General and Systematic Veterinary Pharmacology

ANTACIDS

• Antacids are agents which neutralize excess acid.
• Some of the commonly used antacids include sodium bicarbonate, aluminium hydroxide and dihydroxy-aluminium, calcium carbonate and magnesium hydroxide.
• The weak base reacts with the gastric hydrochloric acid to form a salt and water.
• This reaction causes an increase in the gastric pH and above pH 4, pepsin is inactive.
• Antacids differ in
  • neutralizing capacity - determines dosage
  • time to onset - slow or rapid
  • duration of action - long or brief
  • side effect - constipation vs. diarrhea
  • potential to produce electrolyte disturbances
  • convenience - liquid vs. tablet
  • palatability
  • cost

Sodium bicarbonate

• It has a rapid onset of action.
• But it is not an ideal antacid due to the rebound acidity i.e., stimulation of acid production once the pH exceeds 4, due to gastrin secretion.
• As sodium bicarbonate is readily absorbed into systemic circulation, it alters systemic pH and produces electrolyte disturbances.
• This in turn may lead to edema, hypertension or heart failure.

Aluminium hydroxide

• The insoluble aluminum chloride that is formed due to the reaction of hydrochloric acid and aluminium hydroxide often causes constipation.
• It also binds with tetracycline to inhibit its absorption.

Calcium carbonate

• The absorption of ~10% of calcium chloride may result in hypercalcemia (muscle weakness, kidney stone formation) and rebound gastric acidity.
• Constipation may occur with high doses.

Magnesium hydroxide

• This causes prolonged neutralizing effect due to slow stomach emptying.
• Poor absorption of magnesium salts may result in diarrhoea .
• Combinations of aluminum or calcium containing antacids with magnesium containing antacids can nullify the adverse effects on bowel function.