Hi there.
I have been caring for three frogs that also had severe MBD. They weren't eating, were very lethargic and were having seizures.
One died, but I managed to save the other two.
Here's what I did.
EVERY DAY, I gave the frogs (separately of course) a Pedialyte 1:10 soak- that is one part Pedialyte to ten parts de-chlorinated water. Make it blood temperature water so they don't get too cold. Let them soak for 20 minutes.
EVERY DAY, I gave the frogs a soak of LIQUID CALCIUM. Flukers makes it, it comes in a bottle with a dripper. The packaging is a blue box with Liquid Calcium written on it. The correct dosage for my frogs was one drop per 30mls of de-chlorinated blood temp water. I suspect that since your frog is larger, you should up the dose to perhaps 2 or 3 drops per 30mls. Leave the frog to soak for 20 mins. This will increase blood calcium levels and start you back on the right track. The liquid calcium does not have D3 added, so if you can expose the frog to some UVB light to aid absorption of the calcium that would be ideal.
EVERY 2 DAYS, I gave the frog a Repta-Boost soak. They were too small to successfully force-feed. Add one scoop of Repta-Boost to 120mls blood temp de-chlorinated water . If you can force feed it, check out this video: Feeding Twigs - YouTube courtesy of HeatherAdd a little (small amount is crucial-- too much calcium at one time may cause bad complications) amount of calcium to the Repta-Boost mix. Be gentle.
Good luck. If this is MBD, there is still a possibility you can save him. I wasn't able to take my frogs to a vet, so this is what I did. You cannot substitute the liquid calcium for calcium powder mixed with water. The calcium powder is not water soluble, so the frog won't be able to absorb it easily.