Opioids: a pharmacologist's delight!

Characterization of Opioid Agonist Morphine Derivatives with Emphasis on Medicinal Chemistry

Relieving severe pains is an unmet medical need, in which opioids are of prime importance and in the focus of pharmaceutical companies. The objective of this study is to characterize the physicochemical properties, namely basicity, lipophilicity and permeability of thirty opioid ligands, which include eleven newly synthesized compounds. pH-potentiometry and the shake-flask method were used for the characterization of species-specific basicity and lipophilicity. The effective permeability was determined using a brain-specific parallel artificial membrane permeability assay. Structural modifications, namely O-methylation in position 3, isomerization in position 6, saturation of the double bond in position 7, 14-hydroxylation, and the substitution of N-(β-phenylethyl) and N-cyclobutylmethyl side chains all have various effects on these physicochemical properties, and these are explained and compared to computationally predicted values. Computational predictions inadequately capture hydrogen bond formation with the tertiary amino group in case of 14-hydroxylation, just as the effects of hydroxy oxidation at position 6 and N-methyl substitution with N-(β-phenylethyl). The relationship between lipophilicity, permeability and potency is presented by lipophilic efficiency plots that reveal the most promising compounds. This study emphasizes the importance of experimental determination of these essential physicochemical parameters, furthermore, it can contribute to a more thorough understanding of the pharmacokinetic properties.

Efficacy and safety of sufentanil sublingual tablet system in postoperative pain management: a systematic review and meta-analysis

BACKGROUND

Sufentanil sublingual tablet system (SSTS) is a recently approved formulation for postoperative pain management that has become popular due to its pharmacokinetic properties such as good bioavailability, rapid attainment of equilibrium and elimination without any metabolites, along with its pharmacodynamic properties such as rapid onset and effective pain reduction. It is also relatively well tolerated by patients.

OBJECTIVE

This is a quantitative analysis of the efficacy and safety of SSTS in patients with moderate to severe postoperative pain.

DESIGN

This is a systematic review and meta-analysis. Databases such as Cochrane Library, MEDLINE and EMBASE were searched for eligible articles.

SETTINGS

Randomised controlled trials published after 2000 in English language and which assessed at least one of the outcome measures of interest with pain intensity difference between 12 hours and a maximum of 96 hours.

PARTICIPANTS

Adults with moderate to severe postoperative pain and taking SSTS for pain management.

METHODS

Data were analysed using Review Manager (RevMan) V.5.3. Risk of bias (RoB) assessment was done using RoB-2 scale, and overall grading of evidence of each outcome was done using GRADEpro Guideline Development Tool.

RESULTS

Analysis of SSTS versus control indicates a statistically significant reduction in summed pain intensity difference at 12 hours (mean difference (MD)=-12.33 (95% CI -15.5 to -9.17), p<0.00001), summed pain intensity difference at 48 hours (MD=-43.57 (95% CI -58.65 to -28.48), p<0.00001), time-weighted total pain relief over 12 hours (MD=-4.77 (95% CI -6.28 to -3.27), p<0.00001) and pain intensity difference (MD=-0.73 (95% CI -1.00 to -0.46), p<0.00001) with SSTS, alongside high quality of evidence. Success of treatment as assessed by Patient Global Assessment (OR=4.01 (95% CI 2.74 to 5.89), p<0.00001) and Healthcare Professional Global Assessment (OR=4.46 (95% CI 3.03 to 6.56), p<0.00001) scoring at 72 hours was observed in a significantly high number of individuals using SSTS, with high quality of evidence. There was no difference in adverse events except for dizziness (RR=1.90, 95% CI 1.02 to 3.52). There was a significantly higher number of total adverse events in orthopaedic surgery in the SSTS group than in the comparator.

CONCLUSION

SSTS is effective in postoperative pain management in patients with moderate to severe pain. It also has good tolerability and high patient satisfaction.

PROSPERO REGISTRATION NUMBER

CRD42018115458.

