A fluid transfer assembly, drug container, and method for enabling fluid transfer in an infusion system is taught. The assembly includes a fluid container containing an infusion fluid, and a drug container. The fluid container has at least one inlet port for receiving a medical substance from the drug container. The assembly further includes at least one fluid barrier controlling fluid passage between the drug container and the fluid container. The inlet port exhibits a first luer-lock connector, and the drug container is sealed by a cap exhibiting a second luer-lock connector for attachment to the first luer-lock connector. The fluid barrier is designed and arranged to be ruptured by an external force to allow the fluid passage.