Hi
The dosage doesn't depend so much on weight but on how bad the sterile IC is.
I would however try a full capsule until the IC settles down and then again during flares. You can even give 1 capsule twice daily during a particularly strong flare up shortly for a few days. in between flares you can experiment how low a maintenance dosage he will tolerate.
Please accept that sterile IC is actually a wide spectrum and that th online advice covers the lower to medium segment for the most commonly encountered cases.
Piggies with bad IC will need much stronger concentrations (cartrofen). At the very worst, even that will not be enough.
In my own experience with sterile IC, 1/4 of a capsule per day is too little to be effective for most cases. It is about the lowest maintenance I have been able to get away with in between flares in the mild or gradually petering out IC cases but never in order to get the IC under control - initially and during the regular flare-ups every few weeks/months.