Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your fellow ingested birdseed today and is now vomiting seed and shivering.
My concern for him is that if he is vomiting seed several hours after eating it he may actually have an impaction.
The other possibility is that if the seed sat around for a while it can become moldy, and the toxins in moldy seed can make him very sick.
I know you said that you do not have Pepcid. Do you have generic famotidine? That is the same drug as Pepcid.
To try and settle his stomach tonight you have a few options, either:
1) Pepcid-ac (famotidine) at a dose of one 10mg tablet per 20 to 40 pounds of body weight every 12 hours.
2) Prilosec (omeprazole) at a dose of one 10mg tablet per 20 to 40 pounds of body weight every 24 hours.
3) Zantac (Ranitidine) at a dose of one quarter of a 75mg tablet per 20 to 37.5 pounds of body weight every 12 hours
These will reduce stomach acid and should help if this is related to simple nausea and gastrointestinal irritation from eating something he should not have. They can be given for a few days if necessary.
I would not feed him any food for at least 24 hours even after the acid reducers are started.
This should help stop gut spasms and restore normal gut motility.
Starting a couple hours after the acid reducers small amounts of water or ice cubes given frequently are fine as he needs fluids after all that he has lost with vomiting.
You can give him pedialyte to replace electrolytes too but Gatorade is much too high in sugar which can make his gastrointestinal irritation worse.
If things are going well after the food fast and the acid reducers start a bland diet of 1/3 boiled hamburger (or white skinless chicken), all fats and juices drained off mixed with 2/3 boiled, plain white rice. Feed several small meals a day. Once he feels better (no vomiting for 48 to 72 hours) start mixing in his regular dog food very slowly. Less bland more regular with each day. It should take a week or so to convert him back.
If he continues vomiting though he should be seen at an emergency clinic. Please let me know if you have any further questions.