Intrathecal opioids for intractable pain syndromes

Prevention, diagnosis, and treatment of opioid use disorder under the supervision of opioid stewardship programs: it's time to act now

The third opium war may have already started, not only due to illicit opioid trafficking from the Golden Crescent and Golden Triangle on the international front but also through indiscriminate opioid prescription and opioid diversion at home. Opioid use disorder (OUD), among unintentional injuries, has become one of the top 4 causes of death in the United States (U.S.). An OUD is defined as a problematic pattern of opioid use resulting in clinically significant impairment or distress, consisting of 2 or more of 11 problems within 1 year, as described by the Diagnostic and Statistical Manual for Mental Disorders, Fifth Edition. Observation of aberrant behaviors of OUD is also helpful for overworked clinicians. For the prevention of OUD, the Opioid Risk Tool and the Current Opioid Misuse Measure are appropriate screening tests before and during opioid administration, respectively. Treatment of OUD consists of 3 opioid-based U.S. Food and Drug Administration-approved medications, including methadone, buprenorphine, and naltrexone, and non-opioid-based symptomatic medications for reducing opioid withdrawal syndromes, such as α2 agonists, β-blockers, antidiarrheals, antiemetics, non-steroidal anti-inflammatory drugs, and benzodiazepines. There are at least 6 recommendable guidelines and essential terms related to OUD. Opioid stewardship programs are now critical to promoting appropriate use of opioid medications, improving patient outcomes, and reducing misuse of opioids, influenced by the successful implementation of antimicrobial stewardship programs. Despite the lack of previous motivation, now is the critical time for trying to reduce the risk of OUD.

Evaluation of an Intrathecal Drug Delivery Protocol Leads to Rapid Reduction of Systemic Opioids in the Oncological Population

Objective: The article that follows is purposed at demonstrating how IT opioid plus bupivacaine achieves sustained acceptable pain relief while simultaneously rapidly reducing oral morphine equivalents (OME). Background: Cancer patients represent a population with significant morbidity, pain, and limited life expectancy. It is, therefore, vital to achieve satisfactory analgesia quickly and safely. To date, there is limited data in the literature that discusses efficacy of combined intrathecal (IT) medication therapy in reducing systemic opioids in the oncological population. Methods: This was a retrospective analysis that reviewed cancer pain patients from day of IT pump implantation through the six-month postoperative time point. A cohort of 50 oncological patients who had intrathecal drug delivery systems (IDDSs) implanted at Memorial Sloan Kettering Cancer Center between 2017 and 2019 were studied. Median OMEs were the primary modality of analysis for this review. Mean visual analogue scale scores were secondarily reviewed. Results: Median OMEs decreased from 503 preoperative to 105 at six months postoperative time point. Median time to discharge was 6.5 days. Unfortunately, due to malignant mortality, 27 patients did not make it to the 6-month postoperative time point. Discussion: IDDSs with opioid plus bupivacaine represent a safe and efficient route toward expeditious pain relief and decreased OMEs in the cancer pain population.

Managing Chronic Non-Malignant Pain in the Elderly: Intrathecal Therapy

Intrathecal drug delivery (IDD) was first described in 1981 by Onofrio, who used a pump for continuous and intrathecal delivery of morphine to treat cancer pain. Over the following four decades, many reports supported this treatment method with implanted pumps for cancer and non-cancer pain. To date, more than 300,000 pumps for pain therapy and spasticity have been implanted worldwide. This article reviews current knowledge regarding intrathecal opioid therapy, focusing particularly on the use of IDD in elderly patients. Current literature is presented, and the arguments in favor of and against this therapy in elderly patients are discussed.

Immediate postoperative pain level from lumbar arthrodesis following epidural infiltration of morphine sulfate

Objective

To evaluate the pain level in patients treated with epidural infusion of morphine sulfate in a single dose, after a surgical procedure to perform lumber arthrodesis.

Methods

Forty patients underwent posterolateral lumbar arthrodesis or intersomatic lumbar arthrodesis via a posterior route at one, two or three levels. They were prospectively randomized into two groups of 20. In the first group (study group), 2 mg of morphine sulfate diluted in 10 mL of physiological serum was infiltrated into the epidural space, through the laminectomy area. The second group (controls) did not receive analgesia. The patients were asked about their pain levels before and after the operation, using a visual analog scale (VAS).

Results

It was found that the patients presented a significant diminution of pain as shown by the VAS. From before to after the operation, it decreased by an average of 4.7 points (p = 0.0001), which corresponded to 53.2% (p = 0.0001).

Conclusion

Application of 2 mg of morphine sulfate in a single epidural dose was shown to be a good technique for pain therapy following lumbar spinal surgery.

