Sodium 2–mercapto ethane sulfonate is used as a protective agent in:
**Core Concept**
Sodium 2-mercapto ethane sulfonate, also known as mesna, is an antidote used to prevent hemorrhagic cystitis caused by certain chemotherapy agents, such as cyclophosphamide and ifosfamide. It works by conjugating and neutralizing the toxic metabolites of these drugs.
**Why the Correct Answer is Right**
Mesna acts by conjugating with the acrolein metabolite of cyclophosphamide, thereby preventing it from causing damage to the bladder mucosa. This is achieved through a nucleophilic addition reaction, where mesna's thiol group (-SH) reacts with the aldehyde group of acrolein. This reaction prevents the formation of acrolein's toxic metabolites, which are responsible for the hemorrhagic cystitis associated with cyclophosphamide and ifosfamide.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because mesna is not used as a protective agent for radiation-induced cystitis. While mesna does prevent hemorrhagic cystitis caused by certain chemotherapy agents, it does not have a role in preventing radiation-induced cystitis.
**Option B:** This option is incorrect because mesna is not primarily used as a protective agent for cisplatin-induced nephrotoxicity. While mesna may have some protective effects against certain types of nephrotoxicity, its primary use is in preventing hemorrhagic cystitis caused by cyclophosphamide and ifosfamide.
**Option C:** This option is incorrect because mesna is not used as a protective agent for anthracycline-induced cardiotoxicity. While mesna may have some protective effects against certain types of cardiotoxicity, its primary use is in preventing hemorrhagic cystitis caused by cyclophosphamide and ifosfamide.
**Option D:** This option is incorrect because mesna is not used as a protective agent for methotrexate-induced hepatotoxicity. While mesna may have some protective effects against certain types of hepatotoxicity, its primary use is in preventing hemorrhagic cystitis caused by cyclophosphamide and ifosfamide.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that mesna is specifically used to prevent hemorrhagic cystitis caused by cyclophosphamide and ifosfamide, and not for other types of chemotherapy-induced toxicities. This is a common exam trap, as students may get confused between different types of chemotherapy agents and their associated toxicities.
**Correct Answer: D. Mesna is used to prevent hemorrhagic cystitis caused by cyclophosphamide and ifosfamide, not for the other options listed.**