Antihistamines
CIMETIDINE, FAMOTIDINE, NIZATIDINE, RANITIDINE, ROXATIDINE
DRUG |
RELATIVE POTENCY |
DOSE (mg) |
Cimetidine |
1 |
400-800 |
Ranitidine |
4-10x |
150 |
Nizatidine |
4-10x |
150 |
Famotidine |
20-50x |
20 |
Pharmacokinetics
- t½ of 1-4 hours (depends on dose)
-
prescription doses maintain greater than 50% acid inhibition for 10 hours (i.e., twice daily dosing is sufficient); OTC doses inhibit acid secretion for less than 6 hours
-
cleared by combination of hepatic metabolism, glomerular filtration and renal tubular secretion (decrease of up to 50% in drug clearance and significant reduction in volume of distribution in the elderly)
-
NIZATIDINE undergoes little first-pass metabolism, i.e., it has a bioavailability of ~100%; others have a bioavailability of ~50%
-
CIMETIDINE, FAMOTIDINE and RANITIDINE are available IV for use in the treatment of stress-related ulcers in critically ill patients