Principles of opioid pharmacotherapy: practical implications of basic mechanisms

Review of Top 10 Prescribed Drugs and Their Interaction with Dental Treatment

The proportion of people over age 60 is growing faster than any other group. Many patients take several medications to manage multiple chronic medical conditions. Poor oral health is common and dental visits by patients over the age of 65 are increasing. The dentist must recognize that these medications may interact with dental treatment. This article reviews the top 10 prescribed drugs as listed in the IMS Institute national prescription audit in January 2015 and reviews the interactions between these medications and dental treatment. The medications reviewed include levothyroxine, acetaminophen/hydrocodone, lisinopril, metoprolol, atorvastatin, amlodipine, metformin, omeprazole, simvastatin, and albuterol.

In vivo profiling of seven common opioids for antinociception, constipation and respiratory depression: no two opioids have the same profile

BACKGROUND AND PURPOSE

For patients experiencing inadequate analgesia and intolerable opioid-related side effects on one strong opioid analgesic, pain relief with acceptable tolerability is often achieved by rotation to a second strong opioid. These observations suggest subtle pharmacodynamic differences between opioids in vivo. This study in rats was designed to assess differences between opioids in their in vivo profiles.

EXPERIMENTAL APPROACH

Male Sprague Dawley rats were given single i.c.v. bolus doses of morphine, morphine-6-glucuronide (M6G), fentanyl, oxycodone, buprenorphine, DPDPE ([D-penicillamine(2,5) ]-enkephalin) or U69,593. Antinociception, constipation and respiratory depression were assessed using the warm water tail-flick test, the castor oil-induced diarrhoea test and whole body plethysmography respectively.

KEY RESULTS

These opioid agonists produced dose-dependent antinociception, constipation and respiratory depression. For antinociception, morphine, fentanyl and oxycodone were full agonists, buprenorphine and M6G were partial agonists, whereas DPDPE and U69,593 had low potency. For constipation, M6G, fentanyl and buprenorphine were full agonists, oxycodone was a partial agonist, morphine produced a bell-shaped dose-response curve, whereas DPDPE and U69,593 were inactive. For respiratory depression, morphine, M6G, fentanyl and buprenorphine were full agonists, oxycodone was a partial agonist, whereas DPDPE and U69,593 were inactive. The respiratory depressant effects of fentanyl and oxycodone were of short duration, whereas morphine, M6G and buprenorphine evoked prolonged respiratory depression.

CONCLUSION AND IMPLICATIONS

For the seven opioids we assessed, no two had the same profile for evoking antinociception, constipation and respiratory depression, suggesting that these effects are differentially regulated. Our findings may explain the clinical success of 'opioid rotation'.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

Acquired pharmaco-dynamic opioid tolerance: a concept analysis

AIM

To report an analysis of the concept of acquired pharmaco-dynamic opioid tolerance.

BACKGROUND

Acquired pharmaco-dynamic opioid tolerance is a complex and poorly understood phenomenon associated with strong opioid therapy for managing pain. Critical review of the concept provides greater clarification of the attributes, assisting healthcare professionals in addressing pain and functional management of patients, particularly those with non-malignant pain.

DESIGN

Concept analysis.

DATA SOURCES

A systematic literature search was undertaken using electronic data bases: CINAHL, British Nursing Index, EMBase, Medline, Pubmed and AMED. All literature reviewed was in English and published between 1976 and 2012. The key search terms were 'chronic non-malignant pain', 'strong opioid therapy' and 'development of acquired pharmaco-dynamic opioid tolerance'; all possible variant terms were also searched.

METHOD

The Walker and Avant approach was used to guide the concept analysis.

RESULTS

The concept analysis revealed four empirical referents: plasticity, drug administration, reduced analgesic efficacy and increased drug dosing. Tachyphylexia was identified as a borderline case, opioid induced hyperalgesia as a related case and pseudo-tolerance as a contrary case. The antecedent is administration of an opioid analgesic drug and the consequences, increasing opioid drug dose to maintain analgesic effect.

