Succinylcholine is the ultra-short-acting muscle relaxant used to place the breathing tube in emergencies (full stomach) and in short procedures. It paralyses muscles in under a minute and the effect wears off in 5–10 minutes.
Also known as: Succinilcolina, Anectine
Magnesium sulphate potentiates the neuromuscular blockade of suxamethonium, potentially prolonging apnoea and respiratory weakness.
Mg2+ inhibits presynaptic acetylcholine release and depresses motor plate excitability, reinforcing the depolarising block (MgSO4 and succinylcholine labels).
Apnoea duration, ventilation, serum Mg2+.
Prolonged apnoea, respiratory weakness after reversal.
In pre-eclampsia treated with MgSO4 and general anaesthesia, inform the anaesthesiologist; have ventilatory support available; consider blockade monitoring.
DailyMed — Magnesium Sulfate Injection label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=5b4b4805-a8ff-4efe-94bc-411090ab5f9c; Succinylcholine Chloride Injection label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=efe5a242-5ba0-4b14-844c-206a79850d81
No documented food or drink interactions.
Suxamethonium releases potassium (up to +1 mmol/l) — potentially fatal in established hyperkalaemia, burns, crush or denervation.
Confirm normal potassium before induction in at-risk patients.
EMC-UK — suxamethonium SmPC 4.3 (hyperkalaemia, burns, crush).
In myasthenia the depolarising block is unpredictable (prolonged phase I) — reduced dose and mandatory monitoring.
Reduced dose; monitor neuromuscular transmission.
EMC-UK — suxamethonium SmPC 4.4 (myasthenia).
No specific Annex 1 entry; suxamethonium is the blocker of choice for rapid-sequence intubation (including urgent caesarean) with long experience — it does not cross the placenta at clinical doses. Known risks: prolonged apnoea in newborns and in mothers with plasma cholinesterase deficiency (atypical), malignant hyperthermia (family history = avoid), and hyperkalaemia in maternal denervation/burn states.
Compatible for rapid-sequence intubation (RSI); ask about family history of malignant hyperthermia and prolonged apnoea; avoid in maternal hyperkalaemia.
Compatible — it does not cross the placenta and is rapidly hydrolysed by maternal plasma cholinesterase before passing into milk.
EMC-UK (MHRA) — Suxamethonium chloride SmPC: https://www.medicines.org.uk/emc/product/2872/smpc (section 4.6).
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Fasciculations (10–30 s) followed by flaccid paralysis (45–60 s after dose; duration 5–10 min).
Nicotinic receptor depolarising agonist: keeps the receptor depolarised and insensitive (phase I); not reversible by neostigmine (which would worsen it).
IV exclusive; action < 1 min after brachial infusion.
Rapid hydrolysis by plasma butyrylcholinesterase (pseudocholinesterase) to succinylmonocholine and choline; renal excretion.
~ 3–6 min (pseudocholinesterase deficiency: up to 4–8 h).
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
