Proper worming for what type of worms you have is the key.

- 2 pound chicken ~0.1 ml Valbazen
- 4 pound chicken ~0.25 ml Valbazen
- 7 pound chicken ~0.5 ml Valbazen
Valbazen is a brand name, albendazole is the generic
Lice/Mites and worms - You would need something like Ivermectin applied to the skin. ( Do not give to a very weak bird as they can die from the overload of parasite death)

Ivermectin injectable is useless in chickens, it'll still kill mites, but not worms in chickens. Ivermectin pour on will not kill tapeworms nor lice. Eprinex doesnt kill all worms neither.

Other Types of worms - Safeguard Liquid goat wormer- 1cc per 10lbs of bird, then 3ccs to 1 gallon drinking water for 5 days. repeat in 7-14 days( For very weak birds give 1/2 that amount every 2 days)
Valbazen - same application as Safeguard, can kill some types of Tape worms

Tape worms - I use horse Zimertrican Gold. It contains prazquantol (sp) About a small pea size dollop in the mouth for 8 lb bird.
safeguard goat drench: Administer the safeguard liquid goat wormer orally. Dosage is 1cc for giants, 3/4cc for large fowl, 1/2cc for standards, 1/4cc for smaller birds. Repeat dosing in 10 days.
Valbazen (albendazole)is a cattle/sheep wormer as stated on the label.
Safeguard (fenbendazole/panacur) is an equine paste and there's safeguard liquid goat wormer.
Most ivomec products are for cattle and horses in pastes, injectables, oral drench and pour on.
For rotation purposes, I use valbazen, safeguard liquid goat wormer, and infrequently use zimectrin gold horse paste.
0.5 cc for each large fowl, 0.25cc for bantams. I put it on bread as well -- it wanted to run off and I needed a decent chunk of bread to soak it up. Dawg53 recommends squirting it in their mouth while on the roost. It doesn't work to put it in water.

Give two doses ten days apart. Toss eggs for 14 days after each dose, or a total of 24 days.
Valbazen not on bread... (evidently the Valbazen tastes bad, mine would not take it on bread at all!) Give Valbazen one dose at a time -- down the throat... AVOID THE WINDPIPE (which is right behind the tongue, you will see it when you open their beak)... So... have someone help you.
Take one chicken at a time, out of the coop.. (hoping you can let them free range or have another coop or pen to put them in if you want to keep them contained)....
Lift the head a little... open the beak.. using a measured dropper or more commonly a syringe (no needle).... you put back, to the side, and down the throat...

1/2 CC/ML per standard size chicken

1/4 CC/ML per Bantam or small chicken

orally, individually... giving it to one at a time and then letting that one go or putting that one somewhere else so you don't get mixed up and give a double dose to one, or miss another.

Now... You have to withhold the eggs... no eating eggs, no eating chickens while Valbazen is in them... so... ON THE TENTH DAY... repeat the process.... dose a second time. Then, after a few days, say the fourth day after the second dose, give them some Buttermilk (or yogurt) mixed in with their food...

Wait an additional 14 days.... two weeks.. so.... no eggs/withhold from first treatment ten days to second treatment and then 14 days after that... on the 15th day it is safe to eat eggs or chickens -- a total of 24 days... safe on the 25th.

Watch the poop after the second treatment. IF, if you see tapeworm segments in the poop... you will have to treat more than twice most likely.... and can use Zimectrin Gold -- "pea" size on bread for standard... "BB" size on bread for Bantam... again, one at a time, separating, don't let anyone get a double dose or be missed. This is if you actually see tapeworm segments after two doses of Valbazen... then you would do this "change up" on the tenth day after the second dose of Valbazen and wait the 14 days after that before eating eggs.
It is also a good idea to rotate wormers so worms have a harder time building up resistance to one type.
IMO Valbazen is the best since the old Salsbury worm-all tablets..Kills more worms than any other wormer on the market, Even shows properties against Blackhead,Cocci and the lower form of canker and also has some effect on the unhatched worm eggs..Valbazen kills Ovary Flukes, Gizzard and Cecal worms, Ivomec/Eprinex is practicly useless against these..Also IMO, If you've had chickens for a year or so in the same location 99 times out of 100 they have worms...
Chicken DR suggests mixing 1 cc Valbazen to 8 cc water then give 2 cc's of this soulution per bird, But after worming hundreds with it I've found 1/4 cc undiluted given orally is easier and just as effective..The mixing with water is supposedly for better gut coverage.
And here is the Ivermectin;

Bottle that will be in the box;

Ivermectin Pour-on.. For the pour on Ivermectin for cattle (not Eprinex) the dosage use is as follows:

1 drop - OEGB sized small bantam female (.1cc)
2 drops - OEGB sized small bantam male (.15cc)
3 drops - average bantams (.2cc)
4 drops - large bantams, small commercial fowl (.3cc)
5 drops - most commercial fowl, small giant hens (.4cc)
6 drops - giant breeds of chicken (.5cc)

I always use a 3 cc syringe that I just fill to about 2 cc's withOUT a needle. The drops will be applied to the skin. Not on the feathers. It's a systemic so it will be absorbed.

For location, you'll want to find an easy to reach spot with as little fluff as possible. I've had the best luck with under the wing when I am by myself. I just pick up the chicken in my left hand, ruffle around the feathers with my right hand until I find a nice clear spot, then rotate the syringe around to dispense the drops exactly on the skin.

bairo info pages: https://www.backyardchickens.com/web/viewblog.php?id=79169