中文：

注射用环磷酰胺是一种抗肿瘤药物，主要用于治疗各种恶性肿瘤。但是，什么时候使用注射用环磷酰胺呢？

首先，注射用环磷酰胺通常用于对肿瘤化疗或放疗无效的患者。当其他治疗方法无法控制肿瘤的生长或复发时，医生可能会考虑使用注射用环磷酰胺。此外，注射用环磷酰胺也常用于治疗多发性骨髓瘤和淋巴瘤等恶性肿瘤。

其次，注射用环磷酰胺的使用方法通常是将其溶解在生理盐水中，然后通过静脉注射给予患者。医生会根据患者的具体情况来决定注射用环磷酰胺的剂量和频率。通常，注射用环磷酰胺的使用会伴随其他药物治疗或放疗等综合治疗措施。

需要注意的是，注射用环磷酰胺是一种副作用比较严重的药物。常见的副作用包括恶心、呕吐、脱发、骨髓抑制和出血等。因此，在使用注射用环磷酰胺时，医生需要严格掌握药物的适应症和剂量，并注意密切观察患者的反应和生命体征。

总的来说，注射用环磷酰胺是一种在肿瘤治疗中非常重要的药物，但需要在医生的指导下使用。只有在特定的情况下，如其他治疗方法无效或患者处于危重病情时，医生才会考虑使用注射用环磷酰胺。

英文：

Intravenous Cyclophosphamide is an anti-tumor drug used mainly to treat various malignant tumors. However, when is it used?

Firstly, intravenous Cyclophosphamide is usually used for patients who are refractory to tumor chemotherapy or radiotherapy. When other treatments cannot control tumor growth or recurrence, doctors may consider using intravenous Cyclophosphamide. In addition, intravenous Cyclophosphamide is also commonly used to treat malignant tumors such as multiple myeloma and lymphoma.

Secondly, the use method of intravenous Cyclophosphamide is usually to dissolve it in physiological saline and then inject it intravenously to the patient. Doctors will decide the dose and frequency of intravenous Cyclophosphamide based on the specific condition of the patient. Usually, the use of intravenous Cyclophosphamide will be accompanied by other drug treatments or comprehensive treatment measures such as radiotherapy.

It should be noted that intravenous Cyclophosphamide has serious side effects. Common side effects include nausea, vomiting, hair loss, bone marrow suppression, and bleeding. Therefore, when using intravenous Cyclophosphamide, doctors need to strictly control the indications and doses of the drug, and pay attention to closely observing the patient's reaction and vital signs.

Overall, intravenous Cyclophosphamide is a very important drug in tumor treatment, but it should be used under the guidance of a doctor. Only in specific situations, such as other treatment methods are ineffective or patients are in critical condition, doctors will consider using intravenous Cyclophosphamide.