The pharmacokinetics of morphine and morphine glucuronide metabolites after subcutaneous bolus injection and subcutaneous infusion of morphine

Physiologically Based Pharmacokinetic (PBPK) Model Predictions of Disease Mediated Changes in Drug Disposition in Patients with Nonalcoholic Fatty Liver Disease (NAFLD)

PURPOSE

This study was designed to verify a virtual population representing patients with nonalcoholic fatty liver disease (NAFLD) to support the implementation of a physiologically based pharmacokinetic (PBPK) modeling approach for prediction of disease-related changes in drug pharmacokinetics.

METHODS

A virtual NAFLD patient population was developed in GastroPlus (v.9.8.2) by accounting for pathophysiological changes associated with the disease and proteomics-informed alterations in the abundance of metabolizing enzymes and transporters pertinent to drug disposition. The NAFLD population model was verified using exemplar drugs where elimination is influenced predominantly by cytochrome P450 (CYP) enzymes (chlorzoxazone, caffeine, midazolam, pioglitazone) or by transporters (rosuvastatin, 11C-metformin, morphine and the glucuronide metabolite of morphine).

RESULTS

PBPK model predictions of plasma concentrations of all the selected drugs and hepatic radioactivity levels of 11C-metformin were consistent with the clinically-observed data. Importantly, the PBPK simulations using the virtual NAFLD population model provided reliable estimates of the extent of changes in key pharmacokinetic parameters for the exemplar drugs, with mean predicted ratios (NAFLD patients divided by healthy individuals) within 0.80- to 1.25-fold of the clinically-reported values, except for midazolam (prediction-fold difference of 0.72).

CONCLUSION

A virtual NAFLD population model within the PBPK framework was successfully developed with good predictive capability of estimating disease-related changes in drug pharmacokinetics. This supports the use of a PBPK modeling approach for prediction of the pharmacokinetics of new investigational or repurposed drugs in patients with NAFLD and may help inform dose adjustments for drugs commonly used to treat comorbidities in this patient population.

Developing mathematical models to compare and analyse the pharmacokinetics of morphine and fentanyl

Background and Aims

The two-compartment model is generally used in pharmacokinetics to illustrate the distribution and excretion of drugs. In this study, we evaluated the distribution patterns of morphine and fentanyl by using a two-compartment model.

Methods

Using numeric analysis techniques, non-linear ordinary differential equations were used to mathematically analyse drug distribution, transition, and concentration in the body compartments. Math Works, Inc., MATLAB, version 2023a, a programming tool, was used to characterise the impact of initial concentration and rate constants on the kinetics of the drug. For a definite therapeutic concentration of morphine and fentanyl in blood, pharmacokinetic characteristics were plotted.

Results

The study results showed the time taken by morphine and fentanyl to reach a target concentration in the blood that is sufficient to generate the preferred therapeutic effects. The mathematical models comparing morphine and fentanyl pharmacokinetics showed that fentanyl reached the target therapeutic concentration 125 minutes earlier than morphine and was metabolised and removed from the body more rapidly (44 minutes earlier than morphine).

Conclusion

These comparative mathematical models on morphine and fentanyl enable the determination of drug dosages and understanding of drug efficacy that facilitates optimising dosing regimens. The right choice between them can be made based on the time to reach the target therapeutic concentration in the blood, elimination time, severity of pain, and patient characteristics.

Measures of Dosage for Spinal-Cord Electrical Stimulation: Review and Proposal

This manuscript proposes an electrical definition of therapeutic dose for spinal-cord systems used for the treatment of chronic pain, analogous to the pharmacological definition. Dose-response relationships are fundamental to pharmacology, radio-therapy, and other treatments, but have never been properly established for neuromodulation. This manuscript offers a robust measure of dose, pre-requisite to establishing a reliable and repeatable dose-response relationship. The new definition, enabled by the system transresistance obtained from measurement of evoked action potentials, recognizes the mechanism of action of spinal cord stimulation (SCS), and should improve acceptance of the therapy as compared to pharmacological treatments which are currently used more frequently for the treatment of chronic pain. The new definition suggests methods for personalization and standardization of the dose in SCS, and is potentially generalizable to all neuromodulation therapies in which nervous tissue is excited including sacral nerve stimulation (SNS), vagal nerve stimulation (VNS) and deep-brain stimulation (DBS). Formulas are provided, and applied using patient data. Powerful conclusions are drawn from application of the new measure.

Pharmacological Treatments and Therapeutic Drug Monitoring in Patients with Chronic Pain

Pain is an unpleasant sensory and emotional experience that affects every aspect of a patient's life and which may be treated through different pharmacological and non-pharmacological approaches. Analgesics are the drugs most commonly used to treat pain, and in specific situations, the use of opioids may be considered with caution. These drugs, in fact, do not always induce optimal analgesia in patients, and several problems are associated with their use. The purpose of this narrative review is to describe the pharmacological approaches currently used for the management of chronic pain. We review several aspects, from the pain-scale-based methods currently available to assess the type and intensity of pain, to the most frequently administered drugs (non-narcotic analgesics and narcotic analgesics), whose pharmacological characteristics are briefly reported. Overall, we attempt to provide an overview of different pharmacological treatments while also illustrating the relevant guidelines and indications. We then report the strategies that may be used to reduce problems related to opioid use. Specifically, we focus our attention on therapeutic drug monitoring (TDM), a tool that could help clinicians select the most suitable drug and dose to be used for each patient. The actual potential of using TDM to optimize and personalize opioid-based pain treatments is finally discussed based on recent scientific reports.

A General Picture of Cucurbit[8]uril Host–Guest Binding: Recalibrating Bonded Interactions

Atomic-level understanding of the dynamic feature of host–guest interactions remains a central challenge in supramolecular chemistry. The remarkable guest binding behavior of the Cucurbiturils family of supramolecular containers makes them promising drug carriers. Among Cucurbit[n]urils, Cucurbit[8]uril (CB8) has an intermediate portal size and cavity volume. It can exploit almost all host–guest recognition motifs formed by this host family. In our previous work, an extensive computational investigation of the binding of seven commonly abused and structurally diverse drugs to the CB8 host was performed, and a general dynamic binding picture of CB8-guest interactions was obtained. Further, two widely used fixed-charge models for drug-like molecules were investigated and compared in great detail, aiming at providing guidelines in choosing an appropriate charge scheme in host-guest modelling. Iterative refitting of atomic charges leads to improved binding thermodynamics and the best root-mean-squared deviation from the experimental reference is 2.6 kcal/mol. In this work, we focus on a thorough evaluation of the remaining parts of classical force fields, i.e., the bonded interactions. The widely used general Amber force fields are assessed and refitted with generalized force-matching to improve the intra-molecular conformational preference, and thus the description of inter-molecular host–guest interactions. The interaction pattern and binding thermodynamics show a significant dependence on the modelling parameters. The refitted system-specific parameter set improves the consistency of the modelling results and the experimental reference significantly. Finally, combining the previous charge-scheme comparison and the current force-field refitting, we provide general guidelines for the theoretical modelling of host–guest binding.

