Pharmacokinetics of Morphine, Morphine-3-Glucuronide and Morphine-6-Glucuronide in Terminally Ill Adult Patients

Pharmacological treatment of pain, dyspnea, death rattle, fever, nausea, and vomiting in the last days of life in older people: A systematic review

BACKGROUND

Evidence based guidelines for treatment of physical symptoms during the last days of life in older people are not available.

AIM

We wanted to synthesize the existing evidence on the pharmacological treatment of pain, dyspnea, death rattle, fever, nausea, and vomiting during the last days of life in older people to develop recommendations that can help guide clinical practice.

DESIGN

A systematic review was conducted (PROSPERO #CRD42023406100) and reported in accordance with PRISMA guidelines.

DATA SOURCES

MEDLINE and EMBASE were searched from inception till March 2023, together with national and international guideline databases.

RESULTS

Four predominantly descriptive studies on opioid use were included for the treatment of pain and four for dyspnea, without clear evidence for the choice of one specific opioid, nor a specific opioid dose. For death rattle, five randomized controlled trials and two retrospective studies were included. These provide evidence for the prophylactic treatment of death rattle with hyoscine butylbromide. For fever, nausea, and vomiting, no articles met the inclusion criteria.

CONCLUSION

Limited evidence exists to guide the pharmacological treatment of pain, dyspnea, death rattle, fever, nausea, and vomiting in the last days of life of older people. Other than the use of opioids for treatment of pain and dyspnea and prophylactic administration of hyoscine butylbromide to decrease the likelihood of developing death rattle, no specific recommendations can be formulated for use in clinical practice. This demonstrates the challenging nature of research in the last days of life of older people, despite its pressing need.

Altered Membrane Expression and Function of CD11b Play a Role in the Immunosuppressive Effects of Morphine on Macrophages at the Nanomolar Level

Morphine, one of the most efficacious analgesics, is effective in severe pain, especially in patients with concomitant painful cancers. The clinical use of morphine may be accompanied by increased immunosuppression, susceptibility to infection and postoperative tumor metastatic recurrence, and the specific mechanisms and clinical strategies to alleviate this suppression remain to be investigated. Expression of CD11b is closely associated with the macrophage phagocytosis of xenobiotic particles, bacteria or tumor cells. Here, we find that morphine at 0.1-10 nM levels inhibited CD11b expression and function on macrophages via a μ-opioid receptor (MOR)-dependent mechanism, thereby reducing macrophage phagocytosis of tumor cells, a process that can be reversed by thymopentin (TP5), a commonly used immune-enhancing adjuvant in clinical practice. By knocking down or overexpressing MOR on macrophages and using naloxone, an antagonist of the MOR receptor, and LA1, a molecule that promotes macrophage CD11b activation, we suggest that morphine may regulate macrophage phagocytosis by inhibiting the surface expression and function of macrophage CD11b through the membrane expression and activation of MOR. The CD47/SIRPα axis, which is engaged in macrophage-tumor immune escape, was not significantly affected by morphine. Notably, TP5, when combined with morphine, reversed the inhibition of macrophage phagocytosis by morphine through mechanisms that promote membrane expression of CD11b and modulate its downstream signaling (e.g., NOS2, IFNG, IL1B and TNFA, as well as AGR1, PDGFB, IL6, STAT3, and MYC). Thus, altered membrane expression and function of CD11b may mediate the inhibition of macrophage phagocytosis by therapeutic doses of morphine, and the reversal of this process by TP5 may provide an effective palliative option for clinical immunosuppression by morphine.

Use of Opioids for Adults With Pain From Cancer or Cancer Treatment: ASCO Guideline

PURPOSE

To provide guidance on the use of opioids to manage pain from cancer or cancer treatment in adults.

METHODS

A systematic review of the literature identified systematic reviews and randomized controlled trials of the efficacy and safety of opioid analgesics in people with cancer, approaches to opioid initiation and titration, and the prevention and management of opioid adverse events. PubMed and the Cochrane Library were searched from January 1, 2010, to February 17, 2022. American Society of Clinical Oncology convened an Expert Panel to review the evidence and formulate recommendations.

