What is Cyclophosphamide (Cyc)?
The abbreviation "Cyc" in a medical context most commonly refers to cyclophosphamide, a powerful drug used in the treatment of many types of cancer and certain autoimmune conditions [1.2.1, 1.4.3]. It belongs to a class of medications known as alkylating agents [1.3.3]. While primarily known as a chemotherapy agent, its ability to suppress the immune system makes it valuable for treating non-cancerous diseases as well, such as nephrotic syndrome in children and severe forms of lupus and rheumatoid arthritis [1.3.3, 1.4.4].
Cyclophosphamide is available under brand names like Cytoxan and Neosar [1.8.1, 1.8.2]. It is a prodrug, meaning it is converted into its active, cell-killing forms by enzymes in the liver [1.3.1]. This activation is crucial for its therapeutic effect but also contributes to its toxicity.
How Does Cyclophosphamide Work?
The primary mechanism of action for cyclophosphamide involves its active metabolites, phosphoramide mustard and acrolein [1.3.1]. The phosphoramide mustard is an alkylating agent, which means it works by binding to and damaging the DNA of cells [1.3.1, 1.4.2]. It forms cross-links within the DNA strands, which makes it impossible for the cell to replicate its DNA and divide. This action is particularly effective against rapidly dividing cells, which is a hallmark of cancer [1.3.3]. This DNA damage is permanent and ultimately triggers apoptosis, or programmed cell death [1.3.1]. The other major metabolite, acrolein, does not have anti-tumor activity but is responsible for some of the drug's significant side effects, most notably bladder toxicity [1.3.1, 1.3.2].
What is Cyclophosphamide Used to Treat?
Cyclophosphamide has a broad range of applications due to its cytotoxic and immunosuppressive properties.
- Cancers: It is used alone or in combination with other drugs to treat a wide variety of cancers [1.10.1]. These include lymphomas (Hodgkin's and non-Hodgkin's), multiple myeloma, leukemias (CLL, CML, AML, ALL), breast and ovarian cancers, neuroblastoma, and retinoblastoma [1.3.3, 1.4.2, 1.10.1].
- Autoimmune Diseases: In rheumatology and immunology, cyclophosphamide is used to suppress an overactive immune system in severe or life-threatening autoimmune diseases [1.2.1]. This includes conditions like severe systemic lupus erythematosus (SLE), vasculitis, and rheumatoid arthritis [1.4.4].
- Kidney Disease: It is also used to treat nephrotic syndrome, a kidney disorder caused by kidney damage, specifically in children when other treatments have failed [1.3.3, 1.10.1].
Common and Serious Side Effects
While effective, cyclophosphamide has a narrow therapeutic index and is associated with significant toxicity [1.2.1].
Common Side Effects (occurring in >30% of patients):
- Bone Marrow Suppression (Myelosuppression): This is a very common effect, leading to low counts of white blood cells (leukopenia), red blood cells (anemia), and platelets (thrombocytopenia). This increases the risk of infection, fatigue, and bleeding [1.4.2, 1.7.2].
- Nausea and Vomiting: These are common, especially with higher doses, and often require anti-nausea medications [1.4.4, 1.7.2].
- Hair Loss (Alopecia): Hair loss is common and typically begins 3-6 weeks after starting therapy, but it is usually temporary [1.7.2].
- Loss of Fertility: The drug can interfere with the menstrual cycle and stop sperm production, sometimes causing permanent infertility in both men and women [1.4.4, 1.6.1].
Serious Side Effects:
- Urinary Tract and Bladder Toxicity: A metabolite called acrolein can cause severe bladder irritation, leading to hemorrhagic cystitis (bleeding from the bladder). Staying well-hydrated is critical to reduce this risk [1.4.2, 1.9.3]. In the long term, there's an increased risk of bladder cancer [1.7.1, 1.9.2].
- Cardiotoxicity: At high doses, cyclophosphamide can cause heart problems, including inflammation of the heart muscle (myocarditis) and heart failure [1.4.2, 1.9.3].
- Secondary Cancers: Long-term use increases the risk of developing other cancers, particularly leukemia and bladder cancer [1.4.2, 1.7.1].
- Lung Toxicity: Though rare, it can cause lung scarring (pulmonary fibrosis), which may develop years after treatment [1.4.2, 1.9.3].
Cyclophosphamide vs. Cyclosporine: A Comparison
Though both can be used as immunosuppressants, cyclophosphamide and cyclosporine are very different drugs.
| Feature | Cyclophosphamide | Cyclosporine |
|---|---|---|
| Drug Class | Alkylating Agent [1.3.3] | Calcineurin Inhibitor [1.5.5] |
| Primary Use | Chemotherapy (cancer), Immunosuppression (autoimmune diseases) [1.2.1, 1.3.3] | Immunosuppression (organ transplant rejection, autoimmune diseases) [1.5.5] |
| Mechanism | Damages DNA to prevent cell replication [1.3.1] | Inhibits T-cell activation, preventing an immune response |
| Key Side Effects | Bone marrow suppression, hemorrhagic cystitis, secondary cancers [1.4.2, 1.7.2] | Kidney toxicity, high blood pressure, neurotoxicity [1.5.1] |
| Common Abbreviation | Cyc, CPH | CsA |
Administration and Precautions
Cyclophosphamide can be administered in two ways:
- Orally: as a daily tablet or capsule [1.6.2]. Oral doses should be taken in the morning with plenty of fluids to help prevent bladder issues [1.4.2, 1.10.2].
- Intravenously (IV): as an injection into a vein, typically given in a hospital or clinic setting [1.6.4].
Patients undergo regular monitoring, including blood tests to check blood counts and liver and kidney function [1.6.1, 1.10.3]. Because it can harm a fetus, effective birth control is mandatory for both men and women during and for a period after treatment [1.6.1, 1.10.1]. Live vaccines should be avoided while taking this medication [1.4.4].
Conclusion
Cyclophosphamide, commonly known as "cyc," is a cornerstone medication in oncology and rheumatology. Its power as an alkylating agent makes it highly effective at destroying rapidly dividing cancer cells and taming a dangerously overactive immune system. However, this strength comes with substantial risks, including severe side effects like bone marrow suppression, bladder toxicity, and the long-term potential for secondary malignancies. Careful patient selection, rigorous monitoring, and proactive management of side effects are essential for using this potent drug safely and effectively.
For more detailed information, consult the MedlinePlus drug information page.
