Hello Sue, I'm Dr. Deb and I'll do my best to help you today.I'm sorry that Lady was ill soon after you gave her liquid Drontal; I'm assuming you mean she vomited.This particular drug has two ingredients....Pyrantal Paomate and Praziquantel...which most dogs tolerate very well.However, either one of them can cause vomiting as a possible side effect. Additional side effects which can be seen with Praziquantel are anorexia, lethargy, or diarrhea.If she vomited, she may continue to be nauseous for a little while longer. If so, you can give her Famotidine although it may be difficult to find in the UK. The dose would be 0.25 mg/lb twice a day.Another option would be Omeprazole; the dose would be 0.25 -0.5 mg/lb once a day.I wouldn't feed her for several hours; just give everything a chance to settle down. Then a bland diet of boiled chicken and rice could be fed.
I'm not a huge fan of coincidence so Drontal has to be considered a likely cause of her not feeling well, but given her age, there are other possible causes, too, such as dietary indiscretion or viral/bacterial infections or a foreign body. Therefore, is she continues to vomit or becomes lethargic or is painful/uncomfortable when you press on her abdomen or doesn't want to eat, then you might want to have her seen. I hope this helps. Deb