Effects of Obesity and Leptin Deficiency on Morphine Pharmacokinetics in a Mouse Model.

BACKGROUND: Obesity causes multiorgan dysfunction, specifically metabolic abnormalities in the liver. Obese patients are opioid-sensitive and have high rates of respiratory complications after surgery. Obesity also has been shown to cause resistance to leptin, an adipose-derived hormone that is key in regulating hunger, metabolism, and respiratory stimulation. We hypothesized that obesity and leptin deficiency impair opioid pharmacokinetics (PK) independently of one another. METHODS: Morphine PK were characterized in C57BL/6J wild-type (WT), diet-induced obese (DIO), and leptin-deficient (ob/ob) mice, and in ob/ob mice given leptin-replacement (LR) therapy. WT mice received several dosing regimens of morphine. Obese mice (30 g) received one 80 mg/kg bolus of morphine. Blood was collected at fixed times after morphine injection for quantification of plasma morphine and morphine 3-glucuronide (M3G) levels. PK parameters used to evaluate morphine metabolism included area-under the curve (AUC150), maximal morphine concentration (CMAX), and M3G-to-morphine ratio, and drug elimination was determined by clearance (Cl/F), volume of distribution, and half-life (T1/2). PK parameters were compared between mouse groups by the use of 1-way analysis of variance, with P values less than .05 considered significant. RESULTS: DIO compared with WT mice had significantly decreased morphine metabolism with lower M3G-to-morphine ratio (mean difference [MD]: -4.9; 95% confidence interval [CI]: -8.8 to -0.9) as well as a decreased Cl/F (MD: -4.0; 95% CI: -8.9 to -0.03) Ob/ob compared with WT mice had a large increase in morphine exposure with a greater AUC150 (MD: 980.4; 95% CI: 630.1-1330.6), CMAX (MD: 6.8; 95% CI: 2.7-10.9), and longer T1/2 (MD: 23.1; 95% CI: 10.5-35.6), as well as a decreased Cl/F (MD: -7.0; 95% CI: -11.6 to -2.7). Several PK parameters were significantly greater in ob/ob compared with DIO mice, including AUC150 (MD: 636.4; 95% CI: 207.4-1065.4), CMAX (MD: 5.3; 95% CI: 3.2-10.3), and T1/2 (MD: 18.3; 95% CI: 2.8-33.7). When leptin was replaced in ob/ob mice, PK parameters began to approach DIO and WT levels. LR compared with ob/ob mice had significant decreases in AUC150 (MD: -779.9; 95% CI: -1229.8 to -330), CMAX (MD: -6.1; 95% CI: -11.4 to -0.9), and T1/2 (MD: -19; 95% CI: -35.1 to -2.8). Metabolism increased with LR, with LR mice having a greater M3G-to-morphine ratio compared with DIO (MD: 5.3; 95% CI: 0.3-10.4). CONCLUSIONS: Systemic effects associated with obesity decrease morphine metabolism and excretion. A previous study from our laboratory demonstrated that obesity and leptin deficiency decrease the sensitivity of central respiratory control centers to carbon dioxide. Obesity and leptin deficiency substantially decreased morphine metabolism and clearance, and replacing leptin attenuated the PK changes associated with leptin deficiency, suggesting leptin has a direct role in morphine metabolism.

Management of Cardiac Implantable Electrical Devices in Patients Undergoing Radiofrequency Ablation for Spine Pain: Physician Survey and Review of Guidelines.

BACKGROUND: More patients with cardiac implantable electrical devices (CIEDs) are presenting to spine and pain practices for radiofrequency ablation (RFA) procedures for chronic pain. Although the potential for electromagnetic interference (EMI) affecting CIED function is known with RFA procedures, available guidelines do not specifically address CIED management for percutaneous RFA for zygapophyseal (z-joint) joint pain, and thus physician practice may vary. OBJECTIVES: To better understand current practices of physicians who perform RFA for chronic z-joint pain with respect to management of CIEDs. Perioperative CIED management guidelines are also reviewed to specifically address risk mitigation strategies for potential EMI created by ambulatory percutaneous spine RFA procedures. STUDY DESIGN: Web-based provider survey and narrative review. SETTING: Multispecialty pain clinic, academic medical center. METHODS: A web-based survey was created using Research Electronic Data Capture (REDCap). A survey link was provided via e-mail to active members of the Spine Intervention Society (SIS), American Society of Regional Anesthesia and Pain Medicine, as well as distributed freely to community Pain Physicians and any receptive academic departments of PM&R or Anesthesiology. The narrative review summarizes pertinent case series, review articles, a SIS recommendation statement, and multi-specialty peri-operative guidelines as they relate specifically to spine RFA procedures. RESULTS: A total of 197 clinicians participated in the survey from diverse clinical backgrounds, including anesthesiology, physical medicine and rehabilitation, radiology, neurosurgery, and neurology, with 81% reporting fellowship training. Survey responses indicate wide variability in provider management of CIEDs before, during, and after RFA for z-joint pain. Respondents indicated they would like more specific guidelines to aid in management and decision-making around CIEDs and spine RFA procedures. Literature review yielded several practice guidelines related to perioperative management of CIEDs, but no specific guideline for percutaneous spine RFA procedures. However, combining the risk mitigation strategies provided in these guidelines, with interventional pain physician clinical experience allows for reasonable management recommendations to aid in decision-making. LIMITATIONS: Although this manuscript can serve as a review of CIEDs and aid in management decisions in patients with CIEDs, it is not a clinical practice guideline. CONCLUSIONS: Practice patterns vary regarding CIED management in ambulatory spine RFA procedures. CIED presence is not a contraindication for spine RFA but does increase the complexity of a spine RFA procedure and necessitates some added precautions. KEY WORDS: Radiofrequency ablation, neurotomy, cardiac implantable electrical device, zygapophyseal joint, spondylosis, neck pain, low back pain, chronic pain.