Oral administration of narrow therapeutic index anticoagulants like phenprocoumon (PHP) necessitates careful control of the kinetic release of the drug to avoid dose dumping and severe haemorrhagic effects. This study was carried out to prepare and characterize novel PHP delivery systems based on κ-carrageenan hydrogels, exploring the importance of potassium ion (K⁺) stabilization in controlling the release process. FT-IR, TG/DTG, and in vitro release studies were employed in combination with a new validated RP-HPLC assay. FT-IR and thermal analysis results showed that PHP is physically encapsulated into the polysaccharide matrix, where there are no chemical incompatibilities between them. Furthermore, potassium ions increase the stability and heat resistance of the polymer network. However, when K⁺ was considered for modelling the kinetic release using the Korsmeyer–Peppas equation, it was observed that PHP is released from the K⁺ stabilized matrix in a relaxation dominated diffusion-controlled transport. Ionic cross-linking effectively reduces the initial burst effect, demonstrating that these matrices are promising vehicles for the sustained delivery of phenprocoumon.