For simple duct cleaning try HVCA TR17 (UK) code of practice. This gives methods of cleaning and recomendations for access door intervals etc. I assume that when handling nastys like penicillin, you will have to filter the air entering the space to a suitable clean room level.
I'm not sure about the exhaust though...possibly provided the concentration os low enough and the discharge arranged for high level, you might get away with it on the discharge side.
Incidently our local regional hospital has a drug manufacturing facility and they do just that..filter supply air in, but don't bother filtering on the discharge??
Friar Tuck of Sherwood