Intravenous morphine titration in immediate postoperative pain management: Population kinetic–pharmacodynamic and logistic regression analysis

Factors influencing postoperative pain management among nurses in selected district hospitals in Ghana

BACKGROUND

Poorly managed postoperative pain is linked to numerous postoperative complications worldwide and in Ghana. This is due to the myriad of physical and psychological problems, such as lifelong chronic pain syndromes, impaired functionality and death.

PURPOSE

The aim of this study was to assess the barriers and factors influencing postoperative pain management by Ghanaian nurses working in four hospitals.

METHODS

A quantitative descriptive cross-sectional design was employed for this study. Participants were recruited using a multistage sampling technique by which 146 returned their questionnaires out of 194 participants. The statistical analysis of data was done with the Statistical Package of Social Sciences (SPSS) 20.0 version.

RESULTS

Findings revealed that some verbal and non-verbal cues from patients such as facial grimacing, restlessness, irritability and distress, lack of concentration and moaning or crying (verbalisation) influenced how nurses controlled postoperative pain with analgesia. The participants also identified several barriers to influence postoperative pain management by nurses.

CONCLUSION

In conclusion, postoperative pain control by nurses is influenced by several factors, and hence, nurses need to manage patients' pain effectively in Ghana and abroad using multiple approaches.

Timing of Oversedation Events Following Opiate Administration in Hospitalized Patients

BACKGROUND

Unintended overdoses of opiate medications are potentially lethal events. Monitoring patients for oversedation is fundamental to ensuring safe use of opiates, and the timing of this evaluation is guided by the onset of action, time to max effect and duration of action of the opiate. The study's aim was to describe the timing of oversedation in relation to the predicted duration of action of the administered opiate.

METHODS

This study was conducted as a retrospective review of all opiate-related oversedation events during a 2-year period involving patients admitted to an urban teaching hospital.

RESULTS

Of the 53 opiate-related oversedation events evaluated, 47% occurred after the predicted maximal duration of action of the administered opiate.

CONCLUSION

Opiate-induced oversedation routinely occurs after predicted based upon duration of action. The study findings have profound implications upon nursing practice regarding duration of time required to monitor for opiate-induced oversedation.

Predicted Versus Non-Predicted Opioid Administration Using Preoperative Pain Sensitivity in Patients Undergoing Gynecological Surgery: A Randomized-Controlled Trial

Individualized administration of opioids based on preoperative pain sensitivity may improve postoperative pain profiles. This study aimed to examine whether a predicted administration of opioids could reduce opioid-related adverse effects after gynecological surgery. Patients were randomized to the predicted group or control group. Participants received a preoperative sensory test to measure pressure pain thresholds. Patients were treated with a higher or lower (15 or 10 μg/mL) dose of fentanyl via intravenous patient-controlled analgesia. The opioid dose was determined according to pain sensitivity in the predicted group, while it was determined regardless of pain sensitivity in the control group. The primary outcome was the incidence of nausea over the first 48 h postoperative period. Secondary outcomes included postoperative pain scores and opioid requirements. There was no difference in the incidence of nausea (40.0% vs. 52.5% in predicted and control groups, respectively; p = 0.191) and postoperative pain scores (3.3 vs. 3.5 in predicted and control groups, respectively; p = 0.691). However, opioid consumptions were lower in the predicted group compared to the control group (median 406.0 vs. 526.5 μg; p = 0.042). This study showed that offering a predicted dose of opioids according to pain sensitivity did not affect the incidence of nausea and pain scores.

Post-operative opioid-related adverse events with intravenous oxycodone compared to morphine: A randomized controlled trial

BACKGROUND

The value of intravenous oxycodone compared to morphine remains controversial. The purpose of this trial was to compare opioid-related adverse events (ORAES) of intravenous oxycodone and morphine after total hip arthroplasty.

METHODS

Patients scheduled for total hip arthroplasty were enrolled in this study of post-operative pain treatment with intravenous oxycodone or intravenous morphine (ratio 1:1). After surgery, patients received similar drug regimens for titration in the post-operative care unit followed by intravenous patient-controlled analgesia (PCA). The primary outcome was the number of patients with ≥1 ORAEs within the first 24 hours defined as either nausea, vomiting, respiratory depression, pruritus, urinary retention requiring evacuation, allergy, hallucinations. Secondary outcomes included pain scores and opioid consumption.

