It is important to address your symptoms of anxiety, back pain, and rapid heartbeat while taking Eptoin 300 ER (Phenytoin). These symptoms could be side effects or related to other health issues. You should not stop or change your medication without consulting your healthcare provider.

• Contact your doctor promptly to discuss these symptoms.
• Do not discontinue Eptoin on your own, as sudden stopping can cause seizures or other complications.
• Your doctor may want to evaluate your symptoms, possibly adjust your medication, or investigate other causes.

If you experience severe symptoms like chest pain, severe shortness of breath, or fainting, seek emergency medical care immediately. Your healthcare provider is the best person to guide you safely through managing these symptoms and your medication.To narrow down potential causes, we will need some more information.I understand you're experiencing anxiety, back pain, and a rapid heartbeat. To provide the best advice, could you please share your age and gender? Also, I cannot comment on your medication. Please consult a doctor about Eptoin 300 ER.