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Cyclophosphamide (CP), also known as cytophosphane among other names, is a medication used as chemotherapy and to suppress the immune system. As chemotherapy it is used to treat lymphoma,
multiple myeloma Multiple myeloma (MM), also known as plasma cell myeloma and simply myeloma, is a cancer of plasma cells, a type of white blood cell that normally produces antibodies. Often, no symptoms are noticed initially. As it progresses, bone pain, an ...
, leukemia, ovarian cancer, breast cancer, small cell lung cancer, neuroblastoma, and sarcoma. As an immune suppressor it is used in
nephrotic syndrome Nephrotic syndrome is a collection of symptoms due to kidney damage. This includes protein in the urine, low blood albumin levels, high blood lipids, and significant swelling. Other symptoms may include weight gain, feeling tired, and foamy ...
, granulomatosis with polyangiitis, and following organ transplant, among other conditions. It is taken by mouth or injection into a vein. Most people develop side effects. Common side effects include low white blood cell counts, loss of appetite, vomiting, hair loss, and bleeding from the bladder. Other severe side effects include an increased future risk of cancer,
infertility Infertility is the inability of a person, animal or plant to reproduce by natural means. It is usually not the natural state of a healthy adult, except notably among certain eusocial species (mostly haplodiploid insects). It is the normal state ...
, allergic reactions, and pulmonary fibrosis. Cyclophosphamide is in the alkylating agent and
nitrogen mustard Nitrogen mustards are cytotoxic organic compounds with the chloroethylamine (Cl(CH2)2NR2) functional group. Although originally produced as chemical warfare agents, they were the first chemotherapeutic agents for treatment of cancer. Nitrogen m ...
family of medications. It is believed to work by interfering with the duplication of DNA and the creation of
RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
. Cyclophosphamide was approved for medical use in the United States in 1959. It is on the World Health Organization's List of Essential Medicines.


Medical uses

Cyclophosphamide is used to treat cancers and
autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. At least 80 types of autoimmune diseases have been identified, with some evidence suggesting that there may be more than 100 types. Nearly a ...
s. It is used to quickly control the disease. Due to its toxicity, it is replaced as soon as possible by less toxic drugs. Regular and frequent laboratory evaluations are required to monitor kidney function, avoid drug-induced bladder complications and screen for
bone marrow toxicity Bone marrow suppression also known as myelotoxicity or myelosuppression, is the decrease in production of cells responsible for providing immunity (leukocytes), carrying oxygen (erythrocytes), and/or those responsible for normal blood clotting (t ...
.


Cancer

The main use of cyclophosphamide is with other chemotherapy agents in the treatment of lymphomas, some forms of
brain cancer A brain tumor occurs when abnormal cells form within the brain. There are two main types of tumors: malignant tumors and benign (non-cancerous) tumors. These can be further classified as primary tumors, which start within the brain, and secondar ...
, neuroblastoma, leukemia and some solid tumors. Oncovet C (Chemovet S.A.), is the first-based drug approved in Latin America for veterinary use for canine and feline cancer (carcinomas of anal sacs, bladder carcinomas, urethral carcinomas, hemangiosarcomas, lymphomas, mast cell tumor, osteosarcomas, soft tissue sarcoma), feline cancers (mammary carcinomas, hemangiosarcomas, lymphomas, plasmacytomas, chronic lymphocytic leukemia, acute myelogenous leukemia, mast cell tumor). It can be administered in different treatment schemes, such as induction therapy, adjuvant, neoadjuvant, maintenance and metronomic chemotherapy.


Autoimmune diseases

Cyclophosphamide decreases the immune system's response, and although concerns about toxicity restrict its use to patients with severe disease, it remains an important treatment for life-threatening
autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. At least 80 types of autoimmune diseases have been identified, with some evidence suggesting that there may be more than 100 types. Nearly a ...
s where disease-modifying antirheumatic drugs (DMARDs) have been ineffective. For example,
systemic lupus erythematosus Lupus, technically known as systemic lupus erythematosus (SLE), is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body. Symptoms vary among people and may be mild to severe. Comm ...
with severe
lupus nephritis Lupus nephritis is an inflammation of the kidneys caused by systemic lupus erythematosus (SLE), an autoimmune disease. It is a type of glomerulonephritis in which the glomeruli become inflamed. Since it is a result of SLE, this type of glomerulon ...
may respond to pulsed cyclophosphamide. Cyclophosphamide is also used to treat minimal change disease, severe rheumatoid arthritis, granulomatosis with polyangiitis,
Goodpasture syndrome Goodpasture syndrome (GPS), also known as anti–glomerular basement membrane disease, is a rare autoimmune disease in which antibodies attack the basement membrane in lungs and kidneys, leading to bleeding from the lungs, glomerulonephritis ...
and
multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This d ...
. Because of its potential side effects such as amenorrhea or
ovarian failure Primary ovarian insufficiency (POI) (also called premature ovarian insufficiency, premature menopause, and premature ovarian failure) is the partial or total loss of reproductive and hormonal function of the ovaries before age 40 because of fol ...
, cyclophosphamide is used for early phases of treatment and later substituted by other medications, such as mycophenolic acid or ACA.