RESULTS

The analysis included 238 patients with similar characteristics. There were 55 patients with at least one ORAEs in the oxycodone group vs 46 in the morphine group: 48% vs 40%, P = .19; relative risk = 1.22 (0.91:1.63). Intravenous oxycodone vs intravenous morphine requirements were respectively (median, IQR): 6 (0-11) vs 8 (0-12) mg (P = .06) for titration, 15 (8-26) vs 8 (5-16) mg (P = .001) for PCA, and 22 (12-37) mg vs 19 (11-28) mg for cumulated intravenous consumption (P = .048). During the first 24 hours, there was no difference in secondary outcomes (oxycodone vs morphine, respectively, in %): nausea (15 vs 13), vomiting (5 vs 5), urinary retention (20 vs 12) or pain scores.

CONCLUSION

This study demonstrates that IV oxycodone did not significantly reduce ORAEs within the first 24 hours compared to similar ratio of IV morphine.

Foreseeing postoperative pain in neurosurgical patients: pupillometry predicts postoperative pain ratings-an observational study

Pupillary reflex dilation (PRD) is triggered by noxious stimuli and diminished by opioid administration. In the postoperative period, PRD has been shown to be correlated with pain reporting and a useful tool to guide opioid administration. In this study we assessed whether pupillary measurements taken before extubation were related with the patient's reported pain in the Post-Anesthesia Care Unit (PACU) using the Numerical Rating Scale (NRS). Our objective was to evaluate the correlation of PRD and pupillary variables measured intraoperatively with postoperative pain under the same opioid concentration. This was a prospective observational study of 26 neurosurgical patients undergoing general anesthesia exclusively with propofol and remifentanil. A portable infrared pupillometer was used to provide an objective measure of pupil size and PRD (using the Pupillary Pain Index) before extubation. Pain ratings were obtained from patients after recovery of consciousness, while remifentanil was maintained at 2 ng/mL. A significant correlation was observed between NRS scores and pre-extubation PPI (r_S = 0.62; P = 0.002), as well as between NRS scores and pupil diameter before tetanic stimulation PPI (r_S = 0.56, P = 0.006). We also found a negative correlation between pupil diameter and age (r_S = - 0.42, P = 0.04). The statistically significant correlation between pre-extubation PPI scores and NRS scores, as well as between the pupillary diameter before tetanic stimulation and NRS scores suggest the possibility of titrating analgesia at the end of the intraoperative period based on individual responses. This could allow clinicians to identify the ideal remifentanil concentration for the postoperative period.

A Scoping Review of Intravenous Opioid Pain Protocols and Their Dose-Time Intervals in the Management of Acute Postoperative Pain in the Postanesthesia Care Unit

PURPOSE

This review aims to explore intravenous opioid pain protocols and their dose-time intervals in managing acute postoperative pain in adults in the postanesthesia care unit (PACU).

DESIGN

A scoping review using a systematic search strategy.

METHODS

Sixteen articles were identified from MEDLINE, CINAHL, PubMed, Embase, and Cochrane specific to the aims.

FINDINGS

The literature demonstrated several variations on dose-time intervals used for opioid pain protocol administration globally. Furthermore, opioid analgesic pain protocols in the PACU appear to be effective in postoperative pain management. However, the literature did not identify optimal time intervals related to dose administration within these protocols.

CONCLUSIONS

Literature gaps were identified regarding the significance of dose-time intervals when using opioid analgesic pain protocols in the PACU.

Opioid-related genetic polymorphisms do not influence postoperative opioid requirement: A prospective observational study

BACKGROUND

Among the various factors that may influence the pharmacological response to opioids, genetic polymorphisms [single nucleotide polymorphisms (SNP)] have generated some interest.