Efficacy of opioids for traumatic pain in the emergency department: a systematic review and Bayesian network meta-analysis

Aim: To systematically assess and rank the efficacy of opioid medications for traumatic pain in the emergency department in terms of pain relief, adverse events and rescue analgesia. Methods: Four databases were systematically searched until 26 September 2022: PubMed, Embase, Cochrane Library, and Web of Science. Outcomes were pain relief, adverse events (dizziness, hypotension, pruritus, sedation), and rescue analgesia. For each outcome, network plots were drawn to exhibit direct and indirect comparisons, and rank probabilities were utilized to rank the efficacy of different opioids. Results: Twenty studies of 3,040 patients were eligible for this network meta-analysis. According to the rank probabilities, the top three analgesic medications for pain relief may be sufentanil (78.29% probability of ranking first), buprenorphine (48.54% probability of ranking second) and fentanyl (53.25% probability of ranking third); buprenorphine (31.20%), fentanyl (20.14%) and sufentanil (21.55%) were least likely to cause dizziness; the top three analgesic medications which were least likely to cause hypotension were buprenorphine (81.64%), morphine (45.02%) and sufentanil (17.27%); butorphanol (40.56%), morphine (41.11%) and fentanyl (14.63%) were least likely to cause pruritus; the top three medications which were least likely to cause sedation were hydrocodone + acetaminophen (97.92%), morphine (61.85%) and butorphanol (55.24%); patients who received oxycodone (83.64%), butorphanol (38.31%) and fentanyl (25.91%) were least likely to need rescue analgesia in sequence. Conclusion: Sufentanil, buprenorphine and fentanyl may be superior to other opioid medications in terms of pain relief and the incidence of dizziness, hypotension and pruritus, which might be selected as opioid analgesics for traumatic pain in the emergency setting.

The Newest Battlefield Opioid, Sublingual Sufentanil: A Proposal to Refine Opioid Usage in the U.S. Military

There is an ongoing opioid epidemic in the USA, and the U.S. military is not immune to the health threat. To combat the epidemic, the Department of Defense (DoD) and Department of Veterans' Affairs (DVA) issued new clinical practice guidelines and launched the Opioid Safety Initiative aimed at reducing opioid prescriptions. Furthermore, the DoD continually refined opioid protocols for acute pain on the battlefield, evolving from intramuscular morphine to intravenous morphine administration to oral transmucosal fentanyl citrate lollipops (Actiq) to finally sublingual sufentanil tablets (SSTs, Dsuvia). Interestingly, the newest introduction of SSTs into the military sparked great controversy, as there are concerns over the drug's potential for misuse. However, although the opioid crisis may understandably foster an aversion to new candidate opioids, the therapeutic benefits of effective opioids in acute trauma settings should not be overlooked. SSTs may offer an improved analgesic option to meet the battlefield's unmet needs with its non-invasive, sublingual delivery system and favorable pharmacologic properties that mitigate the risk for side effects, addiction, and adverse outcomes. Accordingly, this commentary aims to (1) review the evolution of opioid use on the battlefield and discuss the medical benefits and limitations of SSTs in acute trauma settings, (2) highlight the importance of chronic pain management post-deployment through evidence-based non-opioid modalities, and (3) explore avenues of future research. Ultimately, we propose that SSTs are an important improvement from existing battlefield opioids and that refining, not abandoning, opioid usage will be key to effectively managing pain in the military.

Patient and Healthcare Professional Satisfaction Ratings and Safety Profile of Sufentanil Sublingual Tablets for Treatment of Acute Pain: A Pooled Demographic Analysis

Objective

This analysis reports the healthcare professional global assessment (HPGA) and patient global assessment (PGA) scores and the adverse event (AE) profile by age, body mass index (BMI), sex, and race from the three Phase III registration studies for sufentanil sublingual tablet (SST) 30 mcg.

Methods

Global assessments and treatment-related AEs were analyzed from patients treated with SST 30 mcg for moderate-to-severe acute pain following surgery or in the emergency department (ED). Pooled data were analyzed across patient demographic subgroups.

Results

A total of 283 patients were included in the HPGA/PGA analyses. The majority underwent abdominal surgery, with the remaining patients undergoing orthopedic or “other” types of surgery. Overall, SST 30 mcg was highly rated by both healthcare professionals and patients across the demographic subgroups. A total of 323 patients were included in the safety evaluation. The majority of patients did not experience any SST-related AEs; however, those that did experienced common opioid-related side effects such as nausea, headache, dizziness, and vomiting. No patients experienced unexpected AEs or required the use of naloxone.

Conclusion

SST 30 mcg was highly rated and well tolerated across demographic subgroups with the majority of patients not experiencing any adverse event related to SST 30 mcg. These findings support the use of sublingual sufentanil in all adult patients, regardless of age, BMI, sex, or race for the treatment of moderate-to-severe acute pain.

