Pet supplies e-retailer Wag.com today said it would sell pet prescription medicine through a deal with VetSource, a pharmacy based in Portland, OR. Wag.com is operated by Quidsi Inc., a wholly owned subsidiary of Amazon.com Inc., No. 1 in the Internet Retailer Top 500 guide.

Here’s how the service works, according to information posted on Wag.com: A consumer shops for the drugs on the Pet Medications section of the e-commerce site. To buy a medication, a consumer must have a prescription from his veterinarian. At checkout, the consumer will enter contact information for the veterinarian, and then VetSource will contact that doctor to obtain the prescription. VetSource then will ship the medication within one business day. For refills, VetSource will ship immediately.

Wag.com says that U.S. law prohibits consumers from faxing or e-mailing prescriptions to VetSource. Wag.com also says that VetSource sources the medications its sends directly from their manufacturers. A Wag.com spokeswoman says the site offers some 300 medications.

“We know that pets are not just animals, they’re part of the family, and our customers want the best, from pet food and toys, to medicine, vitamins and everything in between,” says David Zhang, head of Wag.com. “With pet medications made available through Wag, pet parents can now truly find everything for their pet in one spot, so they can spend more quality time with their loved ones.”