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溫港生
主任 亞東紀念醫院小兒部
鎂是人體內數佰種化學反應中的少量礦物質，一般危急的病人鎂的存量都會下降，繼而導致很多不良的反應。在醫學的疾病中，諸如pre-eclampsia,
eclampsia, ventricular tachycardia, congestive heart failure,
acute myocardial infarction, vascular headache, acute cerebral
insults, chronic lung diseases及asthma，鎂都曾被用作療劑。
兒童氣喘的急性發作是急診處常見的病例，對醫師來說極具挑戰性，因為到目前仍未有足夠的依據去建立一標準的治療模式；雖然beta-agonist噴霧療法仍被用作主要的治療方法，而口服類固醇與高劑量類固醇噴霧療法是阻斷病人氣道炎症反應恢復肺功能的良好用葯，但仍有部份的病人對此等葯物療效不佳。其他如Ipratropium
bromide是較弱的氣管擴張劑，在急性氣喘發作只能用作beta-agonist的輔助療劑，Theophyllin亦無比beta-agonist更強的額外療效，而且其therapeutic
range狹小，基於安全性而被列為最後一線用葯。致於Helium-oxygen mixture在中度氣喘病人並無特別成效，而Leukotreine
modifiers主要是用作慢性氣喘病人的治療，其從靜脈投予治療則仍在評估階段，也許在不久的將來會有未能預期的效果。
急性氣喘的治療主要在快速解除氣管收縮，消除氣管的發炎反應。多項研究顯示，靜脈投予或吸入鎂的氣喘療法，能有助氣管擴張劑及類固醇氣管擴張的作用，其機轉可能為阻撓鈣離子轉入細胞內參與phosphorylation反應所導致平制滑肌的收縮，所以鎂是平滑肌收縮或鬆弛的決定性因子。再者，研究結果証實，在氣喘病人的細胞內鎂的濃度比過敏性鼻炎病人及健康控制組細胞內的鎂含量都為低。臨床上投予25mg/kg或40mg/kg
(Max.2gm)的MgSO4於兒童或成人氣喘病人，尤其是對beta-agonist及類固醇療效不良者都可顯著的改善其臨床症狀分數、住院率、急診回診率，以及改善肺功能包括了FEFR及FEV1。療法是將MgSO4稀釋在0.9%
Normal saline中從靜脈投予20分鐘。其次在MgSO4治療的氣喘病人給與methocholine challenge可明顯的增加病人的PC(20)，亦即可改善病人的氣管敏感度(bronchial
hyperreactivity)。重要的在這劑量下的MgSO4並無任何的副作用報告。再者，亦可利用isotonic
magnesium sulfate作為beta-agonist的溶劑給病人作吸入性治療以增加病人peak flow
response。
結論：致於對中度或嚴重度急性氣喘發作病人是否應及早投予高劑量的MgSO4作為beta-agonist或類固醇的輔助葯物仍有待將來進一步的研究結果；但對beta-agonist或steroid
反應不佳的氣喘病人MgSO4不失為一安全的替代療法。
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