Background: Carbamazepine (CBZ) is considered as first-line treatment for epilepsy. The literature has signified a history of non-uniform drug performance and clinical failures. However, many studies suggested that Oxcarbazepine (OXC), a structural analog of CBZ, may have an equivalent antiepileptic effect. OXC follows a different metabolic pathway other than CBZ. However, both share the same mechanism of action by blocking voltage-gated sodium channels. Objectives: This study aimed to form hydroxypropyl methylcellulose (HPMC) extended-release tablets containing OXC combined with vitamin D. Methods: These formulated tablets were tested for their dissolution rate, tablet hardness, friability, thickness and pharmacokinetic parameters (Cmax and Cmin). Blood sodium levels were additionally investigated to ensure the absence of hyponatremia; the main side effect of long-term use of CBZ and some of its derivatives. Results: The use of HPMC inhibited the formation of dihydrate OXC form thus offering a significant extended-release profile. OXC also showed a highlighted capability to attain high bioavailability. Microcrystalline cellulose (MCC) was also added to tablets formed to inhibit polymorphic transformation. Tablets containing OXC co-delivered with vitamin D ensured significantly decreased susceptibility to hyponatremia, and an extended-release profile was evident. Lower amounts of OXC were loaded in formed tablets containing vitamin D owing to the synergistic effect between vitamin D and antiepileptic drugs. Conclusion: Conclusively, employing these newly HPMC-constructed tablets of OXC co-delivered with vitamin D appeared to be a promising option for the effective management of epilepsy with least side effects.