RT Book, Section
A1 Butterworth IV, John F.
A1 Mackey, David C.
A1 Wasnick, John D.
SR Print(0)
ID 1161426169
T1 Pharmacological Principles
T2 Morgan & Mikhail's Clinical Anesthesiology, 6e
YR 2018
FD 2018
PB McGraw-Hill Education
PP New York, NY
SN 9781259834424
LK accessmedicine.mhmedical.com/content.aspx?aid=1161426169
RD 2024/04/17
AB KEY  CONCEPTS  Drug  molecules  obey  the  law  of  mass  action.  When  the  plasma  concentration  exceeds  the  tissue  concentration,  the  drug  moves  from  the  plasma  into  tissue.  When  the  plasma  concentration  is  less  than  the  tissue  concentration,  the  drug  moves  from  the  tissue  back  to  plasma.  Most  drugs  that  readily  cross  the  blood–brain  barrier  (eg,  lipophilic  drugs  like  hypnotics  and  opioids)  are  avidly  taken  up  in  body  fat.  Biotransformation  is  the  chemical  process  by  which  the  drug  molecule  is  altered  in  the  body.  The  liver  is  the  primary  organ  of  metabolism  for  drugs.  Small  unbound  molecules  freely  pass  from  plasma  into  the  glomerular  filtrate.  The  nonionized  (uncharged)  fraction  of  drug  is  reabsorbed  in  the  renal  tubules,  whereas  the  ionized  (charged)  portion  is  excreted  in  urine.  Elimination  half-life  is  the  time  required  for  the  drug  concentration  to  fall  by  50%.  For  drugs  described  by  multicompartment  pharmacokinetics  (eg,  all  drugs  used  in  anesthesia),  there  are  multiple  elimination  half-lives.  The  offset  of  a  drug’s  effect  cannot  be  predicted  from  half-lives.  The  context-sensitive  half-time  is  a  clinically  useful  concept  to  describe  the  rate  of  decrease  in  drug  concentration  and  should  be  used  instead  of  half-lives  to  compare  the  pharmacokinetic  properties  of  intravenous  drugs  used  in  anesthesia.