Rapid titration with oral sustained-release morphine plus subcutaneous morphine in a multi-center, randomized control study of cancer patients with moderate to severe cancer pain

BACKGROUND

Pain is one of the most common concomitant symptoms among cancer patients. Pharmacologic agents are regarded as a cornerstone of cancer pain management. 'Dose titration' with short-acting morphine is widely accepted. Such a titration method is very complicated. The analgesic background establishment is often delayed. Titration based on sustained-release opioids is also recommended, but the onset of analgesic effect requires hours, whereas the rescue analgesia is always needed. This study evaluated the optimized morphine titration scheme with a simultaneous combination of sustained-release morphine and subcutaneous morphine.

METHODS

In a multicenter, 7-day, randomized controlled study, patients with moderate to severe cancer pain were assigned to receive either sustained-release morphine and subcutaneous morphine simultaneously (rapid titration) or only subcutaneous morphine to dose titration. The primary outcome was the safety and the number of times of rescue therapy as needed in the first 24 h.

RESULTS

A total of 108 patients with moderate to severe cancer pain were included in the study. The number of times of rescue analgesics in the first 24 h significantly reduced in the rapid titration group (0.4 ± 0.48 vs. 2.3 ± 0.78, P = 0.000). No differences in the intensity of opioid-related symptoms were found between the two groups.

CONCLUSIONS

Rapid titration is safe and efficient, which could significantly decrease rescue analgesics in the first 24 h and achieve better analgesic efficacy for cancer pain patients.

A General Picture of Cucurbit[8]uril Host-Guest Binding

Describing, understanding, and designing complex interaction networks within macromolecular systems remain challenging in modern chemical research. Host-guest systems, despite their relative simplicity in both the structural feature and interaction patterns, still pose problems in theoretical modeling. The barrel-shaped supramolecular container cucurbit[8]uril (CB8) shows promising functionalities in various areas, e.g., catalysis and molecular recognition. It can stably coordinate a series of structurally diverse guests with high affinities. In this work, we examine the binding of seven commonly abused drugs to the CB8 host, aiming at providing a general picture of CB8-guest binding. Extensive sampling of the configurational space of these host-guest systems is performed, and the binding pathway and interaction patterns of CB8-guest complexes are investigated. A thorough comparison of widely used fixed-charge models for drug-like molecules is presented. Iterative refitting of the atomic charges suggests significant conformation dependence of charge generation. The initial model generated at the original conformation could be inaccurate for new conformations explored during conformational search, and the newly fitted charge set improves the prediction-experiment correlation significantly. Our investigations of the configurational space of CB8-drug complexes suggest that the host-guest interactions are more complex than expected. Despite the structural simplicities of these molecules, the conformational fluctuations of the host and the guest molecules and orientations of functional groups lead to the existence of an ensemble of binding modes. The insights of the binding thermodynamics, performance of fixed-charge models, and binding patterns of the CB8-guest systems are useful for studying and elucidating the binding mechanism of other host-guest complexes.

Morphine Perinatal Exposure Induces Long-Lasting Negative Emotional States in Adult Offspring Rodents

Psychoactive substances during pregnancy and lactation is a key problem in contemporary society, causing social, economic, and health disturbance. In 2010, about 30 million people used opioid analgesics for non-therapeutic purposes, and the prevalence of opioids use during pregnancy ranged from 1% to 21%, representing a public health problem. This study aimed to evaluate the long-lasting neurobehavioral and nociceptive consequences in adult offspring rats and mice exposed to morphine during intrauterine/lactation periods. Pregnant rats and mice were exposed subcutaneously to morphine (10 mg/kg/day) during 42 consecutive days (from the first day of pregnancy until the last day of lactation). Offspring were weighed on post-natal days (PND) 1, 5, 10, 15, 20, 30, and 60, and behavioral tasks (experiment 1) or nociceptive responses (experiment 2) were assessed at 75 days of age (adult life). Morphine-exposed female rats displayed increased spontaneous locomotor activity. More importantly, both males and female rats perinatally exposed to morphine displayed anxiety- and depressive-like behaviors. Morphine-exposed mice presented alterations in the nociceptive responses on the writhing test. This study showed that sex difference plays a role in pain threshold and that deleterious effects of morphine during pre/perinatal periods are nonrepairable in adulthood, which highlights the long-lasting clinical consequences related to anxiety, depression, and nociceptive disorders in adulthood followed by intrauterine and lactation morphine exposure.

Physiologically-Based Pharmacokinetic Model of Morphine and Morphine-3-Glucuronide in Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH), the progressive form of nonalcoholic fatty liver disease, is increasing in prevalence. NASH-related alterations in hepatic protein expression (e.g., transporters) and in overall physiology may affect drug exposure by altering drug disposition and elimination. The aim of this study was to build a physiologically-based pharmacokinetic (PBPK) model to predict drug exposure in NASH by incorporating NASH-related changes in hepatic transporters. Morphine and morphine-3-glucuronide (M3G) were used as model compounds. A PBPK model of morphine with permeability-limited hepatic disposition was extended to include M3G disposition and enterohepatic recycling (EHR). The model captured the area under the plasma concentration-time curve (AUC) of morphine and M3G after intravenous morphine administration within 0.82-fold and 1.94-fold of observed values from 3 independent clinical studies for healthy adult subjects (6, 10, and 14 individuals). When NASH-related changes in multidrug resistance-associated protein 2 (MRP2) and MRP3 were incorporated into the model, the predicted M3G mean AUC in NASH was 1.34-fold higher compared to healthy subjects, which is slightly lower than the observed value (1.63-fold). Exploratory simulations on other physiological changes occurring in NASH (e.g., moderate decreases in glomerular filtration rate and portal vein blood flow) revealed that the effect of transporter changes was most prominent. Additionally, NASH-related transporter changes resulted in decreased morphine EHR, which could be important for drugs with extensive EHR. This study is an important first step to predict drug disposition in complex diseases such as NASH using PBPK modeling.

Evaluation of Inpatient Opioid Prescribing Resulting in Outpatient Opioid Prescriptions for Previously Opioid-Naive Internal Medicine Patients

BACKGROUND

Little data exist regarding inpatient opioid prescriptions as a potential contribution to the current opioid crisis. While pain management is essential to inpatient care, the ease of which opioids may be prescribed for all levels of pain may contribute to unnecessary inpatient exposure and new outpatient prescriptions. The aim of this study was to observe patterns of opioid prescribing potentially leading to new opioid prescriptions at hospital discharge for previously opioid-naive patients.

