Histamine H2 Antagonists include-
 Cimetidine, Famotidine, Nizatidine, Ranitidine, Roxatidine

Refer - Cimetidine

Interacting drugs - summary

H2 antogonists + Ethanol 
 concurrent use increase plasma ethanol levels and AUC. This  interaction have minimal clinical importance
                                                                       
Antacids/ Anticholinergics /  Metoclopramid + H2 antogonist
 these agents decrease the absorption of cimetidine .    
 Ranitidine absorption decreased by concurrent antacids
  Avoid simultaneous administration.                                                                      
                                                                                                                                                                                                                                                                                                    
Cigerette smoking + Cimetidine
 cigarette smoking reverses cimetidine  inhibition  of nocturnal gastric secretion and ulcer healling. Cigarette   use is closely related to ulcer recurrence

Adverse Reactions-
 
 Famotidine-

Cardiovascular- arrhythmias,AV block, palpitation

CNS- generalised tonic- clonic seizures paresathesis, psychic disturbances, which were reversible in cases for which follow up was obtained

Dermatologic - acne, dry skin, flushing, toxic epidermal necrolysis ( very rare )

GI- anorexia, cholestatic jaundice, dry mouth, liver enzyme abnormalites olr facial edema,
rash, urticaria,

Hypersensitivity -Anaphylaxis, angioedema, conjuntivial injection, orbital or facial edema,
rash, urticaria 

Lab test abnormalities-
Small increase in serum creatinine and elevated ALT levels (at least pretreatment levels)
occurred with ranitidine. Small possibly dose related increases in plasma creatinine and
serum transaminase occurred with cimetidine. These are not common and do not signify
deteriorating renal function.
Elevated AST, ALT, and alkaline phosphatase levels ocur with nizatidine

Hypersens.

Special Precautions:

Impaired renal function.

Gastric carcinoma.

Pregnancy. Lactation.

Approved by FDA in October 1986

Indications:

Duodenal ulcer,benign gastric ulcer,pathological hyper secretory conditions

Dosage:

Acute therapy- 40mg once a day at bed time.

Most patients heal within 4 weeks.

Maintenance - 20mg once a day at bed time.

For Availability/supplies 

Gastro Osephageal Reflux Disease (GORD)

Evidence Based Medicine (MIMS- March 2003)

Beneficial

1. Proton Pump Inhibitors such as omeprazole, Lansoprazole, pantoprazole

2. H-2 Antagonists such as cimetidine, ranitidine, famotidine, (less than proton pump inhibitors)

3. Fundoplication

Likely to be beneficial

1. Medical and surgical tretment of GORD in selected patients with extraoesophageal manifestations.

Unknown effectiveness

1. Medical and surgical treatment of GORD in patients with Barrets oesophagus

2. Surgical treatment for non erosive oesophagitis

Key Points

1. One systemic review of randomised clinical trials has found proton inhibitors to be more effective than H-2 antagonists in both erosive and non-erosive oesophagitis. One trial has found no significant differences in the effectiveness of different proton pump inhibitors

2. Surgical treatment has not been adequately evaluated in controlled clinical trials. Medical and surgical treatments have not been adequately compared

3. It is not clear whether patients with Barretts oesophagitis benefit from medical or surgical treatment of their gastro oesophageal reflux

4. There is limited, conflicting evidence on the basis on the benefits of treating gastro oesophageal reflux in patients with extra oesophageal manifestations (such as asthma)

 Refer - Cimetidine 

1.For patients taking one dose a day- take it at bed time,unless otherwise directed

2.For patients taking two doses- take one in the morning and one at bed time.

3.Take the medicines for the full time of treatment,even if you begin to feel better.

4.Tell your doctor if you ever had any allergic reaction to the medicine.

Pharmacology:

Famotidine is a competitive inhibitor of histamine H2 receptors. The primary pharmacologic activity is inhibition of gastric secrtion.

Both the acid concentration and the volume of gastric secretion are suppressed while changes in pepsin secretion are proportional to volume output.

Pharmacokinetics:

Famotidine is incompletely absorbed. The bioavailabilty of oral doses is 40 to 45%. Bioavailibilty may be slightly increased by food,or slightly decreased by antacids,however these are not of any clinical consequence.After oral dose,peak plasma levels occur in 1 to 3 hours.Plasma protein binding is 15 to 20%.

Metabolism: Elimination half-life is 2.5 to 3.5 hours. Famotidine is eliminated by renal(65 to 70%) and metabolic (30 to 35%) routes.

None.

Pregnancy-

Use only when needed and when the potential benefits outweigh the potentaial hazards to the fetus.

Lactation-

Famotidine- is excreteted in breast milk of rats. It is not known wherher it is excreted in human breast. Decide whether to discontinue nursing or discontinue the drug depending on the importance of the drug to the mother.