The invention relates to the field of oral drug delivery and more in particular, to oral dosage forms for delivery of a high dose of a therapeutically active acid-labile salt, such as sodium thiosulfate (STS). Provided is a pharmaceutical oral dosage form for controlled delivery of an acid-labile salt, the dosage form comprising a core comprising the acid-labile salt in a polymer matrix comprising a combination of (i) a pH- sensitive hydrophilic methacrylic acid— methyl methacrylate copolymer and (ii) a carbomer, wherein the acid-labile salt makes up at least 50wt% of the core; and wherein the outer surface of the core is provided with an enteric coating layer