AL amyloidosis

Cyclophosphamide, used in combination with thalidomide or
lenalidomide Lenalidomide, sold under the trade name Revlimid among others, is a medication used to treat multiple myeloma, smoldering myeloma, and myelodysplastic syndromes (MDS). For multiple myeloma, it is used after at least one other treatment and gene ...
and dexamethasone has documented efficacy as an off-label treatment of AL amyloidosis. It appears to be an alternative to the more traditional treatment with melphalan in people who are ill-suited for autologous stem cell transplant.


Graft-versus-host disease

Graft-versus-host disease Graft-versus-host disease (GvHD) is a syndrome, characterized by inflammation in different organs. GvHD is commonly associated with bone marrow transplants and stem cell transplants. White blood cells of the donor's immune system which remain wit ...
(GVHD) is a major barrier for
allogeneic stem cell transplant Hematopoietic stem-cell transplantation (HSCT) is the transplantation of multipotent hematopoietic stem cells, usually derived from bone marrow, peripheral blood, or umbilical cord blood in order to replicate inside of a patient and to produce ...
because of the immune reactions of donor T cell against the person receiving them. GVHD can often be avoided by
T-cell depletion T-cell depletion (TCD) is the process of T cell removal or reduction, which alters the immune system and its responses. Depletion can occur naturally (i.e. in HIV) or be induced for treatment purposes. TCD can reduce the risk of graft-versus-host ...
of the graft. The use of a high dose cyclophosphamide post-transplant in a half matched or haploidentical donor hematopoietic stem cell transplantation reduces GVHD, even after using a reduced
conditioning regimen Hematopoietic stem-cell transplantation (HSCT) is the transplantation of multipotent hematopoietic stem cells, usually derived from bone marrow, peripheral blood, or umbilical cord blood in order to replicate inside of a patient and to produce ...
.


Contraindications

Like other alkylating agents, cyclophosphamide is
teratogenic Teratology is the study of abnormalities of physiological development in organisms during their life span. It is a sub-discipline in medical genetics which focuses on the classification of congenital abnormalities in dysmorphology. The related t ...
and contraindicated in pregnant women ( pregnancy category D) except for life-threatening circumstances in the mother. Additional relative contraindications to the use of cyclophosphamide include lactation, active infection,
neutropenia Neutropenia is an abnormally low concentration of neutrophils (a type of white blood cell) in the blood. Neutrophils make up the majority of circulating white blood cells and serve as the primary defense against infections by destroying bacteria ...
or bladder toxicity. Cyclophosphamide is a pregnancy category D drug and causes birth defects. First trimester exposure to cyclophosphamide for the treatment of cancer or
lupus Lupus, technically known as systemic lupus erythematosus (SLE), is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body. Symptoms vary among people and may be mild to severe. Comm ...
displays a pattern of anomalies labeled "cyclophosphamide embryopathy", including growth restriction, ear and facial abnormalities, absence of digits and hypoplastic limbs.


Side effects

Adverse drug reactions from cyclophosphamide are related to the cumulative medication dose and include
chemotherapy-induced nausea and vomiting Chemotherapy-induced nausea and vomiting (CINV) is a common side-effect of many cancer treatments. Nausea and vomiting are two of the most feared cancer treatment-related side effects for cancer patients and their families. In 1983, Coates et al. f ...
, bone marrow suppression,
stomach ache Abdominal pain, also known as a stomach ache, is a symptom associated with both non-serious and serious medical issues. Common causes of pain in the abdomen include gastroenteritis and irritable bowel syndrome. About 15% of people have a m ...
, hemorrhagic cystitis, diarrhea, darkening of the skin/nails, alopecia (hair loss) or thinning of hair, changes in color and texture of the hair, lethargy, and profound gonadotoxicity. Other side effects may include easy bruising/bleeding, joint pain, mouth sores, slow-healing existing wounds, unusual decrease in the amount of urine or unusual tiredness or weakness. Potential side effects also include leukopenia, infection, bladder toxicity, and cancer. Pulmonary injury appears rare, but can present with two clinical patterns: an early, acute pneumonitis and a chronic, progressive fibrosis.
Cardiotoxicity Cardiotoxicity is the occurrence of heart dysfunction as electric or muscle damage, resulting in heart toxicity. The heart becomes weaker and is not as efficient in pumping blood. Cardiotoxicity may be caused by chemotherapy (a usual example is th ...
is a major problem with people treated with higher dose regimens. High-dose intravenous cyclophosphamide can cause the syndrome of inappropriate antidiuretic hormone secretion (SIADH) and a potentially fatal hyponatremia when compounded by intravenous fluids administered to prevent drug-induced cystitis. While SIADH has been described primarily with higher doses of cyclophosphamide, it can also occur with the lower doses used in the management of inflammatory disorders.


