Untersuchungen zur StabilitÃ¤t von Antibiotika-Referenzsubstanzen
Eine Studie aus der analytischen Praxis
Lothar Bomblies und RÃ¼diger Leimbeck
Labor L+S AG, Bad Bocklet, Deutschland
Investigations into the Stability of Antibiotic Reference Substances / Results of an analytical study
Various possibilities exist for the correct handling of antibiotic reference substances. The system laid down by the European Pharmacopoeia (EP) for its references - namely the conditions for use of primary standards is, in theory, very good. It allows for use only immediately after opening and does not permit any storage of opened containers. This presents no problems for a user who, due to substantial requirements, calibrates a secondary standard. However, in the case of rarely used substances, this system is very expensive. In the current economic climate, with pressures from all sides to cut costs, the pharmacopoeial procedure is increasingly regarded as not practicable. Our aim, in a stability study of EP references substances used for the microbiological assay of antibiotics, was therefore to devise defined storage conditions for material from opened original containers. These should ensure the stability of the substances -and, in consequence, reliable analytical results as well as enable an efficient use of the primary standard. A shelf life of up to 18 months could be confirmed for aliquots of the primary standard by storing weighed and lyophilised aliquots under the temperature conditions specified in the EP catalogue. Nevertheless, in principle, the system of drying reference standards which is frequently specified by the USP and results in the sanctioned, repeated use of the same reference standards is preferable.
Key words Antibiotika Â· Lagerungsbedingungen Â· Mikrobiologische Wertbestimmung Â· Referenzstandards Â· Referenzsubstanzen