Frogs are actually more susceptible to chemicals than fish or shrimp. This is because the frogs breathe through their skin and if there is anything bad in the water it will be absorbed immediately and affect them more readily than shrimp, snails or fish. Any medication that is safe for frogs will be safe for shrimp, catfish, loaches & snails.
If you are getting an ammonia reading then reduce the amount of food going into the tank. Also do a 50% (instead of 25%) water change to dilute ammonia readings, as the bigger water change will reduce the ammonia faster. Make sure you gravel clean the tank each time you do a water change.
Make sure any new water going in the tank is free of chlorine and has a similar temperature & PH to the tank.
Don’t wash the filter materials out under tap water as it can kill off the beneficial filter bacteria and cause ammonia and nitrite readings.
Maybe ring your local fish shop and ask if they have Triple Sulpha or Tri Sulpha, or any Sulpha/ Sulpher based medications. Any shop that carries “Wardleys” products should be able to get “Wardley’s Triple Sulpha”.
If you still can’t find any contact a company called “Waterlife”. They do a product called “Waterlife Myxazin” and it is meant to be safe for inverts (shrimp). However, I don’t know if it is safe for frogs. You would have to ask them that.
The other products that might help would be “Melafix” or “Pimafix”. They are meant to be safe for most things and are more natural based, rather than chemical based medications.