Magnesium
Mg2+ is a cation that is important for neurotransmission and neuromuscular excitability. Magnesium:
- Inhibits ACh release at the NMJ
- Acts a cofactor in multiple enzyme systems
- Is important in the production of:
| Property | Action |
|---|---|
| Uses | HypoMg, arrhythmia, eclampsia, tocolysis, barium poisoning, asthma, tetanus, autonomic hyperreflexia |
| Presentation | 2mmol.ml-1, made up into 10mmol in 100ml for peripheral administration |
| Route of Administration | PO/IV |
| Dosing | IV: 10-20 mmol |
| Distribution | 30% protein bound |
| Elimination | Significant urinary excretion, even when deficient |
| Resp | Bronchodilation |
| CVS | ↓ SVR, hypotension, ↓HR |
| CNS | CNS depression, anticonvulsant |
| GU | ↓ Uterine tone and contractility |
Clinical Effects of Magnesium
| [Plasma] | Effect |
|---|---|
| < 0.7 mmol.L-1 | Arrhythmia |
| 4-6 mmol.L-1 | Nausea, hyporeflexia, speech impairment |
| 6-10 mmol.L-1 | Weakness, respiratory depression, bradycardia |
| > 10 mmol.L-1 | Cardiac arrest |
References
- Smith S, Scarth E, Sasada M. Drugs in Anaesthesia and Intensive Care. 4th Ed. Oxford University Press. 2011.
- Peck TE, Hill SA. Pharmacology for Anaesthesia and Intensive Care. 4th Ed. Cambridge University Press. 2014.
- Rang HP, Dale MM, Ritter JM, Flower RJ. Rang and Dale's Pharmacology. 6th Ed. Churchill Livingstone.