Q: Our six dogs and cats are on preventives throughout the year to protect them from heartworms, intestinal parasites, fleas, and ticks. We want to continue buying them from our veterinarian, but he can’t match the prices we found online. A friend learned the hard way, though, that some online pharmacies sell counterfeit medications. How can we be sure we’re getting the real thing? A: Buying drugs from an online pharmacy does present risks. Most manufacturers guarantee medications dispensed by your veterinarian, but not those shipped from an online pharmacy. One reason is that freezing winter temperatures and summer heat and humidity can affect the potency and stability of drugs and vaccines. In addition, many online pharmacies sell counterfeit or adulterated medications made by companies that ignore federal and state drug laws. One hint that a pharmacy isn’t legitimate is that it doesn’t require you to provide a prescription for …