METHODS

This study was a single-center observational study of opioid-naïve internal medicine patients who were prescribed inpatient opioids. Patient charts were reviewed to assess the patterns of inpatient opioid and non-opioid analgesic use, new opioid prescriptions upon discharge and medical record documentation justifying the need for outpatient therapy.

RESULTS

Among the 101 patients included in this study, 71 were prescribed IV opioids and 45 were prescribed both IV and oral opioids. Non-opioid analgesics were available for 78 patients. Twenty patients were discharged with a new prescription. The mean duration of outpatient prescriptions was 3.85 +/- 1.85 days with mean morphine milligram equivalents (MME) of 44.25 +/- 22.16. Among patients receiving these outpatient prescriptions, 11 had reference to the therapy in the discharge summary.

CONCLUSIONS

This observational study describes an opportunity to improve inpatient opioid prescribing practices which may reduce new prescriptions for continued outpatient therapy. Further work should focus on optimizing use of non-opioid analgesia, minimizing use of IV opioids and requiring prescribers to justify the indication for new opioid prescriptions upon hospital discharge.

Mitragynine Attenuates Morphine Withdrawal Effects in Rats-A Comparison With Methadone and Buprenorphine

BACKGROUND

Opiate addiction is a major health problem in many countries. A crucial component of the medical treatment is the management of highly aversive opiate withdrawal signs, which may otherwise lead to resumption of drug taking. In a medication-assisted treatment (MAT), methadone and buprenorphine have been implemented as substitution drugs. Despite MAT effectiveness, there are still limitations and side effects of using methadone and buprenorphine. Thus, other alternative therapies with less side effects, overdosing, and co-morbidities are desired. One of the potential pharmacotherapies may involve kratom's major indole alkaloid, mitragynine, since kratom (Mitragyna speciosa Korth.) preparations have been reported to alleviate opiate withdrawal signs in self-treatment in Malaysian opiate addicts.

METHODS

Based on the morphine withdrawal model, rats were morphine treated with increasing doses from 10 to 50 mg/kg twice daily over a period of 6 days. The treatment was discontinued on day 7 in order to induce a spontaneous morphine abstinence. The withdrawal signs were measured daily after 24 h of the last morphine administration over a period of 28 abstinence days. In rats that developed withdrawal signs, a drug replacement treatment was given using mitragynine, methadone, or buprenorphine and the global withdrawal score was evaluated.

RESULTS

The morphine withdrawal model induced profound withdrawal signs for 16 days. Mitragynine (5-30 mg/kg; i.p.) was able to attenuate acute withdrawal signs in morphine dependent rats. On the other hand, smaller doses of methadone (0.5-2 mg/kg; i.p.) and buprenorphine (0.4-1.6 mg/kg; i.p.) were necessary to mitigate these effects.

CONCLUSIONS

These data suggest that mitragynine may be a potential drug candidate for opiate withdrawal treatment.

Integrated Model to Describe Morphine Pharmacokinetics in Humans

The pharmacokinetics (PK) of morphine has been extensively investigated. Though different publications have focused on the various aspects of morphine PK, none have quantitatively interpreted morphine PK across different publications. The objective of this research is to summarize the current understanding of morphine PK in humans quantitatively. In this research, a parent-metabolite compartmental PK modeling approach was used to summarize the current understanding of morphine PK in humans. Plasma concentration-time profiles and cumulative urine recovery time profiles of morphine, morphine-3-glucuronide, and morphine-6-glucuronide were digitized from the previous publications to develop the parent-metabolite PK model. The parent-metabolite PK model successfully described the plasma concentration-time profiles and cumulative urine recovery of morphine as well as its two major metabolites, morphine-3-glucuronide and morphine-6-glucuronide, after intravenous and oral administration of morphine. This research separated out the first-pass effect on morphine metabolism after oral administration. By integrating these results with two mass balance studies of morphine, a clear picture of morphine absorption and disposition is given. Though the results are mainly based on data collected from healthy volunteers or patients whose disease is not expected to impact morphine PK, the parent-metabolite model sets a framework to further evaluate morphine PK in special populations, such as pediatrics and patients with renal impairment.

Prolonged central apnoea after intravenous morphine administration in a 12-year-old male with a UGT1A1 loss-of-function polymorphism

ADVERSE EVENT

Repeated and prolonged episodes of central apnoea and hypoxia after receiving intravenous morphine for analgesia and ketamine for sedation.

DRUG IMPLICATED

Intravenous morphine sulfate.

THE PATIENT

Previously healthy 12-year-old male with no history of sleep apnoea who presented with distal tibia and fibula fracture.

EVIDENCE THAT LINKS DRUG TO EVENT

Pharmacogenomic testing revealed that the patient was homozygous for the T allele at the rs887829 SNP in UGT1A1, an enzyme involved in the metabolism of morphine. This polymorphism is a loss-of-function variant, leading to impaired metabolism of morphine.

MECHANISM

Morphine is metabolized by UDP-glucuronosyltransferase (UGT)-2B7 and UGT1A1 to form its major metabolites morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). Our patient was a poor metabolizer through UGT1A1, likely leading to increased respiratory depression as morphine has greater respiratory depressant effects compared to its metabolites.

IMPLICATIONS

When appropriate, physicians should enquire about prior receipt of opioids, in both the patient and family, to be better prepared for potential adverse reactions. In the patient with excessive sedation or respiratory depression to standard doses of morphine, genetic testing may be warranted, especially if there is a family or past history that supports a metabolic defect in morphine metabolism and/or excretion.

Finding Tmax and Cmax in Multicompartmental Models

Drug absorption data are critical in bioequivalence comparisons, and factors such as the maximum drug concentration (C_max), time to achieve C_max (or T_max), as well as the area under the curve (AUC) are important metrics. It is generally accepted that the AUC is a meaningful estimate of the extent of absorption, and T_max or C_max may be used for assessing the rate of absorption. But estimation of the rate of absorption with T_max or C_max is not always feasible, as explicit solutions relating T_max and C_max to the absorption (k_a) and elimination rate (k) constants exist only for the one and not multicompartmental oral model. Therefore, the determination of T_max or C_max for multicompartmental models is uncertain. Here, we propose an alternate, numerical approach that uses the point-slope method for the first and second derivative(s) of the concentration-versus-time profiles and the Newton-Raphson iteration method for the determination of T_max and C_max We show that the method holds for multicompartmental oral dosing under single or steady-state conditions in the absence of known microconstants, even for flip-flop (k_a < β) models. Simulations showed that the C_max and T_max estimates obtained with the Newton-Raphson method were more accurate than those based on the noncompartmental, observation-based method recommended by the US Food and Drug Administration. The %Bias attributable to sampling frequency and assay error were less than those determined by the noncompartmental method, showing that the Newton-Raphson method is viable for the estimation of T_max and C_max.