RESULTS

The evidence base consisted of 31 systematic reviews and 16 randomized controlled trials. Opioids have primarily been evaluated in patients with moderate-to-severe cancer pain, and they effectively reduce pain in this population, with well-characterized adverse effects. Evidence was limited for several of the questions of interest, and the Expert Panel relied on consensus for these recommendations or noted that no recommendation could be made at this time.

RECOMMENDATIONS

Opioids should be offered to patients with moderate-to-severe pain related to cancer or active cancer treatment unless contraindicated. Opioids should be initiated PRN (as needed) at the lowest possible dose to achieve acceptable analgesia and patient goals, with early assessment and frequent titration. For patients with a substance use disorder, clinicians should collaborate with a palliative care, pain, and/or substance use disorder specialist to determine the optimal approach to pain management. Opioid adverse effects should be monitored, and strategies are provided for prevention and management.Additional information is available at www.asco.org/supportive-care-guidelines.

Morphine-3-glucuronide upregulates PD-L1 expression via TLR4 and promotes the immune escape of non-small cell lung cancer

Objective

Patients with cancer pain are highly dependent on morphine analgesia, but studies have shown a negative correlation between morphine demand and patient outcomes. The long-term use of morphine may result in abnormally elevated serum morphine-3-glucuronide (M3G) levels. Hence, the effects of M3G on tumor progression are worth studying.

Methods

The effects of M3G on PD-L1 expressions in human non-small cell lung cancer (NSCLC) cell lines were first evaluated. Activation of TLR4 downstream pathways after M3G treatment was then determined by Western blot. The effects of M3G on human cytotoxic T lymphocytes (CTL) cytotoxicity and INF-γ release was also detected. Finally, the LLC murine lung adenocarcinoma cell line were used to establish a murine lung cancer model, and the effects of M3G on tumor growth and metastasis were determined.

Results

M3G promoted the expressions of PD-L1 in the A549 and H1299 cell lines in a TLR4-dependent manner (P < 0.05). M3G activated the PI3K and the NFκB signaling pathways, and this effect was antagonized by a TLR4 pathway inhibitor. A PI3K pathway inhibitor reversed the M3G-mediated PD-L1 upregulation. M3G inhibited the cytotoxicity of CTL on A549 cells and decreased the level of INF-γ. Repeated M3G intraperitoneal injections promoted LLC tumor growth and lung metastasis through the upregulation of tumor expressed PD-L1 and the reduction of CTL in the tumor microenvironment.

Conclusions

M3G specifically activated TLR4 in NSCLC cells and upregulated PD-L1 expression through the PI3K signaling pathway, thereby inhibiting CTL cytotoxicity and finally promoting tumor immune escape.

Influence of muscle mass on the estimation of glomerular filtration rate in Japanese terminal cancer patients

BACKGROUND

Estimated glomerular filtration rate (eGFR) based on serum cystatin C (Scys) is useful for patients with decreased muscle mass, but has been also reported to be affected by cancer. The usefulness of Scys in eGFR in terminal cancer patients with decreased muscle mass is unknown. Therefore, we analyzed appropriate eGFR formulae for terminal cancer patients.

METHODS

Study design was a retrospective observational study. Based on creatinine height index (CHI), 184 terminal cancer patients were stratified into CHI ≥ 90% (normal muscle mass, 59 patients); CHI 60-89% (mildly to moderately decreased muscle mass, 64 patients); and CHI < 60% (severely decreased muscle mass, 61 patients) groups. Twenty-four-hour creatinine clearance was measured and converted to the glomerular filtration rate (GFR) as a renal function measure. To estimate GFR, various eGFR formulae for Japanese were used: eGFR_Scys, eGFR_Scr5 and eGFR_Scr3, eGFR_average and eGFR_Scys-Scr, and eGFR_CG, based on Scys, serum creatinine (Scr), Scys and Scr combined, and Cockcroft-Gault formula (CG), respectively. Errors between measured and estimated values of renal function were verified using mean prediction errors (ME). When a 95% confidence interval (CI) of ME included 0, the accuracy of the eGFR formula was graded as good.

