Respect sir, my family have lost my brother Because of Negligence of d

Sir we have belongings to middle-class family, when my brother suffering from I'll that time we met doctor that time he can gave tablet , after taking that tablet my bro start vomiting and his eye vision became blur and next day we met again same doctor, that time he took that tablet and also his medical paper and thrown to waste box again explained to my mother this happen due to high dose of medicine after we met higher hospital their doctor said that his kidney size due vomit , day by day his health conditions are critical and finally we lost my bro so my family want to case on him but we have does not have proper evidence