Blood-brain barrier: mechanisms governing permeability and interaction with peripherally acting μ-opioid receptor antagonists.

The blood-brain barrier (BBB) describes the unique properties of endothelial cells (ECs) that line the central nervous system (CNS) microvasculature. The BBB supports CNS homeostasis via EC-associated transport of ions, nutrients, proteins and waste products between the brain and blood. These transport mechanisms also serve as physiological barriers to pathogens, toxins and xenobiotics to prevent them from contacting neural tissue. The mechanisms that govern BBB permeability pose a challenge to drug design for CNS disorders, including pain, but can be exploited to limit the effects of a drug to the periphery, as in the design of the peripherally acting μ-opioid receptor antagonists (PAMORAs) used to treat opioid-induced constipation. Here, we describe BBB physiology, drug properties that affect BBB penetrance and how data from randomized clinical trials of PAMORAs improve our understanding of BBB permeability

Managing Prolonged Pain After Surgery: Examining the Role of Opioids.

A notable minority of patients experience persistent postsurgical pain and some of these patients consequently have prolonged exposure to opioids. Risk factors for prolonged opioid use after surgery include preoperative opioid use, anxiety, substance abuse, and alcohol abuse. The window to intervene and potentially prevent persistent opioid use after surgery is short and may best be accomplished by both surgeon and anesthesiologist working together. Anesthesiologists in particular are well positioned in the perioperative surgical home model to affect multiple aspects of the perioperative experience, including tailoring intraoperative medications and providing consultation for possible discharge analgesic regimens that can help minimize opioid use. Multimodal analgesia protocols reduce opioid consumption and thereby reduce exposure to opioids and theoretically the risk of persistent use. Regional anesthesia and analgesia techniques also reduce opioid consumption. Although many patients will recover without difficulty, the small minority who do not should receive customized care which may involve multiple office visits or consultation of a pain specialist. Enhanced recovery pathways are useful in optimizing outcomes after surgery

Managing Opioid-Tolerant Patients in the Perioperative Surgical Home.

Management of acute postoperative pain is important to decrease perioperative morbidity and improve patient satisfaction. Opioids are associated with potential adverse events that may lead to significant risk. Uncontrolled pain is a risk factor in the transformation of acute pain to chronic pain. Balancing these issues can be especially challenging in opioid-tolerant patients undergoing surgery, for whom rapidly escalating opioid doses in an effort to control pain can be associated with increased complications. In the perioperative surgical home model, anesthesiologists are positioned to coordinate a comprehensive perioperative analgesic plan that begins with the preoperative assessment and continues through discharge

HTX-011 reduced pain intensity and opioid consumption versus bupivacaine HCl in bunionectomy: phase III results from the randomized EPOCH 1 study.

BACKGROUND AND OBJECTIVES: There is a need for local anesthetics that provide consistent analgesia through 72 hours after surgery. This study evaluates the use of HTX-011 (bupivacaine and meloxicam in Biochronomerpolymer technology), an extended-release, dual-acting local anesthetic, in reducing both postoperative pain over 72 hours and postoperative opioid use when compared with bupivacaine hydrochloride (HCl) and saline placebo. Inclusion of low-dose meloxicam in HTX-011 is designed to reduce local inflammation caused by surgery, potentiating the analgesic effect of bupivacaine. Previously, significant synergy has been observed with bupivacaine and meloxicam with both given locally together. METHODS: EPOCH 1 was a randomized, double-blind, placebo-controlled and active-controlled phase III study in subjects undergoing a primary unilateral, distal, first metatarsal bunionectomy in which subjects received either a single intraoperative dose of HTX-011, immediate-release bupivacaine HCl or saline placebo. RESULTS: A total of 412 subjects were dosed. The results for the primary and all four key secondary endpoints were statistically significant in favor of HTX-011. HTX-011 demonstrated superior, sustained pain reduction through 72 hours, significantly reduced opioid consumption and resulted in significantly more opioid-free subjects compared with saline placebo and bupivacaine HCl. Safety was similar across groups with fewer opioid-related adverse events observed in the HTX-011 group. CONCLUSIONS: HTX-011 demonstrated significant reduction in postoperative pain through 72 hours with significant reduction in opioid consumption and a significant increase in the proportion of opioid-free subjects compared with saline placebo and the most widely used local anesthetic, bupivacaine HCl. TRIAL REGISTRATION NUMBER: NCT03295721

