I'm sure I've heard soda crystals poured down the throat suggested. Not done it myself. Hope he is okay.
Poisoning
Unfortunately many dogs like nothing better than to eat toxic substances, such as rat poison, slug bait, plain chocolate or human tablets like Neurofen in nice shiny foil. In most cases it is best to make the dog vomit as soon as possible. Most poisons take a few hours to be fully absorbed from the stomach so inducing vomiting is useful up to 2 hours after ingestion. The best way to do this is to place a small handful of Washing Soda Crystals on the back of the dogs tongue and hold his mouth shut until he swallows it or starts retching. You may need to do it 2 or 3 times before any thing happens. If no washing soda is available, then you can try very salty water and mustard instead.
The only exception is if the dog has swallowed something that is caustic e.g. bleach, as this could damage the throat again on the way back up. In all cases, contact the vet with details of the poison and in what quantity it has been eaten. They can then check with the national Poisons Service to see what treatment is necessary.
from
http://www.emersonvet.co.uk/content.php ... =First+Aid