TY  - CHAP
M1  - Book, Section
TI  - CIMETIDINE AND OTHER H2 BLOCKERS
A1  - Kearney, Thomas E.
A2  - Olson, Kent R.
A2  - Anderson, Ilene B.
A2  - Benowitz, Neal L.
A2  - Blanc, Paul D.
A2  - Clark, Richard F.
A2  - Kearney, Thomas E.
A2  - Kim-Katz, Susan Y.
A2  - Wu, Alan H. B.
PY  - 2018
T2  - Poisoning & Drug Overdose, 7e
AB  - Pharmacology.  Cimetidine,  ranitidine,  famotidine,  and  nizatidine  are  selective  competitive  inhibitors  of  histamine  on  H2  receptors.  These  receptors  modulate  smooth  muscle,  vascular  tone,  and  gastric  secretions  and  may  be  involved  in  clinical  effects  associated  with  anaphylactic  and  anaphylactoid  reactions  as  well  as  ingestion  of  histamine  or  histamine-like  substances  (eg,  scombroid  fish  poisoning).  Cimetidine,  as  an  inhibitor  of  cytochrome  P450  enzymes,  has  been  proposed  or  studied  in  animals  as  an  agent  to  block  the  production  of  toxic  intermediate  metabolites  (eg,  acetaminophen,  carbon  tetrachloride,  halothane,  Amanita  mushroom  poisoning,  dapsone),  but  this  has  not  been  shown  to  be  beneficial  for  human  poisonings  or  toxicity  with  the  possible  exception  of  patients  on  chronic  dapsone  therapy  (see  "Indications").  Cimetidine  is  also  an  inhibitor  of  alcohol  dehydrogenase  (see  "Drug  or  Laboratory  Interactions")  and  has  been  suggested  for  use  in  patients  with  an  atypical  aldehyde  dehydrogenase  enzyme  to  minimize  a  disulfiram  reaction  ("Oriental  flushing")  to  acute  alcohol  ingestion.IndicationsAdjunctive  with  H1  blockers  such  as  diphenhydramine  in  the  management  and  prophylactic  treatment  of  anaphylactic  and  anaphylactoid  reactions  (see  chapters  on  various  antivenoms).Adjunctive  with  H1  blockers  such  as  diphenhydramine  in  the  management  of  scombroid  fish  poisoning.Ranitidine  has  been  used  to  reduce  vomiting  associated  with  theophylline  poisoning.  Because  cimetidine  may  interfere  with  hepatic  elimination  of  theophylline,  it  should  not  be  used.Cimetidine  has  been  used  to  decrease  methemoglobin  levels  by  inhibiting  oxidative  metabolite  formation  and  thereby  improve  tolerance  for  patients  on  chronic  dapsone  therapy.Contraindications.  Known  hypersensitivity  to  H2  blockers.Adverse  effectsHeadache,  drowsiness,  fatigue,  and  dizziness  have  been  reported  but  are  usually  mild.Confusion,  agitation,  hallucinations,  and  even  seizures  have  been  reported  with  cimetidine  use  in  the  elderly,  the  severely  ill,  and  patients  with  renal  failure.  A  case  was  reported  of  a  dystonic  reaction  after  IV  cimetidine  administration.A  reversible,  dose-dependent  rise  in  serum  alanine  aminotransferase  activity  has  been  reported  with  nizatidine,  a  related  agent.  Hepatitis  has  also  occurred  with  ranitidine.Cardiac  dysrhythmias  (bradycardia,  tachycardia)  and  hypotension  have  been  associated  with  rapid  IV  bolus  of  cimetidine  and  ranitidine  (rare).  Note:  Maximum  infusion  rates  provided  on  Table  III–5.Severe  delayed  hypersensitivity  after  high  oral  doses  of  cimetidine  (case  report).Preparations  containing  the  preservative  benzyl  alcohol  have  been  associated  with  "gasping  syndrome"  in  premature  infants.Use  in  pregnancy.  FDA  Category  B  (Introduction).  Fetal  harm  is  extremely  unlikely.Drug  or  laboratory  interactionsCimetidine,  and  to  a  lesser  extent  ranitidine,  reduces  hepatic  clearance  and  prolongs  the  elimination  half-life  of  several  drugs  as  a  result  of  inhibition  of  cytochrome  P450  activity  and  reduction  of  hepatic  blood  flow.  Examples  of  drugs  affected  include  phenytoin,  theophylline,  phenobarbital,  cyclosporine,  morphine,  lidocaine,  calcium  channel  blockers,  tricyclic  antidepressants,  and  warfarin.Cimetidine,  ranitidine,  and  nizatidine  inhibit  gastric  mucosal  alcohol  dehydrogenase  and,  therefore,  increase  the  systemic  absorption  of  ethyl  alcohol.Increased  gastric  pH  may  inhibit  the  absorption  of  some  pH-dependent  drugs,  such  as  ketoconazole,  ferrous  salts,  and  tetracyclines.Dosage  and  method  of  administration.  In  general,  there  are  no  clinically  proven  advantages  of  any  one  of  the  H2  blockers,  although  cimetidine  is  more  likely  to  be  associated  with  drug-drug  interactions.  The  lowest-strength  dosage  forms  are  available  over  the  counter,  and  several  oral  dosage  form  options  (chewable  tablets,  oral  solutions)  may  enhance  ...
SN  - 
PB  - McGraw-Hill Education
CY  - New York, NY
Y2  - 2024/04/19
UR  - accessmedicine.mhmedical.com/content.aspx?aid=1179992897
ER  -