I. Drug Therapy Evaluation
A. Mechanism Of Action
1. Maalox plus, suspension
Maalox is a balanced mixture of 2 antacids:
* Aluminum hydroxide is a slow-acting antacid and magnesium hydroxide is fast acting. The 2 are frequently combined in antacid mixtures. Aluminum hydroxide on its own is astringent and may cause constipation. This effect is balanced by the effect of magnesium hydroxide, which, im common with other magnesium salts, may cause diarrhea.
* The absorpyion of aluminum and magnesium from antacids is small. Aluminum hydroxide is slowly converted to aluminum chloride in the stomach.
* Mechanism of action: ranitidine is a specific, rapidly acting histamine H2-antagonist. It inhibits basal and stimulated secretion of gastric acid, reducing both the volume and the acid and pepsin content of the secretion.
* Absorption of ranitidine after IM injection is rapid and peak plasma concentrations are usually achieved within 15 min of administration.
* Ranitidine is not extensively bound to plasma protein (15%) but exhibits a large volume of distribution ranging from 96-142 L.
* Ranitidine is not extensively metabolized. The fraction of the dose recovered as metabolites is similar after both oral and IV dosing: and includes 6% of the dose in urine as an N-oxide, 2 % as the S-oxide, 2 % as desmethylranitidine and 1-2 % as the furoic acid analog.
* Plasma concentration decline biexponentially with the termal t1/2 of 2-3 hours. The major route of elimination is renal. After IV administration of 3H-ranitidine 150 mg, 98% of dose recovered, including 5% in feces and 93 % in urine, of which 70% was unchanged parent drug. Less than 3 % of the dose is excreted in bile. Renal clearance is approximately 500ml/min, which exceeds glomerular...