The correct answer is "Ciprofloxacin."

This choice is correct because the combined oral contraceptive pill (OCP) is metabolized and inactivated by the cytochrome P-450 (CYP450) enzyme complex, and ciprofloxacin, a fluoroquinolone antibiotic, is an inhibitor of CYP450. Therefore, when ciprofloxacin is taken, the efficacy of inactivation of drugs, like OCP's, is impaired, which increases the effective level of OCP's circulating in the patient's blood. Consequently, even if the patient is taking the prescribed dose of OCP's, the effect of the drug may be greater than intended if taken with ciprofloxacin or other drugs that inhibit CYP450, which can make the potential adverse effects of OCP's more likely to occur, or occur with greater severity than if that patient had not taken ciprofloxacin with it. 

Neither lisinopril (an ACE inhibitor), fluoxetine (an SSRI), Docusate (a stool softener), nor aspirin (an anti-inflammatory, anti-platelet agent) appreciably induce or inhibit CYP450 and therefore none of them has an appreciable effect on OCP metabolism.

The correct answer is "St. John's wort." 

This question tests your knowledge of factors that influence the metabolism of warfarin. In this case, you are told that the patient is taking an appropriate dose of warfarin, but still is not achieving the desired therapeutic effect, which raises the possibility of drug interactions and/or use of other medications that may impact the metabolism of warfarin.

Warfarin is metabolized by the CYP450 enzyme complex, which is known to be induced and inhibited by a variety of other common medications, supplements, and foods. Since this patient's International Normalized Ratio (INR) is sub-therapeutic, meaning that warfarin is not achieving a great enough effect, this should raise the possibility of increased metabolism of warfarin by CYP450, which means that warfarin will be inactivated more quickly than usual. The only agent listed that is known to induce or activate CYP450, which would speed the inactivation of warfarin, is St. John's wort, an herb commonly used for antidepressant activity and anti-inflammatory activity.

Gemfibrozil, quinidine, cimetidine, and azithromycin all are inhibitors of CYP450, not inducers, and therefore would slow the metabolism of warfarin, increasing the effective circulating dose of warfarin, which would raise the INR. Therefore, these are not correct answer choices for this case.

The correct answer is "Do not consume alcohol while taking this medication." 

In this question, what is really being tested is your knowledge of side effects/interactions with metronidazole. One of the major interactions to be aware of with metronidazole is that it can cause an unpleasant interaction when consumed with alcohol that is very similar to the symptoms that occur when one consumes alcohol while taking the alcohol deterrent, Antabuse. This reaction includes severe abdominal pain/cramping, nausea, vomiting, facial flushing, and headaches. Patients should avoid drinking alcohol while taking metronidazole and for three days after completing their course.

Eating spinach, lying flat for 30 minutes after taking metronidazole, taking cholesterol medication while taking metronidazole, and operating heavy machinery while taking metronidazole are inappropriate recommendations, as there are no known direct associations between metronidazole and spinach consumption, head elevation, cholesterol medications, or level of consciousness.