CONCLUSION

Untangling the antecedents, empirical referents and consequences of tolerance help healthcare professionals understand its complexities. Improved knowledge may ultimately influence patient outcomes through the construction of better monitoring systems. This concept analysis may also provide insights for policy change and give empirical direction for future research.

Oral transmucosal fentanyl citrate for cancer breakthrough pain: a review

PURPOSE/OBJECTIVES

To review the dose titration, efficacy, and safety of oral transmucosal fentanyl citrate (OTFC).

DATA SOURCES

Phase I and II clinical trial abstracts and evidence-based review articles.

DATA SYNTHESIS

OTFC has an onset, peak, and duration of action similar to that of an IV dose of an opioid and has been demonstrated to be effective and well tolerated for the management of breakthrough pain in patients with cancer.

CONCLUSIONS

Studies of OTFC demonstrate that it is easy to use,noninvasive, effective, safe, and acceptable to patients, caregivers, and healthcare providers. However, OTFC is expensive and approved for use only in opioid-tolerant patients with cancer.

IMPLICATIONS FOR NURSING

Breakthrough pain in patients with cancer is a common problem with characteristics that make it difficult to treat. Oncology nurses should familiarize themselves with OTFC's unique characteristics to be able to best help patients manage their therapy.

A Comparison of the Antinociceptive and Adverse Effects of the mu-Opioid Agonist Morphine and the delta-Opioid Agonist SNC80

delta-Opioid receptor agonists have been postulated to induce analgesia without the adverse effects commonly associated with mu-opioids e.g. morphine. In the present study, we evaluated the occurrence of antinociceptive and opioid-like side effects in rats (n=5-7) treated with a single dose of subcutaneous morphine (0.01 to 40 mg/kg) or SNC80 (0.63 to 80 mg/kg). The antinociceptive effects of morphine and SNC80 were compared using a range of nociceptive tests including the tail withdrawal test, the acetic acid-induced abdominal constriction (writhing) assay, the automated formalin test and a model of inflammation-induced thermal hyperalgesia. The adverse effects of both drugs were examined in animal models for gastrointestinal (GI) inhibition (charcoal test; ricinus oil test), respiratory depression (blood-gas analysis), motor disturbances (automated rotarod model) and abuse liability (drug discrimination learning). Morphine displayed significant antinociceptive and adverse effects in all the animal models employed. SNC80 exhibited a significant effect in the writhing test and limited efficacy in a model of inflammation-induced thermal hypersensitivity. A delay in the occurrence of diarrhoea and some limited increases in PCO(2) were observed with the higher doses of SNC80 (> or =40 mg/kg). In conclusion, the delta-opioid agonist SNC80 lacks both the analgesic efficacy and adverse effects of mu-opioids. However, the activity of SNC80 in the inflammatory model suggests delta-opioid agonists may be useful analgesics in the treatment of some forms of inflammatory pain.

The drug-seeking patient in the emergency room

Drug-seeking patients include recreational drug abusers, addicts whose dependence occurred through abuse or the injudicious prescription of narcotics, and pseudoaddicts who have chronic pain that has not been appropriately managed. Opioids produce euphoria in some patients, providing the motivation for abuse, which can be detrimental even with occasional use. Even in the absence of overt euphoria, opioids are highly self-reinforcing and can be problematic in a large number of patients, requiring that acute care physicians exercise caution in whom they are administered. Habitual patient files, narcotic contracts, pain management letters, and patient tracking and management programs can be used for the benefit of both drug seeking-patients and chronic pain patients. For many patients, drug-seekers and chronic pain patients alike, withholding opioids may be an important part of their long-term management. For others, long-acting opioids such as long-acting morphine or methadone are a reasonable option.

