There may be another drug from the same family available if you ask the vet, there certainly are in humans (cimetidine = Tagamet, ranitidine=Zantac). Easiest way to divide a tablet into tiny amounts is to crush it and split the powder with a razor blade, then try to get that down. My pharmacy is rather rusty but given that these drugs are sold without prescription I suspect they are pretty safe if you get the dose a little wrong. Cimetidine can be used in very small children and there is a liquid form which would be easy to dose, tho whether you can get a veterinary version I couldn't say.