A pregnant woman presents with erythema migrans after a hike. What is the best medical therapy for her condition?

Erythema migrans is a characteristic skin rash associated with Lyme disease, which is transmitted through tick bites. The best medical therapy for a pregnant woman diagnosed with Lyme disease and exhibiting erythema migrans is amoxicillin.

Amoxicillin is considered the treatment of choice during pregnancy because it is effective against the bacteria Borrelia burgdorferi, the causative agent of Lyme disease, and it has an established safety profile for use in pregnant women.

In contrast, doxycycline, while effective for treating Lyme disease in non-pregnant individuals, is contraindicated during pregnancy due to potential risks of tooth discoloration and bone growth abnormalities in the developing fetus. Azithromycin is not the first-line therapy for Lyme disease, as it may not be as effective as amoxicillin. Ciprofloxacin is not suitable either because it is a fluoroquinolone, which is generally avoided during pregnancy due to concerns about potential adverse effects on the developing fetus.

Therefore, for a pregnant woman with erythema migrans, the appropriate choice of treatment is amoxicillin, as it balances efficacy and safety for both the mother and the unborn child.