Very few medications are actually approved for chickens because of egg or meat withdrawals. FARAD publishes a list of approved medications every few years. For worms I would use Valbazen (albendazole) or SafeGuard Liquid Goat Wormer (fenbendazole) which are safe, but not approved. In some countries piperazine, levamisole, or others may be used. But none of those are approved unless given in small dosage over 5-7 days. It is best to ask specific questions about what disease or worm you are treating.
For bacterial diseases, it depends what you are treating. For bacterial respiratory diseases such as mycoplasma gallisepticum (MG,) Tylosin powder for pigeons which you can find online is approved and there is no egg withdrawal. Coryza is better treated with sulfonamides, such as sulfadimethoxine or bactrim, which are not approved for chickens. Viruses will require no antibiotics.
For reproductive infections, amoxicillin (Fish Mox) can help treat those. Some use the banned enrofloxacin/Baytril, since it is effective against more bacteria.
For mold in the respiratory tract, the only treatment is to remove the mold. Some mold fungi in the digestive tract will respond to Medistatin powder, Nystatin, or Monistat cream given orally. For eating moldy feed an emergency flush of Epsom salts or molasses may be given orally, but check for dosages.