Association of an Opioid Standard of Practice Intervention With Intravenous Opioid Exposure in Hospitalized Patients

IMPORTANCE

Opioids are commonly used to treat pain in hospitalized patients; however, intravenous administration carries an increased risk of adverse effects compared with oral administration. The subcutaneous route is an effective method of opioid delivery with favorable pharmacokinetics.

OBJECTIVE

To assess an intervention to reduce intravenous opioid use, total parenteral opioid exposure, and the rate of patients administered parenteral opioids.

DESIGN, SETTING, AND PARTICIPANTS

A pilot study was conducted in an adult general medical unit in an urban academic medical center. Attending physicians, nurse practitioners, and physician assistants who prescribed drugs were the participants. Use of opioids was compared between a 6-month control period and 3 months following education for the prescribers on opioid routes of administration.

INTERVENTIONS

Adoption of a local opioid standard of practice, preferring the oral and subcutaneous routes over intravenous administration, and education for prescribers and nursing staff on awareness of the subcutaneous route was implemented.

MAIN OUTCOMES AND MEASURES

The primary outcome was a reduction in intravenous doses administered per patient-day. Secondary measures included total parenteral and overall opioid doses per patient-day, parenteral and overall opioid exposure per patient-day, and daily rate of patients receiving parenteral opioids. Pain scores were measured on a standard 0- to 10-point Likert scale over the first 5 days of hospitalization.

RESULTS

The control period included 4500 patient-days, and the intervention period included 2459 patient-days. Of 127 patients in the intervention group, 59 (46.5%) were men; mean (SD) age was 57.6 (18.5) years. Intravenous opioid doses were reduced by 84% (0.06 vs 0.39 doses per patient-day, P < .001), and doses of all parenteral opioids were reduced by 55% (0.18 vs 0.39 doses per patient-day, P < .001). In addition, mean (SD) daily parenteral opioid exposure decreased by 49% (2.88 [0.72] vs 5.67 [1.14] morphine-milligram equivalents [MMEs] per patient-day). The daily rate of patients administered any parenteral opioid decreased by 57% (6% vs 14%; P < .001). Doses of opioids given by oral or parenteral route were reduced by 23% (0.73 vs 0.95 doses per patient-day, P = .02), and mean daily overall opioid exposure decreased by 31% (6.30 [4.12] vs 9.11 [7.34] MMEs per patient-day). For hospital days 1 through 3, there were no significant postintervention vs preintervention differences in mean reported pain score for patients receiving opioid therapy: day 1, -0.19 (95% CI, -0.94 to 0.56); day 2, -0.49 (95% CI, -1.01 to 0.03); and day 3, -0.54 (95% CI, -1.18 to 0.09). However, significant improvement was seen in the intervention group on days 4 (-1.07; 95% CI, -1.80 to -0.34) and 5 (-1.06; 95% CI, -1.84 to -0.27).

CONCLUSIONS AND RELEVANCE

An intervention targeting the use of intravenous opioids may be associated with reduced opioid exposure while providing effective pain control to hospitalized adults.

A Prospective Population Pharmacokinetic Study on Morphine Metabolism in Cancer Patients

Background

Oral and subcutaneous morphine is widely used for the treatment of cancer-related pain; however, solid pharmacokinetic data on this practice are lacking. Furthermore, it is largely unknown which factors contribute to the variability in clearances of morphine and its metabolites and whether morphine clearance is related to treatment outcome.

Methods

Blood samples from 49 cancer patients treated with oral and/or subcutaneous morphine were prospectively collected and were used to develop a population pharmacokinetic model for morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G). The influence of age, gender, renal function and several polymorphisms possibly related to the pharmacokinetics of the three compounds was investigated. In addition, the relation between treatment failure and morphine and metabolite clearances was explored.

Results

A one-compartment model including an extensive first-pass effect adequately described the data of morphine and its metabolites. Estimated mean area under the plasma concentration–time curve (AUC) ratios following oral versus subcutaneous administration were: M3G/morphine 29.7:1 vs. 11.1:1; M6G/morphine 5.26:1 vs. 1.95:1; and M3G/M6G 5.65:1 vs. 5.70:1. Renal function was significantly correlated with clearance of the metabolites, which increased 0.602 L/h per every 10 mL/min/1.73 m² increase of estimated glomerular filtration rate (eGFR), reaching a plateau for eGFR >90 mL/min/1.73 m². The clearance of morphine or its metabolites was not found to be correlated with treatment failure.

Conclusion

The influence of age-, gender- and pharmacokinetic-related polymorphisms was not identified on the pharmacokinetics of morphine. Clearance of morphine or its metabolites was not found to explain treatment outcome; however, large variations in plasma concentrations of morphine, M3G and M6G support further studies on the relation between plasma concentrations and treatment outcome.

Dutch Trial Register ID: NTR4369.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-016-0471-7) contains supplementary material, which is available to authorized users.

Age-dependent antinociception and behavioral inhibition by morphine

In current clinical practice, morphine is dosed in older patients based on patient-weight, with different calculations for adjustment. However, at present, neither clinical experience nor the literature offers a clear evidence base for the relationship between antinociception, behavioral effects and morphine administration in older patients. In this study, we compared the nociceptive response of 8 and 24 week old rats after subcutaneous administration of morphine per body weight and analyzed their behavior using an advanced multi-conditioning system. Residual morphine in all major tissues was determined. We observed prolonged morphine-induced antinociception in older rats compared to younger rats. Moreover, morphine significantly stimulated locomotor and rearing behavior 180 min after injection, which was significantly higher in the 8 week compared to 24 week old rats. Tissue analysis from animals extracted 240 min post-injection revealed a significantly higher concentration of residual morphine in the brains of older versus younger animals when standardized on tissue weight. However, this effect was not observed when residual morphine was standardized on protein content. Collectively, our data suggest that in older rats morphine exhibits higher antinociception and increased behavioral inhibition compared to younger animals. This effect is likely due to a significantly higher accumulation of morphine in the brain of older animals.

Evaluation of 25% Poloxamer As a Slow Release Carrier for Morphine in a Rat Model

The objectives of this study were to evaluate poloxamer as a slow release carrier for morphine (M) and potential tissue irritation after subcutaneous poloxamer-morphine (PM) injection in a rat model. Based on the result of a previous in vitro work, 25% poloxamer, with and without morphine, and saline were administered in 14 rats' flanks. Blood for morphine concentrations was automatically sampled at multiple preprogrammed time points using the Culex™ unit for 48 h. Skin tissues from the injection sites were harvested and evaluated for histopathological changes. Following M or PM administration, it was determined that the half-life (t_1/2) was significantly longer in the PM (5.5 ± 7.2 h) than M (0.7 ± 0.8 h) indicated a slow dissolution of poloxamer with morphine. The t_max was within 15 min and C_max was approximately three times higher with M than with PM, reaching 716.8 (±153.7 ng/ml) of plasma morphine concentrations. There was no significant difference in total area under the curve and clearance of M versus PM. Histology inflammatory scores were similar between M, PM, and poloxamer but were significantly higher than saline control. We concluded that 25% poloxamer was capable of increasing the t_1/2 of morphine, without a significant tissue irritation.

