GIT Lec 2 - Antacids

Question 1

What are antacids?

Answer 1

Antacids are weak bases that react with gastric acids to produce water and salt thereby neutralizing the acid and suppressing its erosive effect.

Question 2

How are antacids classified?

Answer 2

Antacids are classified in three different manners according to different criteria as follows:
A. According to distribution:
a. Systemic Antacids: Sodium bicarbonate
b. Non-systemic antacids: Aluminum, magnesium and calcium salts.
B. According to their onset of action:
a. Fast Acting: Sodium bicarbonate, magnesium oxide and hydroxide, and magnesium carbonate
b. Slow Acting: magnesium trisilicate and Aluminum hydroxide
C. According to potency:
NaHCo3 —> Mg(OH)2 or MgO —> Mg2O8Si3 —> MgCO3 —> Al(OH)3

Question 3

How do we determine the efficacy and side effects of antacids?

Answer 3

According to the type of metal bound to the weak base

Question 4

What are the pharmacokinetics of magnesium oxide, hydroxide and trisilicate?

Answer 4

MgO and Mg(OH)2 act quickly but they cause diarrhea; thereby systemic acid-base balance is NOT disturbed.

Question 5

What are the pharmacokinetics of Aluminum hydroxide?

Answer 5

Al(OH)3 reacts with HCl forming a compound called Al(Cl)3 or aluminum chloride which reacts with intestinal secretions forming insoluble salts especially phosphate salts.
The Cl is secreted and reabsorbed thereby no systemic acid-base balance disturbance occurs.
Can cause hypophosphatemia and constipation

Question 6

What are the pharmacokinetics of Sodium Bicarbonate (baking soda)?

Answer 6

NaHCo3 reacts quickly with a short duration of action. It is absorbed thereby it may cause systemic metabolic alkalosis (increased pH).
Absorption of Na+ ions can cause edema and heart failure in patients with cardiac and/or renal problems.
It can also cause belching and flatulence.

Question 7

What are the pharmacokinetics of Bismuth and Calcium containing antacids?

Answer 7

They are avoided.
Calcium containing antacids can cause hypercalcemia, rebound acid hyper secretion and alkalosis.

Question 8

What are the pharmacokinetics of antacids in general?

Answer 8

1. Aluminum hydroxide decreases H. Pylori colonization and stimulates the production of endogenous PGE (both protective measures)
2. Calcium contains antacids are not currently used due to the fact that they can cause rebound acid hypersecretion, however they are still used as calcium supplements in patients with osteoporosis.
3. Cations from antacids like (Mg, Al, Ca and Na) can be easily absorbed and excreted in patients with normal renal function, however they can cause adverse effects in patients with renal impairment.
4. Pepsin is inactive in a pH greater than 4, which means antacids indirectly inhibit the action of pepsin by decreasing the acidity of the stomach.
5. Antacids interfere with the absorption of a lot of drugs like H2-receptor antagonists, iron supplements, tetracyclines, and antifungal agents, that’s why they should be stopped or taken at least 2 hours before or after the administration of said medications.

Question 9

What are the indications of antacids?

Answer 9

1. For the treatment of GERD and ulcers, especially in the first few days in the course of treatment with H2-receptor antagonists.
2. Large amounts of antacids have been shown to increase the healing capacity of duodenal and gastric ulcers especially as a last-line medication, however patient compliance is not great.

Question 10

What are some of the combinations of antacids?

Answer 10

1. Alginic Acid (Gaviscon)
2. Dimethicone: added to reduce flatulence.