Antacids

• any substance, generally a base or basic salt, which decrease gastric acidity by neutralizing HCl

• antacids are gastric acid neutralizers

Mechanism of action:

Antacids (base) + gastric HCl NaCl + H2O

• Reduction of intragastric acidity

• Promote mucosal defense mechanism through stimulation of mucosal prostaglandin production

Types of Antacids

• SYSTEMIC antacids– Soluble and readily absorbed– decrease acidity but cause systemic alkalosis, due

to absorption of bicarbonate, hence acid base balance is disturbed

• ex: sodium bicarbonate • disadv: CO2 released belching of flatulence

gastric distention, posing a risk to people who have gastric ulcers approaching the perforation stage

• NON SYSTEMIC antacids– Insoluble compounds– not absorbed after administration, hence acid- base

balance is minimally disturbed– Serves as protective film to the gastric lining

• Ex: – Al(oH)2– magnesium carbonate– mg(oH)2 – calcium carbonate

• Disadvantage:– It has a tendency to produce constipation– “Milk-Alkali Syndrome”

• Prolonged administration of large doses of CaCo3 together with large amount of milk

• Metabolic alkalosis• Hypercalcemia• Renal insufficiency

Sodium bicarbonate

• “baking soda”, Alka SeltzerNaHCO3 + gastric HCl NaCl + CO2CO2

• decrease gastric acidity rapidly

Gastric distention & belching

Pharmacokinetics

• Onset of action: oral - rapid

IV – 15 minutes

• Duration of action: oral - 8 – 10 mins

IV – 1-2 hours

• Absorption: oral - well absorbed

• Excretion: Renal (urine)

Adverse effects:

• METABOLIC ALKALOSIS– When given in high doses, unreacted alkali

are readily absorbed, thereby increasing the plasma concentration of bicarbonate, blood ph rises

• Electrolyte imbalance– hypernatremia

• Seizures and tetany– Inc. blood ph dec. free Ca =hypocalcemia

Contraindications:

• heart problems

• high blood pressure

• swelling of the arms or legs– Edema secondary to Na overload

• kidney disease

Calcium carbonate

• Tums, Os-Cal

• Less soluble, reacts more slowly that NaHCo3

• MOA:

CaCO3 + gastric HCl CaCl2 + CO2

• A/E: belching, constipation, Milk-Alkali Syndrome, hypercalcemia,

renal insufficiency

Magnesium hydroxide & Aluminum hydroxide

• Maalox, Mylanta, Kremil-S

Mg(OH)2 + gastric HCl MgCl2 + H2O

Al(OH)3 + gastric HCl AlCl3 + H2O

• No CO2 production, therefore no belching

• Metabolic alkalosis is uncommon

Neutralization rxn:

• Unabsorbed Mg salts Osmotic diarrhea

• Unabsorbed Al salts Constipation– Administered together to minimize impact on

bowel function– Excreted through kidneys

• Contraindicated to patients with renal insufficiency

Drug Interaction of Antacids

• Antacids may affect absorption of other medications by binding the drug reducing it’s absorption

• Increasing intragastric ph affecting the drug’s dissolution or solubility

• Ex: · tetracycline• Fluroquinolones• Itraconazole• Iron

All antacids

increases

intragastric ph