Investigation of Slow-wave Activity Saturation during Surgical Anesthesia Reveals a Signature of Neural Inertia in Humans

BACKGROUND

Previously, we showed experimentally that saturation of slow-wave activity provides a potentially individualized neurophysiologic endpoint for perception loss during anesthesia. Furthermore, it is clear that induction and emergence from anesthesia are not symmetrically reversible processes. The observed hysteresis is potentially underpinned by a neural inertia mechanism as proposed in animal studies.

METHODS

In an advanced secondary analysis of 393 individual electroencephalographic data sets, we used slow-wave activity dose-response relationships to parameterize slow-wave activity saturation during induction and emergence from surgical anesthesia. We determined whether neural inertia exists in humans by comparing slow-wave activity dose responses on induction and emergence.

RESULTS

Slow-wave activity saturation occurs for different anesthetics and when opioids and muscle relaxants are used during surgery. There was wide interpatient variability in the hypnotic concentrations required to achieve slow-wave activity saturation. Age negatively correlated with power at slow-wave activity saturation. On emergence, we observed abrupt decreases in slow-wave activity dose responses coincident with recovery of behavioral responsiveness in ~33% individuals. These patients are more likely to have lower power at slow-wave activity saturation, be older, and suffer from short-term confusion on emergence.

CONCLUSIONS

Slow-wave activity saturation during surgical anesthesia implies that large variability in dosing is required to achieve a targeted potential loss of perception in individual patients. A signature for neural inertia in humans is the maintenance of slow-wave activity even in the presence of very-low hypnotic concentrations during emergence from anesthesia.

Cancer Pain Management: Opioid Analgesics, Part 2

Opioid analgesics are the cornerstone of moderate to severe cancer pain management, and do not have ceiling doses unless unmanageable adverse effects occur. Oral, short-acting pure μ agonists such as morphine are most frequently used, but other agents and administration formulations allow finding the right opioid and dose for most patients. In addition, clinicians must understand the metabolism, pharmacokinetics, and elimination of particular drugs to individualize opioid selection, select initial doses, and appropriately escalate doses to satisfactory pain relief or uncontrollable toxicity. Anticipation and proactive management of possible adverse effects, particularly constipation, confusion or delirium, opioid-specific adverse effects, and opioid abuse, are also integral to primary and secondary prophylaxis and management.

Development of a Whole-Body Physiologically Based Pharmacokinetic Approach to Assess the Pharmacokinetics of Drugs in Elderly Individuals

Background

Because of the vulnerability and frailty of elderly adults, clinical drug development has traditionally been biased towards young and middle-aged adults. Recent efforts have begun to incorporate data from paediatric investigations. Nevertheless, the elderly often remain underrepresented in clinical trials, even though persons aged 65 years and older receive the majority of drug prescriptions. Consequently, a knowledge gap exists with regard to pharmacokinetic (PK) and pharmacodynamic (PD) responses in elderly subjects, leaving the safety and efficacy of medicines for this population unclear.

Objectives

The goal of this study was to extend a physiologically based pharmacokinetic (PBPK) model for adults to encompass the full course of healthy aging through to the age of 100 years, to support dose selection and improve pharmacotherapy for the elderly age group.

Methods

For parameterization of the PBPK model for healthy aging individuals, the literature was scanned for anthropometric and physiological data, which were consolidated and incorporated into the PBPK software PK-Sim^®. Age-related changes that occur from 65 to 100 years of age were the main focus of this work. For a sound and continuous description of an aging human, data on anatomical and physiological changes ranging from early adulthood to old age were included. The capability of the PBPK approach to predict distribution and elimination of drugs was verified using the test compounds morphine and furosemide, administered intravenously. Both are cleared by a single elimination pathway. PK parameters for the two compounds in younger adults and elderly individuals were obtained from the literature. Matching virtual populations—with regard to age, sex, anthropometric measures and dosage—were generated. Profiles of plasma drug concentrations over time, volume of distribution at steady state (V_ss) values and elimination half-life (t_½) values from the literature were compared with those predicted by PBPK simulations for both younger adults and the elderly.

Results

For most organs, the age-dependent information gathered in the extensive literature analysis was dense. In contrast, with respect to blood flow, the literature study produced only sparse data for several tissues, and in these cases, linear regression was required to capture the entire elderly age range. On the basis of age-informed physiology, the predicted PK profiles described age-associated trends well. The root mean squared prediction error for the prediction of plasma concentrations of furosemide and morphine in the elderly were improved by 32 and 49 %, respectively, by use of age-informed physiology. The majority of the individual V_ss and t_½ values for the two model compounds, furosemide and morphine, were well predicted in the elderly population, except for long furosemide half-lifes.

Conclusion

The results of this study support the feasibility of using a knowledge-driven PBPK aging model that includes the elderly to predict PK alterations throughout the entire course of aging, and thus to optimize drug therapy in elderly individuals. These results indicate that pharmacotherapy and safety-related control of geriatric drug therapy regimens may be greatly facilitated by the information gained from PBPK predictions.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-016-0422-3) contains supplementary material, which is available to authorized users.

Characterization of Contributing Factors to Variability in Morphine Clearance Through PBPK Modeling Implemented With OCT1 Transporter

Morphine shows large interindividual variability in its pharmacokinetics; however, the cause of this has not been fully addressed. The variability in morphine disposition is considered to be due to a combination of pharmacogenetic and physiological determinants related to morphine disposition. We previously reported the effect of organic cation transporter (OCT1) genotype on morphine disposition in pediatric patients. To further explore the underlying mechanisms for variability arising from relevant determinants, including OCT1, a physiologically based pharmacokinetic (PBPK) model of morphine was developed. The PBPK model predicted morphine concentration‐time profiles well, in both adults and children. Almost all of the observed morphine clearances in pediatric patients fell within a twofold range of median predicted values for each OCT1 genotype in each age group. This PBPK modeling approach quantitatively demonstrates that OCT1 genotype, age‐related growth, and changes in blood flow as important contributors to morphine pharmacokinetic (PK) variability.