Preclinical toxicity evaluation of AAV for pain: evidence from human AAV studies and from the pharmacology of analgesic drugs

Gene therapy with adeno-associated virus (AAV) has advanced in the last few years from promising results in animal models to >100 clinical trials (reported or under way). While vector availability was a substantial hurdle a decade ago, innovative new production methods now routinely match the scale of AAV doses required for clinical testing. These advances may become relevant to translational research in the chronic pain field. AAV for pain targeting the peripheral nervous system was proven to be efficacious in rodent models several years ago, but has not yet been tested in humans. The present review addresses the steps needed for translation of AAV for pain from the bench to the bedside focusing on pre-clinical toxicology. We break the potential toxicities into three conceptual categories of risk: First, risks related to the delivery procedure used to administer the vector. Second, risks related to AAV biology, i.e., effects of the vector itself that may occur independently of the transgene. Third, risks related to the effects of the therapeutic transgene. To identify potential toxicities, we consulted the existing evidence from AAV gene therapy for other nervous system disorders (animal toxicology and human studies) and from the clinical pharmacology of conventional analgesic drugs. Thereby, we identified required preclinical studies and charted a hypothetical path towards a future phase I/II clinical trial in the oncology-palliative care setting.

Overall self-perceived health in Restless legs treated with intrathecal morphine

OBJECTIVES

Restless legs syndrome (RLS) has a high prevalence in the general population. Treatment with intrathecal morphine has been shown to be successful in a small number of patients. Our aim was to quantify the effect on RLS-related symptoms, health and quality of life in three patients treated with intrathecal morphine.

MATERIALS AND METHODS

Three patients with medically refractory RLS received an implanted pump for delivery of intrathecal morphine. Severity of RLS and self-assessed health were rated using the International Restless Legs Syndrome Study Group (IRLSSG) rating scale and the Short Form health survey (SF-36). Assessments were made preoperatively and after 6 months of follow-up.

RESULTS

Preoperatively two patients had very severe RLS, scoring 35 and 36 on the IRLSSG rating scale, and one patient had severe RLS (score, 26). All three patients were free of symptoms of RLS post-operatively and also at the 6-month follow-up. The daily doses of intrathecal morphine ranged from 73 to 199 µg. Results from the SF-36 health survey showed that all three patients had a better physical health compared to before surgery.

CONCLUSION

Intrathecal morphine may be efficient in the treatment for medically refractory RLS. All three patients became completely free of symptoms, and there was also improvement in self-perceived overall health.

Local loperamide injection reduces mechanosensitivity of rat cutaneous, nociceptive C-fibers

Loperamide reverses signs of mechanical hypersensitivity in an animal model of neuropathic pain suggesting that peripheral opioid receptors may be suitable targets for the treatment of neuropathic pain. Since little is known about loperamide effects on the responsiveness of primary afferent nerve fibers, in vivo electrophysiological recordings from unmyelinated afferents innervating the glabrous skin of the hind paw were performed in rats with an L5 spinal nerve lesion or sham surgery. Mechanical threshold and responsiveness to suprathreshold stimulation were tested before and after loperamide (1.25, 2.5 and 5 µg in 10 µl) or vehicle injection into the cutaneous receptive field. Loperamide dose-dependently decreased mechanosensitivity in unmyelinated afferents of nerve-injured and sham animals, and this effect was not blocked by naloxone pretreatment. We then investigated loperamide effects on nerve conduction by recording compound action potentials in vitro during incubation of the sciatic nerve with increasing loperamide concentrations. Loperamide dose-dependently decreased compound action potentials of myelinated and unmyelinated fibers (ED50 = 8 and 4 µg/10 µl, respectively). This blockade was not prevented by pre-incubation with naloxone. These results suggest that loperamide reversal of behavioral signs of neuropathic pain may be mediated, at least in part, by mechanisms independent of opioid receptors, most probably by local anesthetic actions.

Intrapleural migration of a spinal catheter in a patient with arachnoiditis and extensive epidural scarring after tethered cord release: a case report and review of literature

OBJECTIVE

The objective of this study was to report a case of new onset refractory pain from intrapleural migration of a spinal catheter five months after the implantation of an intrathecal drug delivery system (IDDS).

MATERIALS AND METHODS

A 57-year-old man had intractable pain because of multiple intradural spinal explorations for tethered cord release. His pain was effectively treated with intrathecal morphine via an IDDS. Five months after the implantation, the patient developed return of the original pain more than two weeks after intrapleural migration of the intrathecal catheter.

RESULTS

The migration was documented by computed tomography, and repositioning of the catheter rendered the patient comfortable. The gradual onset of pain may have been due to decreasing delivery of drug to the cerebrospinal fluid as the catheter tip migrated further away from the dura. To our knowledge, this complication has not been reported in the literature.

CONCLUSION

Physicians and nursing staff that place and manage an IDDS should be aware of this complication.

[Selected interventional methods for the treatment of chronic pain : part 2: regional anesthetic techniques close to the spinal cord and neuromodulative methods]

Approximately 5-8 million people in Germany suffer from chronic pain and some patients can profit from specific interventional techniques. In detail these are regional anesthetic techniques close to the spinal cord, neuromodulation, blocks of the sympathetic chain and peripheral nerve blocks. Part 2 of the article presents regional anesthetic techniques close to the spinal cord and neuromodulative methods. Regional anesthetic techniques close to the spinal cord are of high importance for the treatment of chronic low back pain although the efficiency is highly disputed due to the lack of evidence. Neuromodulation includes amongst others intrathecal pharmacotherapy and spinal cord stimulation, which are used for highly selected patients and can lead to very good results for these patients.

