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2D Structure
Also known as: 55-98-1, Myleran, Busulphan, Sulphabutin, Leucosulfan, Busulfex
Molecular Formula
C6H14O6S2
Molecular Weight
246.3  g/mol
InChI Key
COVZYZSDYWQREU-UHFFFAOYSA-N
FDA UNII
G1LN9045DK

An alkylating agent having a selective immunosuppressive effect on BONE MARROW. It has been used in the palliative treatment of chronic myeloid leukemia (MYELOID LEUKEMIA, CHRONIC), but although symptomatic relief is provided, no permanent remission is brought about. According to the Fourth Annual Report on Carcinogens (NTP 85-002, 1985), busulfan is listed as a known carcinogen.
Busulfan is an Alkylating Drug. The mechanism of action of busulfan is as an Alkylating Activity.
1 2D Structure

2D Structure

2 Identification
2.1 Computed Descriptors
2.1.1 IUPAC Name
4-methylsulfonyloxybutyl methanesulfonate
2.1.2 InChI
InChI=1S/C6H14O6S2/c1-13(7,8)11-5-3-4-6-12-14(2,9)10/h3-6H2,1-2H3
2.1.3 InChI Key
COVZYZSDYWQREU-UHFFFAOYSA-N
2.1.4 Canonical SMILES
CS(=O)(=O)OCCCCOS(=O)(=O)C
2.2 Other Identifiers
2.2.1 UNII
G1LN9045DK
2.3 Synonyms
2.3.1 MeSH Synonyms

1. Busulfan Wellcome

2. Busulfex

3. Busulphan

4. Glyzophrol

5. Myelosan

6. Mylran

7. Mylecytan

8. Myleran

9. N-butane-1,3-di(methylsulfonate)

10. Wellcome, Busulfan

2.3.2 Depositor-Supplied Synonyms

1. 55-98-1

2. Myleran

3. Busulphan

4. Sulphabutin

5. Leucosulfan

6. Busulfex

7. Myelosan

8. Citosulfan

9. Mielucin

10. Misulban

11. Mitostan

12. Myeloleukon

13. Mylecytan

14. Sulfabutin

15. Mablin

16. Mielevcin

17. Milecitan

18. Mielosan

19. Mileran

20. Butane-1,4-diyl Dimethanesulfonate

21. Buzulfan

22. 1,4-dimesyloxybutane

23. 1,4-butanediol Dimethanesulfonate

24. Myeleukon

25. Busulfanum

26. Myelosanum

27. 1,4-dimethanesulfonoxybutane

28. Tetramethylene Dimethane Sulfonate

29. 1,4-butanediol, Dimethanesulfonate

30. Busilvex

31. Busulfano

32. Busulphane

33. 1,4-dimethylsulfonyloxybutane

34. Nci-c01592

35. 1,4-dimethanesulfonyloxybutane

36. 1,4-bis(methanesulfonoxy)butane

37. 1,4-butanediol Dimethylsulfonate

38. 1,4-dimethylsulfonoxybutane

39. 1,4-bis(methanesulfonyloxy)butane

40. Gt 41

41. 4-methylsulfonyloxybutyl Methanesulfonate

42. Nsc-750

43. Cb 2041

44. 1,4-butanediol Dimethanesulphonate

45. An 33501

46. Methanesulfonic Acid, Tetramethylene Ester

47. Tetramethylene Bis(methanesulfonate)

48. 1,4-dimethanesulphonyloxybutane

49. Nsc 750

50. Tetramethylenester Kyseliny Methansulfonove

51. C.b. 2041

52. X 149

53. Gt 2041

54. Tetramethylene Bis[methanesulfonate]

55. 1,4-butanediol, Dimethanesulphonate

56. Nsc750

57. 1,4-bis[methanesulfonoxy]butane

58. Chebi:28901

59. 2041 C. B.

