Hello, I'm Dr Gary. I've been practicing veterinary medicine since 2007. I look forward to helping with your questions/ concerns.
It sounds like your dog has a collapsing trachea. This is common in small breed dogs where the trachea (windpipe) collapses down on itself as it enters the chest. This causes a dry hacking cough that can sometimes sound like a honking sound almost like a duck. They will often hack and then cough up some white foam as well.
As for what you can give tonight, the only over the counter cough suppressant that you can give is Robitussin DM
. You can give 1/4 teaspoon every 8-12 hours as needed. The other thing that may help is Benadryl at 1 mg/lb. We usually use Benadryl for allergic reactions but it is a mild sedative so we may use it for it's sedation properties.
For more long term treatment, we typically use a combination of a sedative (Acepromazine) + a cough suppressant (Butorphanol/ Torb) as needed. In the severely affected dogs, we go to surgery to place a tracheal stent that holds the trachea open. This is not often needed, but it's an option.
I hope this helps, let me know if you have any other questions.