Stability data on β-lactam-filled elastomeric devices used in outpatient settings in subtropical and tropical climates is lacking. While extensive stability studies have been performed on β-lactam antibiotics at lower room temperatures, there is not enough evidence to assure their physicochemical stability in elastomeric devices at high temperature conditions. This study aimed to develop and validate simple precise analytical tests for stability determination, and to evaluate the in-use physicochemical stability of β-lactam-filled elastomeric devices in subtropical climates. With outpatient practices rising in popularity, validated analytical tests for stability assessment of elastomeric devices are a necessity, especially when used in warmer weathers. This study successfully developed and validated analytical tests, and stability assessments of β-lactam-filled elastomeric devices incubated under room temperature conditions of 30°C and 40°C were conducted. The results showed that the two different β-lactam-filled elastomeric devices tested remained stable after 24 h of continuous infusion at constant temperatures of 30°C and 40°C. These results suggest that flucloxacillin and cefazolin-filled elastomeric devices are stable at temperatures of 30°C and 40°C and safe to be used in subtropical climates. However, this is only a pilot study and larger scale field-based studies that contemplate multiple real-life ambient fluctuations are needed to ensure the stability of such devices.