CPD ARTICLE
H 2
-RAs Misoprostol current recommended dose is 1 mg / kg , q12h , PO . Omeprazole is sensitive to degradation by gastric acid and the enteric-coated granules packaged in gelatin capsules needs to be repackage in gelatin capsules if a smaller dose is needed .
PPI
Sucralfate
Figure 2 : A shematic representation of the gastric mucousal parietal cell . The proton pump is on the luminal cell surface . the receptors for acetylcholine , prostagalndin , gastrin and histamine are on the inner cell membrane . Proton pump inhibitors work on the luminal surface and thus will block the effects of all receptors on the inner cell surface . Sucralfate attached to damaged and exposed gastric mucousa
in understanding of the effects of various antacids on intragastric pH in animals .
Omeprazole Omeprazole is a potent proton pump inhibitor commonly utilised in the management of gastrointestinal ulceration . Proton pump inhibitors block the final step of acid production on the luminal surface of the parietal cells , thus also blocking the effect of other acid stimulatory factors such as histamine , gastrin and acetylcholine .
Omeprazole acts by irreversibly binding to the proton pump . This initially causes transient activation of additional proton pumps in an attempt to bypass the blockade . Omeprazole thus takes approximately 2-4 days for optimal acid suppressive effects with only a 33 % reduction occurring during the first day .
Parietal cells re-establish acid production only by producing new proton pumps lending the drug some lasting effect after discontinuation of a few days . Considering the efficacy of omeprazoles ’ blockade of the acid production pathway it is not surprising that several recent studies have shown that it is superior to H2 blockers at inhibiting acid secretion . Moreover , additional studies have shown that the twice daily administration of omeprazole further improves acid suppression relative to the previously used once-daily practice in dogs and cats .
Because the amount of proton pump enzymes present in the parietal cell is maximal after a prolonged fast it is advised that proton pump inhibitors be administered 30 – 60 minutes before feeding for optimal effect . The
A recent study in cats comparing fractionated omeprazole , enteric-coated omeprazole and famotidine to a placebo indicated that omeprazole is a superior antacid in this species as well and that disruption of the enteric coating did not negate the acid suppressing effect of omeprazole 8 .
H2 blockers Drugs such as ranitidine , cimetidine and famotidine antagonise the H2 receptor on the gastric side of the parietal cell and decrease acid production . However recent studies have raised concerns regarding their lack of efficacy in managing gastric ulceration . Bersenas et al . determined the degree of gastric acid suppression associated with the administration of ranitidine , famotidine , pantoprazole and omeprazole compared to saline solution in healthy dogs 9 . Famotidine , pantoprazole , and omeprazole significantly suppressed gastric acid secretion compared to saline and ranitidine failed to do so . In addition , administration of famotidine three times daily instead of twice daily did not affect gastric pH significantly , suggesting that increased frequency of administration of this drug is of no benefit . There also appears to be a diminishing effect over time when this drug is used for a prolonged period 10 .
Some clinicians use the histamine antagonists together with a proton pump inhibitor in the initial phase of treatment due to the slight delay in maximal acid suppression seen with proton pump inhibitors compared to the relative quick onset of action with H2 blockers . However , there is concern that this practice may interfere with proton pump inhibitor activation , decreasing the efficacy of this drug . In addition , the approach of using famotidine and a proton pump inhibitor simultaneously was shown not to be superior to using a proton pump inhibitor alone 11 .
Ranitidine is approximately 10 times more potent than cimetidine at receptor blockade . With recent evidence suggesting that ranitidine is not superior to saline at causing acid suppression it can be argues that cimetidine would not be affective either . In conclusion , famotidine appears to be the only promising H2 antagonist with some effect on gastric acid suppression and this drug is not readily available in South Africa .
Sucralfate Sucralfate is commonly used in the treatment of oesophagitis and gastric ulceration . This sulphated disaccharide forms an adherent gel that binds to the ulcerated surface , protecting it from further degradation by hydrochloric acid and pepsin .
Issue 03 | JULY 2018 | 31