OBJECTIVES

To examine the influence on morphine dose requirements and adverse events in the postoperative period of four SNP [opioid receptor mu1 (OPRM1), ATP-binding cassette subfamily B, member 1 (ABCB1) ex-21 and ex-26, catechol-o-methyltransferase (COMT)] in candidate genes involved in morphine pharmacodynamics and pharmacokinetics.

DESIGN

A single centre prospective study.

SETTING

University Hospital, Paris, France, from 2 January 2007 to 15 November 2011.

PATIENTS

A total of 438 white adults scheduled for major orthopaedic surgery (spine, hip and knee) under general anaesthesia. The main exclusion criteria were receiving opioids for chronic pain, nonopioid drugs within 2 days prior to surgery, pregnancy, renal insufficiency, sleep apnoea obstruction syndrome, morbid obesity, severe hepatic impairment, cognitive dysfunction.

INTERVENTIONS

Assays of plasma concentrations of morphine and metabolites (morphine 3-glucuronide and morphine 6-glucuronide) were performed and common polymorphisms in four candidate genes [OPRM1 A118G rs1799971; P-glycoprotein (ABCB1) T3435C (rs1045642) and G2677T/A (rs2032582); COMT Val 158 Met (rs4680)] were analysed.Morphine was titrated by staff in the postanaesthesia care unit (PACU) and in the ward patient-controlled intravenous analgesia was used for 24 h.

MAIN OUTCOME MEASURES

The dose of morphine required to achieve pain relief and the influence of SNP in genes involved in morphine pharmacodynamics and kinetics on morphine dose requirements. Secondary endpoints were the concentrations of morphine, morphine 6-glucuronide and morphine 3-gluguronide, the proportion of patients requiring a rescue analgesic and the proportion of morphine-related adverse events.

RESULTS

A total of 404 patients completed the study to final analysis. The mean ± SD morphine dose to achieve pain relief was 15.8 ± 8.8 mg in the PACU and 22.7 ± 18.6 mg during patient-controlled intravenous administration. Morphine-related adverse events were observed in 37%. There was no relationship between any genetic polymorphisms and morphine dose, morphine 3-gluguronide and morphine 6-glucuronide concentration, morphine-related adverse events or pain level. In the PACU only, P-glycoprotein polymorphisms (ex-21; ex-26) were significantly associated with morphine concentration but the prediction of the model was poor (R = 0.04) CONCLUSION: No major relationship has been demonstrated between SNP of OPRM1, ABCB1, COMT and morphine requirement, pain level or adverse effects in the postoperative period.

TRIAL REGISTRATION

NCT00822549 (www.clinicaltrials.gov).

Comparison of dexmedetomidine vs. remifentanil combined with sevoflurane during radiofrequency ablation of hepatocellular carcinoma: a randomized controlled trial

BACKGROUND

Remifentanil is widely used for ultrasound-guided percutaneous radiofrequency ablation (RFA) of small hepatocellular carcinoma (HCC). We determined whether dexmedetomidine could be an alternative to remifentanil for RFA of HCC under general anesthesia with sevoflurane.

METHODS

We prospectively randomized patients scheduled to undergo RFA for HCC to a dexmedetomidine (DEX) group or remifentanil (REMI) group (47 patients each). In the DEX group, a bolus infusion (0.4 μg kg^- 1) was started 15 min before anesthesia induction and continued at 0.2 μg kg^- 1 h^- 1 until 10 min before the end of surgery. In the REMI group, 3 μg kg^- 1 h^- 1 of remifentanil was administered from 15 min before anesthesia induction to the end of the surgery. The primary endpoint was postoperative pain intensity. Secondary endpoints included analgesic requirement, postoperative liver function, patient comfort, and hemodynamic changes. Group allocation was concealed from patients and data analysts but not from anesthesiologists.

RESULTS

Postoperative pain intensity, analgesic consumption, comfort, liver function, and time to emergence and extubation did not differ between the two groups. Heart rate, but not mean arterial pressure, was significantly lower in the DEX group than in the REMI group, at 1 min after intubation and from 30 min after the start of the surgery until anesthesia recovery. Sevoflurane concentration and dosage were significantly lower in the DEX group than in the REMI group.

