Thanks for posting your query on health care magic.
Enzyme inducing drugs do cause early excretion of drugs like OC pills.
In your case spotting could be due to breakthrough bleeding
It is usually seen in the first 3 months.
There is no need of treatment.
If the symptoms persists then consult your Gynecologist for the change of OC pills with higher dose of Oestrogen and Progesterone
Hope this helps.