Sufentanil Sublingual for Acute Post-Operative Pain: A Systematic Literature Review Focused on Pain Intensity, Adverse Events, and Patient Satisfaction

CONTEXT

Pain is commonly experienced among patients after surgical procedures. Clinical pain management after surgery is far from being successful. Patients may control postoperative pain by self-administration of intravenous opioids using devices designed for this purpose (patient-controlled analgesia or PCA). PCA devices have been developed including the sufentanil sublingual tablet system (SSTS). A systematic review of the use of SSTS for postoperative pain is needed to identify an alternative method of pain management.

OBJECTIVES

To systematically review literature to establish the efficacy and the safety of PCA with SSTS used in the treatment of moderate-to-severe acute post-operative pain in a hospital setting.

METHODS

Embase, MEDLINE, Google Scholar, and Cochrane Central Trials Register were systematically searched in December 2019 for studies examining SSTS for pain in adult after surgical procedures. The methodological quality of the studies and their results were appraised using the Consensus-based Standards for the Selection of Health Measurement Instruments (COSMIN) checklist and specific measurement properties criteria, respectively.

RESULTS

Sixteen studies evaluating SSTS were included for a total of 2311 patients. All participants in the SSTS group reported NRS ≤ 4 within 24 h after surgery. Patient satisfaction was high, with a minimum of 70% satisfaction among patients treated with SSTS. The most common adverse events (AEs) overall for SSTS 15 and 30 mcg were nausea, vomiting, and headache. AEs observed in the studies were generally consistent with those associated with opioids and the postsurgical setting.

CONCLUSIONS

SSTS is an important system for the management of moderate-to-severe acute pain in a hospital setting. SSTS is well tolerated, with no unexpected adverse events (AEs) and no clinically meaningful vital sign changes. These data confirm the safety and tolerability of the SSTS. Successful pain management resulted in a high level of acceptance of the SSTS by patients with high satisfaction for the method of pain control.

Pooled Dosing and Efficacy Analysis of the Sufentanil Sublingual Tablet 30 mcg Across Demographic Subgroups for the Management of Moderate-to-Severe Acute Pain

PURPOSE

To aid nurses in dosing sufentanil sublingual tablet (SST) 30 mcg administered via a single-dose applicator, dosing requirements and efficacy of SST 30 mcg were analyzed across age, sex, race, and body mass index subgroups.

DESIGN

Patient characteristics were pooled from three postoperative studies (two placebo-controlled and one open-label) and one open-label emergency department study. Drug dosing and efficacy data were pooled from the postoperative studies.

METHODS

Efficacy was assessed through summed pain intensity difference to baseline during 12 hours across subgroups.

FINDINGS

Mean (standard deviation) drug doses administered from 0 to 12 hours was 3.9 (2.0) for SST 30 mcg and was less frequent for older (≥65 years) versus younger patients. The summed pain intensity difference to baseline during 12 hours was superior with SST 30 mcg versus placebo across all subgroups.

CONCLUSIONS

SST 30 mcg is a sublingual opioid analgesic with efficacy across demographic subgroups.

Sufentanil 30 µg Sublingual Tablet: A Review in Acute Pain

The sufentanil 30 μg sublingual tablet (hereafter referred to as the sufentanil ST) is approved in the EU for acute moderate to severe pain in adults (Dzuveo™) and in the USA for acute pain severe enough to require an opioid analgesic and for which alternative treatments are inadequate (Dsuvia™). It is a single-strength tablet housed in a single-dose applicator (which may minimize the likelihood of dosing errors) and is strictly for use in medically supervised/monitored settings. It is administered by a healthcare professional and has a minimum re-dose interval of 1 h and no drug delivery setup requirements. In placebo-controlled or noncomparative phase 2 or 3 trials, the sufentanil ST provided effective analgesia for adults with moderate to severe acute pain due to surgery or trauma/injury, reducing the intensity of pain within 15-30 min after the first dose and maintaining analgesic benefit over the 2-24 h study periods. Such short-term use of the sufentanil ST was also generally well tolerated. Studies directly comparing the sufentanil ST with other opioids in terms of efficacy, tolerability, usability and cost effectiveness would be beneficial, as would analyses of its abuse potential, given sufentanil is considerably more potent than fentanyl or morphine. In the meantime, current data indicate that the sufentanil ST is a noninvasive, fast-acting, opioid formulation for managing moderate to severe acute pain in medically supervised/monitored settings that may be of particular use when oral or intravenous opioid analgesia is not possible/feasible.