Management of Chronic Pain in the Acute Care Setting

Chronic nonmalignant pain requires evaluation and treatment different from acute pain. The pathophysiology is different, and there is commonly some degree of psychosocial dysfunction. Opioids tend to be much less effective as analgesics for chronic pain, and may increase the sensitivity to pain when given long-term. Because they are self-reinforcing, opioids may be sought and be reported to improve chronic pain, even when they may make the condition worse over time. There are many effective alternatives to opioids for the treatment of chronic pain, but their use is complicated and may require considerable time and effort to determine which ones work. Patients, particularly those who have already been prescribed opioids, may resist these alternatives. An extensive physical and psychosocial evaluation is required in the management of chronic pain, which is difficult if not impossible to achieve in the emergency or urgent care settings. Consequently, emergency and urgent care physicians should work closely with the patient's pain management specialist or personal physician. Systems should be set up in advance to identify those patients whose frequent use of acute care services for obtaining opioids may be compromising their long-term management, putting themselves at risk for psychological and tolerance-induced adverse effects of frequent opioid use. Opioids may be used in carefully selected patients in consultation with their pain management specialist or personal physician, but care must be exercised not to initiate or exacerbate psychological or tolerance-related complications of chronic pain.

Pharmacologic Treatment of Opioid-Induced Sedation in Chronic Pain

OBJECTIVE:

To review the literature for pharmacologic management of opioid-induced sedation (OIS) in patients with chronic pain.

DATA SOURCES:

A search of MEDLINE (1966–October 2004) for English-language literature and selected bibliographies was completed. Search terms included pain, opioid, sedation, psychostimulants, amphetamines, modafinil, and donepezil.

DATA SYNTHESIS:

Amphetamines and amphetamine-like agents, caffeine, donepezil, and modafinil have been evaluated for OIS. Available literature is limited by numbers of subjects, duration, and trial design; however, there is limited support for the use of methylphenidate, donepezil, and modafinil.

CONCLUSIONS:

Pharmacologic treatment of OIS should be utilized selectively, given the available literature. Methylphenidate, donepezil, and modafinil may be considered in appropriate patients.

A preclinical comparison between different opioids: antinociceptive versus adverse effects

Reduced side-effect liability of opioids may enhance the patient's quality of life and decrease the incidence of opioid-insensitive pain. Literature offers few comparative data between different opioids at equianalgesic doses. Therefore morphine, fentanyl, buprenorphine, codeine, hydrocodone and oxycodone were compared for analgesic properties and side-effect profiles in rats. Analgesic efficacy was analysed using a tail withdrawal test for acute thermal nociception, a formalin test for chemically induced inflammatory pain and a von Frey test for mechanical hypersensitivity. For side-effect profiling inhibition of gastrointestinal activity was evaluated in a charcoal and ricinus oil test, arterial PCO(2) was determined for measuring respiratory depression, the discriminative stimulus properties linked to the narcotic cue were assessed using a drug discrimination learning test, and motor coordination was tested through rotarod performance. ED(50)'s for the occurrence of side-effects were compared to ED(50)'s in behavioural pain tests. Fentanyl had a strong analgesic potency and, compared to other opioids, an acceptable side-effect profiling at analgesic ED(50)'s. Also consistent was the ceiling effect of buprenorphine implying an increased safety margin for side-effects, but a decreased analgesic efficacy. Differences between opioids as observed in this study can have important indications for their use in acute as well as in the onset of chronic treatments.

A comparison of the effectiveness of an opioid analgesic and a nonpharmacologic intervention to improve incentive spirometry volumes

The purpose of this study was to compare the effects of opioid analgesics and relaxation as interventions for incentive spirometry in postcardiovascular surgery patients. With the use of incentive spirometry change scores from pre- to posttreatment, 72 patients received either relaxation, opioid analgesia, or no intervention. Pre- to posttreatment differences in achieved spirometry volumes were significantly different for the 3 groups (F[2, 69] = 7.32; p =.002), whereas no difference in spirometry volume was found between the opioid and relaxation groups. Relaxation was as effective as opioid analgesia in permitting postcardiovascular surgical patients to deep breathe.

