Combining Opioid and Adrenergic Mechanisms for Chronic Pain

A Critical Review of the Pharmacokinetics and Pharmacodynamics of Opioid Medications Used in Avian Patients

Opioid drugs are used to manage moderate to severe pain in mammals and avian species. In dosing opioids for a particular species, it is optimal to use dosing regimens based on pharmacokinetics or pharmacodynamics studies conducted in the same species as variability in the physiology among different species may result in differences in drug pharmacokinetics and pharmacodynamics. Unfortunately, dosing regimens are typically extrapolated from closely related avian species or even mammals, which is unideal. Therefore, this critical review aims to collate and evaluate the dosing regimens of selected opioids: tramadol, hydromorphone, buprenorphine, butorphanol, and fentanyl, in avian species and its related safety, efficacy and pharmacokinetic data. Our review found specific dosing regimens not described in the Exotic Animal Formulary for tramadol used in Indian Peafowl (Pavo cristatus), Muscovy Duck (Cairina moschata) and Hispaniolan Parrot (Amazona ventralis); hydromorphone used in Orange-winged Parrot (Amazona amazonica); buprenorphine used in Cockatiel (Nymphicus hollandicus), American Kestrel (Falco sparverius) and Grey Parrot (Psittacus erithacus); and butorphanol used in Hispaniolan Parrot (Amazona ventralis), Broiler Chicken and Indian Peafowl (Pavo cristatus). Cockatiel appeared to not experience analgesic effects for hydromorphone and buprenorphine, and American Kestrel exhibited sex-dependent responses to opioids. The selected opioids were observed to be generally safe, with adverse effects being dose-dependent.

Opioid Exposure Negatively Affects Antidepressant Response to Venlafaxine in Older Adults with Chronic Low Back Pain and Depression

OBJECTIVE

Serotonin norepinephrine reuptake inhibitors (SNRIs) are commonly co-prescribed with opioids for chronic pain. The purpose of this study was to describe pain and mood response to venlafaxine among older adults with chronic low back pain (CLBP) and depression relative to opioid exposure.

DESIGN

Secondary analyses were collected from a randomized clinical trial testing a stepped-care approach to comorbid pain and depression in older patients: the Addressing Depression and Pain Together study (ADAPT: 2010-2016).

SETTING

University-based late-life mental health research clinic.

SUBJECTS

Two hundred twenty-seven adults aged 65+ years with CLBP and depression.

METHODS

Participants received six weeks of lower-dose venlafaxine (≤150 mg/d). Pain and depression were measured each week. Response for both pain and depression at the end of six weeks was defined by a ≥30% improvement on a 0-20 numeric rating scale for low back pain and a Patient Health Questionnaire-9 score ≤5. Opioid exposure was analyzed as prescribed (yes or no) and by morphine equivalent dosing (MED).

RESULTS

Patients co-prescribed an opioid were less likely to report a pain response to venlafaxine. MED was negatively correlated with pain response. Depression response was not impacted.

CONCLUSIONS

Opioids are negatively associated with older adults' early analgesic response to lower-dose venlafaxine. These findings suggest that clinicians may wish to consider either nonopioid or alternative antidepressant approaches to pain management in these complex patients. It is reassuring that opioids do not prevent depression response. Future research should examine both longer duration of treatment and a wider range of doses.

Four single nucleotide polymorphisms in genes involved in neuronal signaling are associated with Opioid Use Disorder in West Virginia

Objective

Pilot study to assess utility in opioid use disorder (OUD) of a panel of single nucleotide polymorphisms in genes previously related to substance use disorder (SUD) and/or phenotypes that predispose individuals to OUD/SUD.

Design

Genetic association study.

Setting

West Virginia University's Chestnut Ridge Center Comprehensive Opioid Abuse Treatment (COAT) clinic for individuals diagnosed with OUD.

