Doxycycline is used for malaria prophylaxis or treatment. When it is administered for treatment of P falciparum malaria, this drug must be used as part of combination therapy (eg, typically with quinine or quinidine).
If you buy goods and are not charged the Rhode Island Sales Tax by the retailer, such as with online and out-of-state purchases, you are supposed to pay the 7% sales tax (less any foreign sales tax paid) for these items yourself as the Rhode Island Use Tax.
Rhode Island has a state sales tax of 7%. The rate was raised from 5% to 6% as a temporary measure in the 1970s, but has not since been lowered. Rhode Island raised its sales tax from 6% to 7% in the early 1990s to pay for the bailout of the state's failed credit unions.