The total of minutes the treatment will take is 2 hours x 60 minutes/hour = <<2*60=120>>120 minutes
After 120 minutes has passed the total amount of drops that the patient will receive is 20 drops/minute x 120 minutes = <<20*120=2400>>2400 drops
Knowing the number of drops, we know that the patient has taken 2400 drops x 5 ml/100 drops = 120 ml
#### 120