治療咳嗽藥物一般是通過直接抑制腦部咳嗽中樞而發揮作用, 當中可待因(codeine)和右美沙芬(dextromethorphan)是咳嗽治療藥的常用成份之一。右美沙芬具有與codeine相當的止咳效果, 但不具有止痛作用, 一般情況下是安全和易耐受的, 然而當右美沙芬的劑量超出10mg/kg時, 可能會出現嚴重毒性反應, 包括呼吸抑制。由於基因的差異性, 約有10%的人士對右美沙芬的酶降解代謝較慢, 從而產生血藥濃度過高及造成危險的情況。右美沙芬的不良反應雖然罕見, 但包括嘔吐在內的胃腸不適﹑嗜睡和頭暈時有發生。目前, 文獻並沒有收載右美沙芬用於兩歲以下小孩的正規治療方案。
基於右美沙芬在兩歲以下兒童的劑量還未確定, 且該藥物用於兩歲以下小孩的安全性還未證實, 藥物監測暨管理處提醒醫生﹑藥劑師及其他衛生專業人士：
1. 應儘量避免處方右美沙芬於兩歲以下的兒童病人, 倘必要時, 醫生應根據臨床情況謹慎作風險效益評估, 並按個體需要訂定用藥劑量。
2. 提醒兒童的家長和照護者須嚴格依從醫生指示服用含有右美沙芬的藥物, 如出現不良反應, 須立即就診。
3. 提醒市民右美沙芬屬醫生處方藥物, 須嚴格依照醫囑服用。
Antitussives elicict their clinical effect by directly inhibiting the cough center in the brain, of which codeine and dextromethorphan are compounds found in cough medicines. Dextromethorphan has equal antitussive effects as codeine but does not possess analgesic property. It is generally safe and well tolerated, but serious toxicity including respiratory distress can be seen at doses of 10 mg/kg or greater. Approximately 10% of the population are slow metabolizers of dextromethorphan, owing to a genetic polymorphism for its enzymatic degradation, the plasma concentration of the medication in this group of patients will be elevated, placing them at higher risk. Adverse effects with dextromethorphan are rare, but nausea and/or other gastrointestinal disturbances, slight drowsiness, and dizziness sometimes occur. Currently, it is not well documented that dextromethorphan being regularly used in children <2 years of age.
Since the absence of dosing recommendations of dextrommethorphan and the safety has not been established in children less than 2 years old, Division of Pharmacovigilance and Pharmacoeconomics would like to recommend the following important messages for physicians, pharmacists, and other healthcare professionals:
1. physicians should avoid prescribing dextromethorphan-containing medication for pediatric patients less than 2 years old unless, otherwise, absolutely necessary after cautious clinical valuation validating benefit over risk. In situation that warrants such use, dosage of dextromethorphan for this group of patients must be individualized.
2. remind parents and caregivers to strictly adhere and follow the instructions as given by the prescribers when administering dextromethorphan-containing medication to their children. Seek for immediate medical attention in case of adverse reactions.
3. remind the public that as dextromethorphan is classified as Prescription Medication Only (PMO), ensure strict adherence to the instructions as given by the prescribers when administering dextromethorphan-containing medication.
參考資料/References and website：
1. Current Opinions in Pediatrics 2006, 18: 184-188, p. 185
2. Dynamed.com - https://dynaweb.ebscohost.com/Detail?id=AN+233183&sid=878644f3-afe9-4451-9913-c3b9802f0f61@sessionmgr11