RESULTS

eGFR_Scys ME was 0.2 (95% CI lower limit - 3.7, upper limit 4.0) mL/min/1.73 m² in CHI 60-89% group and 9.2 (6.1, 12.9) mL/min/1.73 m² in CHI < 60% group. eGFR_Scys was most accurate among the eGFR formulae.

CONCLUSIONS

eGFR based on Scys was demonstrated as useful in terminal cancer patients with decreased muscle mass.

Vancomycin Pharmacokinetics in Patients with Advanced Cancer Near End of Life

BACKGROUND AND OBJECTIVE

The effect of cancer cachexia on the pharmacokinetics of vancomycin remains unclear. We investigated whether the pharmacokinetics of vancomycin and the risk of kidney injury are altered with the development of cancer cachexia.

METHODS

A retrospective analysis was conducted using therapeutic drug monitoring data obtained from 86 cancer patients who received vancomycin intravenously for infection. The patients were classified into four groups according to the stage of cachexia defined by international consensus-non-cachexia (n = 26), pre-cachexia (n = 10), cachexia (n = 21) and refractory cachexia (n = 29). Vancomycin pharmacokinetics were analyzed by a traditional one-compartment model and Bayesian method using plasma concentrations measured in these patients. Renal function and pharmacokinetic parameters were compared between the non-cachexia patients (n = 26) and total cancer cachexia patients (n = 60).

RESULT

No significant difference in estimated glomerular filtration rate was observed between the non-cachexia and the total cancer cachexia patients. In contrast, systemic clearance of vancomycin was significantly lower in the total cancer cachexia patients compared with the non-cachexia patients when analyzed by the traditional one-compartment model [median (range)-49.7 (9.8‒98.7) vs 70.2 (12.5‒211.8) mL/min, p < 0.01] and by the Bayesian method [45.6 (12.5-84.7) vs 63.3 (12.2-102.5) mL/min, p < 0.05]. None of the non-cachexia patients developed kidney injury, whereas 15% (9 of 60 patients) of the total cancer cachexia patients developed kidney injuries (p = 0.052).

CONCLUSIONS

The present study revealed that cancer patients with cachexia may have reduced vancomycin clearance compared with those without cachexia. Cancer cachexia may be a risk factor of vancomycin-associated kidney injury, independent of renal function.

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.

Amikacin Pharmacokinetics in Terminal Stage of Hematological Malignancy

BACKGROUND

The influence of cancer cachexia on the pharmacokinetics of and kidney injury caused by amikacin remains unclear. This study investigated whether the pharmacokinetics of amikacin and the risk of kidney injury are altered with the progression of cancer cachexia.

METHODS

A retrospective analysis was conducted using therapeutic drug monitoring data obtained from 52 cancer patients who received amikacin intravenously for infection(s). The patients were classified into 2 groups based on the status of cachexia using a consensus definition: noncachexia group (n = 31) and cachexia group (n = 21). Differences in amikacin pharmacokinetics and occurrence of kidney injury were compared between the 2 groups. Amikacin pharmacokinetics was calculated based on a 1-compartment model using peak and trough concentrations measured clinically for therapeutic drug monitoring. In addition, intrapatient analysis was conducted based on patients who received amikacin treatments more than once during the study period to examine the alteration in amikacin pharmacokinetics with the progression of cancer cachexia.

RESULTS

Systemic clearance of amikacin [median (range)] was significantly (P < 0.05) lower in the cachexia group [37.3 (11.2-87.3) (mL/min)] than in the noncachexia group [52.0 (19.1-133.4) (mL/min)]. In contrast, volume of distribution was significantly (P < 0.05) increased in the cachexia group [0.47 (0.20-1.45) L/kg] compared with the noncachexia group [0.32 (0.21-1.00) L/kg]. There was no difference in the occurrence of kidney injuries between the 2 groups. In an intrapatient analysis of the longitudinal alteration of amikacin pharmacokinetics, an approximately 50% reduction in clearance and 30% increase in volume of distribution were observed as cancer cachexia progressed.

