I was having the same problem with doxycycline recently with a few rats--rats who normally aren't so picky about food--and read over some relevant pages in Deb Ducommon's book. I've read these pages dozens of times, but didn't remember some of her advice. Two things worked well for me: 1) Try splitting the dose in two and mixing each dose with more flavoring. I've been using Ensure (kind of a high protein drink for old people in the US, in case you don't have it in the Netherlands). This further dilutes the flavor and worked really well for me. 2) Try sprinkling a light pinch of salt on the medicine once it's mixed. This also seems to mask the taste of the meds.
I read Lilspaz say somewhere that if your rat doesn't like the taste, you're not doing enough to hide the taste of the meds.
I agree with splitting the doses. We tried the "masking" method with the medicine Cabergoline, and that was a fail. Forcing often soils them on it alltogether (rats are so smart and stubborn as we know).
I've heard of people having success making medicine balls with rat safe cookie dough, and mixing the medicine in. Our vet suggested mixing baby food in a similar flavor to whatever they added to the meds (usually cherry or banana) to the dropper with her meds vs trying to just get them to eat it.
We however have just had to split up the doses and do our best, since thats been the only effective way. I'm sure you know, but you just wrap them in a towel as best as you can, head upright to prevent choking, and try to fit quickly and gently between the back teeth. We don't force it though and try to be patient until we can get it in her mouth. Then release it slowly (obviously not TOO slow, but gentle).
I'm not good with patience, but it's the only way for us.
Yeah our girl is on 0.3 ml, and we have to split it up in 0.1ml doses, so we're already at 3 squirts. She clamps her mouth shut and fights us all the way, so adding more squirts would be so tricky! That's a good idea though. I think we ruined things by forcing the first dose not realizing how bitter it tastes and she has never forgiven us.
She also hates the tutti fruti flavor they added, so we're hoping next months round we can get in banana.
It was pain to feed medicine to my rats, but i started to mix it in a bit of pate(not sure how it's called in english)
I think that one which i used was made of chicken livers. And i used just tiny bit. My rats were going crazy for it.
I don't know if this is the healthiest solution but i think not taking medicine is worst