Amphenicols efficiency of therapy and toxical after-effects. Amphenicols are a group of antibiotics used in human and veterinary medicine. All amphenicols inhibit the synthesis of proteins in bacterial cells. In Poland there are four drugs of this group in use chloramphenicol, azidamphenicol, thiamphenicol and florfenicol. All of them have a very good rate of absorption and penetration to tissues and fluids. The oldest and the best known amphenicol is chloramphenicol, now rather rare and used only in most difficult cases because of its inhibition of bone marrow. Not so popular as chloramphenicol is thiamphenicol, which causes less important side effects. Thiamphenicol is more active against bacteria resistant to chloramphenicol and azidamphenicol. The last one, florfenicol is used only in veterinary medicine.