CONCLUSIONS

The present study suggests that progression of cancer cachexia may reduce amikacin clearance and increase the volume of distribution, but cancer cachexia does not increase amikacin-induced kidney injury.

Palliative Sedation for the Terminally Ill Patient

Palliative sedation (PS) is performed in the terminally ill patient to manage one or more refractory symptoms. Proportional PS, which means that drugs can be titrated to the minimum effective dose, is the form most widely used. From a quarter to a third of all terminally ill patients undergo PS, with a quarter of these requiring continuous deep sedation. The prevalence of PS varies according to the care setting and case mix. The most frequent refractory physical symptoms are delirium and dyspnea, but PS is also considered for existential suffering or psychological distress, which is an extremely difficult and delicate issue to deal with. Active consensus from the patient and advanced care planning is recommended for PS. The decision-making process concerning the continuation or withdrawal of other treatments is not the same as that used for PS. The practice differs totally from euthanasia in its intentions, procedures, and results. The most widely used drugs are midazolam and haloperidol for refractory delirium, but chlorpromazine and other neuroleptics are also effective. In conclusion, some patients experience refractory symptoms during the last hours or days of life and PS is a medical intervention aimed at managing this unbearable suffering. It does not have a detrimental effect on survival.

Reduced Clearance of Phenobarbital in Advanced Cancer Patients near the End of Life

BACKGROUND AND OBJECTIVES

Little is known about the pharmacokinetics of phenobarbital in terminally ill cancer patients. We investigated whether phenobarbital clearance alters depending on the length of survival.

METHODS

We retrospectively reviewed the clinical, laboratory, and therapeutic drug monitoring (TDM) records of patients who received parenteral or oral phenobarbital for 21 consecutive days or longer between 2000 and 2016. Patients were divided into non-cancer and cancer groups. Cancer patients were further stratified according to the survival interval after TDM: those who survived > 3 months were classified as long-surviving and the remainders short-surviving cancer patients. Phenobarbital clearance (CL_PB) was calculated at steady state. Multiple comparisons of median CL_PB were conducted among the three groups.

RESULTS

Data were collected from 44 non-cancer patients and 34 cancer patients comprising 24 long-surviving and 10 short-surviving cancer patients. Among 10 short-surviving cancer patients, 4 had hepatic metastasis. Median CL_PB (range) in short-surviving cancer patients [0.076 (0.057‒0.114) L/kg/day] was significantly (p < 0.05) lower than that in non-cancer patients [0.105 (0.060‒0.226) L/kg/day] and in long-surviving cancer patients [0.100 (0.082‒0.149) L/kg/day].

CONCLUSION

Terminally ill patients with advanced cancer may have reduced CL_PB, thereby TDM is recommended for these patients particularly near the end of life.

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.

Safety and Effectiveness of Palliative Drug Treatment in the Last Days of Life-A Systematic Literature Review

CONTEXT

Dying patients commonly experience potentially distressing symptoms. Palliative care guidelines recommend opioids, anticholinergics, antipsychotics, and benzodiazepines for symptom relief.

OBJECTIVES

The objective of this study was to systematically review the effectiveness and safety of palliative drug treatment in the last days of life of adult patients, focusing on the management of pain, dyspnea, anxiety, restlessness, and death rattle.

METHODS

A systematic search of the literature was published before December 2016 in PubMed/MEDLINE, Embase, CINAHL, PsycINFO, Cochrane, ClinicalTrials.gov, and SveMed+. Studies on safety or effectiveness of drug therapy in dying adults with at least one outcome on symptom control, adverse effects, or survival were included. Data for included studies were extracted. Study quality was assessed using the Effective Public Health Practice Quality assessment tool for quantitative studies.

