How old is he? You may not have a choice other than hospital and IV meds. You can't force someone to swallow and as you found, there's fallout when you try.
You CAN bribe, however. I'd stay calm, describe a liberal bribe scheme, describe what will happen re hospital if. Ruble fails, and then follow through calmly on whichever is applicable.
Worth giving your ped a call to ask for options, too. Maybe in-home injections or similar are possible.