A method for oral administration of an active ingredient to a subject is provided whereby a plurality of bubbles containing the active ingredient t are formed in a small intestinal of the subject. The method includes administering orally to the subject an effective amount of the above-mentioned pharmaceutical composition. The pharmaceutical composition includes a drug layer and an enteric coating layer. The drug layer comprises an active ingredient, a surfactant, an acidic component and an effervescent ingredient. The active ingredient comprises a nucleic acid, a peptide or a protein. When the acidic component of the drug layer is dissolved in the small intestinal to react with the effervescent ingredient for generating carbon dioxide and the plurality of bubbles containing the active ingredient, and the active ingredient is embedded in a gap formed between an inner layer and an outer layer of an double-layer structure formed by the surfactant.
