The 7-year-old dachshund, named Oskar, is receiving care at a Sunset District animal hospital. He is now listed in stable condition.
Dr. Carrie Journey says Oskar's symptoms are consistent with strychnine, an animal poison.
"This is a very rapidly absorbed toxin," she said. "This is something that gets in the system within 10 to 15 minutes. So it's important that people act quickly and get to a veterinarian ASAP if they think their dog has eaten something."
Oskar may not be the only victim. Another dog is showing symptoms of strychnine poisoning, which includes agitation, hyper-reactivity to light and noise, and seizures.
Police say they're still looking for those responsible for leaving some 50 poisoned meatballs on a Twin Peaks street. And according to the vet, dozens of meatballs stuffed with pellets have also been found in Diamond Heights, Cole Valley, and Lower Haight.
At the moment, investigators do not have a motive.
Anyone with information is asked to contact police or the anonymous tip line at 415-575-4444 or text a tip to TIP411 with SFPD in the beginning of the message. If you find one of the poisoned meatballs, officials urge you to use gloves to handle them and call police.