60. G.t. 41

61. G1ln9045dk

62. 4-(methanesulfonyloxy)butyl Methanesulfonate

63. Ncgc00090905-06

64. Mitosan

65. Dsstox_cid_910

66. Busulfanum [inn-latin]

67. Dsstox_rid_75857

68. Busulfano [inn-spanish]

69. Dsstox_gsid_20910

70. Methanesulfonic

71. Cas-55-98-1

72. Ccris 418

73. Sr-01000765405

74. Einecs 200-250-2

75. Brn 1791786

76. Unii-g1ln9045dk

77. Bisulfex

78. Ai3-25012

79. Busulfan;

80. Busulfan/myleran

81. Busulfan Solution

82. Busulfex Iv

83. Busulfan [usp:inn:ban:jan]

84. Hsdb 7605

85. Tetramethylenester Kyseliny Methansulfonove [czech]

86. Prestwick_989

87. Mfcd00007562

88. Tetramethylene {bis[methanesulfonate]}

89. Spectrum_000092

90. Busulfan [hsdb]

91. Busulfan [iarc]

92. Busulfan [inn]

93. Busulfan [jan]

94. 2041 C.b.

95. Busulfan [mi]

96. Busulfan [vandf]

97. Spectrum2_000067

98. Spectrum3_000320

99. Spectrum4_000259

100. Spectrum5_000928

101. Busulfan [mart.]

102. Busulfan [who-dd]

103. Busulfan [who-ip]

104. Chembl820

105. Ncimech_000192

106. Schembl4373

107. Busulfan [ema Epar]

108. Myelosanum [who-ip]

109. Wln: Ws1&o4osw1

110. Bspbio_001920

111. Kbiogr_000698

112. Kbioss_000512

113. Mls001076666

114. Busulfan (myleran, Busulfex)

115. Busulfan Fresenius Kabi

116. Divk1c_000847

117. Spectrum1500152

118. Busulfan (jp17/usp/inn)

119. Spbio_000253

120. Busulfan [ep Impurity]

121. Busulfan [orange Book]

122. Gtpl7136

123. Busulfan [ep Monograph]

124. Busulfan [usp Monograph]

125. Dtxsid3020910

126. Covzyzsdywqreu-uhfffaoysa-

127. Hms502k09

128. Kbio1_000847

129. Kbio2_000512

130. Kbio2_003080

131. Kbio2_005648

132. Kbio3_001420

133. Butane-1,4-diyldimethanesulfonate

134. Busulfanum [who-ip Latin]

135. Ninds_000847

136. Hms1920i07

137. Hms2091o09

138. Hms2233h04

139. Hms3259g15

140. Hms3370e11

141. Hms3655a21

142. Hms3712a20

143. Pharmakon1600-01500152

144. Amy33355

145. Hy-b0245

146. Zinc1530572

147. Tox21_111038

148. Tox21_201848

149. Tox21_300318

150. 1, {4-bis[methanesulfonoxy]butane}

151. 2041cb

152. Ac-198

153. Bdbm50237623

154. Ccg-35458

155. Nsc755916

156. S1692

157. Akos003614975

158. Tox21_111038_1

159. Db01008

160. Ks-5212

161. Nc00498

162. Nsc-755916

163. Idi1_000847

164. Ncgc00090905-01

165. Ncgc00090905-02

166. Ncgc00090905-03

167. Ncgc00090905-04

168. Ncgc00090905-05

169. Ncgc00090905-07

170. Ncgc00090905-08

171. Ncgc00090905-09

172. Ncgc00090905-10

173. Ncgc00090905-11

174. Ncgc00090905-12

175. Ncgc00254038-01

176. Ncgc00259397-01

177. Nci60_041640

178. Smr000058613

179. Tetramethylene Di(methanesulfonate)

180. Sbi-0051300.p003

181. Ft-0623291

182. Ft-0663910

183. Sw198555-3

184. C06862

185. D00248

186. D88731

187. 4-[(methylsulfonyl)oxy]butyl Methanesulfonate #

188. Ab00051929-10

189. Ab00051929-11

190. Ab00051929_12

191. Ab00051929_14

192. Busulfan, Analytical Standard, For Drug Analysis

193. Q348922

194. Sr-01000765405-2

195. Sr-01000765405-3

196. Sr-01000765405-7

197. Busulfan, European Pharmacopoeia (ep) Reference Standard

198. Z276508890

199. 129316-96-7

2.4 Create Date
2005-03-25
3 Chemical and Physical Properties
Molecular Weight 246.3 g/mol
Molecular Formula C6H14O6S2
XLogP3-0.5
Hydrogen Bond Donor Count0
Hydrogen Bond Acceptor Count6
Rotatable Bond Count7