CONCLUSION

During RFA for HCC, low-dose dexmedetomidine reduced the heart rate and need for inhalational anesthetics, without exacerbating postoperative discomfort or liver dysfunction. Although it did not exhibit outstanding advantages over remifentanil in terms of pain management, dexmedetomidine could be a safe alternative adjuvant for RFA under sevoflurane anesthesia.

TRIAL REGISTRATION

Chinese Clinical Trial Registry, ChiCTR-OPC-15006613 . Registered on 16 June 2015.

Challenging the dose-response-time data approach: Analysis of a complex system

This study presents an extensive dose-response-time (DRT) meta-analysis of the nicotinic acid-induced inhibition of free fatty acids and insulin release. The purpose was to quantify the implications of lacking exposure data when analysing complex pharmacodynamic systems. The DRT model successfully characterised various response behaviours-including time-delays, rebound, feedback mechanisms, and adaptation-on both the individual and the population level. Comparing the fitted DRT model to an exposure-driven reference analysis showed that bias and uncertainty were introduced in the parameter estimates. However, most estimates were within one standard error from the reference. In both approaches, a few parameters suffered from practical identifiability issues, likely due to large differences in half-lives of the different rate processes. Moreover, the optimal dosing strategies predicted by the DRT model differed slightly from those of the exposure-driven analysis, having a lower optimal steady-state reduction of free fatty acids exposure.

Intravenous morphine titration vs. oral hydrocodone/acetaminophen for adults with lower extremity displaced fracture in an emergency department setting: A randomized controlled trial

The objective of the present study was to test the hypothesis that intravenous morphine titration provides superior analgesia to oral hydrocodone/acetaminophen for patients with lower extremity displaced fracture in an emergency department (ED) setting. A prospective, randomized clinical trial of ED patients suffering acute lower extremity displaced fracture pain was performed with a total of 206 participants included. After application of exclusion criteria, the cohort comprised 166 patients, 85 of which were randomly allocated to the oral hydrocodone/acetaminophen (5 mg/500 mg) group and 81 to the intravenous morphine titration (every 5 min by 3-mg increments) group. The main outcome was the visual analogue scale (VAS) at different time-points after the first dose of analgesic was administered. Secondary outcomes included the VAS change during the skeletal traction operation and short-term adverse events. The results demonstrated that the initial VSA of the participants was similar at the baseline on arrival at the ED (P=0.2582). At the time-points of 5, 15, 30 min after the first dose of analgesic administered, the intravenous morphine titration group exhibited a greater VAS reduction compared with that in the oral hydrocodone/acetaminophen group (P<0.01). The differences between the 2 groups were not statistically significant at 1 h or thereafter. The incidence of short-term adverse events was similar between the 2 groups but sedation, whose incidence in the morphine group was markedly increased, may not be arbitrarily attributed to adverse events. It was concluded that, compared with oral hydrocodone/acetaminophen, intravenous morphine titration provided a rapid and sufficient pain relief and equivalent short-term adverse events for patients with lower extremity displaced fracture in an ED setting.

Naloxone Triggering the RRT: A Human Antidote?

OBJECTIVES

At our institution, we observed an increase in opioid-related adverse events after instituting a new pain treatment protocol. To prevent this, we programmed the Omnicell drug dispensing system to page the RRT whenever naloxone was withdrawn on the general wards.

METHODS

Retrospective review of a prospectively collected database with a before and after design.

RESULTS

When comparing the two 12-month periods, there was a decrease in monthly opioid-related cardiac arrests from 0.75 to 0.25 per month (difference = 0.5; 95% CI, 0.04-0.96, P = 0.03) and a nearly significant decrease in code deaths from 0.25 to 0 per month (difference = -0.25; 95% CI, -0.02-0.52, P = 0.07) without a significant decrease in pain satisfaction scores (difference = -2.3; 95% CI, -4.4 to 9.0, P = 0.48) over the study period. There were also decreased RRT interventions from 7.3 to 5.6 per month (difference = -1.7; 95% CI, -0.31 to -3.03, P = 0.02) and decreased inpatient transfers from 2.9 to 1.8 transfers per month (difference = -1.2; 95% CI, -0.38 to -1.96, P = 0.005). When adjusting for inpatient admissions and inpatient days, there was a decrease in opioid-related cardiac arrests from 2.9 to 0.1 per 10,000 admissions (difference = -2.0; 95% CI, -0.2 to -3.8, P = 0.03) and a decrease in cardiac arrests from 0.5 to 0.2 per 10,000 patients (difference = -0.34; 95% CI, -.02 to -0.65, P = 0.04).

