Jacinta L. Johnson

Medication-overuse headache and opioid-induced hyperalgesia: A review of mechanisms, a neuroimmune hypothesis and a novel approach to treatment

Introduction Patients with chronic headache who consume large amounts of analgesics are often encountered in clinical practice. Excessive intake of analgesics is now considered to be a cause, rather than simply a consequence, of frequent headaches, and as such the diagnosis “medication-overuse headache” (MOH) has been formulated. Despite the prevalence and clinical impact of MOH, the pathophysiology behind this disorder remains unclear and specific mechanism-based treatment options are lacking. Discussion Although most acute headache treatments have been alleged to cause MOH, here we conclude from the literature that opioids are a particularly problematic drug class consistently associated with worsening headache. MOH may not be a single entity, as each class of drug implicated may cause MOH via a different mechanism. Recent evidence indicates that chronic opioid administration may exacerbate pain in the long term by activating toll-like receptor-4 on glial cells, resulting in a pro-inflammatory state that manifests clinically as increased pain. Thus, from the available evidence it seems opioid-overuse headache is a phenomenon similar to opioid-induced hyperalgesia, which derives from a cumulative interaction between central sensitisation, due to repeated activation of nociceptive pathways by recurrent headaches, and pain facilitation due to glial activation. Conclusion Treatment strategies directed at inhibiting glial activation may be of benefit alongside medication withdrawal in the management of MOH.

Codeine-induced hyperalgesia and allodynia: investigating the role of glial activation

Chronic morphine therapy has been associated with paradoxically increased pain. Codeine is a widely used opioid, which is metabolized to morphine to elicit analgesia. Prolonged morphine exposure exacerbates pain by activating the innate immune toll-like receptor-4 (TLR4) in the central nervous system. In silico docking simulations indicate codeine also docks to MD2, an accessory protein for TLR4, suggesting potential to induce TLR4-dependent pain facilitation. We hypothesized codeine would cause TLR4-dependent hyperalgesia/allodynia that is disparate from its opioid receptor-dependent analgesic rank potency. Hyperalgesia and allodynia were assessed using hotplate and von Frey tests at days 0, 3 and 5 in mice receiving intraperitoneal equimolar codeine (21 mg kg−1), morphine (20 mg kg−1) or saline, twice daily. This experiment was repeated in animals with prior partial nerve injury and in TLR4 null mutant mice. Interventions with interleukin-1 receptor antagonist (IL-1RA) and glial-attenuating drug ibudilast were assessed. Analyses of glial activation markers (glial fibrillary acid protein and CD11b) in neuronal tissue were conducted at the completion of behavioural testing. Despite providing less acute analgesia (P=0.006), codeine induced similar hotplate hyperalgesia to equimolar morphine vs saline (−9.5 s, P<0.01 and −7.3 s, P<0.01, respectively), suggesting codeine does not rely upon conversion to morphine to increase pain sensitivity. This highlights the potential non-opioid receptor-dependent nature of codeine-enhanced pain sensitivity—although the involvement of other codeine metabolites cannot be ruled out. IL-1RA reversed codeine-induced hyperalgesia (P<0.001) and allodynia (P<0.001), and TLR4 knock-out protected against codeine-induced changes in pain sensitivity. Glial attenuation with ibudilast reversed codeine-induced allodynia (P<0.001), and thus could be investigated further as potential treatment for codeine-induced pain enhancement.

The relationship between opioids and immune signalling in the spinal cord.

Opioids are considered the gold standard for the treatment of moderate to severe pain. However, heterogeneity in analgesic efficacy, poor potency and side effects are associated with opioid use, resulting in dose limitations and suboptimal pain management. Traditionally thought to exhibit their analgesic actions via the activation of the neuronal G-protein-coupled opioid receptors, it is now widely accepted that neuronal activity of opioids cannot fully explain the initiation and maintenance of opioid tolerance, hyperalgesia and allodynia. In this review we will highlight the evidence supporting the role of non-neuronal mechanisms in opioid signalling, paying particular attention to the relationship of opioids and immune signalling.

Glial Attenuation With Ibudilast in the Treatment of Medication Overuse Headache: A Double-Blind, Randomized, Placebo-Controlled Pilot Trial of Efficacy and Safety

Medication overuse headache (MOH) is a condition bordering between a chronic pain condition and a substance dependence disorder. Activation of immunocompetent glial cells in the central nervous system has been linked to both pathological pain and drug addiction/reward. Preclinically, ibudilast attenuates glial activation and is able to reduce neuropathic pain and markers of substance dependence. We therefore hypothesized ibudilast would reduce headache burden and opioid analgesic requirements in patients with opioid overuse headache.