Exact Mass246.02318051 g/mol
Monoisotopic Mass246.02318051 g/mol
Topological Polar Surface Area104 Ų
Heavy Atom Count14
Formal Charge0
Complexity294
Isotope Atom Count0
Defined Atom Stereocenter Count0
Undefined Atom Stereocenter Count0
Defined Bond Stereocenter Count0
Undefined Bond Stereocenter Count0
Covalently Bonded Unit Count1
4 Drug and Medication Information
4.1 Drug Information
1 of 4  
Drug NameBusulfex
PubMed HealthBusulfan (Injection)
Drug ClassesAntineoplastic Agent
Drug LabelBusulfan is a bifunctional alkylating agent known chemically as 1,4- butanediol, dimethanesulfonate. BUSULFEX (busulfan) Injection is intended for intravenous administration. It is supplied as a clear, colorless, sterile, solution in 10 mL single u...
Active IngredientBusulfan
Dosage FormInjectable
RouteInjection
Strength6mg/ml
Market StatusPrescription
CompanyOtsuka Pharm

2 of 4  
Drug NameMyleran
PubMed HealthBusulfan
Drug ClassesAntineoplastic Agent
Drug LabelMYLERAN (busulfan) is a bifunctional alkylating agent. Busulfan is known chemically as 1,4-butanediol dimethanesulfonate and has the following structural formula:CH3SO2O(CH2)4OSO2CH3Busulfan is not a structural analog of the nitrogen mustards. MYLERA...
Active IngredientBusulfan
Dosage FormTablet
RouteOral
Strength2mg
Market StatusPrescription
CompanyAspen Global

3 of 4  
Drug NameBusulfex
PubMed HealthBusulfan (Injection)
Drug ClassesAntineoplastic Agent
Drug LabelBusulfan is a bifunctional alkylating agent known chemically as 1,4- butanediol, dimethanesulfonate. BUSULFEX (busulfan) Injection is intended for intravenous administration. It is supplied as a clear, colorless, sterile, solution in 10 mL single u...
Active IngredientBusulfan
Dosage FormInjectable
RouteInjection
Strength6mg/ml
Market StatusPrescription
CompanyOtsuka Pharm

4 of 4  
Drug NameMyleran
PubMed HealthBusulfan
Drug ClassesAntineoplastic Agent
Drug LabelMYLERAN (busulfan) is a bifunctional alkylating agent. Busulfan is known chemically as 1,4-butanediol dimethanesulfonate and has the following structural formula:CH3SO2O(CH2)4OSO2CH3Busulfan is not a structural analog of the nitrogen mustards. MYLERA...
Active IngredientBusulfan
Dosage FormTablet
RouteOral
Strength2mg
Market StatusPrescription
CompanyAspen Global

4.2 Therapeutic Uses

Busulfan is used in combination with cyclophosphamide as a conditioning regimen prior to allogeneic hematopoietic progenitor cell transplantation in patients with chronic myelogenous leukemia (CML) and is designated an orphan drug by the US Food and Drug Administration (FDA) for the treatment of this disease.

American Society of Health System Pharmacists. AHFS Drug Information 2008. Bethesda, Maryland 2008, p. 951


/VET/ Antineoplastic agent used in adjunct therapy of acute granulocytic leukemias in small animals.

Milne, G.W.A. Veterinary Drugs: Synonyms and Properties. Ashgate Publishing Limited, Aldershot, Hampshire, England 2002., p. 93


Busulfan is an alkylating agent with myeloablative properties and activity against non-dividing marrow cells and, possibly, non-dividing malignant cells. Its use has been well established in the treatment of hematological malignancies, particularly in patients with chronic myeloid leukemia and other myeloproliferative syndromes.

