What happens if neostigmine is given immediately after succinylcholine (scoline)?

Neostigmine Administration After Succinylcholine: Potential Dangers and Interactions

Administering neostigmine immediately after succinylcholine can cause prolonged neuromuscular blockade and potentially dangerous respiratory depression due to interference with succinylcholine metabolism. 1

Mechanism of Interaction

• Succinylcholine is a depolarizing skeletal muscle relaxant that combines with cholinergic receptors at the motor end plate to produce depolarization, resulting in rapid onset (less than one minute) of flaccid paralysis that typically lasts 4-6 minutes 2
• Neostigmine is an acetylcholinesterase inhibitor that increases acetylcholine concentration in the synaptic cleft, normally used to reverse non-depolarizing neuromuscular blockade 3
• When administered immediately after succinylcholine, neostigmine inhibits plasma cholinesterase, which is responsible for metabolizing succinylcholine, thus prolonging the neuromuscular blockade 1

Clinical Consequences

• Markedly prolonged neuromuscular blockade can occur when neostigmine is given shortly after succinylcholine administration 4
• This prolonged blockade may result in:
  • Extended respiratory depression requiring continued mechanical ventilation 1
  • Inability to extubate the patient's trachea for potentially hours 5
  • Transition to a Phase II block (resembling non-depolarizing blockade) that may be difficult to reverse 2

Risk Factors for Severe Reactions

• Patients with renal insufficiency are at higher risk for prolonged succinylcholine blockade after neostigmine administration 4
• Patients with atypical pseudocholinesterase may experience extremely prolonged blockade (10+ hours) if neostigmine is administered 5
• Concurrent use of other medications that decrease plasma cholinesterase activity (contraceptive pills, cyclophosphamide) can exacerbate this interaction 1

Monitoring and Management

• If succinylcholine has been administered, wait for spontaneous recovery before considering administration of neostigmine 2, 1
• Quantitative neuromuscular monitoring is essential to assess the degree of blockade and recovery 3
• If neostigmine must be administered after succinylcholine:
  • Ensure at least 4 responses to train-of-four (TOF) stimulation are present 3
  • Be prepared for potential prolonged ventilatory support 4
  • Monitor closely for signs of cardiovascular effects including bradycardia and AV block 6

Prevention

• For rapid sequence induction, if reversal will be needed soon after intubation, consider using rocuronium (≥0.9 mg/kg) instead of succinylcholine 7
• If using succinylcholine, allow for complete spontaneous recovery before administering any acetylcholinesterase inhibitors 1
• Always administer an anticholinergic agent (atropine 0.02 mg/kg or glycopyrrolate) when giving neostigmine to prevent muscarinic side effects 8, 3

Special Considerations

• Anticholinesterase drugs like neostigmine may not be effective in reversing Phase II block from prolonged succinylcholine administration and may actually prolong paralysis 2, 9
• In cases of suspected succinylcholine apnea due to atypical plasma cholinesterase, anticholinesterases provide only partial and unsustained antagonism 9

The interaction between neostigmine and succinylcholine represents an important clinical consideration in anesthetic practice that can significantly impact patient safety and recovery.