If your asking can you take Baclofen and gabapentin (Neurontin) together - this is a question for your Dr. as they both have have central nervous system activity.
Baclofen is a muscle relaxer and an antispastic agent.
Gabapentin is used to treat partial and secondarily generalized seizures. It is legal (and common) to prescribe medicines for “off-label” uses even though the FDA has not formally approved such uses. So gabapentin is often used off-label for many types of pain, most often the pain of diabetic neuropathy, as well as for some mood disorders, such as anxiety. In fact, more people take gabapentin to treat pain than to control seizures.
Not sure in what context your question is meant ? Where does it connect to GERD for you ?
Please remember, I am not a Dr.