Most wormers are used off label for chickens. The road to approval is complicated and expensive, so many have not sought it for poultry due to the cost. The poultry industry does not generally have long lived birds, or birds that are outside on the ground, so the need has not been considered great, or that the profits will make up for the costs. Wazine (piperazine) was used and approved, but has been discontinued. Safeguard Aquasol is approved (same medication as Safeguard in other forms) but is extremely expensive. For backyard/small flock keepers wormers are a much more important part of keeping our flocks healthy. All the wormers listed in this thread are commonly used by many, many of us, and for quite some time. The only issue with what you have is the form, it's pellets and has to be eaten, leaving the issue of knowing, or not knowing, if the birds eat enough to get the appropriate dose. Under dosing can result in parasites that become resistant to that medication. Sometimes a bird that is sick from parasites may not eat or drink well, which can also contribute to them not getting enough. That is why so many of us recommend using a form of medication that is directly dosed so that you know without question that they got the correct amount. I do 27 (currently-numbers do fluctuate) birds every three months, and it's not that difficult to do.
There is a method of using Safeguard made into a mash they eat, which some people do mostly to avoid an egg withdrawal period (this method should not be used if your birds have capillary worms). You might be able to convert the recommended amounts in that in order to use the pellets, you would have to re-figure feed amounts etc, and the instructions are for using the goat wormer liquid. Again, whether they eat enough will be an unknown. I have personally never used this method. If you choose to do it that way, I would recommend a fecal test afterwards to confirm you have successfully treated. Info here:
https://www.backyardchickens.com/threads/safeguard-mash-zero-day-egg-withdrawal.1254653/
There is a method of using Safeguard made into a mash they eat, which some people do mostly to avoid an egg withdrawal period (this method should not be used if your birds have capillary worms). You might be able to convert the recommended amounts in that in order to use the pellets, you would have to re-figure feed amounts etc, and the instructions are for using the goat wormer liquid. Again, whether they eat enough will be an unknown. I have personally never used this method. If you choose to do it that way, I would recommend a fecal test afterwards to confirm you have successfully treated. Info here:
https://www.backyardchickens.com/threads/safeguard-mash-zero-day-egg-withdrawal.1254653/