Patients

Sixty patients 18 years of age or older with OUD undergoing medication (buprenorphine/naloxone)-assisted treatment (MAT); all sixty patients recruited contributed samples for genetic analysis.

Outcome Measures

Minor allele frequencies for single nucleotide polymorphisms.

Results

Four of the fourteen single nucleotide polymorphisms examined were present at frequencies that are statistically significantly different than in a demographically-matched general population.

Conclusions

For the purposes of testing WV individuals via genetic means for predisposition to OUD, at least four single nucleotide polymorphisms in three genes are likely to have utility in predicting susceptibility. Additional studies with larger populations will need to be conducted to confirm these results before use in a clinical setting.

Medication and orthodontic tooth movement

As any pharmaceutical substance may influence the events associated with orthodontic tooth movement, it is of importance for the clinician to be able to recognize any prospective patient's history and patterns of medicinal consumption. This review presents the effects of various commonly prescribed medications on the rate of orthodontic tooth movement. The article concludes that it remains, to a degree, unclear which types of medication may have a clinically significant effect in everyday clinical scenarios. However, since both prescription and over-the-counter medication use have recently increased significantly among all age groups, good practice suggests that it is important to identify patients consuming medications and consider the possible implications in orthodontic therapy.

Does long-term use of pain relievers have an impact on the rate of orthodontic tooth movement? A systematic review of animal studies

Background

Pain relief drugs are used and misused widely and may theoretically affect the events leading to orthodontic tooth movement.

Objective

To systematically investigate and appraise the quality of the available evidence regarding the effect of pain relief medications on the rate of orthodontic tooth movement.

Search methods

Search without restrictions in eight databases (including grey literature) and hand searching until October 2018.

Selection criteria

Animal controlled studies investigating the effect of pain relievers on the rate of orthodontic tooth movement.

Data collection and analysis

Following study retrieval and selection, relevant data were extracted and the risk of bias was assessed using the SYRCLE’s risk of bias tool.

Results

Fourteen studies were finally identified, most of which at unclear risk of bias. Ibuprofen and loxoprofen did not show any significant effects on the rate of orthodontic tooth movement, whereas indomethacin, ketorolac, morphine, and high doses of etoricoxib were found to decrease it. Inconsistent or conflicting effects were noted after the administration of acetaminophen, acetylsalicylic acid, celecoxib, meloxicam, and tramadol. The quality of the available evidence was considered at best as low.

Conclusions

Long-term consumption of pain relievers may affect the rate of orthodontic tooth movement. The orthodontist should be capable of identifying patients taking pain relievers independently of orthodontic treatment and consider the possible implications.

Trial registration

PROSPERO (CRD42017078208).

Considering tapentadol as a first-line analgesic: 14 questions

Tapentadol is the newest centrally acting analgesic to be approved by the US FDA and regulatory bodies in other countries. It has been called the first-in-class of a novel-acting analgesic mechanism of action that combines µ-opioid receptor agonist activity with neuronal norepinephrine-reuptake inhibition in a single molecule. This duality of action should combine inhibition of ascending (afferent) pain-transmitting signals with activation of descending (efferent) pain-attenuating systems (e.g., diffuse noxious inhibitory controls). However, not all novel mechanisms of action impart the characteristics needed for an analgesic to be considered for first-line therapy. These key questions may help inform clinical decision making.

Why sickness hurts: A central mechanism for pain induced by peripheral inflammation