Efficacy and tolerability of celecoxib versus hydrocodone/acetaminophen in the treatment of pain after ambulatory orthopedic surgery in adults

BACKGROUND

Current outpatient management of postoperative pain includes the use of oral opioid analgesics or nonsteroidal anti-inflammatory drugs; however, both types of medications are associated with side effects that can limit their usefulness in the outpatient setting.

OBJECTIVE

Two studies with identical protocols assessed the single- and multiple-dose analgesic efficacy and tolerability of celecoxib, a specific cyclooxygenase-2 inhibitor, in the treatment of acute pain after orthopedic surgery.

METHODS

These were multicenter, randomized, placebo- and active-controlled, double-blind, parallel-group trials conducted between January and June 1998. Both consisted of a single-dose assessment period (SDAP) and a multiple-dose assessment period (MDAP). In the SDAP, patients who had undergone orthopedic surgery received a single oral dose of celecoxib 200 mg, hydrocodone 10 mg/acetaminophen 1000 mg, or placebo within 24 hours after the end of anesthesia, with pain assessments conducted over the following 8-hour period. In the MDAP, extending from 8 hours after the first dose of study medication up to 5 days, patients who had received < or =1 dose of rescue medication during the SDAP continued on study medication (placebo recipients were rerandomized to active treatment), which could be taken up to 3 times a day as needed.

RESULTS

A total of 418 patients were enrolled in the 2 trials. During the SDAP, 141 patients received celecoxib, 136 received hydrocodone/acetaminophen, and 141 received placebo. During the MDAP, 185 patients received celecoxib and 181 received hydrocodone/acetaminophen. When the combined data were analyzed, mean pain intensity difference (PID) scores generally favored the active treatments over placebo from 1 to 6 hours (with the exception of 1.5 hours) after dosing (P < or = 0.016) and favored celecoxib over the other treatments at 7 and 8 hours after dosing (P < 0.001). The active treatments demonstrated superior summed PID scores through 8 hours (P < 0.001), significantly shorter median times to onset of analgesia (P < 0.05), and significantly longer median times to first use of rescue medication (P < 0.05). During the MDAP, more hydrocodone/acetaminophen-treated patients (20%) than celecoxib-treated patients (12%) required rescue medication (P < 0.05), and the celecoxib group had significantly lower maximum pain intensity scores (P < 0.001, days 2-5), required fewer doses of study medication (P < or = 0.01, days 3-5), and had superior scores on a modified American Pain Society Patient Outcome Questionnaire (P < or = 0.013). In addition, a significantly lower proportion of celecoxib-treated patients experienced adverse events (43%) compared with hydrocodone/acetaminophen-treated patients (89%; P < 0.001).

CONCLUSIONS

Over 8 hours, patients with moderate to severe pain after orthopedic surgery experienced comparable analgesia with single doses of celecoxib and hydrocodone/acetaminophen. Over a 5-day period, oral doses of celecoxib 200 mg taken 3 times a day demonstrated superior analgesia and tolerability compared with hydrocodone 10 mg/acetaminophen 1000 mg taken 3 times a day. Most patients required no more than 2 daily doses of celecoxib 200 mg for the control of their postorthopedic surgical pain.

Physiology of pain

The substantial increase in our collective knowledge of pain physiology and pharmacology over the past decade has had a significant effect on the practice of clinical veterinary medicine. An overview of the basic anatomical and physiologic components of nociceptive processing is presented, as well as a discussion of the sensitizing events that occur within the nervous system in acute and chronic pathologic pain states. The unique features of visceral and neuropathic pain are also outlined. With the goal of improving the success of our therapeutic interventions, the final section is devoted to the various classes of analgesic drugs and techniques, and how they are best incorporated into pain management strategies.

Pediatric acute pain management

The past decade has brought about an explosion of knowledge about the physiology of nociception and many new techniques for pain relief, new analgesic drugs, and new applications of old analgesic drugs. These techniques include methods of opioid administration by transdermal and transmucosal absorption and the use of neuraxial analgesia for the management of pain in children. Interest in the use of regional anesthesia in children has been rekindled, and analgesic properties and pre-emptive analgesic properties of many agents not typically considered analgesics, such as clonidine and ketamine, have been recognized. Perhaps the greatest advance has been the paradigm shift in the recognition that pain not only exists in infants and children but also is a significant cause of morbidity and even mortality. Given the unprecedented interest in pain management in adults and children, physicians can now look forward to the development of new methods of drug delivery and of receptor-specific drugs that divorce analgesia from the untoward side effects of existing analgesics. Improvement in the quality of life of hospitalized children also will occur.

