Enzyme inducers will increase the rate of metabolism of co-administered drugs and thus their effect will decrease or will be at lower therapeutic dose. As a result, the dose of such drugs (which are metabolized by microsomal enzymes) should be increased when administered along with enzyme inducers.
Enzyme inhibitors will decrease the metabolism of drugs metabolized by microsomal enzymes, thus predisposes to the toxicity by such agents.
So, to remember the examples for each type, here is a nice method to call them :
Enzyme inducers:
GPRS Cell Phone
G – Griseofulvin
P – Phenytoin
R – Rifampicin
S – Smoking
Cell – Carbamazepine
Phone – Phenobarbitone
Enzyme inhibitors:
Vitamin K Cannot Cause Enzyme Inhibition
Vitamin – Valporate
K – Ketoconazole
Cannot – Cimetidine
Cause – Ciprofloxacin
Enzyme – Erythromycin
Inhibition – Isoniazid