How much Benadryl can I safely take to stop the itching of a rash on my feet. If I take 50 mg every?

I am prescribed injectable Benadryl 50mg vials. I am prescribed ( if needed up to 400mg in a 24hr period.) I of course do not take this much. If needed I can take 100mg at a time. However my case is extremely rare! My body has the adverse effect from this medication. If you read the label on any Benadryl, whether its OTC for adults or liquid for children you will see a caution that mostly in young children Benadryl can cause excitability and cause them to be hyper. In adults you will see the opposite, that amount would normally put most people out. Well I'm one of those adults whose side effects mimicks young kids. I get a ton of energy almost like when most people get a vit B shot they feel energized. I get extremely sick from vit B and it puts me out. I have a very rare autoimmune Diease so what works for 90% of people the way it is supposed to work doesn't work for me.
It sounds like you have built a tolerance and that's why you can take the 50mg. Just read the packaging it will tell you the limit you can take a day. For me it's 400mg but mine is by rx only! So the OTC might be lower. I would think its 300mgs daily but it could be 200. The box will tell you. If not you could always ask a pharmacist. I hope this helps you.

If I took 50 mg every 2 hrs I'd be comatose. Have you tried a longer acting antihistamine, like zyrtec or claritin? The maximum amount of it you should take in a day (24 hrs) is 300 mg. If you take one every 2 hrs you will be taking double that.