NSAIDs for analgesia in the era of COVID-19

Globally, non-steroidal anti-inflammatory drugs (NSAIDs) are highly used to treat pain. With the rise of the COVID-19 pandemic, the safety of NSAIDs use has been called into question. These concerns are worthy of review. At present, there is no compelling data showing that NSAIDs worsen the severity of COVID-19 symptoms or increase one\u27s likelihood of contracting the illness. For patients in pain and without symptoms that could potentially be attributed to COVID-19 (cough, fevers/chills, lethargy, myalgias, anosmia and so on), NSAIDs should continue to remain a viable option to provide analgesia to patients in need

The Efficacy of Peripheral Opioid Antagonists in Opioid-Induced Constipation and Postoperative Ileus: A Systematic Review of the Literature.

Opioid-induced constipation has a negative impact on quality of life for patients with chronic pain and can affect more than a third of patients. A related but separate entity is postoperative ileus, which is an abnormal pattern of gastrointestinal motility after surgery. Nonselective μ-opioid receptor antagonists reverse constipation and opioid-induced ileus but cross the blood-brain barrier and may reverse analgesia. Peripherally acting μ-opioid receptor antagonists target the μ-opioid receptor without reversing analgesia. Three such agents are US Food and Drug Administration approved. We reviewed the literature for randomized controlled trials that studied the efficacy of alvimopan, methylnaltrexone, and naloxegol in treating either opioid-induced constipation or postoperative ileus. Peripherally acting μ-opioid receptor antagonists may be effective in treating both opioid-induced bowel dysfunction and postoperative ileus, but definitive conclusions are not possible because of study inconsistency and the relatively low quality of evidence. Comparisons of agents are difficult because of heterogeneous end points and no head-to-head studies

Intravenous meloxicam for the treatment of moderate to severe acute pain: a pooled analysis of safety and opioid-reducing effects.

BACKGROUND AND OBJECTIVES: To describe the safety and tolerability of intravenous meloxicam compared with placebo across all phase II/III clinical trials. METHODS: Safety data and opioid use from subjects with moderate to severe postoperative pain who received ≥1 dose of intravenous meloxicam (5-60 mg) or placebo in 1 of 7 studies (4 phase II; 3 phase III) were pooled. Data from intravenous meloxicam 5 mg, 7.5 mg and 15 mg groups were combined (low-dose subset). RESULTS: A total of 1426 adults (86.6% white; mean age: 45.8 years) received ≥1 dose of meloxicam IV; 517 (77.6% white; mean age: 46.7 years) received placebo. The incidence of treatment-emergent adverse events (TEAEs) in intravenous meloxicam and placebo-treated subjects was 47% and 57%, respectively. The most commonly reported TEAEs across treatment groups (intravenous meloxicam 5-15 mg, 30 mg, 60 mg and placebo, respectively) were nausea (4.3%, 20.8%, 5.8% and 25.3%), headache (1.5%, 5.6%, 1.6% and 10.4%), vomiting (2.8%, 4.6%, 1.6% and 7.4%) and dizziness (0%, 3.5%, 1.1% and 4.8%). TEAE incidence was generally similar in subjects aged \u3e65 years with impaired renal function and the general population. Similar rates of cardiovascular events were reported between treatment groups. One death was reported (placebo group; unrelated to study drug). There were 35 serious adverse events (SAEs); intravenous meloxicam 15 mg (n=5), intravenous meloxicam 30 mg (n=15) and placebo (n=15). The SAEs in meloxicam-treated subjects were determined to be unrelated to study medication. Six subjects withdrew due to TEAEs, including three treated with intravenous meloxicam (rash, localized edema and postprocedural pulmonary embolism). In trials where opioid use was monitored, meloxicam reduced postoperative rescue opioid use. CONCLUSIONS: Intravenous meloxicam was generally well tolerated in subjects with moderate to severe postoperative pain. TRIAL REGISTRATION NUMBERS: NCT01436032, NCT00945763, NCT01084161, NCT02540265, NCT02678286, NCT02675907 and NCT02720692

