Complex sentence: When chloroquine resistance is common or when chloroquine is contraindicated, then artesunate is the drug of choice, except in the U.S., where it is not approved for use; mefloquine is a good alternative and in some countries is more readily available.
Split into simpler sentences: When chloroquine resistance is common or when chloroquine is contraindicated, then artesunate is the drug of choice, except in the U.S., where it is not approved for use. Mefloquine is a good alternative and in some countries is more readily available.