Mechanistic Population Pharmacokinetics of Morphine in Neonates With Abstinence Syndrome After Oral Administration of Diluted Tincture of Opium

Conducting and analyzing clinical trials in vulnerable neonates are extremely challenging. The aim of this analysis is to develop a morphine population pharmacokinetics (PK) model using data collected during a randomized control trial in neonates with abstinence syndrome (NAS). A 3-compartment morphine structural PK model after intravenous (IV) administration from previously published work was utilized as prior, whereas an allometric scaling method with physiological consideration was used to extrapolate a PK profile from adults to pediatrics. The absorption rate constant and bioavailability were estimated in NAS after oral administration of diluted tincture of opium (DTO). Goodness-of-fit plots along with normalized prediction distribution error and bootstrap method were performed for model evaluation. We successfully extrapolated the PK profile from adults to pediatrics after IV administration. The estimated first-order absorption rate constant and bioavailability were 0.751 hour(-1) and 48.5%, respectively. Model evaluations showed that the model can accurately and precisely describe the observed data. The population pharmacokinetic model we derived for morphine after oral administration of DTO is reasonable and acceptable; therefore, it can be used to describe the PK and guide future studies. The integration of the previous population PK knowledge as prior information successfully overcomes the logistic and practical issue in vulnerable neonate population.

Subcutaneous fluid and drug delivery: safe, efficient and inexpensive

Patients with difficult venous access or oral intolerance and clinical situations with inadequate response to oral therapy have generated the need for alternative routes of delivery for drugs and fluids.

The purpose of this study was to conduct a systematic review examining the evidence for subcutaneous (SC) administration of drugs and/or fluids.

We used a broad search strategy using electronic databases CINAHL, EMBASE, PubMed and Cochrane library, key terms and ‘Medical Subject Headings’ (MeSH) such as ‘subcutaneous route’, ‘hypodermoclysis’ and the name/group of the most used drugs via this route (e.g. ‘ketorolac, morphine, ceftriaxone’, ‘analgesics, opioids, antibiotics’).

We conclude that the SC route is an effective alternative for rehydration in patients with mild–moderate dehydration and offers a number of potential advantages in appropriately selected scenarios. Experience of administering drugs by this route suggests that it is well tolerated and is associated with minimal side-effects.

Optimization and pharmacological characterization of a refined cisplatin-induced rat model of peripheral neuropathic pain

Chemotherapy-induced peripheral neuropathy (CIPN) is the major dose-limiting side-effect of many front-line anticancer drugs. This study was designed to establish and pharmacologically characterize a refined rat model of cisplatin-induced CIPN. Adult male Sprague-Dawley rats received four (n=18) or five (n=18) single intraperitoneal bolus doses of cisplatin at 3 mg/kg, or saline (control group), once-weekly. Body weight and general health were assessed over a 49-day study period. von Frey filaments and the Hargreaves test were used to define the time course for the development of mechanical allodynia and thermal hypoalgesia in the hindpaws and for efficacy assessment of analgesic/adjuvant agents. The general health of rats administered four cisplatin doses was superior to that of rats administered five doses. Mechanical allodynia was fully developed (paw withdrawal thresholds≤6 g) in the bilateral hindpaws from day 32 to 49 for both cisplatin dosing regimens. They also showed significant thermal hypoalgesia in the bilateral hindpaws. In cisplatin-treated rats with paw withdrawal thresholds of up to 6 g, single bolus doses of gabapentin and morphine produced dose-dependent analgesia, whereas meloxicam and amitriptyline lacked efficacy. We have established and pharmacologically characterized a refined rat model of CIPN that is suitable for efficacy profiling of compounds from analgesic discovery programmes.

Pharmacokinetics of tramadol after subcutaneous administration in a critically ill population and in a healthy cohort

Background

Tramadol is an atypical centrally acting analgesic agent available as both oral and parenteral preparations. For patients who are unable to take tramadol orally, the subcutaneous route of administration offers an easy alternative to intravenous or intramuscular routes. This study aimed to characterise the absorption pharmacokinetics of a single subcutaneous dose of tramadol in severely ill patients and in healthy subjects.

Methods/design

Blood samples (5 ml) taken at intervals from 2 minutes to 24 hours after a subcutaneous dose of tramadol (50 mg) in 15 patients (13 male, two female) and eight healthy male subjects were assayed using high performance liquid chromatography. Pharmacokinetic parameters were derived using a non-compartmental approach.

Results

There were no statistically significant differences between the two groups in the following parameters (mean ± SD): maximum venous concentration 0.44 ± 0.18 (patients) vs. 0.47 ± 0.13 (healthy volunteers) mcg/ml (p = 0.67); area under the plasma concentration-time curve 177 ± 109 (patients) vs. 175 ± 75 (healthy volunteers) mcg/ml*min (p = 0.96); time to maximum venous concentration 23.3 ± 2 (patients) vs. 20.6 ± 18.8 (healthy volunteers) minutes (p = 0.73) and mean residence time 463 ± 233 (patients) vs. 466 ± 224 (healthy volunteers) minutes (p = 0.97).

Conclusions

The similar time to maximum venous concentration and mean residence time suggest similar absorption rates between the two groups. These results indicate that the same dosing regimens for subcutaneous tramadol administration may therefore be used in both healthy subjects and severely ill patients.

Trial registration

ACTRN12611001018909

Evaluation of a Multimodal Approach to Postoperative Pain in Patients Undergoing Flank Incision in the Urology Operating Room

OBJECTIVE

In this study, we evaluated subcutaneous (sc) morphine in combination with multimodal analgesia for postoperative pain control after radical nephrectomy and pyeloplasty with flank incision.

METHODS

Forty-nine patients under The American Society of Anesthesiologists Physical Status classification (ASA) I-III aged 18-85 years undergoing radical nephrectomy and pyeloplasty with flank incision were included in this prospective, randomised study. The patients were divided into two groups (Group O [n=25] and Group M [n=24]) and received standard general anaesthesia. Tramadol (100 mg) and paracetamol (100 mg) were given intravenously before fascia closure and 20 mL of 0.25% levobupivacaine was injected locally at surgical incisions in all patients. Patients in Group M also received 0.1 mg kg(-1) morphine subcutaneously. Patient-controlled analgesia (PCA) with tramadol was used for postoperative pain control in both groups. Postoperative pain scores (VAS), vital parameters, side effects, the need for rescue analgesia during 24 hours postoperatively, and patient satisfaction were recorded.

RESULTS

Groups were comparable with respect to demographic data, ASA status, and duration of surgery. There were no significant differences between the groups in postoperative PCA tramadol consumption, rescue analgesia, side effects, or vital parameters. Postoperative pain scores (VAS) in Group M were significantly lower at 30, 45, 60, and 120 minutes compared to Group O (p<0.05).

CONCLUSION

In patients undergoing radical nephrectomy and pyeloplasty with flank incision, subcutaneous morphine in combination with multimodal analgesia decreases early postoperative pain scores compared to multimodal analgesia alone.

Variability in UDP-glucuronosyltransferase genes and morphine metabolism: observations from a cross-sectional multicenter study in advanced cancer patients with pain

OBJECTIVE

The objective of the present study was to determine whether genetic variability in UDP-glucuronosyltransferase (UGT) genes, together with clinical factors, contribute to variability in morphine glucuronide (M6G and M3G) to morphine serum concentration ratios in patients with advanced cancer receiving chronic morphine therapy.

