Background: Preventing infections associated with cardiac implantable electronic devices (CIED) and neurostimulators is essential to optimizing patient outcomes. This study aimed to evaluate the antimicrobial performance of a biologic CIED envelope incorporating a bioabsorbable disc infused with rifampin and minocycline. Methods: The antimicrobial activity was evaluated in a rabbit model and in vitro elution tests. Based on in vivo–in vitro correlation studies, a modified AATCC-100 method was used to quantitatively assess antibacterial activity across seven bacterial strains relevant to CIED infections. Results: Pharmacokinetic analysis showed a biphasic elution profile, with rapid initial release followed by more gradual elution over 14 days. The AATCC results showed no bacterial recovery for any tested species, with complete eradication in all replicates. Conclusions: These results support the use of antibiotic-eluting bioenvelopes as an effective strategy for preventing bacterial infections associated with CIED. The modified AATCC-100 test and in vivo–in vitro correlation studies provide new tools for the evaluation of the antibiotic activity of implantable biomaterials.