Side effects are there.
I have gone through your query.
LA 12 contains Benzathine Penicillin 12 lac unit
. Duration of Penidure injection depends upon the type of disease.
It is usually given for long term in case of rheumatic fever
You have mentioned only skin itching and palpitation
with normal echo.
I would like to know the details of your condition for which you are suggested to take penidure?
There are adverse effect of using Penidure for longer duration, but most of them soon after taking injection after negative sensitivity test like:
serum sickness-like reactions;
CNS toxicity including convulsions;
with candida (fungus).
For prophylaxis of Rheumatic fever patients have taken penidure for over 30 years without any significant adverse effect.
Hope I have answered your query. If you have any further questions I will be happy to help.