Effect of Dexmedetomidine combined with sufentanil for post- thoracotomy intravenous analgesia:a randomized, controlled clinical study

Background

Few studies have investigated the use of dexmedetomidine in patient-controlled intravenous analgesia (PCIA) after thoracic surgery. This study to evaluate the effect of dexmedetomidine combined with sufentanil for PCIA after thoracotomy under general anaesthesia.

Methods

Ninety-seven adults patients scheduled for thoracotomy surgery. All two groups received PCIA with either sufentanil alone (control group) or combining dexmedetomidine with sufentanil (dexmedetomidine group). Hemodynamic measurements, visual analog scale (VAS) scores at rest and at coughing, Ramsay sedation score (RSS), analgesic consumption, and postoperative nausea and vomiting (PONV) as well as drug-related adverse effects were compared at 2, 6, 12, 24, 36 and 48 h postoperatively.

Results

In the patients of the dexmedetomidine group, compared to the control group, the pain scores at rest or at coughing during 48 h postoperatively were lower (P < 0.001), the sedation scores were lower, the consumption of sufentanil and rescue meperidine were lower, and the number of episode of moderate PONV was three times lower. No signs of toxicity or local complications were observed. There was a non-significant trend for a lower HR and BP in the dexmedetomidine group vs. Control.

Conclusion

The combining dexmedetomidine with sufentanil for post-thoracotomy PCIA can improve pain control together with the decrease in sufentanil requirements, and improve postoperative patient’s satisfaction compared with sufentanil alone in PCIA.

Trial Registration

This trial was retrospectively registered on 27 April 2016 at the Chinese Clinical Trial Register (number: ChiCTR-ONC-16008376).

Sufentanil sublingual tablet system for the management of postoperative pain

INTRODUCTION

Intravenous patient-controlled opioid analgesia has been an important improvement in addressing insufficient management of acute postoperative pain for over 40 years. However, there are number of weaknesses for intravenous patient-controlled analgesia, including operator and device error, intravenous line patency issues, and risk of catheter-related infection, all of which contribute to the complications and increase in cost of care. The sublingual sufentanil tablet system is a major evolution in both drug and technological management of postoperative pain. Areas covered: We reviewed the use of the sublingual sufentanil tablet system in management of moderate to severe postoperative pain in hospitalized patients, with a particular focus on the pharmacological properties of sufentanil and clinical use in different surgical patients. Expert opinion: The sublingual sufentanil tablet system can decrease intravenous opioid based patient-controlled analgesia related complications and safety issues. Current clinical studies have demonstrated this noninvasive-novel system to be safe and effective in management of acute pain in the postsurgical setting. Researchers should focus on comparing it with other available patient controlled analgesia modalities and evaluating the efficiency and cost effectiveness of the sublingual sufentanil tablet system.

Sufentanil sublingual formulation for the treatment of acute, moderate to severe postoperative pain in adult patients

INTRODUCTION

Sufentanil is a highly selective µ-opioid agonist commonly used by intravenous and intrathecal routes for acute pain. Sublingual sufentanil formulation for patient controlled analgesia (PCA) uses an innovative administration device that suspends a 15 µg nanotablet with a fixed lockout interval. The system is a non-invasive, less burdensome method of opioid delivery compared to intravenous and intrathecal routes. Sublingual nanotablet PCA transmucosal bioavailability is 59% and the meaningful analgesic onset time is 60 minutes. Areas covered: This paper focuses on the effectiveness, safety and feasibility of sufentanil PCA sublingual formulation for the management of postoperative pain. The paper is based on PubMed searches and the European Medicine Agency assessment report. Expert commentary: Under-treatment of acute pain is a substantial clinical problem. The initial experiences with the sublingual delivery system are encouraging. Sufentanil sublingual nanotablets intended for PCA device use are approved in Europe, and approval is pending in the United States.

Evolution of Patient-Controlled Analgesia: From Intravenous to Sublingual Treatment

