How does Voltaren Patch compare to Voltaren Gel in relieving lower back pain?

The effect of the patch vs the gel is related to the dose or concentration of the active ingredient, Diclofenac. The patch has 180mg of the active ingredient, Diclofenac. The instructions are to apply a patch every twelve hours. The gel has 10mg per g of gel. So when you apply 2 gm of gel you are getting 20 mg of Diclofenac. The gel requires four applications every 24 or an application every six hours for a total of 80mg of Diclofenac/day.
Thus the difference in “effectiveness”.

My right arm has been sore for the last few weeks. My doctor prescribed Voltaren tablets, but would only prescribe 4 days at a time.

I dropped by the drugstore to see what they have over the counter, and the pharmacist said they had the patches and gel, but he said the patches are more effective, and only need changing one a day. So I bought some today and will see.

The cost here (Tokyo) is 980 yen ($9.17) for 7, or twice that for 21.

The cost of Voltaren Gel, 1% is only about $39 bucks. I use it often even daily on elbow, hands, toes. I find that two applications really works better for pain, an I also use a little water to "reactivate" the dried gel, which works nicely.
It's a bother, smells of ammonia upon application, and rubs in well. My Medicare covers the price.
I finally got an increase of supply, 3 tubes a month which I use when the arthritis flares. I have no experience with the patch. The gell is swell.

I don't think the gel will work nearly as well. The patch is better for acute pain. It targets the pain site and has minimal systemic effects (side-effects) . Voltaren gel is not particularly expensive and is available over the counter at your pharmacy. You could try it and see what you think.