Edrophonium is used diagnostically in myasthenia gravis because it produces a rapid onset of action. Which of the following best explains this pharmacokinetic property?

Question

Accepted Answer

B. It is a reversible inhibitor of acetylcholinesterase with a very short duration of action due to rapid renal excretion. ## Edrophonium: Pharmacokinetics and Clinical Use

**Key Point:** Edrophonium is a **reversible, competitive inhibitor** of acetylcholinesterase with an **onset of 30–60 seconds** and a **duration of only 5–10 minutes**, making it ideal for diagnostic testing (Tensilon test) in myasthenia gravis.

### Mechanism of Rapid Onset and Offset

1. **Reversible binding** — edrophonium forms weak, transient electrostatic interactions with the anionic site of acetylcholinesterase
2. **Rapid renal excretion** — as a quaternary ammonium compound, edrophonium is highly hydrophilic and is filtered and excreted unchanged by the kidneys within minutes
3. **No metabolism** — minimal hepatic or plasma metabolism means kinetics are determined purely by renal clearance

### Comparison with Other Anticholinesterases

| Drug | Reversibility | Onset | Duration | Route of Elimination |
|------|---------------|-------|----------|----------------------|
| **Edrophonium** | Reversible | 30–60 sec | 5–10 min | Renal (quaternary amine) |
| **Neostigmine** | Reversible (carbamate) | 7–15 min | 30–60 min | Renal + hydrolysis |
| **Physostigmine** | Reversible (carbamate) | 3–8 min | 30–60 min | Hepatic metabolism |
| **Pralidoxime** | Reactivator (not inhibitor) | 1 min | 1–2 hrs | Renal |

**High-Yield:** The **Tensilon test** relies on edrophonium's ultra-short duration: if the patient has myasthenia gravis, acetylcholine accumulation will transiently improve muscle strength within seconds; the effect wears off within 5–10 minutes, allowing safe reversal with atropine if needed.

**Clinical Pearl:** Edrophonium is now rarely used in clinical practice (largely replaced by serology and electromyography) but remains a high-yield concept for NEET PG because it illustrates the relationship between reversibility, ionization, and renal clearance.

**Mnemonic:** **REDO** — **R**eversible, **E**drophonium, **D**iagnostic, **O**nset rapid.

[cite:KD Tripathi 8e Ch 6]

Answer

A. It is a prodrug that requires enzymatic activation in the blood

Answer

C. It undergoes extensive hepatic metabolism, resulting in rapid clearance

Answer

D. It is a non-competitive inhibitor that binds irreversibly to the enzyme active site

Edrophonium is used diagnostically in myasthenia gravis because it produces a rapid onset of action. Which of the following best explains this pharmacokinetic property?

Explanation

Practice similar questions