Anesthetics and other medical solutions are stored in a cartridge including a hollow body having a needle-penetrable septum at one end and a plunger at another end. A protective plug is inserted into the open plunger end of the cartridge and protects the cartridge from contamination per use. A buffer or other material may be injected into the cartridge, causing displacement of the protective plug, allowing the cartridge to then be used in a syringe or other delivery system. The anesthetic may contain at least one solute and have an initial tonicity and an initial pH. A volume of buffer may be injected through the septum into the anesthetic, where the initial solute concentration and initial pH of the anesthetic may be selected to provide a target pH and target tonicity after the buffer is introduced.
