Medicines used to treat Gastrointestinal problems

treatment of ulcer, treatment of heartburn, GIT drugs Classification

Many people suffer from gastrointestinal problems, especially heartburn caused by gastroesophageal reflux disease (GERD). Peptic ulcers can also occur, often due to certain medications used in lupus treatment, including NSAIDs and steroids. Doctor may prescribe PPI drugs such as Nexium, Prevacid, Prilosec, Protonix, or Aciphex to treat the GIT problems.

Chapter 1: Peptic ulcers

Imbalance between aggressive (acid, pepsin, bile, H.pylori) and defensive factors (mucus, NO, bicarbonate, PG). Aim of the therapy is to reduce acid aggressiveness. Acid is released by proton pump from parietal cells by histamine (through H2), gastrin and acetylcholine (M3). Acetylcholine is released by vagus nerve (M1) also that acts on histaminocyte to release histamine which acts on parietal cells. Remember acid secreting response of gastrin and acetylcholine is expressed fully only in presence of cAMP generated by histamine. Antihistamines thus not only decrease histamine effect but also those of Ach and gastrin.

Drugs:

Class 1: Aim to reduce acid secretion

  • H2 blocker: Cimetidine, Ranitidine, Famotidine, Roxatidine.

    Points to remember:
    Cimetidine is antiandrogenic and also cytochrome inhibitor thus increasing half life of phenytoin, phenobarbitone, sulfonylurea, carbamezapine, quinidine, warfarin. (PPSCQW)

  • Proton Pump Inhibitors: Omeprazole At acidic pH it forms 2 active species (Sulfenic acid and sulfenamide) that inturn blocks proton pump.
  • Prostaglandin analogue: Misoprostol.

    Produce bicarbonate, mucous. Decrease cAMP level to reduce acid secretion (see top).

    Used against ulcers caused by NSAIDs.

  • Anticholinergic: Pirenzipine, Oxyphenonium, Propanthelene All are M1 blocker.

    Class 2: Antacid

  • MOA: Neutralise acid and pepsin.
  • Systemic: NaHCO3
  • Points to remember:
    Cause systemic alkalosis, Na+ load may worsen oedma and CHF. Carbon dioxide production may cause ulcer perforation.

  • Non-Systemic:

    Points to remember

  • Magnesium hydroxide: Aqueous suspension is known as milk of magnesia. Have laxative
    action.

  • Aluminium hydroxide: have constipating effect. Decrease phosphate absorption. May cause osteomalacea and may be beneficial to treat phosphate stones.
  • Calcium carbonate: cause Milk Alkali syndrome (Burnett’s syndrome).

    Class 3: Ulcer Protective

    Sucralfate, Colloidal Bisumth Subcitrate

    Points to remember

  • Below a particular pH (4-5) they form gel like consistency that physically protect ulcer base. CBS also increase mucus and bicarbonate secretion, increase PG production and kills H.pylori.
  • CBS have drawback of causing darkening of stool, denture and tongue.

    Class 4: Anti H. pylori

    H. pylori has urease activity. Tetracycline, amoxicillin etc.

    Chapter 2: Emesis and Antiemetic:

    Points to remember:

  • CTZ and NTS are two important areas in medulla oblongata that on Histaminergic, Cholinergic, Opioids, Serotonergic, Dopaminergic. Conversely antagonists of abovereceptors are useful in treating emesis.
  • Body rotation (as during mountain travelling) disturbs vestibular apparatus of ear. Pathway that communicate message from vestibular apparatus to brain involves cholinergic and histaminergic links. So antihistamines and anticholinergic drugs are effective in treatment of mountain and motion sickness.
  • On the other hand irritant effects of cytotoxic drugs and radiotherapy involve serotonergic pathway. Antiserotonergic drugs are useful in this case.

    Drugs:

  • Anticholinergic like hyoscine,
  • Antihistamine like promethazine, cinnarazine, diphenhydramine etc.
  • Neuroleptics: block D2 receptors. Example proch;orperazine
  • Prokinetic drugs (Gastric hurrying):
    Metoclopramide: It acts by following mechanism

    Points to remember

  • Mechanism of action : D2 blockade. In GIT it promotes transit of food and in CNS it directly antagonizes effect of dopaminergic drugs. 5- HT3 antagonism. 5-HT4 agonism:
    release acetylcholine that causes gastric peristalsis.

  • Drawback: due to D2 blockade it may cause Parkinson. So we need some drugs that do not cause central dopamine blocker. Domperidone is devoid of such side effects as it acts only by blocking peripheral D2 receptors of GIT.
  • Cisapride and mosapride are similar drugs that cause 5- HT3 antagonism and 5-HT4 agonism. But cisapride has arrythmogenic potential.

    5- HT3 antagonist: Ondansetron used to treat cancer chemotherapy induced vomiting.

    Methyl polysiloxane: (Simethicone, Dimethicone):

    Silicone polymer, viscous amphiphilic liquid, acts as antifoaming agent. With antacid decreases dispersion and form coating. Prevent GERD.

    post About Medicines used to treat Gastrointestinal problems

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