Poly-lactic acid (PLA) is a synthetic polymer that has gained popularity as a scaffold due to well-established manufacturing processes, predictable biomaterial properties, and sustained therapeutic release rates. However, its drawbacks include weak mechanical parameters and reduced medicinal delivery efficacy after PLA degradation. The development of synthetic polymers that can release antibiotics and other medicines remains a top research priority. This study proposes a novel approach to produce PLA by converting Brewer’s spent grain (BSG) into lactic acid by bacterial fermentation followed by lactide ring polymerization with a metal catalyst. The elution properties of the PLA polymer are evaluated using modified Kirby–Bauer assays involving the antimicrobial chemotherapeutical, trimethoprim (TMP). Molded PLA polymer disks are impregnated with a known killing concentration of TMP, and the PLA is evaluated as a drug vehicle against TMP-sensitive Escherichia coli. This approach provides a practical means of assessing the polymer’s ability to release antimicrobials, which could be beneficial in exploring new drug-eluting synthetic polymer strategies. Overall, this study highlights the potential of using BSG waste materials to produce valuable biomaterials of medical value with the promise of expanded versatility of synthetic PLA polymers in the field of drug-impregnated tissue grafts.