The use of polymers as excipients for drug delivery has afforded stable formulations that reliably control the release of active pharmaceutical ingredients (APIs). While many materials are available and used, few polymers exhibit the numerous advantages, including amorphous characteristics, noninflammatory properties, and resorbable degradation products, like those of poly(ester urea)s (PEUs). Furthermore, stability issues that arise in various APIs can make formulation optimization difficult. Herein, a series of PEUs were synthesized that vary by the fraction of l-phenylalanine monomer incorporated into the copolymerization. The various PEUs and entecavir monohydrate were dry-mixed at different weight percentages (15, 30, and 50%). Filaments of the PEU formulations were extruded and analyzed quantitatively for drug loading and content uniformity by using μ-CT and UPLC analysis. Drug dissolution profiles from filament segments were monitored over a 4-week period and ultimately showed that the controlled release of entecavir was influenced by the incorporation of the l-phenylalanine within the polymer.