Brief Answer:
They act on different targets.

Detailed Answer:
I read your question and I understand your concern and wish to understand how medications work together.

From what you describe the burning sensation in the left is a manifestation of central neuropathic pain, usually resulting from a lesion in a region called thalamus. It is a relay for all sensory stimuli, so lesions in that area may result in abnormal chemical and electrical discharges leading to abnormal, unpleasant, often painful sensations like the burning you describe.

There are many medications used for neuropathic pain. The reason for that is that nerve cell connections are very complex, there are many different neurotransmitter types and channels involved, it is not only one single pathway which may be addressed with only one drug. So since there are different neurotransmitters involved one medication working on inhibiting one particular pain pathway may not be enough, as there may be other pathways involved not addressed by that drug. That is why treatment of neuropathic pain is difficult, commonly the first prescribed drug may not be enough and switching or adding another drug with a different mechanism of action is needed.
I understand it may not sound nice, that this trial method is not enough, but that's the best medicine has to offer for now, there is not one drug covering all pathways and there is no test which can determine which neurotransmitters are involved at a cellular level, several medications may need to be tried.

So your doctor has tried Gabapentin first, a first choice option for neuropathic pain, as it is one of the medications which has shown to work in the greatest percentage of patients by acting on calcium channels and inhibiting calcium currents through cell membranes.
Since that was seen not to be enough he thought to add Baclofen which acts mainly by inhibiting release of excitatory neurotransmitters like aspartate and glutamate. It has a mild action on calcium channels as well but not that relevant.
So the combination is not done because they directly interact and work together, but with the aim to combine two drugs with different mechanism thus influencing more than one excitatory pain pathway and increasing chances of success.

I remain at your disposal for other questions.

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Brief Answer:
I said they work in different ways. There is a chance of non-success though

Detailed Answer:
I don't think I said they work the same way, actually I think I stated it clearly in the last paragraph that it is a combination of two drugs with different mechanism of action, not working in the same way.

This way the chances of the medications working are increased. Whether their failing to work is a possibility, yes it is, as I said neuropathic pain is difficult to treat and different drugs and combinations may be needed to be tried. Hopefully that won't be your case and the current combination will work for you, but there is a chance of non-success I am afraid.

Let me know if I can further assist you.

Brief Answer:
You're welcome, hope you feel better soon.

Detailed Answer:
Glad to have been of help. I really hope you'll feel better soon.

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