To clear the current drug data click the "New drug" icon.
To retrieve a drug: click the drop down selector 
on the drug input to display a list of available drugs. Then click the drug name to select it.
To enter an unlisted drug: click the "New" icon on the data bar to clear the current drug data.
Drug data fields:
Drug: name of additive
Amount: amount of additive in mg or units
Volume: volume of additive (leave blank if pre-mixed solution)
Solution: name of solution
Volume: volume of solution.
Drug concentration is calculated from the drug data you supplied.