MATERIALS AND METHODS

A total of 41 polymorphisms and predicted haplotypes in the UGT2B7, UGT1A1, and UGT1A8 genes were analyzed in 759 patients who were recruited from the European Pharmacogenetic Opioid Study and received chronic morphine therapy by the oral route (n=635) or parenterally (n=124). The administration groups were analyzed separately by multiple linear regression analyses.

RESULTS

Two haplotypes in UGT1A1/UGT1A8 were weak predictors of reduced M6G/morphine and M3G/morphine serum ratios after oral administration (false discovery rate-corrected P-values<0.1). No effect of genotype was seen in the parenteral group. Of the clinical variables (age, sex, BMI, renal function, Karnofsky performance status, and presence of liver metastases), renal function was the major contributor to variation in serum concentration ratios. Concomitant administration of paracetamol predicted significantly higher morphine metabolic ratios after oral administration of morphine (false discovery rate-corrected P-values<2.1E-12). The regression models explained about 35% of the total variability in the data.

CONCLUSION

Genetic variation in the UGT genes together with clinical factors influence morphine metabolic ratios in patients with advanced cancer disease and who are scheduled with oral morphine. This information may be included in future research that develop and test new classification systems for opioid treatment in patients with advanced cancer.

Effect of 12-oxochenodeoxycholate on the pharmacokinetics and pharmacodynamics of morphine 6-glucuronide in Wistar rats

Objectives

The semi-synthetic bile salt, 12-oxochenodeoxycholate (OCDC also known as 12-monoketocholate), has been shown to enhance drug permeation across biological membranes with low cytotoxicity. Its effect on the analgesic potency and brain concentration of morphine 6-glucuronide (M6G) was studied in male Wistar rats.

Methods

Four groups of animals (n = 8) were given 5, 10 or 20 mg/kg OCDC or normal saline (control) by subcutaneous injection 30 min before a subcutaneous injection of 5 mg/kg M6G after which the hotplate test was performed on each rat at various times. After a 2 week wash-out period, the same rats (n = 30) were randomized to two equal groups and given OCDC (20 mg/kg) or normal saline 30 min before 5 mg/kg M6G. At five time points up to 3 h after M6G administration, three rats from each group were euthanized and blood and brain analyzed for M6G.

Key findings

The area under the analgesic effect versus time curve (AUAE) was found to be significantly (P &lt; 0.05) greater in rats given 20 mg/kg OCDC than in control rats. Area under the curve (AUC) for M6G in both plasma and brain was greater in OCDC-treated rats than in control rats, but the brain : plasma AUC ratio was lower.

Conclusions

OCDC enhances the analgesic effect of M6G but gives a lower brain : plasma ratio due to increasing M6G plasma levels probably by reducing its renal clearance.

From Pediatric Covariate Model to Semiphysiological Function for Maturation: Part II-Sensitivity to Physiological and Physicochemical Properties

To develop a maturation function for drug glucuronidation in children, that can be used in population and physiologically based modeling approaches, the physiological and physicochemical basis of a semiphysiological glucuronidation function for children was untangled using Simcyp. The results show that using the currently available in vitro data, in vivo morphine and zidovudine clearances were under predicted by the physiologically based model in Simcyp. The maturation profile was similar to the clinically observed profile except for the first 2 weeks of life, and liver size and UGT2B7 ontogeny are the physiological drivers of the maturation of glucuronidation. Physicochemical drug parameters did not affect this maturation profile, although log P and pKa influenced the absolute value of clearance. The results suggest that the semiphysiological glucuronidation function for young children can be used to predict the developmental clearance profile of other UGT2B7 substrates, though scenarios with nonlinear kinetics and high-extraction ratios require further investigation.CPT: Pharmacometrics & Systems Pharmacology (2012) 1, e10; doi:10.1038/psp.2012.12; advance online publication 10 October 2012.

Novel patch for transdermal administration of morphine

CONTEXT

Transdermal absorption of morphine into the systemic circulation through intact skin has not been reported.

OBJECTIVES

To describe a novel transdermal formulation for a morphine hydrochloride patch consisting of polyethylene sponge foam as the retaining agent and adjusted proportions of morphine hydrochloride and adjunctive drugs.

METHODS

In this study, the transdermal morphine hydrochloride patch was administered to intact skin in five subjects and the plasma concentrations of morphine and its metabolites were examined.

RESULTS

Morphine was absorbed systemically, producing plasma morphine concentrations above the assay detection limit by at least 24 hours after attachment of patches containing a total dose of 180mg of morphine. The levels gradually increased in a time-dependent manner without serious events. The area under the concentration-time curve from 0 to 72 hours (AUC(0-72)) values for morphine, morphine-6-glucuronide, and morphine-3-glucuronide were 60.4±13.4, 133.7±17.4, and 861.5±126.7ng·h/mL, respectively. The mean plasma area under the concentration-time curve from 0 to 72 hours ratio for morphine-6-glucuronide relative to morphine was 2.64.

CONCLUSION

These data provide useful information for developing a transdermal morphine system.

The INFUSE-Morphine IIB study: use of recombinant human hyaluronidase (rHuPH20) to enhance the absorption of subcutaneous morphine in healthy volunteers

Morphine is usually given intravenously (IV) for the treatment of moderate-to-severe pain, but subcutaneous (SC) administration is a viable alternative for parenteral delivery. The pharmacokinetics of SC morphine may be enhanced by coadministration with a hyaluronidase product. In this Phase IV, double-blind, randomized, crossover study, 18 healthy adults received a single dose of 2mg morphine SC with 150U of recombinant human hyaluronidase (rHuPH20), SC with 0.9% normal saline, or IV on three consecutive days. The primary endpoint was time to maximum plasma morphine concentration (T(max)) for SC injection with rHuPH20 vs. SC injection without rHuPH20. Safety and tolerability were assessed each study day, the day after the last injection, and 28 days after the last injection. After SC dosing, morphine mean T(max) was significantly shorter with rHuPH20 than without it. Mean maximum plasma morphine concentration (C(max)) after SC dosing was 29% greater with rHuPH20 than without rHuPH20 (P=0.023), although the extent of exposure of morphine was similar. T(max) was shortest and C(max) was highest with IV administration. For the major active metabolite of morphine, morphine-6-glucuronide, mean T(max) after SC morphine was significantly shorter with rHuPH20 than without rHuPH20 (a difference of approximately 17.5 minutes; P=0.0169). Coadministration of morphine with rHuPH20 appeared safe and well tolerated. Compared with SC morphine alone, rHuPH20 shortens morphine T(max) and raises C(max) in healthy adults, without changing the extent of exposure.

