Toxoplasmosis is a very serious infection, and treatment SHOULD NOT be delayed for your cat. Here is an informational sheet for you to read more about it.
I highly recommend trying to get the medication directly into his mouth. If he is having trouble with the liquid, you can try the capsules. The capsules can be pilled directly, or hidden in a treat called Pill Pockets that you can purchase from your vet.
My concern with hiding the liquid in his food is if he does not ingest the entire dose. If you want to try it this evening, I would separate the cats for feeding, and first offer the medication in a small amount of his favorite canned food. Ideally, he'll like the bowl clean before you give him the rest of his regular meal. If it goes smoothly, this could be a fine way to medicate him.
My last suggestion is asking a technician at your vet hospital to come to the house and medicate your cat until you return. He really cannot wait 3 weeks until you get home!
Please let me know if you have any further questions. If you are satisfied with my answer, please hit the green accept button. Positive feedback is always appreciated. Thanks!
Good plan, I hope the isolation works. I don't think we'll ever know for sure when he was infected!!
Veterinarian
4 years clinical experience with specialty in pain management, surgery, urology, and geriatrics.