Get Your Dog Care Questions Answered by Experts
Is there any Acetaminophen in the tablets? If so, how many mg per tablet?
If it's just the oxy, then we can see some pretty significant sedation and GI upset (nausea, vomiting). If he's sleepy but still responsive when you stimulate him, that is ok. In that case, you can usually just ride out the signs over 4-6 hours.
If he's not very responsive, then I would worry about significant mental depression. In that case, I would take him in to a vet where they can give a reversal medication- Naloxone. Most of the time it's not needed, but occasionally we'll see one so sedate that it's recommended.
He's pretty small, so watch him closely over a few hours in case he needs to get in to an ER vet.