Mechanism of action of HTX-011: a novel, extended-release, dual-acting local anesthetic formulation for postoperative pain

Background and objectives Obtaining consistent efficacy beyond 12–24 hours with local anesthetics, including extended-release formulations, has been a challenging goal. Inflammation resulting from surgery lowers the pH of affected tissues, reducing neuronal penetration of local anesthetics. HTX-011, an investigational, nonopioid, extended-release dual-acting local anesthetic combining bupivacaine and low-dose meloxicam, was developed to reduce postsurgical pain through 72 hours using novel extended-release polymer technology. Preclinical studies and a phase II clinical trial were conducted to confirm the mechanism of action of HTX-011. Methods In a validated postoperative pain pig model and a phase II bunionectomy trial, the analgesic effects of HTX-011, oral meloxicam (preclinical only), liposomal bupivacaine (preclinical only) and saline placebo were evaluated. The optimal meloxicam:bupivacaine ratio for HTX-011 and the effect of HTX-011 on incisional tissue pH were also evaluated preclinically. Results Preclinical data demonstrate the ability of HTX-011 to address local tissue inflammation as demonstrated by a less acidic tissue pH, which was associated with potentiated and prolonged analgesic activity. In the phase II bunionectomy study, HTX-011 achieved superior and sustained pain relief through 72 hours after surgery compared with each component in the polymer. Conclusions Preclinical animal and clinical results confirm that the low-dose meloxicam in HTX-011 normalizes the local pH in the incision, resulting in superior and synergistic analgesic activity compared with extended-release bupivacaine. HTX-011 represents an extended-release local anesthetic with a dual-acting mechanism of action that may provide an important advancement in the treatment of postoperative pain

Ketamine for Refractory Headache: A Retrospective Analysis.

BACKGROUND AND OBJECTIVES: The burden of chronic headache disorders in the United States is substantial. Some patients are treatment refractory. Ketamine, an N-methyl-D-aspartate antagonist, provides potent analgesia in subanesthetic doses in chronic pain, and limited data suggest it may alleviate headache in some patients. METHODS: We performed a retrospective study of 61 patients admitted over 3 years for 5 days of intravenous therapy that included continuous ketamine to determine responder rate and patient and ketamine infusion characteristics. Pain ratings at 2 follow-up visits were recorded. An immediate responder was a patient with decrease of 2 points or greater in the numerical rating scale (0-10) from start to final pain in the hospital. Sustained response at office visits 1 and 2 was determined based on maintaining the 2-point improvement at those visits. Patients were assessed daily for pain and adverse events (AEs). RESULTS: Forty-eight (77%) of the 61 patients were immediate responders. There were no differences regarding demographics, opioid use, or fibromyalgia between immediate responders and nonresponders. Maximum improvement occurred 4.56 days (mean) into treatment. Sustained response occurred in 40% of patients at visit 1 (mean, 38.1 days) and 39% of patients at visit 2 (mean, 101.3 days). The mean maximum ketamine rate was 65.2 ± 2.8 mg/h (0.76 mg/kg per hour). Ketamine rates did not differ between groups. Adverse events occurred equally in responders and nonresponders and were mild. CONCLUSIONS: Ketamine was associated with short-term analgesia in many refractory headache patients with tolerable adverse events. A prospective study is warranted to confirm this and elucidate responder characteristics