Bladder bleeding

Acrolein Acrolein (systematic name: propenal) is the simplest unsaturated aldehyde. It is a colorless liquid with a piercing, acrid smell. The smell of burnt fat (as when cooking oil is heated to its smoke point) is caused by glycerol in the burning fa ...
is toxic to the bladder
epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
and can lead to hemorrhagic cystitis, which is associated with microscopic or gross hematuria and occasionally dysuria. Risks of hemorrhagic cystitis can be minimized with adequate fluid intake, avoidance of nighttime dosage and mesna (sodium 2-mercaptoethane sulfonate), a sulfhydryl donor which binds and detoxifies acrolein. Intermittent dosing of cyclophosphamide decreases cumulative drug dose, reduces bladder exposure to acrolein and has equal efficacy to daily treatment in the management of
lupus nephritis Lupus nephritis is an inflammation of the kidneys caused by systemic lupus erythematosus (SLE), an autoimmune disease. It is a type of glomerulonephritis in which the glomeruli become inflamed. Since it is a result of SLE, this type of glomerulon ...
.


Infection

Neutropenia Neutropenia is an abnormally low concentration of neutrophils (a type of white blood cell) in the blood. Neutrophils make up the majority of circulating white blood cells and serve as the primary defense against infections by destroying bacteria ...
or lymphopenia arising secondary to cyclophosphamide usage can predispose people to a variety of bacterial, fungal and
opportunistic infection An opportunistic infection is an infection caused by pathogens (bacteria, fungi, parasites or viruses) that take advantage of an opportunity not normally available. These opportunities can stem from a variety of sources, such as a weakened immune ...
s. No published guidelines cover PCP prophylaxis for people with rheumatological diseases receiving immunosuppressive drugs, but some advocate its use when receiving high-dose medication.


Infertility

Cyclophosphamide has been found to significantly increase the risk of premature menopause in females and of
infertility Infertility is the inability of a person, animal or plant to reproduce by natural means. It is usually not the natural state of a healthy adult, except notably among certain eusocial species (mostly haplodiploid insects). It is the normal state ...
in males and females, the likelihood of which increases with cumulative drug dose and increasing patient age. Such infertility is usually temporary, but can be permanent. The use of
leuprorelin Leuprorelin, also known as leuprolide, is a manufactured version of a hormone used to treat prostate cancer, breast cancer, endometriosis, uterine fibroids, as part of transgender hormone therapy, for early puberty, or to perform chemical castra ...
in women of reproductive age before administration of intermittently dosed cyclophosphamide may diminish the risks of premature menopause and infertility.


Cancer

Cyclophosphamide is carcinogenic and may increase the risk of developing lymphomas, leukemia, skin cancer, transitional cell carcinoma of the bladder or other malignancies. Myeloproliferative neoplasms, including acute leukemia, non-Hodgkin lymphoma and
multiple myeloma Multiple myeloma (MM), also known as plasma cell myeloma and simply myeloma, is a cancer of plasma cells, a type of white blood cell that normally produces antibodies. Often, no symptoms are noticed initially. As it progresses, bone pain, an ...
, occurred in 5 of 119 rheumatoid arthritis patients within the first decade after receiving cyclophosphamide, compared with one case of
chronic lymphocytic leukemia Chronic lymphocytic leukemia (CLL) is a type of cancer in which the bone marrow makes too many lymphocytes (a type of white blood cell). Early on, there are typically no symptoms. Later, non-painful lymph node swelling, feeling tired, fever, nigh ...
in 119 rheumatoid arthritis patients with no history. Secondary acute myeloid leukemia (therapy-related AML, or "t-AML") is thought to occur either by cyclophosphamide-inducing mutations or selecting for a high-risk myeloid clone. This risk may be dependent on dose and other factors, including the condition, other agents or treatment modalities (including
radiotherapy Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radia ...
), treatment length and intensity. For some regimens, it is rare. For instance, CMF-therapy for breast cancer (where the cumulative dose is typically less than 20 grams of cyclophosphamide) carries an AML risk of less than 1/2000, with some studies finding no increased risk compared to background. Other treatment regimens involving higher doses may carry risks of 1–2% or higher. Cyclophosphamide-induced AML, when it happens, typically presents some years after treatment, with incidence peaking around 3–9 years. After nine years, the risk falls to background. When AML occurs, it is often preceded by a myelodysplastic syndrome phase, before developing into overt acute leukemia. Cyclophosphamide-induced leukemia will often involve complex cytogenetics, which carries a worse prognosis than ''de novo'' AML.