Low-grade systemic inflammation has been implicated in chronic pain, as well as in comorbid diseases like depression and fatigue. We have previously shown that women's pain perception and regulation is more affected by systemic inflammation than that of men. Here we investigated the neural substrates underlying these effects using an fMRI paradigm previously employed in a clinical population. Fifty-one participants (29 women) were injected with 0.6ng/kg lipopolysaccharide (LPS) or saline to induce a peripheral inflammatory response. The subjects were then tested with a pressure pain fMRI paradigm designed to capture descending pain inhibitory activity 2h after injection, and blood was sampled for cytokine analysis. The subjects injected with LPS became more pain sensitive compared to the placebo group, and the heightened pain sensitivity was paralleled by decreased activity in the ventrolateral prefrontal cortex and the rostral anterior cingulate cortex (rACC) compared to placebo; areas involved in descending pain regulation. The LPS group also had higher activity in the anterior insular cortex, an area underpinning affective and interoceptive pain processing. Women displayed overall less pain-evoked rACC activity compared to men, which may have rendered women less resilient to immune provocation, possibly explaining sex differences in LPS-induced pain sensitivity. Our findings elucidate the pain-related brain circuits affected by experimental peripheral inflammation, strengthening the theoretical link between systemic inflammation and weakened pain regulation in chronic pain disorders. The results further suggest a possible mechanism underlying the female predominance in many chronic pain disorders.

Opioid-induced redistribution of 6TM and 7TM μ opioid receptors: A hypothesized mechanistic facilitator model of opioid-induced hyperalgesia

Opioids are still the most popular form of pain treatment, but many unavoidable side effects make opioids a big challenge in effective pain management. Opioid-induced hyperalgesia (OIH), a paradoxical phenomenon, portrays an increased sensitivity to harmful stimuli caused by opioid exposure. Changes in the neural modulation are considered a major contributor to the development of OIH. Activation of opioid receptors (ORs) and corresponding downstream molecules are the vital composition of functional performance of opioids. Increasing interests were proposed of the interaction between ORs and other neural transmitter systems such as glutamatergic, GABAergic and adrenergic ones to the genesis of OIH. G protein coupled μ-opioid receptor (MOR) was studied comprehensively on its role in the development of OIH. In addition to the relationship between MOR and other neurotransmitter receptors, a new intracellular MOR that has six transmembrane (6TM) domains was identified, and found to perform a pro-nociceptive task in contrast to the counterpart 7TM isoform. A mechanistic model of OIH in which both 6TM and 7TM MORs undergoing membrane redistribution upon opioid exposure is proposed which eventually facilitates the neurons more sensitive to nociceptive stimulation than that of the preceding opioid exposure.

Correlation of ADRB1 rs1801253 Polymorphism with Analgesic Effect of Fentanyl After Cancer Surgeries

BACKGROUND Our study aimed to explore the association between β1-adrenoceptor (ADRB1) rs1801253 polymorphism and analgesic effect of fentanyl after cancer surgeries in Chinese Han populations. MATERIAL AND METHODS Postoperative fentanyl consumption of 120 patients for analgesia was recorded. Genotype distributions were detected by allele specific amplification-polymerase chain reaction (ASA-PCR) method. Postoperative pain was measured by visual analogue scale (VAS) method. Differences in postoperative VAS score and postoperative fentanyl consumption for analgesia in different genotype groups were compared by analysis of variance (ANOVA). Preoperative cold pressor-induced pain test was also performed to test the analgesic effect of fentanyl. RESULTS Frequencies of Gly/Gly, Gly/Arg, Arg/Arg genotypes were 45.0%, 38.3%, and 16.7%, respectively, and passed the Hardy-Weinberg Equilibrium (HWE) test. The mean arterial pressure (MAP) and the heart rate (HR) had no significant differences at different times. After surgery, the VAS score and fentanyl consumption in Arg/Arg group were significantly higher than in other groups at the postoperative 2nd hour, but the differences were not obvious at the 4th hour, 24th hour, and the 48th hour. The results suggest that the Arg/Arg homozygote increased susceptibility to postoperative pain. The preoperative cold pressor-induced pain test suggested that individuals with Arg/Arg genotype showed worse analgesic effect of fentanyl compared to other genotypes. CONCLUSIONS In Chinese Han populations, ADRB1 rs1801253 polymorphism might be associated with the analgesic effect of fentanyl after cancer surgery.