Describe Neostigmine in detail.

Mechanism & Use

Neostigmine is an anticholinesterase used to reverse a non-depolarising neuromuscular block. By inhibiting acetylcholinesterase, it increases the amount of acetylcholine at the neuromuscular junction, which competes with and displaces the relaxant from the receptor, restoring transmission.

Muscarinic Effects & Limitations

The extra ACh also stimulates muscarinic receptors, causing bradycardia, salivation, bronchoconstriction, increased gut motility and miosis — so neostigmine is always co-administered with an antimuscarinic (glycopyrrolate or atropine). It can only reverse a block that has already begun to recover (it cannot reverse a dense block), and it worsens a depolarising phase I block.

Timing & Adequacy of Reversal

Neostigmine is given only once some spontaneous recovery is present (at least one or two twitches of the train-of-four), because attempting to reverse a dense block simply fails and wastes time, and its effect takes several minutes to reach a peak. The adequacy of reversal is then confirmed objectively — ideally a train-of-four ratio above 0.9 — rather than by clinical signs alone, since residual weakness can persist despite a patient who appears to be breathing and moving, and it is this residual block that endangers the airway after extubation.

Note

Given too early to a dense block it simply fails, so at least a twitch or two of the train-of-four should be present first.

Muscarinic effects require concurrent antimuscarinic cover.

• Neostigmine: anticholinesterase → ↑ACh at junction → displaces non-depolarising relaxant.
• Muscarinic effects (bradycardia, secretions) → always give with an antimuscarinic (glycopyrrolate/atropine).
• Reverses only a partially-recovered block; worsens depolarising phase I block.
• Confirm reversal with TOF ratio > 0.9.