有些药品稳定性差，在贮存中易受光、空气和温湿度等环境因素的影响，药效降低，毒性增高，甚至不能药用。为了保证用药安全、有效，必须给这类药品规定有效期限。这类药物大致包括以下几类：抗生素这类药品在有效期药品中占有相当大的比例，有效期限一般在２～４年，例如青霉 Some drugs have poor stability, are easily affected by environmental factors such as light, air and temperature and humidity during storage, reduce efficacy, increase toxicity, and even can not be used medicinally. In order to ensure drug safety, effective, must provide for such drugs expiration date. These drugs generally include the following categories: Antibiotics such drugs in the expiry date of medicines occupy a large proportion of the effective period of usually 2 to 4 years, such as Penicillium