain management of musculoskeletal injuries in children: current state and future directions

BACKGROUND

Pain is the most common reason for seeking health care in the Western world and is a contributing factor in up to 80% of all emergency department (ED) visits. In the pediatric emergency setting, musculoskeletal injuries are one of the most common painful presentations. Inadequate pain management during medical care, especially among very young children, can have numerous detrimental effects. No standard of care exists for the management of acute musculoskeletal injury-related pain in children. Within the ED setting, pain from such injuries has been repeatedly shown to be undertreated.

OBJECTIVES

Upon completion of this CME article, the reader should be better able to (1) distinguish multiple nonpharmacological techniques for minimizing and treating pain and anxiety in children with musculoskeletal injuries, (2) apply recent medical literature in deciding pharmacological strategies for the treatment of children with musculoskeletal injuries, and (3) interpret the basic principles of pharmacogenomics and how they relate to analgesic efficacy.

RESULTS

Pediatric musculoskeletal injuries are both common and painful. There is growing evidence that, in addition to pharmacological therapy, nonpharmacological methods can be introduced to improve analgesia in the ED and after discharge. Traditionally, acetaminophen with codeine has been used to treat moderate orthopedic injury-related pain in children. Other oral opioids (hydrocodone, oxycodone) are gaining popularity, as well. Current data suggest that ibuprofen is at least as effective as acetaminophen-codeine and codeine alone. Medication compliance might be improved if adverse effects were minimized, and ibuprofen has been shown to have a similar or better adverse effect profile than the oral opioids to which it has been compared. Pharmacogenomic data show that nearly 50% of individuals have at least 1 reduced functioning allele resulting in suboptimal conversion of codeine to active analgesic, so it is not surprising that codeine analgesic efficacy is not optimal. At the same time, nonpharmacological therapies are emerging as commonly used treatment options by parents and adjuncts to analgesic medication. The efficacy and role of techniques (massage, music therapy, transcutaneous electrical nerve stimulation), although promising, require further clarification in the treatment of orthopedic injury pain.

CONCLUSIONS

There is a need to optimize the measurement, documentation, and treatment of pain in children. There is growing evidence that nonpharmacological methods can be introduced to improve analgesia in the ED, and efforts to help parents implement these methods at home might be advantageous to optimize outpatient treatment plans. In pharmacotherapy, ibuprofen has emerged as an appropriate first-line choice for mild-moderate orthopedic pain. Other oral opioids (hydrocodone, oxycodone) are gaining popularity over codeine, because of the current understanding of the pharmacogenomics of such medications.

Uptake of codeine into intestinal epithelial (Caco-2) and brain endothelial (RBE4) cells

Orally administered codeine has to permeate both the intestinal and the blood-brain barrier in order to act as analgesic and cough suppressant. In this study we characterized the uptake of codeine at intestinal epithelial (Caco-2) and brain endothelial (RBE4) cells. At both cell types, uptake of [(3)H]codeine was independent of an inwardly directed Na(+) gradient. Uptake was, however, strongly stimulated by an outwardly directed H(+) gradient and inhibited by the protonophore FCCP. [(3)H]Codeine uptake into Caco-2 cells was strongly temperature dependent. In the presence of excess amounts of unlabeled codeine, the uptake was inhibited by up to 87% (Caco-2) or 94% (RBE4), respectively. Synthetic opioids and some non-opioid organic cations like propranolol, pyrilamine and quinidine potently inhibited [(3)H]codeine uptake. Several prototype substrates of known transporters for amino acids, neurotransmitters and organic cations were ineffective. Our data are consistent with a hypothetic saturable, H(+)-dependent (antiport) mechanism not yet identified on a molecular level. The pH dependence of codeine uptake and its intracellular accumulation can partially also be explained by a model comprising diffusional membrane permeation of unionized species of codeine followed by codeine sequestration into acidic vesicles and distribution into cellular lipids.

Influence of the CYP2D6 polymorphism and hemodialysis on codeine disposition in patients with end-stage renal disease

OBJECTIVE

We studied the influence of three factors on drug disposition: genetic polymorphism, impaired renal excretion of drug metabolites, and the possible elimination by hemodialysis (HD), using codeine as a model drug.

METHODS

Based on the genotyping of three CYP2D6 polymorphisms in 228 HD patients, nine extensive metabolizers (EMs) and two poor metabolizers (PMs) were given a single oral dose of 50 mg codeine phosphate. Plasma concentrations of its metabolites codeine-6-glucuronide (C6G), morphine-3-glucuronide (M3G), and morphine-6-glucuronide (M6G) were determined after 2, 4, 6, 8 and 24 h (beginning of the HD session) and again after 4 h of HD (28 h). Codeine metabolites in plasma were quantitated by liquid chromatography-mass spectrometry (LC-MS).

RESULTS

The concentrations of C6G in plasma were high and similar in EMs and PMs. Two hours after the codeine intake, the mean concentration of M3G was 210 nM in EMs vs. 3.5 nM in PMs. The M6G metabolite concentrations could be quantitated in EMs but were below the limit of quantification in PMs (<1 nM). All three codeine metabolites/glucuronides remained unchanged or even increased until the start of HD, and thereafter, the concentrations decreased dramatically during the HD procedure.

CONCLUSIONS

Formation of the codeine metabolites M3G and M6G was dependent on the CYP2D6 genotype, as previously shown in healthy individuals. Elimination of glucuronides in these patients was absent until HD was performed. These factors need to be taken into consideration when drugs metabolized by CYPs are prescribed in HD patients.

Oral fluid testing for drugs of abuse

BACKGROUND

Oral fluid (OF) is an exciting alternative matrix for monitoring drugs of abuse in workplace, clinical toxicology, criminal justice, and driving under the influence of drugs (DUID) programs. During the last 5 years, scientific and technological advances in OF collection, point-of-collection testing devices, and screening and confirmation methods were achieved. Guidelines were proposed for workplace OF testing by the Substance Abuse and Mental Health Services Administration, DUID testing by the European Union's Driving under the Influence of Drugs, Alcohol and Medicines (DRUID) program, and standardization of DUID research. Although OF testing is now commonplace in many monitoring programs, the greatest current limitation is the scarcity of controlled drug administration studies available to guide interpretation.

CONTENT

This review outlines OF testing advantages and limitations, and the progress in OF that has occurred during the last 5 years in collection, screening, confirmation, and interpretation of cannabinoids, opioids, amphetamines, cocaine, and benzodiazepines. We examine controlled drug administration studies, immunoassay and chromatographic methods, collection devices, point-of-collection testing device performance, and recent applications of OF testing.

SUMMARY

Substance Abuse and Mental Health Services Administration approval of OF testing was delayed because questions about drug OF disposition were not yet resolved, and collection device performance and testing assays required improvement. Here, we document the many advances achieved in the use of OF. Additional research is needed to identify new biomarkers, determine drug detection windows, characterize OF adulteration techniques, and evaluate analyte stability. Nevertheless, there is no doubt that OF offers multiple advantages as an alternative matrix for drug monitoring and has an important role in DUID, treatment, workplace, and criminal justice programs.

Guidelines for maternal codeine use during breastfeeding

QUESTION

In light of the recent evidence of adverse events in infants whose mothers use codeine medication, we have been struggling with the issue of how to manage codeine analgesia in our postpartum patients. What are some guidelines for the safe use of codeine during breastfeeding?

ANSWER

Motherisk has summarized recent scientific evidence into suggested guidelines for the safe use of codeine during breastfeeding.