Life Sci. 2006 Aug 2; [Epub ahead of print]
Examination of the interaction between peripheral diclofenac and gabapentin on the 5% formalin test in rats.
Picazo A, Castaneda-Hernandez G, Ortiz MI.
Putting 5 capsules of 300 mg gabapentin in a 60 ml bottle of Pennsaid may triple its analgesic power…
The actual study was done with the diclo-gaba injected subcutaneously so not exactly topical.The Gabapentin – Diclofenac mix had 3 times the analgesic effect of either separately.
With a vehicle like DMSO(in Pennsaid) the penetration should be somewhat like subcutaneous.
Note – I did studies to see how well 1% lidocaine in 50% DMSO would work – it takes 30 minutes to topically numb an area and I am not convinced phonophoresis (ultrasounding it)or ionophoresis improves that. So if you want top level effect to a spot – tape a cotton ball to area(do that first as once wet will not stick) and soak ball and leave on 30 minutes – irritation of skin was always a problem and steroids creams were useful there.
The ratio of Diclo to Gaba was 1:1.5 so theoretically if you took the commercial topical Pennsaid (1.5 % Diclofenac in 50% DMSO) – 60 mls. bottle and added 5 caps of 300 mg gabapentin (actually amount is 1.35 gm but this is close) – you should triple its effectiveness – DMSO is such a good solvent you would not have to use powdered gagapentin – just out of the capsules. If wanted to use other vehicle, that would be something like 1.5% Diclofenac and 2.25% Gabapentin. Anyone using such a mix?