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Section IVOther important drugsUses
Ranitidine has similar uses to cimetidine. However, because it does not inhibit hep-
atic cytochrome P450, it is often used in preference to cimetidine. It is used in com-
bination with antibiotics to eradicateH. pylori.Itisalso used widely in labour with
apparently no deleterious effects on the fetus or progress of labour.Mechanism of action
Similar to that of cimetidine.Effects
Gut–similar to that of cimetidine.
Cardiovascular – it may produce cardiac arrhythmias during rapid intravenous
administration.
Metabolic – it should be avoided in porphyria, although reports detailing this inter-
action are inconclusive. It has no anti-androgenic effects.
Miscellaneous – rarely it may cause thrombocytopenia, leucopenia, reversible
abnormalities of liver function and anaphylaxis.Kinetics
Ranitidine is well absorbed from the gut, poorly protein bound (15%) and partially
metabolized in the liver. It undergoes a greater degree of first-pass metabolism than
cimetidine (oral bioavailability approximately 50%), while 50% of an administered
dose is excreted unchanged in the urine.
Nizatidineandfamotidineare newer H 2 antagonists with increased potency. Like
ranitidine they do not inhibit hepatic cytochrome P450.Proton pump inhibitors
Omeprazole
Uses
Omeprazole is used for similar indications to that of ranitidine but also in cases
where H 2 blockade is insufficient. It may be given orally or intravenously.Mechanism of action
Aproton pump (K+/H+ATPase) in the membrane of the parietal cell mediates the
final common pathway of gastric acid secretion. Omeprazole reversibly blocks the
proton pump and so achieves complete achlorhydria.Effects
Gut–the acidity and volume of gastric secretions is reduced, while no change is
seen in lower oesophageal sphincter tone or gastric emptying.