Pharmacokinetic and pharmacodynamic study of morphine and morphine 6-glucuronide after oral and intravenous administration of morphine in children with cancer

The aim of this study was to characterize the pharmacokinetics and pharmacodynamics of morphine and morphine 6-glucuronide (M6G) in children with cancer. Serum concentrations of morphine and M6G in children who received single oral or short term continuous intravenous morphine were determined by HPLC and ELISA assays, respectively. The serum C(max) of morphine and M6G after i.v. morphine administration was 560.5 and 309.0 nM and the T(max) was 61 and 65 min, respectively. The elimination half-life was 140.0 and 328.7 min, respectively. After oral administration of morphine, the serum C(max) of morphine and M6G was 408.34 and 256.3 nM and the T(max) was 40.0 and 60 min, respectively. The half-life was 131.0 and 325.8 min, respectively. The side effects were: drowsiness (100%), nausea and/or vomiting (57%), pruritus (28%) and urinary retention (14%). There were no reports of respiratory complications. This study showed that pharmacokinetics factors of morphine and M6G in children were significantly different from adults. Therefore the required dose for children should be different from that of adults and should be based on studies performed on children rather than on studies on adults. Some adverse effects, particularly nausea and pruritus, may be commoner than is usually thought, while others, particularly respiratory problems did not occur.

Morphine bioavailability from a topical gel formulation in volunteers

Although available therapies provide relief to many patients with cancer-related pain, swallowing difficulties or intestinal obstruction may preclude oral analgesic delivery in some. Topical morphine might provide an alternate delivery form but morphine bioavailability from a topical gel formulation has not been reported in humans. We conducted a randomized, placebo-controlled, double-blind, crossover study of five volunteers after they provided institutionally-approved, written, informed consent. They were admitted to the Northwestern University General Clinical Research Center twice, being randomly assigned to receive either 1mL of morphine compounded at 10mg/mL in pluronic lecithin organogel (PLO) base applied to the wrist and 1mL of normal saline administered subcutaneously, or 1mL of topical drug-free PLO base and 1mL of subcutaneous morphine, 3mg/mL, the first time and the opposite combination the second. Seventeen blood samples were collected from 5minutes to 10hours after dose administration for morphine concentration determination. Plasma samples were prepared by solid-phase extraction and morphine concentrations measured by a mass spectrometric technique with a linear range of 0.5-500ng/mL. Bioavailability of the topical formulation relative to the subcutaneous dose was to be estimated from doses and the plasma morphine concentration versus time relationships. Because morphine was seldom detected in plasma samples after topical administration and was unquantifiable when it was, the low bioavailability of topical morphine was unquantifiable. These results suggest that topical administration of morphine compounded in a PLO base for transdermal drug delivery is unlikely to provide relief of cancer-related pain.

Pharmacokinetics of morphine and oxycodone following intravenous administration in elderly patients

BACKGROUND

An increased and prolonged duration of pain relief after morphine administration has been found in elderly patients. Whether this is due to alterations in pharmacokinetics, receptor binding profile or other factors remains unsolved. The aims were to elucidate the pharmacokinetics after intravenous administration of morphine and oxycodone in elderly patients older than 70 years.

METHODS

A randomized non-blinded study with 16 patients aged older than 70 years scheduled for elective hip replacement receiving morphine or oxycodone 0.05 mg/kg as an IV infusion over 15 minutes.

RESULTS

A 2-compartment pharmacokinetic model best described the disposition of morphine and oxycodone. The estimated elimination half-lives for morphine and oxycodone were (mean +/- SD) 2.7 +/- 3.6 (range 0.8-11.6) and 3.1 +/- 1.3 (range 1.1-4.8) hr, respectively. Volume of distribution at steady state was estimated to be 243 +/- 256 and 277 +/- 187 L, and clearance to be 1748 +/- 623 and 1206 +/- 546 ml/min for morphine and oxycodone, respectively.

CONCLUSION

The increased and prolonged duration of pain relief after morphine administration seen in some elderly patients cannot, based on these findings, be ascribed to changes in the pharmacokinetic parameters between elderly and younger patients. Similar for oxycodone, no changes in the pharmacokinetic could be found when comparing the parameters found in elderly patients with those from younger healthy volunteers. A great variability within the individual pharmacokinetic parameters was seen for both drugs. Therefore, we recommend that treatment with morphine and oxycodone in elderly patients is initiated very conservatively and is titrated slowly to effect.

Continuous Subcutaneous Infusion of Opiates at End-of-Life

OBJECTIVE:

To review pertinent controlled trials using the continuous subcutaneous infusion of opioids (CSIO) at end-of-life and offer insight to pharmacists and clinicians into the appropriate use of this route of administration.

DATA SOURCES:

A MEDLINE search for information regarding the subcutaneous administration of opioids in terminally ill patients (1975-December 2002) was conducted using the key words subcutaneous, narcotics, morphine, hydromorphone, fentanyl, pain, hospices, and palliative care. Additional references were located through review of bibliographies of the articles cited. Case reports and postsurgical studies were excluded. Searches were limited to English-language studies using humans.

STUDY SELECTION AND DATA EXTRACTION:

Experimental and observational studies were evaluated, using prospective trials as the evidence base for conclusions and including pertinent retrospective trials as they relate to the subcutaneous infusion of opioids at end-of-life.

DATA SYNTHESIS:

CSIO is effective and safe for use in terminal illness. Appropriate situations for consideration of CSIO are when difficulties arise in using the oral route, standard oral opiate therapy has failed adequate trials, the patient has limited intravenous access, adequate supervision of the CSIO is present, and CSIO will not unduly limit the functional activity of the patient.

CONCLUSIONS:

CSIO has a proven role in the management of pain at end-of-life. CSIO should not be considered the first route for administration of opiates, but does offer distinct advantages in the appropriate setting. CSIO continues to be a choice for end-of-life patients and is gradually becoming a standard practice in palliative medicine.

The bioavailability of morphine applied topically to cutaneous ulcers

A number of studies have reported the analgesic effect of morphine when applied topically to painful skin ulcers. It has been suggested that morphine may exert a local action, as opioid receptors have been demonstrated on peripheral nerve terminals. In this study, we investigated the bioavailability of topically applied morphine to cutaneous ulcers. Six hospice inpatients with skin ulcers were given morphine sulfate 10 mg in Intrasite gel topically and morphine sulfate 10 mg subcutaneously over 4 hours, at least 48 hours apart, in randomized order. Morphine, morphine-6-glucuronide (M6G), and morphine-3-glucuronide (M3G) were determined in plasma using a specific HPLC method. In five patients morphine and its metabolites were undetectable when applied topically. In one patient (with the largest ulcer), morphine and M6G were detected. The calculated morphine and M6G bioavailability in this patient were 20% and 21%, respectively. M3G was also detected but was below the lower limit of quantitation. When applied topically to ulcers, morphine was not absorbed in the majority of patients, suggesting any analgesic effect would be mediated locally rather than systemically. However, in ulcers with a large surface area, systemic absorption may occur.