Review article: alginate-raft formulations in the treatment of heartburn and acid reflux

Alginate-based raft-forming formulations have been marketed word-wide for o ver 30 years under various brand names, including Gaviscon. They are used f or the symptomatic treatment of heartburn and oesophagitis, and appear to a ct by a unique mechanism which differs from that of traditional antacids. I n the presence of gastric acid, alginates precipitate, forming a gel. Algin ate-based raft-forming formulations usually contain sodium or potassium bic arbonate; in the presence of gastric acid, the bicarbonate is converted to carbon dioxide which becomes entrapped within the gel precipitate, converti ng it into a foam which floats on the surface of the gastric contents, much like a raft on water. Both in vitro and in vivo studies have demonstrated that alginate-based rafts can entrap carbon dioxide, as well as antacid com ponents contained in some formulations, thus providing a relatively pH-neut ral barrier. Several studies have demonstrated that the alginate raft can p referentially move into the oesophagus in place, or ahead, of acidic gastri c contents during episodes of gastro-oesophageal reflux; some studies furth er suggest that the raft can act as a physical barrier to reduce reflux epi sodes. Although some alginate-based formulations also contain antacid compo nents which can provide significant acid neutralization capacity, the effic acy of these formulations to reduce heartburn symptoms does not appear to b e totally dependent on the neutralization of bulk gastric contents. The strength of the alginate raft is dependant on several factors, includin g the amount of carbon dioxide generated and entrapped in the raft, the mol ecular properties of the alginate, and the presence of aluminium or calcium in the antacid components of the formulation. Raft formation occurs rapidl y, often within a few seconds of dosing; hence alginate-containing antacids are comparable to traditional antacids for speed of onset of relief. Since the raft can be retained in the stomach for several hours, alginate-based raft-forming formulations can additionally provide longer-lasting relief th an that of traditional antacids. Indeed, clinical studies have shown Gavisc on is superior to placebo, and equal to or significantly better than tradit ional antacids for relieving heartburn symptoms. Alginate-based, raft-forming formulations have been used to treat reflux sy mptoms in infants and children, and in the management of heartburn and refl ux during pregnancy. While Gaviscon is effective when used alone, it is com patible with, and does not interfere with the activity of antisecretory age nts such as cimetidine. Even with the introduction of new antisecretory and promotility agents, alginate-rafting formulations will continue to have a role in the treatment of heartburn and reflux symptoms. Their unique non-sy stemic mechanism of action provides rapid and long-duration relief of heart burn and acid reflux symptoms.