I have finished my full course of antibiotic 4 hours before so can n I drink alcohol?

Depends on… The antibiotic: some like Flagyl (metronidazole) can interact with alcohol & cause marked nausea & vomiting. Bactrim (sulfamethoxazole and trimethoprim) alone can cause nausea/vomiting even without alcohol. No drug interactions r listed for bactrim, (sulfamethoxazole and trimethoprim) amoxicillin, & alcohol, but it's never a good idea to mix alcohol with meds. Bactrim (sulfamethoxazole and trimethoprim) & alcohol both affect the liver. Best to wait until you've finished antibiotics before drinking.
Generally it's ok. Whilst many drugs should not be taken with alcohol antibiotics are not usually affected to a significant degree.