Microbiology One unit of diphtheria antitoxin was defined as the smallest amount of antitoxin required to neutralise ? A 100 MLD of toxin B 200 MLD of toxin C 300 MLD of toxin D 400 MLD of toxin 💡 Explanation One unit of diphtheria antitoxin was defined as the smallest amount of antitoxin required to neutralise ? ✓ Correct Answer: A. 100 MLD of toxin