Hi.. Pimples on the face is unlikely to be the effects of metronidazole.. The best way of treating this would be to leave it alone.. It will spontaneously heal.. Avoid manipulation, excessive face wash, use of cosmetics.. Good nutrition and better stress management is needed.. If the pimple enlarges and if there are signs of infecition such as redness, severe pain, you may need antibiotics creams or ointment.. Contact your doctor in such cases...