Acid-containing oral pharmaceutical compositions are provided wherein the pharmaceutical active agents are peptide compounds (i.e., those that include a plurality of amino acids and at least one peptide bond in their molecular structures). Certain barrier layers and/or particulate coated acid are used to reduce any adverse interactions that might otherwise occur between the acid of the compositions and other components of the composition. Use of these barrier layers and/or use of particulate coated acid is believed to promote a more simultaneous release of the components of the composition than is achieved by prior art acid-protection techniques, thus enhancing, and making more consistent, the bioavailability of the active peptide compounds.