Pharmacology

Oral cyclophosphamide is rapidly absorbed and then converted by mixed-function
oxidase In biochemistry, an oxidase is an enzyme that catalyzes oxidation-reduction reactions, especially one involving dioxygen (O2) as the electron acceptor. In reactions involving donation of a hydrogen atom, oxygen is reduced to water (H2O) or hydro ...
enzymes (
cytochrome P450 Cytochromes P450 (CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are ...
system) in the liver to active metabolites. The main active metabolite is
4-hydroxycyclophosphamide 4-Hydroxycyclophosphamide is in the class of oxazaphosphorine compounds, and is the main, active metabolite of cyclophosphamide and of mafosfamide after they partially metabolized by cytochrome P450. It is then partially tautomerized into aldoph ...
, which exists in equilibrium with its
tautomer Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hydr ...
,
aldophosphamide Cyclophosphamide (CP), also known as cytophosphane among other names, is a medication used as chemotherapy and to suppress the immune system. As chemotherapy it is used to treat lymphoma, multiple myeloma, leukemia, ovarian cancer, breast cancer ...
. Most of the aldophosphamide is then oxidised by the enzyme aldehyde dehydrogenase (ALDH) to make
carboxycyclophosphamide Carboxycyclophosphamide is an inactive metabolite of the cytotoxic antineoplastic drug cyclophosphamide. In the metabolic pathway of cyclophosphamide inactivation it first metabolizes to 4-hydroxycyclophosphamide, then partially tautomerizes into ...
. A small proportion of aldophosphamide freely diffuses into cells, where it is decomposed into two compounds, phosphoramide mustard and acrolein. The active metabolites of cyclophosphamide are highly protein bound and distributed to all tissues, are assumed to cross the placenta and are known to be present in
breast milk Breast milk (sometimes spelled as breastmilk) or mother's milk is milk produced by mammary glands located in the breast of a human female. Breast milk is the primary source of nutrition for newborns, containing fat, protein, carbohydrates ( lacto ...
. It is specifically in the oxazaphosphorine group of medications. Cyclophosphamide metabolites are primarily excreted in the urine unchanged, and drug dosing should be appropriately adjusted in the setting of renal dysfunction. Drugs altering hepatic microsomal enzyme activity (e.g.,
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
,
barbiturates Barbiturates are a class of depressant drugs that are chemically derived from barbituric acid. They are effective when used medically as anxiolytics, hypnotics, and anticonvulsants, but have physical and psychological addiction potential as ...
,
rifampicin Rifampicin, also known as rifampin, is an ansamycin antibiotic used to treat several types of bacterial infections, including tuberculosis (TB), mycobacterium avium complex, ''Mycobacterium avium'' complex, leprosy, and Legionnaires’ disease. ...
, or phenytoin) may result in accelerated metabolism of cyclophosphamide into its active metabolites, increasing both pharmacologic and toxic effects of the drug; alternatively, drugs that inhibit hepatic microsomal enzymes (e.g.
corticosteroids Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involve ...
,
tricyclic antidepressant Tricyclic antidepressants (TCAs) are a class of medications that are used primarily as antidepressants, which is important for the management of depression. They are second-line drugs next to SSRIs. TCAs were discovered in the early 1950s and we ...
s, or allopurinol) result in slower conversion of cyclophosphamide into its metabolites and consequently reduced therapeutic and toxic effects. Cyclophosphamide reduces plasma pseudocholinesterase activity and may result in prolonged
neuromuscular blockade Neuromuscular-blocking drugs block neuromuscular transmission at the neuromuscular junction, causing paralysis of the affected skeletal muscles. This is accomplished via their action on the post-synaptic acetylcholine (Nm) receptors. In clin ...
when administered concurrently with succinylcholine. Tricyclic antidepressants and other anticholinergic agents can result in delayed bladder emptying and prolonged bladder exposure to acrolein.


