What is the most important associated with Pyrazolone derivatives like Phenylbutazone which necessitated the withdrawal of a number of these drugs from the market?

• A. Severe hepatotoxicity
• B. Nephrotoxicity
• C. Hematologic toxicity
• D. Gastric ulceration

Answer: (C)

The key safety concern with pyrazolone derivatives like phenylbutazone is their potential to cause serious bone marrow suppression, leading to hematologic toxicity. This can manifest as conditions such as aplastic anemia and agranulocytosis, where the production of blood cells drops dramatically. These effects are life-threatening, unpredictable, and not easily reversible, so regulators and clinicians treated them as a major red flag. While these drugs can also cause liver, kidney, or gastric side effects, the hematologic toxicity poses the most severe, dose- and time-independent risk that led to widespread withdrawals from the market.