CONCLUSION

Naloxone-triggered activation of the RRT resulted in reduced opioid-related inpatient cardiac arrests without adversely affecting pain satisfaction scores.

Intravenous morphine titration as a rapid and efficient analgesia for adult patients with femoral shaft fractures after injury

This study aimed to compare the analgesic effects of intravenous ibuprofen and intravenous morphine titration for femoral shaft fractures in adult patients. In total, 293 participants were enrolled and randomly received intravenous ibuprofen or intravenous morphine titration. Their visual analogue scale (VAS) results were recorded every 5 minutes after the first administration. The VAS scores before and during transport were also measured. Meanwhile, the type and frequency of the adverse effects were also recorded in both groups. Patients treated with morphine showed a faster and greater reduction in the VAS than those in the ibuprofen group within 1 hour after the first administration. Interestingly, intravenous morphine titration provided consistent analgesia even during the further transport. No significant immediate adverse event was observed in all of the participants, except for sedation, which might be beneficial for keeping the patient quiet and might not be arbitrarily attributed to adverse effects. No addiction was noted in the morphine group. This study demonstrated that intravenous morphine titration is a faster and more efficient analgesia for femoral shaft fractures than ibuprofen in adult patients immediately after injury.

Preoperative and early postoperative quality of life after major surgery - a prospective observational study

BACKGROUND

Changes in health-related quality of life (HRQoL) several days after surgery have rarely been investigated. We aimed to estimate the perioperative change of HRQoL, to identify patients with clinically relevant decrease in postoperative HRQoL and to establish factors associated with this decrease in HRQoL at day 30 after major surgery.

METHODS

Patients scheduled for major surgery at a university hospital were enrolled. Based on the HRQoL SF-12 questionnaire, the preoperative physical component summary (PCS) score, preoperative mental component summary (MCS) score, and postoperative PCS and MCS scores at day 30 were recorded. Minimal clinically important difference (MCID) was defined as those with a decrease of at least one half of the standard deviation (SD) of preoperative PCS or MCS scores. Differences between the groups with or without decreased HRQoL were investigated using univariate comparisons. A multiple logistic regression model was performed to evaluate the predictive value of potential perioperative variables.

RESULTS

The mean ± SD preoperative PCS score was 38.5 ± 10.6, postoperative score was 35.1 ± 7.8 (p = .004) in 85 patients. Thirty-five patients (41.2%) had a clinically relevant decrease of the postoperative PCS score. A normal to high preoperative exercise metabolic capacity measured with metabolic equivalent of task (MET) (p = .01) was a predictor of the decrease in postoperative PCS. The mean preoperative MCS scores (p = .395) were 42.2 (SD 12.8) preoperative, and 43.45 (SD 12.4) postoperative, respectively.

CONCLUSIONS

Major surgery decreases postoperative PCS scores of HRQoL at 30 days. A normal to high exercise capacity was a predictor of a clinically relevant decrease of postoperative PCS scores.

TRIAL REGISTRATION

07-107 (Ethical Committee NAC of Geneva University Hospitals).

MORPHIT: an observational study on morphine titration in the postanesthetic care unit in children

BACKGROUND

Little information is available on the titration of morphine postoperatively in children. This observational study describes the technique in terms of the bolus dose, the number of boluses required, the time to establish analgesia, and side effects noted.

METHODS

Morphine was administered if pain score (VAS or FLACC) was >30. Patients weighing less than 45 kg received a 50 μg·kg(-1) bolus of morphine with subsequent boluses of 25 μg kg(-1) as required. Patients weighing over 45 kg received boluses of 2 mg. Pain and Ramsay scores were recorded up to 90 min after the end of the titration and any side effect or complication was noted. Data are presented as the median [interquartile Q1-Q3 range].