Mechanism of action

The main effect of cyclophosphamide is due to its metabolite phosphoramide mustard. This metabolite is only formed in cells that have low levels of
ALDH Aldehyde dehydrogenases () are a group of enzymes that catalyse the oxidation of aldehydes. They convert aldehydes (R–C(=O)) to carboxylic acids (R–C(=O)). The oxygen comes from a water molecule. To date, nineteen ALDH genes have b ...
. Phosphoramide mustard forms DNA crosslinks both between and within DNA strands at guanine N-7 positions (known as interstrand and intrastrand crosslinkages, respectively). This is irreversible and leads to cell
apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes incl ...
. Cyclophosphamide has relatively little typical chemotherapy toxicity as ALDHs are present in relatively large concentrations in bone marrow stem cells, liver and intestinal
epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
. ALDHs protect these actively proliferating tissues against toxic effects of phosphoramide mustard and acrolein by converting
aldophosphamide Cyclophosphamide (CP), also known as cytophosphane among other names, is a medication used as chemotherapy and to suppress the immune system. As chemotherapy it is used to treat lymphoma, multiple myeloma, leukemia, ovarian cancer, breast cancer ...
to
carboxycyclophosphamide Carboxycyclophosphamide is an inactive metabolite of the cytotoxic antineoplastic drug cyclophosphamide. In the metabolic pathway of cyclophosphamide inactivation it first metabolizes to 4-hydroxycyclophosphamide, then partially tautomerizes into ...
that does not give rise to the toxic metabolites phosphoramide mustard and acrolein. This is because carboxycyclophosphamide cannot undergo β-elimination (the carboxylate acts as an electron-donating group, nullifying the potential for transformation), preventing nitrogen mustard activation and subsequent alkylation. Cyclophosphamide induces beneficial immunomodulatory effects in adaptive immunotherapy. Suggested mechanisms include: # Elimination of T regulatory cells (CD4+CD25+ T cells) in naive and tumor-bearing hosts # Induction of T cell growth factors, such as type I IFNs, and/or # Enhanced grafting of adoptively transferred, tumor-reactive effector T cells by the creation of an immunologic space niche. Thus, cyclophosphamide
preconditioning In mathematics, preconditioning is the application of a transformation, called the preconditioner, that conditions a given problem into a form that is more suitable for numerical solving methods. Preconditioning is typically related to reducing ...
of recipient hosts (for donor T cells) has been used to enhance immunity in naïve hosts, and to enhance adoptive T cell immunotherapy regimens, as well as active vaccination strategies, inducing objective antitumor immunity.


History

As reported by O. M. Colvin in his study of the development of cyclophosphamide and its clinical applications, Cyclophosphamide and the related
nitrogen mustard Nitrogen mustards are cytotoxic organic compounds with the chloroethylamine (Cl(CH2)2NR2) functional group. Although originally produced as chemical warfare agents, they were the first chemotherapeutic agents for treatment of cancer. Nitrogen m ...
–derived alkylating agent ifosfamide were developed by Norbert Brock and ASTA (now Baxter Oncology). Brock and his team synthesised and screened more than 1,000 candidate oxazaphosphorine compounds. They converted the base nitrogen mustard into a nontoxic "transport form". This transport form was a prodrug, subsequently actively transported into cancer cells. Once in the cells, the prodrug was
enzymatically Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...
converted into the active, toxic form. The first clinical trials were published at the end of the 1950s. In 1959 it became the eighth cytotoxic anticancer agent to be approved by the
FDA The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food s ...
.


Society and culture

The abbreviation CP is common, although abbreviating drug names is not best practice in medicine.


Research

Because of its impact on the immune system, it is used in animal studies. Rodents are injected intraperitoneally with either a single dose of 150 mg/kg or two doses (150 and 100 mg/kg) spread over two days. This can be used for applications such as: * The
EPA The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
may be concerned about potential human pathogenicity of an engineered microbe when conducting an MCAN review. Particularly for bacteria with potential consumer exposure they require testing of the microbe on immuno-compromised rats. * Cyclophosphamide provides a positive control when studying immune-response of a new drug.


References


External links

* * Novel cyclic phosphoric acid ester amides, and the production thereof. (patent for cyclophosphamide). {{portal bar, Medicine Hepatotoxins IARC Group 1 carcinogens Nitrogen mustards Organochlorides Oxazaphosphinans Phosphorodiamidates Prodrugs Chloroethyl compounds World Health Organization essential medicines Wikipedia medicine articles ready to translate