Classification and generations of drugs
This pharmacological group is part of antisecretory agents along with proton pump inhibitors and M-anticholinergics. H2-receptor blockers themselves comprise several generations:
- Cimetidine is a representative of the first generation.
- Ranitidine is a second-generation drug with a duration of action up to 10–12 hours, surpassing its predecessor in efficacy.
- Famotidine is a third-generation drug with good tolerability.
- Nizatidine and roxatidine are the fourth and fifth generations, possessing a dual mechanism of action.
Pharmacodynamics and mechanism of action
The drugs block the effects of histamine released by enterochromaffin-like cells. This produces the following effects:
- Inhibition of hydrochloric acid secretion by parietal cells.
- Reduction of basal secretion at rest and during the day.
- Decrease in acid secretion during nighttime hours.
- Inhibition of pepsin production.
Later generations (nizatidine and roxatidine) additionally stimulate the production of protective mucus and normalize gastrointestinal motility.
Clinical application and dosing
These medications are used for gastric and duodenal ulcers, hyperacid conditions, as well as Zollinger-Ellison syndrome and NSAID-induced ulcers.
- Cimetidine: prescribed 3 times a day plus at bedtime, the course is 4–8 weeks. Abrupt discontinuation causes a rebound syndrome with ulcer recurrence.
- Ranitidine: taken twice a day.
- Famotidine: in acute ulcers, it is used at a dosage of 40 mg once daily at bedtime.
Side effects and interactions
The safety profile varies depending on the generation and the specific active substance:
- Cimetidine: causes antiandrogenic effects (hyperprolactinemia, galactorrhea, gynecomastia, impotence), diarrhea, as well as renal and hepatic impairment. It is an inhibitor of microsomal oxidation, inhibits cytochrome P450, and slows down the metabolism of tricyclic antidepressants and anticoagulants.
- Ranitidine: practically causes no adverse reactions (rare constipation or headaches are possible) and does not affect the metabolism of other medications.
- Famotidine: is characterized by good tolerability, but has restrictions: contraindicated in pregnancy, lactation, and childhood.
Briefly: answers to topical questions
What is the exact mechanism of the antiandrogenic action of cimetidine?
The antiandrogenic action of cimetidine, a 1st-generation H2 histamine receptor blocker, is accompanied by hyperprolactinemia. In women, this can manifest as galactorrhea, and in men, as gynecomastia and impotence. The more precise molecular mechanism of cimetidine's antiandrogenic action is not specified in the presented sources.
Cimetidine targets the endocrine system (causes antiandrogenic effects and inhibits cytochrome P450), while ranitidine and famotidine behave more mildly.
Class and exam questions
What is the difference between cimetidine and ranitidine in terms of drug interactions?
Cimetidine inhibits cytochrome P450 and microsomal oxidation, slowing down the metabolism of other drugs, whereas ranitidine does not affect the metabolism of concomitant medications.
What happens upon abrupt discontinuation of cimetidine?
A withdrawal or rebound syndrome occurs, which manifests as a recurrence of peptic ulcer disease.
What additional mechanism do nizatidine and roxatidine have?
In addition to H2 receptor blockade, they stimulate the production of protective mucus and normalize gastrointestinal motility.
What are the specific contraindications for famotidine?
Famotidine is contraindicated in hypersensitivity, acute porphyria, as well as in children, during pregnancy, and the lactation period.
What else to study on this topic
- Full classification of antisecretory drugs and the role of M-anticholinergics
- Comparison of proton pump inhibitors and H2 receptor blockers
- Detailed analysis of Zollinger-Ellison syndrome
- The effect of cytochrome P450 on the pharmacokinetics of other drug groups
- Features of the use of NSAID-associated ulcers
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