RESULTS

Overall, 103 children were studied. The median age was 4.2 years [0.8-12.2 years]. The median weight was 15.5 kg [8.2-35.0 kg]. The protocol was effective for pain control with a significant decrease in pain scores over time. The median pain score (VAS or FLACC) was 70 [50-80] prior to the initial bolus and 0 [0-10] 90 min after the last bolus. Median Ramsay score was 1 [1-2] before the initial bolus administration and 4 [2-4] at 90 min. The median total dose of morphine was 100 [70-140] μg·kg(-1) , and the median number of boluses was 3 [2-5]. Side effects were observed in 17% of cases. No serious complications were observed.

CONCLUSIONS

Our study of morphine titration for children shows that our protocol was effective for pain control with a significant decrease in pain scores over time. No serious complications were encountered. More studies on larger cohorts of patients are needed to confirm the efficacy and safety of this protocol.

Do we have clarity on the therapeutic levels of morphine and its metabolites: seeking answers for the dilemma?

In spite of numerous investigations and decades of research, there is still a void in the complete understanding of the therapeutic action of morphine due to the complex nature of its pharmacokinetic/metabolic disposition coupled with elusive pharmacodynamics. This commentary attempts to collate current information on this very important topic and provide perspective to further tease out the relationship between morphine and its metabolites to its purported clinical effect. Similar to numerous acute therapies that need a close vigil for therapy optimization, postoperative pain management with morphine is a challenge due to its extreme intrasubject variability, a fragile therapeutic index, and complex pharmacology interlinked with formation and transport of active metabolite(s). Although numerous investigations of pharmacokinetics and pharmacodynamic effects of morphine and its active glucuronide metabolites have been carried out and excellent data published, still there remains a void in complete understanding of desired therapeutic levels for a meaningful therapeutic outcome without the avoidance of morphine-related side effect profile. The 2009 report of Hammoud et al. (Pain. 2009;144:139-146) confirms the challenges of which one need to be aware during postoperative pain management with morphine in spite of well-controlled intravenous titration using an institutional protocol. These authors have attempted to correlate the plasma concentrations of morphine and its key metabolites, morphine-3-glucuronide (3MG) and morphine-6-glucuronide (6MG), with clinical outcomes such as sedation and adverse effects. This report assumes high significance, since such an investigation to titrate postoperative patients to a fixed desired clinical efficacy outcome has hitherto been not performed in patients who underwent postoperative pain managemnt. Moreover, the intravenous titration option used in the study provided a clean collection of pharmacokinetic surrogate data of morphine along with its metabolites without the issue of absorption and/or oral bioavailability setback if morphine was given by oral route. However, the various pharmacokinetic surrogates used in this study was found insufficient to distinguish the clinical effects. Given the complicated pharmacokinetic and pharmacodynamic profiles of morphine and its metabolites (6MG and 3MG), this commentary provides some thoughts to seek answers for this interesting dilemma.

Does midazolam enhance pain control in prehospital management of traumatic severe pain?

PURPOSE

Midazolam comedication with morphine is a routine practice in pre and postoperative patients but has not been evaluated in prehospital setting. We aimed to evaluate the comedication effect of midazolam in the prehospital traumatic adults.

METHODS

A prehospital prospective randomized double-blind placebo-controlled trial of intravenous morphine 0.10 mg/kg and midazolam 0.04 mg/kg vs morphine 0.10 mg/kg and placebo. Pain assessment was done using a validated numeric rating scale (NRS). The primary end point was to achieve an efficient analgesic effect (NRS≤3) 20 minutes after the baseline. The secondary end points were treatment safety, total morphine dose required until obtaining NRS≤3, and efficient analgesic effect 30 minutes after the baseline.

FINDINGS

Ninety-one patients were randomized into midazolam (n=41) and placebo (n=50) groups. No significant difference in proportion of patients with a pain score≤3 was observed between midazolam (43.6%) and placebo (45.7%) after 20 minutes (P=.849). Secondary end points were similar in regard with proportion of patients with a pain score≤3 at T30, the side effects and adverse events except for drowsiness in midazolam vs placebo, 43.6% vs 6.5% (P<.001). No significant difference in total morphine dose was observed, that is, midazolam (14.09 mg±6.64) vs placebo (15.53 mg±6.27) (P=.315).

