My guinea pig Totoro had a horrible reoccurring URI, and it took months to help her. She constantly had a runny nose and would breathe like a squeaky tire. URIs in guinea pigs are really scary, and I'm writing this post about my own experience to help newer owners with their own pigs. I tried a medication called "VetRx" sadly, its positive affects did not last long for Totoro, and her condition only worsened. I constantly would feed her lots of hay and vitamin C to try and keep her strong, while I researched into anti biotic options. After reading several websites and comments posted by others I decided that Bactrim would have been the best since it is for treating URIs, and it is safe for younger guinea pigs. I contacted a vet to get a safe dosage, and I was lucky to be friends with a doctor who was willing to give me the medication. I did a ten day long treatment, every twelve hours I would need to give her another dose, and I couldn't miss a day. After her ten day treatment, Totoro was no longer ill. She is lively, the healthiest I have seen her in months, and gained a significant amount of weight. Even though I was lucky to get the medication free, it is something that will save your guinea pigs life if he or she has a URI, and it is worth the investment. I encourage other owners to research into safe antibiotics, talk to others, and consult a vet. I hope this was helpful to anyone with a pig that has a URI and to know that there is still hope for your sick pig.