European Medicines Agency (EMEA), Committee for Medicinal Products for Human Use; European Public Assessment Report (EPAR) (Science Discussion); Busilvex, p.3 (2005).https://www.emea.europa.eu/humandocs/PDFs/EPAR/busilvex/168603en6.pdf as of July 15, 2008


Busilvex followed by cyclophosphamide (BuCy4) or melphalan (BuMel) is indicated as conditioning treatment prior to conventional hematopoietic progenitor cell transplantation in pediatric patients.

European Medicines Agency (EMEA), Committee for Medicinal Products for Human Use; European Public Assessment Report (EPAR) (Annex I: Summary of Product Characteristics); Busilvex, p.2 (2005). Available from, as of July 15, 2008: https://www.emea.europa.eu/humandocs/PDFs/EPAR/busilvex/H-472-PI-en.pdf


4.3 Drug Warning

Myleran is a potent drug. It should not be used unless a diagnosis of chronic myelogenous leukemia has been adequately established and the responsible physician is knowledgeable in assessing response to chemotherapy. Myleran can induce severe bone marrow hypoplasia. Reduce or discontinue the dosage immediately at the first sign of any unusual depression of bone marrow function as reflected by an abnormal decrease in any of the formed elements of the blood. A bone marrow examination should be performed if the bone marrow status is uncertain.

Thomson Health Care Inc.; Physicians' Desk Reference 62 ed., Montvale, NJ 2008, p. 1524


Life-threatening hepatic veno-occlusive disease has occurred in patients receiving busulfan (usually in combination with cyclophosphamide or other antineoplastic agents as a component of marrow-ablative therapy prior to bone marrow transplantation). The manufacturer states that a clear causal relationship to busulfan has not been demonstrated. Hepatic veno-occlusive disease diagnosed by clinical examination and laboratory findings occurred in 8% (5/61) of patients receiving IV busulfan in the allogeneic transplant clinical trial and was fatal in 40% (2/5) of cases. Overall mortality from hepatic veno-occlusive disease was 3% for the entire study population. Retrospectively, 3 of the 5 patients diagnosed with hepatic veno-occlusive disease were found to meet the Jones' criteria for this condition. In patients receiving high-dose oral busulfan as a component of a conditioning regimen prior to bone marrow transplant in randomized, controlled studies, the incidence of hepatic veno-occlusive disease was 7.7-12%.

American Society of Health System Pharmacists. AHFS Drug Information 2008. Bethesda, Maryland 2008, p. 953


Interstitial pneumonitis and pulmonary fibrosis, which rarely were fatal, also have been reported in patients receiving high oral doses of busulfan as a component of a conditioning regimen prior to allogeneic bone marrow transplantation. Nonspecific interstitial fibrosis was diagnosed by lung biopsy in one patient receiving IV busulfan who subsequently died from respiratory failure.

American Society of Health System Pharmacists. AHFS Drug Information 2008. Bethesda, Maryland 2008, p. 953


In patients receiving oral busulfan, pancytopenia generally occurs with failure to adequately monitor hematologic status and promptly discontinue the drug in response to a large or rapid decrease in leukocyte or platelet counts. Although individual variation in response to the drug does not appear to be an important contributing factor, some patients may be especially sensitive to busulfan and experience abrupt onset of neutropenia or thrombocytopenia. Busulfan-induced pancytopenia may be more prolonged than that induced by other alkylating agents; although recovery may take 1 month to 2 years, the toxicity is potentially reversible and patients should be vigorously supported through any period of severe pancytopenia. Some patients develop bone marrow fibrosis or chronic aplasia which is probably due to busulfan toxicity. Aplastic anemia, sometimes irreversible, has been reported rarely in patients receiving oral busulfan; aplastic anemia usually has occurred following high doses of the drug or long-term administration of conventional doses.

American Society of Health System Pharmacists. AHFS Drug Information 2008. Bethesda, Maryland 2008, p. 952


For more Drug Warnings (Complete) data for BUSULFAN (42 total), please visit the HSDB record page.