CONCLUSIONS

According to our study, midazolam does not enhance pain control as an adjunctive to morphine regimen in the management of trauma-induced pain in prehospital setting. However, such midazolam use seems to be associated with an increase in drowsiness.

Translational PK-PD modeling in pain

The current gap between animal research and clinical development of analgesic drugs presents a challenge for the application of translational PK-PD modeling and simulation. First, animal pain models lack predictive and construct validity to accurately reflect human pain etiologies and, secondly, clinical pain is a multidimensional sensory experience that can't always be captured by objective and robust measures. These challenges complicate the use of translational PK-PD modeling to project PK-PD data generated in preclinical species to a plausible range of clinical doses. To date only a few drug targets identified in animal studies have shown to be successful in the clinic. PK-PD modeling of biomarkers collected during the early phase of clinical development can bridge animal and clinical pain research. For drugs with novel mechanism of actions understanding of the target pharmacology is essential in order to increase the success of clinical development. There is a specific interest in the application of human pain models that can mimic different aspects of acute/chronic pain symptoms and serves as link between animal and clinical pain research. In early clinical development the main objective of PK-PD modeling is to characterize the relationship between target site binding and downstream biomarkers that have a potential link to the clinical endpoint (e.g. readouts from the human pain models) so as to facilitate the selection of doses for proof of concept studies. In patient studies, the role of PK-PD modeling and simulation is to characterize and confirm patient populations in terms of responder profiles with the aim to find the right dose for the right patient.

Pharmacokinetic-pharmacodynamic modeling in acute and chronic pain: an overview of the recent literature

In acute and chronic pain, the objective of pharmacokinetic-pharmacodynamic (PKPD) modeling is the development and application of mathematical models to describe and/or predict the time course of the pharmacokinetics (PK) and pharmacodynamics (PD) of analgesic agents and link PK to PD. Performing population PKPD modeling using nonlinear mixed effects modeling allows, apart from the estimation of fixed effects (the PK and PD model estimates), the quantification of random effects as within- and between-subject variability. Effect-compartment models and mechanism-based biophase distribution models that incorporate drug-association and -dissociation kinetics are applied in PKPD modeling of pain treatment. Mechanism-based models enable the quantification of the rate-limiting factors in drug effect owing to drug distribution versus receptor kinetics (since receptor kinetics are nonlinear they are discernable from the linear effect-compartment kinetics). It is a helpful technique in understanding the complex behavior of specific analgesics, such as buprenorphine, but also morphine and its active metabolite morphine-6-glucuronide, especially with respect to the reversal of opioid-induced side effects, most importantly life-threatening respiratory depression. One approach in chronic pain studies is the application of mixture models. Mixture models do not necessarily need to take PK data into account and allow the objective differentiation of measured responses to analgesics into specific response subgroups, and as such, may play an important role in analyzing Phase I and II analgesia studies. Appropriate application of PKPD modeling leads to the improvement of current therapeutics with respect to dose design and outcome, understanding the interaction of analgesics within complex chronic pain disease processes and may play an important role in drug development. In the current article, novel observations using the aforementioned techniques on opioids, NSAIDs, epidural analgesia, ketamine and GABA-ergic drugs in acute and chronic pain are discussed.

Phase I studies of sirolimus alone or in combination with pharmacokinetic modulators in advanced cancer patients

PURPOSE

Sirolimus is the eponymous inhibitor of the mTOR; however, only its analogs have been approved as cancer therapies. Nevertheless, sirolimus is readily available, has been well studied in organ transplant patients, and shows efficacy in several preclinical cancer models.

EXPERIMENTAL DESIGN

Three simultaneously conducted phase I studies in advanced cancer patients used an adaptive escalation design to find the dose of oral, weekly sirolimus alone or in combination with either ketoconazole or grapefruit juice that achieves similar blood concentrations as its intravenously administered and approved prodrug, temsirolimus. In addition, the effect of sirolimus on inhibition of p70S6 kinase phosphorylation in peripheral T cells was determined.