Opioid administration delivered intravenously (IV) by patient-controlled analgesia (PCA) devices has been an important development in addressing insufficient management of acute pain in the postsurgical setting. However, IV PCA has several disadvantages, including operator error, risk of patient exposure to analgesic gaps, IV line patency issues, and risk of catheter-related infection, all of which contribute to the total cost of care. Morphine, the most commonly used opioid in IV PCA, has a relatively slow onset of analgesia, which may leave patients with inadequate initial pain control and at risk of opioid dose-stacking. Sufentanil is an opioid with no major active metabolites and a rapid onset of analgesia. The sufentanil sublingual tablet system (SSTS) with a 20-minute lockout and other safety features is a novel noninvasive PCA system in development for on-demand relief of moderate to severe acute pain in the hospital setting. Data from phase 3 trials of the use of SSTS after elective major open abdominal and orthopedic surgery show that analgesia is rapidly achieved, with a longer mean interdosing interval compared with IV PCA morphine (81 vs 47 minutes) and a high level of patient and nurse satisfaction. These data suggest that SSTS may also aid in the avoidance of some of the pitfalls inherent with IV PCA, which may help reduce hospital costs associated with IV PCA-related issues. This article describes the evolution, benefits, issues, and costs associated with IV PCA and reviews data from preclinical studies of sufentanil through SSTS phase 3 trials.

A review of sufentanil and the sufentanil sublingual tablet system for acute moderate to severe pain

The sufentanil sublingual tablet system (SSTS) is a novel patient-controlled analgesia (PCA) system that is pending approval from the US FDA for the management of moderate to severe acute pain in hospitalized patients. SSTS offers a noninvasive alternative to intravenous (iv.) PCA and optimized on-demand analgesia with the rapid onset and titratibility of sublingual sufentanil. Phase III clinical trials have demonstrated that SSTS has greater efficacy for the treatment of pain during the 72-h postoperative period after open abdominal and major orthopedic (total knee or total hip arthroplasty) surgery compared with iv. PCA with morphine sulfate (MS) or a placebo system. Safety assessments indicate that adverse events are typical for postoperative patients taking opioid analgesics. While the frequency of adverse events is comparable between patients using SSTS and iv. PCA MS, the incidence of oxygen desaturation is lower in those using SSTS.

Sufentanil Sublingual Tablet System vs. Intravenous Patient‐Controlled Analgesia with Morphine for Postoperative Pain Control: A Randomized, Active‐Comparator Trial

Background

Problems with intravenous patient-controlled analgesia (IV PCA) are well known, including invasive route of delivery and pump programming errors. The primary objective of this study was to evaluate patient satisfaction with a novel sublingual sufentanil PCA system (sufentanil sublingual tablet system 15 mcg with a 20-minute lockout interval; SSTS) to IV PCA morphine sulfate 1 mg with a 6-minute lockout interval (IV PCA MS) for the management of acute postoperative pain.

Methods

This was a randomized, open-label, 48-hour non-inferiority study with optional extension to 72 hours at 26 U.S. sites enrolling patients scheduled for elective major open abdominal or orthopedic (hip or knee replacement) surgery. The primary outcome measure was the proportion of patients who responded “good” or “excellent” (collectively “success”) at the 48-hour timepoint on the Patient Global Assessment of method of pain control (PGA48).

Results

A total of 357 patients received study drug and 78.5% vs. 65.6% of patients achieved PGA48 “success” for SSTS vs. IV PCA MS, respectively, demonstrating non-inferiority (P < 0.001 using the one-side Z-test against the non-inferiority margin) as well as statistical superiority for treatment effect (P = 0.007). Patients using SSTS reported more rapid onset of analgesia and patient and nurse ease of care and satisfaction scores were higher than IV PCA MS. Adverse events were similar between the 2 groups; however, SSTS had fewer patients experiencing oxygen desaturations below 95% compared to IV PCA MS (P = 0.028).

Conclusions

Sufentanil sublingual tablet system is a promising new analgesic technology that may address some of the concerns with IV PCA.

Finding the 'ideal' regimen for fentanyl-based intravenous patient-controlled analgesia: how to give and what to mix?

PURPOSE

This analysis was done to investigate the optimal regimen for fentanyl-based intravenous patient-controlled analgesia (IV-PCA) by finding a safe and effective background infusion rate and assessing the effect of adding adjuvant drugs to the PCA regimen.

MATERIALS AND METHODS

Background infusion rate of fentanyl, type of adjuvant analgesic and/or antiemetic that was added to the IV-PCA, and patients that required rescue analgesics and/or antiemetics were retrospectively reviewed in 1827 patients who underwent laparoscopic abdominal surgery at a single tertiary hospital.

