MoonGoddess wrote: What would you do if it was your chicken then, keljonma?
As Dr. Brown stated, the Wazine brand of Piperazine is labeled for use for Chickens.  But there are no wormers that can be given to chickens that are in egg production for human consumption and still eat the eggs. Even Wazine (Piperazine) is labeled 
Not approved for eggs that will be used for human consumption.
We are trying for a more natural approach to raising our flock of standard heritage breed chickens. Personally, we don't use anything on our chickens or pets that we wouldn't use ourselves. (We haven't used antibiotics or over the counter drugs for years. .. Do you hear me knocking on wood? 
		
		
	
	
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We knew from the start the identity of some of our egg customers. A couple of them have life-threatening health conditions that require them to take various prescription medications on a daily basis. We did not want anything we would feed our flock to effect these customers. Also it has always been our plan to, and we will soon begin, supplying eggs to a local family farm group to be sold to local groceries. The local demand is for drug- and chemical-free products. 
Therefore, we made a conscience decision not to use anything with our chickens that states in its usage notes: 
'Not Approved For Eggs That Will Be Used For Human Consumption' or 
'Do Not Use On Food Producing Animals'. 
So we don't drug or worm our chickens. We do use Food Grade DE and provide garlic, apple cider vinegar, cayenne pepper, parsley, grated carrots, apples, pumpkin and flax seeds, plain yogurt w/active cultures and buttermilk to our flock. Some people have strong opinions about the use of Food Grade DE, but it works for us. Fecal tests show no worms to date, the current flock will be 1 year old in June. New chicks arriving this year will be treated identically.
If a bird appears to be having breathing difficulties, I put eucalyptus oil on the nostrils, try to look in it's mouth, and clean it out if necessary. Then I put some ACV in a needless syringe and release drops of it at the side of the beak. Then follow with plain water. If the bird is still experiencing difficulties, I would isolate it in my laundry/mud room with heat and fog it with eucalyptus oil in a warm mist vaporizer.
I recommend researching what is out there and making your own determinations about how you want to raise your flock. Read as much as you can about chicken care. If you see someone recommending a treatment, do the research, check the ingredients, read the warnings and what they mean. Remember a great deal of the literature has been written for someone raising large commercial flocks of chickens. I'm not an avian vet and don't claim to be an expert. I've been researching poultry for a decade and still learn something new all the time. 
Someone else on this board will have to answer your questions about using the wormer.
Whatever you do, raise your flock in the manner that best suits you. Both you and your flock will live easier. 
Glad to hear your chicken is doing better! I can hear that huge sigh of relief from here! 
regards,
keljonma
if edited, probably for typos..