TY  - CHAP
M1  - Book, Section
TI  - Chapter 42. Pharmacology of Opioid Analgesics
A1  - Rosow, Carl
A1  - Dershwitz, Mark
A2  - Longnecker, David E.
A2  - Brown, David L.
A2  - Newman, Mark F.
A2  - Zapol, Warren M.
PY  - 2012
T2  - Anesthesiology, 2e
AB  - An  opioid  is  any  natural  or  synthetic  compound  that  has  effects  similar  to  those  of  morphine  or  that  acts  as  an  antagonist  at  the  same  receptors  to  which  morphine  binds.Because  opioid  agonists  relieve  pain,  they  are  classified  as  analgesics.  In  contrast  to  the  local  anesthetics  (which  interrupt  the  transmission  of  all  nerve  impulses,  including  pain)  and  the  anti-inflammatory  analgesics  such  as  aspirin  (which  decrease  some  of  the  pathologic  processes  leading  to  pain),  the  opioid  analgesics  act  primarily  to  alter  the  perception  of  pain  as  a  noxious  entity.The  “classic”  pharmacologic  effects  of  morphine,  such  as  analgesia  and  ventilatory  depression,  are  mediated  by  μ  receptors.  The  κ  receptor  shares  a  number  of  effects  with  the  μ  receptor,  including  analgesia,  sedation,  and  ventilatory  depression.  The  δ  receptor  is  responsible  for  mediating  some  of  the  analgesic  effects  of  the  endogenous  opioid  peptides,  especially  in  the  spinal  cord.All  opioid  receptors  are  G-protein  coupled  receptors.  The  actions  of  both  μ  and  δ  agonists  result  in  overall  neuronal  depression,  and  they  share  several  signal  transduction  mechanisms,  including  inhibition  of  adenylyl  cyclase,  activation  of  K+  currents,  and  suppression  of  Ca2+  currents.Five  families  of  endogenous  opioid  peptides  bind  to  the  various  opioid  receptors.  Although  some  of  these  peptides  undoubtedly  function  in  nociceptive  pathways,  they  also  appear  to  play  fundamental  roles  in  processes  like  thermoregulation  and  hormone  release,  as  well  as  gastrointestinal  and  cardiovascular  control.The  most  widely  used  opioid  analgesics  are  the  pure  agonists  that  are  relatively  selective  for  μ-opioid  receptors.  Unlike  the  volatile  anesthetics,  opioid  agonists  produce  a  group  of  highly  specific  depressant  and  stimulant  effects  by  acting  at  discrete  sites  within  the  central  nervous  system.Opioid  analgesic  effects  result  from  actions  at  several  different  levels  of  the  neuraxis.  Patients  given  morphine  will  typically  report  that  pain  is  still  present,  but  the  intensity  is  decreased  and  it  no  longer  bothers  them  as  much.  Sufficient  doses  of  opioids  will  relieve  almost  any  pain,  although  some  types  of  pain  are  typically  more  responsive  than  others.  Prolonged,  burning  pain,  for  example,  is  more  effectively  blunted  than  the  brief,  sharp  pain  of  an  incision.  Neuropathic  pain  (eg,  pain  of  nerve  root  compression)  can  be  very  resistant  to  opioid  treatment.  Intraoperatively  the  opioids  can  produce  sufficient  analgesia  to  reduce  or  abolish  autonomic  and  somatic  responses  to  surgical  stimuli.In  usual  analgesic  doses,  morphine-like  drugs  may  produce  drowsiness,  feelings  of  heaviness,  and  difficulty  concentrating.  Unlike  benzodiazepines,  opioids  do  not  usually  produce  anterograde  amnesia.  Doses  of  opioids  that  are  sufficient  to  produce  apnea  and  profound  analgesia  do  not  reliably  produce  unconsciousness  in  healthy  individuals.True  seizures  have  been  reported  after  repeated  doses  of  meperidine  because  its  major  metabolite,  normeperidine,  is  a  potent  convulsant.Opioids  produce  a  dose-related  depression  of  the  ventilatory  response  to  CO2  by  a  direct  effect  on  ventilatory  centers  in  the  medulla.  Morphine  also  blunts  the  response  to  hypoxia.  It  is  important  to  remember  that  a  decrease  in  ventilatory  rate  is  not  a  very  sensitive  indicator  of  opioid  effect.  A  patient's  drive  to  breathe  may  be  abnormal  despite  an  apparently  normal  ventilatory  rate  and  state  of  consciousness.  Sleep  will  further  ...
SN  - 
PB  - The McGraw-Hill Companies
CY  - New York, NY
Y2  - 2024/04/19
UR  - accessanesthesiology.mhmedical.com/content.aspx?aid=56636370
ER  -