To suppress temporal increases of N-formylpiperidine (NFP) in a lyophilized formulation that is sealed with a rubber stopper, is charged into a medical container, and contains teriparatide acetate of 67.9 μg as an active ingredient.SOLUTION: The present invention provides a process for suppression including the step of blending sodium chloride in the formulation, prior to lyophilization treatment in the production process of the formulation.SELECTED DRAWING: None【課題】ゴム栓で封栓され、医療用容器に充填されている、67.9μgのテリパラチド酢酸塩を有効成分として含有する凍結乾燥製剤中のN-ホルミルピぺリジン(NFP)の経時的増加を抑制する。【解決手段】前記製剤の製造過程における凍結乾燥処理前に、塩化ナトリウムを前記製剤に含有せしめる工程を含む抑制方法。【選択図】なし