肉毒桿菌毒素A型：從毒藥到救人良藥

Botulinum Toxin Type A: From Toxin to Therapeutic Agent

肉毒桿菌是一種愛好生長在缺氧環境的細菌，在罐頭食品或密封醃漬食物中能以芽孢型式極富抵抗力的生存著。人們以往因誤食此細菌所污染的食物，便產生視力模糊，口渴全身無力以致呼吸肌肉麻痺、呼吸困難、嚴重時也可導致死亡。肉毒桿菌毒素是世上最毒的毒素之一。此毒素依據血清抗原分類，至少有七型；A、B、C（C1和C2）、D、E、F和G型。其中又以A型最具有毒性及療效最久，而月也最廣為臨床使用。近十年來，肉毒桿菌毒素卻變成救人的良藥，藉其使注射肌肉麻痺，透過阻斷神經肌肉接合處突觸前乙醯膽鹼釋放的機轉，來治療因肢體或臉部肌肉過度收縮或痙攣，而導致身體扭曲行動不便的患者。目前，臨床上在眼科方面如斜視；在神經科方面如眼輪匝肌痙攣症、半側面神經痙攣症、斜頸症（一種肌緊張不全症）、痙攣性聲音障礙和下頜閉口緊縮症，都已證實其成效良好。對其他相關病症的運用上，也有日益擴大使用的情形。從動物實驗和人體治療上證實，在治療劑量內使用肉毒桿菌毒素，沒有明顯和永久下可逆的局部或全身性的副作用，而且安全性和耐受性也相當高。不過有關孩童和孕婦的使用及劑量，長期注射治療的效果，以及人體最大劑量的使用，仍然需要日後更進一步的研究。

The botulinum toxin (BTX) is one of the most lethal poisons known to the mankind. With ho toxic qualities, it has proved to be a remarkable therapeutic agent for thousands of victims with a poorly understood group of neurological conditions characterized by uncontrollable, excessive and frequently painful muscular contractions. BTX is a presynaptic neuromuscular blocking agent. BTX, when injected intramuscularly in minute quantities, can produce selective muscle weakness followed by symptomatic relief with improved functional disability. It has been proved to be effective in the management of the strabismus, blepharospasm, hemifacial spasm, cervical dystonia, spasmodic dysphonia and the jaw closing dystonia. It may also be useful for a long list of medical conditions. In studies on various animal species have shown no serious adverse local or systemic reactions following intramuscular administration of the BTX at therapeutic doses. However, its safe dosage, long-term effects, all the use for children and in pregnancy, need further studies.