RESULTS

Of the 5940 unique titles identified, 12 studies met the inclusion criteria. Five studies assessed anticholinergics for death rattle, providing no evidence that scopolamine hydrobromide and atropine were superior to placebo. Five studies examined drugs for dyspnea, anxiety, or terminal restlessness, providing some evidence supporting the use of morphine and midazolam. Two studies examined opioids for pain, providing some support for morphine, diamorphine, and fentanyl. Eight studies included safety outcomes, revealing no important differences in adverse effects between the interventions and no evidence for midazolam shortening survival.

CONCLUSION

There is a lack of evidence concerning the effectiveness and safety of palliative drug treatment in dying patients, and the reviewed evidence provides limited guidance for clinicians to assist in a distinct and significant phase of life.

A gold nanoparticle-single-chain fragment variable antibody as an immunoprobe for rapid detection of morphine by dipstick

Gold nanoparticle (AuNP)-based optical assays are of significant interest since the molecular phenomenon can be examined easily with change in the color of AuNPs. Herein, we report the development of a dipstick using a AuNP-labeled single-chain fragment variable (scFv) antibody for the detection of morphine. The scFv antibodies for morphine were developed using phage display-based antibody library. Immunoglobulin variable regions of heavy (V H)- and light (V L)-chain genes were connected via a glycine-serine linker isolated from murine immune repertoire and cloned into the expression vector pIT2. The scFv was produced in Escherichia coli HB2151, yielding a functional protein with a molecular weight of approximately 32 kDa. The morphine scFv was labeled with gold nanoparticles and used as an optical immunoprobe in a dipstick. The competitive dipstick assay characterized the ability of the scFv antibody to recognize free morphine. The detection range was 1-1000 ng mL-1 with a limit of detection (LOD) of 5 ng mL-1 under optimal conditions, and the IC50 value was 14 ng mL-1 for morphine. The developed optical dipstick kit of scFv antibody was capable of specifically binding to free morphine and its analogs in a solution in less than 5 min and could be useful for on-site screening of a real sample in blood, urine, and saliva.

An immunochromatographic dipstick as an alternate for monitoring of heroin metabolites in urine samples

Pathway of heroin degradation post oral administration in mice.

Population pharmacodynamic modelling of midazolam induced sedation in terminally ill adult patients

Aims

Midazolam is the drug of choice for palliative sedation and is titrated to achieve the desired level of sedation. A previous pharmacokinetic (PK) study showed that variability between patients could be partly explained by renal function and inflammatory status. The goal of this study was to combine this PK information with pharmacodynamic (PD) data, to evaluate the variability in response to midazolam and to find clinically relevant covariates that may predict PD response.

Method

A population PD analysis using nonlinear mixed effect models was performed with data from 43 terminally ill patients. PK profiles were predicted by a previously described PK model and depth of sedation was measured using the Ramsay sedation score. Patient and disease characteristics were evaluated as possible covariates. The final model was evaluated using a visual predictive check.

Results

The effect of midazolam on the sedation level was best described by a differential odds model including a baseline probability, Emax model and interindividual variability on the overall effect. The EC50 value was 68.7 μg l^–1 for a Ramsay score of 3–5 and 117.1 μg l^–1 for a Ramsay score of 6. Comedication with haloperidol was the only significant covariate. The visual predictive check of the final model showed good model predictability.

Conclusion

We were able to describe the clinical response to midazolam accurately. As expected, there was large variability in response to midazolam. The use of haloperidol was associated with a lower probability of sedation. This may be a result of confounding by indication, as haloperidol was used to treat delirium, and deliria has been linked to a more difficult sedation procedure.

Judicial oversight of life-ending withdrawal of assisted nutrition and hydration in disorders of consciousness in the United Kingdom: A matter of life and death

Mr Justice Baker delivered the Oxford Shrieval Lecture 'A Matter of Life and Death' on 11 October 2016. The lecture created public controversies about who can authorise withdrawal of assisted nutrition and hydration (ANH) in disorders of consciousness (DOC). The law requires court permission in 'best interests' decisions before ANH withdrawal only in permanent vegetative state and minimally conscious state. Some clinicians favour abandoning the need for court approval on the basis that clinicians are already empowered to withdraw ANH in other common conditions of DOC (e.g. coma, neurological disorders, etc.) based on their best interests assessment without court oversight. We set out a rationale in support of court oversight of best interests decisions in ANH withdrawal intended to end life in any person with DOC (who will lack relevant decision-making capacity). This ensures the safety of the general public and the protection of vulnerable disabled persons in society.