Adversity impacting on oxytocin and behaviour: timing matters.

The endogenous oxytocin system plays a vital role in facilitating parturition, lactation and social interaction in humans and other mammals. It also impacts on a number of important endocrine, immune and neurotransmitter systems. A well-regulated oxytocin system has been proposed to increase resilience, and therefore reduce the likelihood of an individual developing mental illness or substance dependence. This review discusses the adverse external influences that can modulate oxytocin receptor and protein levels and impact on substance use and mental health. The paper highlights the impact of adversity such as poor maternal care, parental substance use and child abuse or neglect. We review clinical and preclinical data on the impact of adversity on the basis of the time of exposure from infancy and early childhood, to adolescence, adulthood to older age. Previous research suggests that dysregulation of the endogenous oxytocin system may be implicated in determining susceptibility to stress, anxiety, addiction and mental health conditions. The impact of external influence seems to be strongest in specific time periods where the system shows experience-based development or natural fluctuations in oxytocin levels. Interventions that target the oxytocin system during or soon after exposure to adversity may prove protective.

Identifying and treating codeine dependence: a systematic review

Objectives: Codeine dependence is a significant public health problem, motivating the recent rescheduling of codeine in Australia (1 February 2018). To provide information for informing clinical responses, we undertook a systematic review of what is known about identifying and treating codeine dependence.

Paradoxical topiramate-induced hyperphagia successfully treated with phentermine in a woman with migraine

We report a 49-year-old female migraineur who experienced paradoxical hyperphagia and concurrent intrusive food thoughts leading to rapid weight gain and a substantial increase in waist circumference. A significant reduction in migraine frequency was also observed during topiramate treatment, a widely used migraine prophylactic agent which is generally associated with weight loss. Withdrawal of topiramate saw appetite return to baseline levels, however, migraine frequency was again increased. Topiramate was reinitiated in combination with phentermine, a drug indicated for weight management, without reoccurrence of adverse effects. Migraine control was maintained and progressive weight loss ensued. Combination treatment with phentermine may be a useful strategy should other patients experience this adverse reaction while gaining therapeutic anti-migraine benefit from topiramate.

Counting the cost of over-the-counter codeine containing analgesic misuse: A retrospective review of hospital admissions over a 5 year period

INTRODUCTION AND AIMS Combination analgesics containing codeine (CACC) are currently available over-the-counter (OTC) in many countries following a pharmacists advice. Published case reports detail life-threatening morbidities associated with OTC-CACC misuse, although the cost of treating such patients has not been quantified. This study aims to: (i) identify and detail patients admitted to an Australian tertiary teaching hospital over a 5 year period with sequelae of OTC-CACC misuse; and (ii) estimate the costs of identified hospital admissions. DESIGN AND METHODS Using International Classification of Diseases (10th revision) diagnostic codes, a structured search was performed to identify admissions to a tertiary teaching hospital, relating to CACC misuse, over the defined period. A retrospective case note review provided data detailing patient characteristics, presenting morbidities and resultant interventions, and an approximate cost was calculated for identified admissions. RESULTS Ninety-nine OTC-CACC-related admissions (for 30 individual patients) were identified. Most related to gastrointestinal morbidities secondary to ibuprofen/codeine misuse. Mean length of stay per admission was 5.9 days, with 10.1% of admissions requiring intensive care. Patients consumed a daily mean of 28 OTC-CACC tablets for a mean of 606 days prior to admission. These 99 admissions were estimated to cost the health system AU

Managing acute pain in patients who report lactose intolerance: the safety of an old excipient re-examined:

1 008 082 with a mean cost per admission of AU

MANAGEMENT OF SLOW COLONIC TRANIT CONSTIPATION IN PARKINSON'S DISEASE: CURRENT EVIDENCE AND A COMMUNITY PHARMACY PERSPECTIVE Review Article

10 183. DISCUSSION AND CONCLUSIONS The outcomes of OTC-CACC misuse are serious and come at a significant cost to patient health and the Australian health-care system. Identification and management of this cohort appears sub-optimal with delays in diagnosis and high readmission rates.