Hello and Welcome to "Ask A Doctor" service. I have reviewed your query and here is my advice.
How much does he weigh now?
Lactodex is a milk-protein based product that contains protein, fats, carbohydrates, minerals, and
vitamins. It is recommended for babies born at less than 37wk gestation or weight less than 2.5kg.
It is considered to be a milk supplement and not a full replacement to mother's milk. Also,
breastfeeding is free unlike formula.
Because it contains calories, when added to what he is already drinking, it will increase his weight.
I would suggest that you continue to breastfeed.
Being better nourished will improve his health.
Hope I have answered your query. Let me know if I can assist you further.