Hypoalbuminaemia and decreased midazolam clearance in terminally ill adult patients, an inflammatory effect?

AIMS

Midazolam is the drug of choice for palliative sedation and is titrated to achieve the desired level of sedation. Because of large inter-individual variability (IIV), however, the time it takes to achieve adequate sedation varies widely. It would therefore greatly improve clinical care if an individualized dose could be determined beforehand. To find clinically relevant parameters for dose individualization, we performed a pharmacokinetic study on midazolam, 1OH-midazolam (1-OH-M) and 1OH-midazolam-glucuronide (1-OH-MG) in terminally ill patients.

METHODS

Using nonlinear mixed effects modelling (NONMEM 7.2), a population pharmacokinetic analysis was conducted with 192 samples from 45 terminally ill patients who received midazolam either orally or subcutaneously. The covariates analysed were patient characteristics, co-medication and blood chemistry levels.

RESULTS

The data were accurately described by a one compartment model for midazolam, 1-OH-M and 1-OH-MG. The population mean estimates for midazolam, 1-OH-M and 1-OH-MG clearance were 8.4 l h^-1 (RSE 9%, IIV 49%), 45.4 l h^-1 (RSE 12%, IIV 60.5%) and 5.1 l h^-1 (RSE 11%, IIV 49.9%), respectively. 1-OH-MG clearance was correlated with the estimated glomular filtration rate (eGFR) explaining 28.4% of the IIV in 1-OH-MG clearance. In addition, low albumin levels were associated with decreased midazolam clearance, explaining 18.2% of the IIV.

CONCLUSION

Our study indicates albumin levels and eGFR as relevant clinical parameters to optimize midazolam dosing in terminally ill patients. The correlation between low albumin levels and decreased midazolam clearance is probably a result of inflammatory response as high CRP levels were correlated in a similar way.

Population pharmacokinetics and analgesic potency of oxycodone

AIMS

This prospective study aimed to characterize the population pharmacokinetics of intravenous oxycodone and to determine the minimum effective concentration (MEC) and minimum effective analgesic concentration (MEAC) of oxycodone for major open intra-abdominal surgery.

METHODS

In the pharmacokinetic study, patients were administered intravenous oxycodone (0.1 mg kg^-1 ), and arterial blood was sampled at pre-set intervals. In the analgesic-potency study, patients were administered intravenous oxycodone (0.1 mg kg^-1 ) 30 min before the end of the surgery, were placed in the postoperative anaesthesia care unit (PACU), and were asked to rate their pain every 10 min using a visual analogue scale (0 = no pain, 10 = most severe pain). On the first occasion that wound pain at rest and during compression was rated as ≥3 or ≥5, respectively, the first blood sample was obtained to determine the MEC. A second blood sample was obtained after titration with 2 mg of oxycodone to yield wound pain <3 at rest and <5 during wound compression, and MEAC was determined. MEC and MEAC were determined again in each patient.

RESULTS

In the population pharmacokinetic study (n = 54), oxycodone plasma concentration over time was well described by a three-compartment mammillary model. Lean body mass and age were significant covariates for the volume of distribution and metabolic clearance of the pharmacokinetic model of oxycodone, respectively. The analgesic-potency study (n = 50) showed that the median (95% CI) MEC and MEAC were 31.5 (19.2-42.8) and 74.1 (29.2-128.3) ng ml^-1 (first measurements) and 63.4 (15.6-120.1) and 76.1 (32.9-132.7) ng ml^-1 (second measurements), respectively.

CONCLUSIONS

In major intra-abdominal open surgery, the MEAC and analgesic potency of oxycodone were 75 ng ml^-1 and 60 ng ml^-1 , respectively.