Opioid Equianalgesic Calculations

Among the knowledge required by healthcare professionals to manage pain is an understanding of the differences between opioid agents and formulations. As the list of new opioid formulations continues to grow, it is increasingly important that clinicians understand the basic pharmacology of these analgesics and how to calculate equianalgesic doses. Administering an equianalgesic dose increases the likelihood that the transition to another opioid or route will be tolerated without loss of pain control or excessive side effects. Although calculation of equianalgesic doses requires relatively simple mathematical skills, few clinicians are prepared to compute them. The purpose of this article is to provide a basic review of the pharmacology of opioids, explain how to calculate an equianalgesic dose, and briefly describe some of the current controversies of the relative potencies of opioids listed in equianalgesic tables.

Changes in plasma cortisol concentrations in bitches in response to different combinations of halothane and butorphanol, with or without ovariohysterectomy

Changes in plasma cortisol concentrations were assessed in bitches in response to nine treatments: control, anaesthesia, analgesia, analgesia followed by anaesthesia, anaesthesia followed by analgesia at intubation, anaesthesia followed by analgesia at extubation, anaesthesia plus surgery, analgesia followed by anaesthesia plus surgery, and anaesthesia plus surgery followed by analgesia. The anaesthetic was halothane, the analgesic was butorphanol (0.4 mg kg(-1)) and the surgery was ovariohysterectomy. Blood samples, for plasma cortisol assays, were taken regularly from before treatment for five hours and then again after 24 hours. A small transient rise in plasma cortisol concentration in the control group was attributed to mild distress associated with novel experiences. A more pronounced and protracted rise in cortisol concentration in the analgesia group was ascribed to a dysphoric state of bitches under the influence of the agonist-antagonist butorphanol. Halothane anaesthesia alone resulted in no change in plasma cortisol concentration. When butorphanol was given after anaesthesia was induced or while the animal was still under the influence of anaesthesia (immediately after tracheal extubation), there was no immediate rise in plasma cortisol concentration and low concentrations were maintained for up to 60 minutes after halothane withdrawal. A marked rise in plasma cortisol concentration, which was sustained above pretreatment values for at least five hours, occurred in all surgery groups. Giving intravenous butorphanol 30 minutes prior to surgery had no effect on the surgically-induced rise in plasma cortisol concentration and no effect on the postsurgical plasma cortisol concentration. In contrast, butorphanol given at extubation did reduce plasma cortisol concentrations during the postsurgical period. These observations did not support the hypothesis that preoperative use of butorphanol would reduce the cortisol response after surgery under halothane anaesthesia.

Endomorphins have orexigenic and anxiolytic activities in mice

This study was designed to investigate the effects of endomorphin 1 and 2, recently identified mu-opioid receptor selective peptides, on food intake and anxiety in non-food-deprived mice. The intracerebroventricular (i.c.v.) injection of either endomorphin 1 or 2 (0.03-30 nmol) increased food intake in a dose-related manner. A significant increase was observed 20 min after i.c.v. injection of endomorphin 1 or 2 and continued for 4 h. In the elevated plus maze test, the i.c.v. injection of endomorphin 1 (30 nmol) significantly decreased the normal preference for the closed arms. These results suggest that endomorphin produces orexigenic and anxiolytic effects, and that the mu-opioid receptor contributes to the regulation of feeding and anxiety in mice.

Endogenous opiates: 1996

This paper is the nineteenth installment of our annual review of research concerning the opiate system. It summarizes papers published during 1996 reporting the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects, although stress-induced analgesia is included. The specific topics covered this year include stress, tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.