RESULTS

Upon multivariate analysis, lower background infusion rates, younger age, and IV-PCA without adjuvant analgesics were identified as independent risk factors of rescue analgesic administration. Higher background infusion rates, female gender, and IV-PCA without additional 5HT₃ receptor blockers were identified as risk factors of rescue antiemetics administration. A background infusion rate of 0.38 μg/kg/hr [area under the curve (AUC) 0.638] or lower required rescue analgesics in general, whereas, addition of adjuvant analgesics decreased the rate to 0.37 μg/kg/hr (AUC 0.712) or lower. A background infusion rate of 0.36 μg/kg/hr (AUC 0.638) or higher was found to require rescue antiemetics in general, whereas, mixing antiemetics with IV-PCA increased the rate to 0.37 μg/kg/hr (AUC 0.651) or higher.

CONCLUSION

Background infusion rates of fentanyl between 0.12 and 0.67 μg/kg/hr may safely be used without any serious side effects for IV-PCA. In order to approach the most reasonable background infusion rate for effective analgesia without increasing postoperative nausea and vomiting, adding an adjuvant analgesic and an antiemetic should always be considered.

Novel delivery systems for postoperative analgesia

Moderate-to-severe postoperative pain is usually controlled using a multimodal approach, including opioids. Intravenously administered patient-controlled analgesia (IV PCA) with opioids, popular for over 40 years, enables patients to control their level of analgesia and has advantages over a nurse-administered approach, including more satisfied patients and improved pain relief. Unfortunately, IV PCA has drawbacks such as device programming errors, medication prescribing errors, pump malfunction, limitations on patient mobility, IV patency issues, and transmission of infection. Furthermore, the setup of an infusion pump is often complex, time-consuming, and requires witnessed confirmation. Complicating IV PCA is the problem of commonly used compounds, morphine and hydromorphone, having significantly reduced brain/effector-site permeability and active metabolites, both of which create the risk of delayed adverse events. Novel patient-controlled modalities that incorporate rapid effector site-permeating opioids and non-invasive routes of administration offer great promise to enhance both patient and caregiver experiences with postoperative analgesia systems.

Current and developing methods of patient-controlled analgesia

Moderate-to-severe acute postoperative pain is commonly controlled with opioids administered via programmable intravenous (IV) patient-controlled analgesia (PCA) infusion pumps. Intravenously administered opioids provide effective relief of postoperative pain, and IV PCA enables patients to control their level of analgesia, which has advantages over nurse-administered approaches, including more satisfied patients and improved pain relief. Unfortunately, commonly used opioid analgesics can cause significant adverse effects. Furthermore, IV PCA has drawbacks, such as device programming errors, system errors, medication errors, limitations in patient mobility, and potential for IV tubing kinks, clogging, and transmission of infection. The IV route of administration is also characterized by a rapid, high peak in analgesic drug concentration followed by rapidly decreasing concentrations. Consequently, respiratory depression, excessive sedation, and inadequate pain control can occur. Furthermore, the technical assembly of an infusion pump is often complex and time-consuming. PCA modalities that incorporate superior opioid analgesics, such as sufentanil, and novel noninvasive routes of administration offer great promise for enhancing the patient and caregiver experience with the use of postoperative PCA.

The influence of putrefaction and sample storage on post-mortem toxicology results

There are numerous biochemical and biological processes that occur after death that may have a significant influence on post-mortem drug concentrations. These processes may render the quantification of particular drugs unreliable, or even result in drugs being undetectable in some instances, despite the use of several methods. Problems may occur with changes in the drug concentration via bacterial degradation, residual tissue enzymatic activity, or via post-mortem redistribution from tissues of a higher to a lower concentration. Many analytical techniques can suffer from interferences due to co-extracted putrefactive compounds that mask or alter the way a drug is detected, depending on the analytical technique utilised. The following paper reviews problems associated with post-mortem drug concentration changes, and the significance of microbial influences during the post-mortem interval and sample storage.

Lack of local anaesthetic efficacy of fentanyl in the abaxial sesamoid block model

Fentanyl and other opioid drugs have their effect in the central nervous system; however, activity at peripheral sites has also been demonstrated. Pain-suppression activity at peripheral sites raises the possibility of skilled individuals producing local anaesthetic effects with small doses of opioid drugs that would be difficult to detect forensically and could be used to affect the outcome of a race. Therefore, the local pain-suppression effect (peripheral nerve inhibition) of fentanyl was tested using an abaxial sesamoid block/hoof withdrawal model. With this model, fentanyl did not produce significant anaesthesia when tested in eight Thoroughbred horses. This suggests that fentanyl at this or lower doses is unlikely to reduce pain perception when applied directly to sensory neurons. However, the effect of fentanyl and other opioids on joint pain perception of horses, especially inflamed joints, is unknown.