In vivo study of flow-rate accuracy of the MedStream Programmable Infusion System

OBJECTIVE

  Flow-rate accuracy and precision are important parameters to optimizing the efficacy of programmable intrathecal (IT) infusion pump delivery systems. Current programmable IT pumps are accurate within ±14.5% of their programmed infusion rate when assessed under ideal environmental conditions and specific flow-rate settings in vitro. We assessed the flow-rate accuracy of a novel programmable pump system across its entire flow-rate range under typical conditions in sheep (in vivo) and nominal conditions in vitro.

MATERIALS AND METHODS

  The flow-rate accuracy of the MedStream Programmable Pump was assessed in both the in vivo and in vitro settings. In vivo flow-rate accuracy was assessed in 16 sheep at various flow-rates (producing 90 flow intervals) more than 90 ± 3 days. Pumps were then explanted, re-sterilized and in vitro flow-rate accuracy was assessed at 37°C and 1013 mBar (80 flow intervals).

RESULTS

  In vivo (sheep body temperatures 38.1°C-39.8°C), mean ± SD flow-rate error was 9.32% ± 9.27% and mean ± SD leak-rate was 0.028 ± 0.08 mL/day. Following explantation, mean in vitro flow-rate error and leak-rate were -1.05% ± 2.55% and 0.003 ± 0.004 mL/day (37°C, 1013 mBar), respectively.

CONCLUSIONS

  The MedStream Programmable Pump demonstrated high flow-rate accuracy when tested in vivo and in vitro at normal body temperature and environmental pressure as well as when tested in vivo at variable sheep body temperature. The flow-rate accuracy of the MedStream Programmable Pump across its flow-rate range, compares favorably to the accuracy of current clinically utilized programmable IT infusion pumps reported at specific flow-rate settings and conditions.

Addressing neurological disorders with neuromodulation

Neurological disorders are becoming increasingly common in developed countries as a result of the aging population. In spite of medications, these disorders can result in progressive loss of function as well as chronic physical, cognitive, and emotional disability that ultimately places enormous emotional and economic on the patient, caretakers, and the society in general. Neuromodulation is emerging as a therapeutic option in these patients. Neuromodulation is a field, which involves implantable devices that allow for the reversible adjustable application of electrical, chemical, or biological agents to the central or peripheral nervous system with the objective of altering its functioning with the objective of achieving a therapeutic or clinically beneficial effect. It is a rapidly evolving field that brings together many different specialties in the fields of medicine, materials science, computer science and technology, biomedical, and neural engineering as well as the surgical or interventional specialties. It has multiple current and emerging indications, and an enormous potential for growth. The main challenges before it are in the need for effective collaboration between engineers, basic scientists, and clinicians to develop innovations that address specific problems resulting in new devices and clinical applications.

Optimizing pain control through the use of implantable pumps

Intrathecal therapy represents an effective and well established treatment of nonmalignant as well as malignant pain. Devices available include mechanical constant flow pumps as well as electronic variable flow pumps with patient-controlled bolus release. The latter provide faster dose finding, individual pain control, and good acceptance by patients. New technologies such as membrane pumps and rechargeable devices are expected to be developed to clinical perfection. The available drugs for intrathecal therapy are listed according to the polyanalgesic consensus on intrathecal therapy. The integration of remote patient-controlled analgesia into electronic implantable devices, and the peptide analgesic ziconotide, have significantly improved intrathecal therapy. Complications include infections, catheter ruptures or disconnections, catheter granulomas, and technical dysfunctions. Further possibilities for optimizing intrathecal therapy include development of new drugs, drug side effects, catheter and pump technologies, and surgical techniques.

An initial animal proof-of-concept study for central administration of clozapine to schizophrenia patients

While clozapine is the acknowledged superior pharmacotherapeutic for the treatment of schizophrenia, the side effect profile, which includes potentially fatal complications, limits its usefulness. Central administration of clozapine directly into the brain could circumvent many of the side effect issues due to the dramatic reduction in dose and the limitation of the drug primarily to the CNS. The present study demonstrates that clozapine can be formulated as a stable solution at physiological pH, which does not have in vitro neurotoxic effects at concentrations which may be effective at treating symptoms. Acute central administration improved auditory gating deficits in a mouse model of schizophrenia-like deficits. Assessment of behavioral alterations in rats receiving chronic central infusions of clozapine via osmotic minipump was performed with the open field and elevated plus mazes. Neither paradigm revealed any detrimental effects of the infusion. While these data represent only an initial investigation, they none-the-less suggest that central administration of clozapine may be a viable alternate therapeutic approach for schizophrenia patients which may be effective in symptom reduction without causing behavioral or neurotoxic effects.