RESULTS

Collectively, the three studies enrolled 138 subjects. The most commonly observed toxicities were hyperglycemia, hyperlipidemia, and lymphopenia in 52%, 43%, and 41% of subjects, respectively. The target sirolimus area under the concentration curve (AUC) of 3,810 ng-h/mL was achieved at sirolimus doses of 90, 16, and 25 mg in the sirolimus alone, sirolimus plus ketoconazole, and sirolimus plus grapefruit juice studies, respectively. Ketoconazole and grapefruit juice increased sirolimus AUC approximately 500% and 350%, respectively. Inhibition of p70 S6 kinase phosphorylation was observed at all doses of sirolimus and correlated with blood concentrations. One partial response was observed in a patient with epithelioid hemangioendothelioma.

CONCLUSION

Sirolimus can be feasibly administered orally, once weekly with a similar toxicity and pharmacokinetic profile compared with other mTOR inhibitors and warrants further evaluation in studies of its comparative effectiveness relative to recently approved sirolimus analogs.

Aspiration pneumonitis caused by delayed respiratory depression following intrathecal morphine administration

Opioid analgesia is the primary pharmacologic intervention for managing pain. However, opioids can cause various adverse effects including pruritus, nausea, constipation, and sedation. Respiratory depression is the most fatal side effect. Therefore, cautious monitoring of respiratory status must be done after opioid administration. Here, we report a patient who suffered from respiratory depression with deep sedation and aspiration pneumonitis after intrathecal morphine administration.

Trend of analgesic consumption and pain scores in the post anesthetic care unit (A 9-year survey in surgical cancer patients)

As part of a quality assurance program, we assessed the trend of our analgesic consumption using our anesthesia database which include anesthesia and postanesthetic care records for all patients. In recent years, emphasis was made on anesthesia personnel to decrease postoperative opioid analgesic at the expense of non-opioid analgesics in order to decrease opioid related side effects. The following items were recorded: intraoperative opioid consumption, total morphine consumption, non-opioid analgesic consumption pain and sedation scores in the postoperative care unit (PACU). The database consisted of 57,967 patients for 9 consecutive years from 2002 to 2010, mean data exhaustivity was of 95%. Total morphine consumption per patient in the operative room and in the PACU decreased significantly from 11 ± 4 mg in year 2002 to 7 ± 3 mg in 2010, P < 0.05. In the intraoperative period, remifentanil/sufentanil ratio increased significantly from 33/67 to 87/13% of patients (P < 0.05) without affecting pain scores in the PACU. This multi-year trend shows a significant decrease in overall postoperative morphine consumption, in addition we showed that computerized database can easily follow the trend of analgesic consumption and can be used therefore as a powerful tool with easy access as part of a quality assurance program.

Population pharmacokinetics and pharmacodynamics in anesthesia, intensive care and pain medicine

PURPOSE OF REVIEW

Population modeling is a relatively new pharmacological discipline, the development of which has largely been stimulated by the need for accurate models for the pharmacokinetics and dynamics of anesthetic agents.

RECENT FINDINGS

Population-based modeling is now considered superior to older, more traditional modeling methods. Nonlinear mixed-effect modeling - a commonly used population-based modeling approach - estimates intraindividual and interindividual variability, limits the influence of outlying samples and individuals through the use of Bayesian statistical analysis, and provides a potential means of optimizing drug delivery regimens, especially when used to define pharmacokinetic-dynamic models for target-controlled infusion systems. In addition to being used for pharmacokinetic modeling, in which the influence of factors such as age, weight and illness can be studied, it is a powerful tool for the study of the influence of multiple factors on drug pharmacodynamics.

SUMMARY

Nonlinear mixed-effect population-based modeling has become the gold standard method of pharmacokinetic and pharmacodynamic analysis during new drug development and during subsequent pharmacological studies. Population-based modeling techniques have been applied to numerous aspects of drug delivery in anesthesia, intensive care and pain medicine.