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.
In Rhode Island sales for resale are not subject to sales and use tax. The burden of proving that a sale of tangible personal property is not a sale at retail is on the seller unless the seller, in good faith, takes an exemption certificate from a purchaser. Resale exemption certificate requirements.