The present invention provides a method for preparing an intravenously administrable aqueous composition comprising acetaminophen, and optionally one or more non-steroidal anti-inflammatory drugs (NSAIDs), whereby the dissolved oxygen of the composition in a closed container is maximally 1.0 ppm, said method comprises rinsing at least once a compounding vessel with water of a temperature of at least 80℃, thereby heating the vessel and creating an oxygen low environment in said vessel； and in said rinsed vessel dissolving acetaminophen in water for injection, said water for injection is at a temperature of at least 80℃, whereby optionally one or more NSAIDS are added prior or after dissolving of acetaminophen.本發明提供製備含乙醯胺苯酚及任意一或多種非類固醇抗發炎藥物(NSAID)之靜脈內可投予的水性組成物之方法，其中在封閉容器中的該組成物之溶氧量為最大1.0ppm，該方法包含將化合容器以溫度至少80℃之水沖洗至少一次，由此加熱該容器且在該容器中創造低氧環境；及將乙醯胺苯酚溶解在該沖洗之容器中的注射用水中，該注射用水係在至少80℃之溫度下，其中任意一或多種NSAID係在溶解乙醯胺苯酚之前或之後添加。
