title: Opiate pharmacology of intrathecal granulomas.
abstract: BACKGROUND
  Chronic intrathecal morphine infusion produces intradural granulomas. The authors examined a variety of opioids infused intrathecal for analgesic activity and toxicity.
  
  
  METHODS
  Two sets of experiments were undertaken in dogs with chronic intrathecal catheters: (1) Six-hour intrathecal infusions were used to determine the full analgesic dose and the maximum tolerated dose. (2) To establish toxicity, the maximum tolerated dose was given for up to 28 days by continuous intrathecal infusion. Drugs examined were morphine sulfate, hydromorphone, D/L-methadone, L-methadone, D-methadone, fentanyl, [d-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO), naloxone, or saline. RESULTS ANALGESIA AND TOLERABILITY: Six-hour intrathecal infusion of agonists resulted in a time-dependent increase in thermal escape latency. At higher concentrations, dose-limiting motor dysfunction and sedation occurred, and hypersensitivity occurred. The concentrations, in mg/ml, for full analgesic dose/maximum tolerated dose were as follows: morphine, 0.9/12.0; hydromorphone, 1.0/3.0; D/L-methadone, 2.8/3; L-methadone, 1.0/> 1.0; fentanyl, 0.3/2.0; DAMGO, 0.1/> 2.0; D-methadone, > 1/> 1; naloxone, > 10/> 10. SPINAL PATHOLOGY: Chronic intrathecal infusion of the maximum tolerated dose revealed 100% intradural granuloma formation after morphine, hydromorphone, L-methadone, and naloxone. DAMGO induced a mass in only a single animal (one of three). D/L- and D-methadone produced intradural granulomas but were also associated with parenchymal necrosis. Saline and fentanyl animals displayed no granulomas.
  
  
  CONCLUSIONS
  Intrathecal opiate-induced granulomas are not strictly dependent on opioid receptor activation. Therefore, opiates at equianalgesic doses present different risks for granuloma formation. Importantly, D/L- and D-methadone also resulted in parenchymal necrosis, an affect associated with the N-methyl-D-aspartate antagonist action of the D-isomer.
authors.affiliation: Department of Anesthesiology, University of California, San Diego, CA 92093-0818, USA.
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Allen
authors.forename: Kjersti A
authors.initials: KA
authors.lastname: Horais
authors.forename: Nicolle A
authors.initials: NA
authors.lastname: Tozier
authors.forename: Tony L
authors.initials: TL
authors.lastname: Yaksh
mesh_terms: D000701:Analgesics, Opioid / Q000134:cerebrospinal fluid / Q000633:toxicity*; D000818:Animals; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000633:toxicity; D005283:Fentanyl / Q000633:toxicity; D006099:Granuloma / Q000139:chemically induced* / Q000473:pathology; D007278:Injections, Spinal; D008297:Male; D020714:Maximum Tolerated Dose; D008691:Methadone / Q000633:toxicity; D009020:Morphine / Q000633:toxicity; D013116:Spinal Cord / Q000187:drug effects* / Q000473:pathology
chemical_list: D000701:Analgesics, Opioid; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009020:Morphine; D008691:Methadone; D005283:Fentanyl