The medication doesn't have to be given with food. I usually worm my birds first thing in the morning before they've had food or water. That way the first thing that gets to the worms is the medication. If worms are his issue, then hopefully if he starts feeling better, he will start eating...
Wanted to add, that is a fairly large volume to dose, so draw up your dose, and give it no more than .5 ml at a time and let him swallow in between, until the entire dose is given. To minimize the chance he aspirates any. And don't squirt it forcefully into his beak.
How much does he weigh?
Albendazole dose is 20 mg/kg. Example: If he were 6 lbs, that would be 2.72 kg, at 20 mg/kg the correct dose would be 54.4 mg of albendazole (2.72 x 20 mg). Your product contains 25 mg of albendazole per ml. 54.4 mg divided 25 mg = 2.176 ml, and I'd round that up to...
Correct dosing of Valbazen (albendazole) is by body weight.
Weight in lbs / 2.2 X 20 mg / 113.6 = dose
So a 6 lb bird would get .48 ml (just round it to .5 ml) this is based on the concentration in Valbazen liquid.
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