4.4 Drug Indication

For use in combination with cyclophosphamide as a conditioning regimen prior to allogeneic hematopoietic progenitor cell transplantation for chronic myelogenous (myeloid, myelocytic, granulocytic) leukemia (FDA has designated busulfan as an orphan drug for this use). It is also used as a component of pretransplant conditioning regimens in patients undergoing bone marrow transplantation for acute myeloid leukemia and nonmalignant diseases.


FDA Label


Busulfan Fresenius Kabi followed by cyclophosphamide (BuCy2) is indicated as conditioning treatment prior to conventional haematopoietic progenitor cell transplantation (HPCT) in adult patients when the combination is considered the best available option.

Busulfan Fresenius Kabi followed by cyclophosphamide (BuCy4) or melphalan (BuMel) is indicated as conditioning treatment prior to conventional haematopoietic progenitor cell transplantation in paediatric patients.


Busilvex followed by cyclophosphamide (BuCy2) is indicated as conditioning treatment prior to conventional haematopoietic progenitor cell transplantation (HPCT) in adult patients when the combination is considered the best available option.

Busilvex following fludarabine (FB) is indicated as conditioning treatment prior to haematopoietic progenitor cell transplantation (HPCT) in adult patients who are candidates for a reduced-intensity conditioning (RIC) regimen.

Busilvex followed by cyclophosphamide (BuCy4) or melphalan (BuMel) is indicated as conditioning treatment prior to conventional haematopoietic progenitor cell transplantation in paediatric patients.


5 Pharmacology and Biochemistry
5.1 Pharmacology

Busulfan is an antineoplastic in the class of alkylating agents and is used to treat various forms of cancer. Alkylating agents are so named because of their ability to add alkyl groups to many electronegative groups under conditions present in cells. They stop tumor growth by cross-linking guanine bases in DNA double-helix strands - directly attacking DNA. This makes the strands unable to uncoil and separate. As this is necessary in DNA replication, the cells can no longer divide. In addition, these drugs add methyl or other alkyl groups onto molecules where they do not belong which in turn leads to a miscoding of DNA. Alkylating agents are cell cycle-nonspecific and work by three different mechanisms, all of which achieve the same end result - disruption of DNA function and cell death. Overexpression of MGST2, a glutathione s-transferase, is thought to confer resistance to busulfan. The role of MGST2 in the metabolism of busulfan is unknown however.


5.2 MeSH Pharmacological Classification

Antineoplastic Agents, Alkylating

A class of drugs that differs from other alkylating agents used clinically in that they are monofunctional and thus unable to cross-link cellular macromolecules. Among their common properties are a requirement for metabolic activation to intermediates with antitumor efficacy and the presence in their chemical structures of N-methyl groups, that after metabolism, can covalently modify cellular DNA. The precise mechanisms by which each of these drugs acts to kill tumor cells are not completely understood. (From AMA, Drug Evaluations Annual, 1994, p2026) (See all compounds classified as Antineoplastic Agents, Alkylating.)


Immunosuppressive Agents

Agents that suppress immune function by one of several mechanisms of action. Classical cytotoxic immunosuppressants act by inhibiting DNA synthesis. Others may act through activation of T-CELLS or by inhibiting the activation of HELPER CELLS. While immunosuppression has been brought about in the past primarily to prevent rejection of transplanted organs, new applications involving mediation of the effects of INTERLEUKINS and other CYTOKINES are emerging. (See all compounds classified as Immunosuppressive Agents.)


Myeloablative Agonists

Agents that destroy bone marrow activity. They are used to prepare patients for BONE MARROW TRANSPLANTATION or STEM CELL TRANSPLANTATION. (See all compounds classified as Myeloablative Agonists.)


Alkylating Agents

Highly reactive chemicals that introduce alkyl radicals into biologically active molecules and thereby prevent their proper functioning. Many are used as antineoplastic agents, but most are very toxic, with carcinogenic, mutagenic, teratogenic, and immunosuppressant actions. They have also been used as components in poison gases. (See all compounds classified as Alkylating Agents.)


5.3 FDA Pharmacological Classification
5.3.1 Active Moiety
BUSULFAN
5.3.2 FDA UNII
G1LN9045DK
5.3.3 Pharmacological Classes
Alkylating Drug [EPC]; Alkylating Activity [MoA]
5.4 ATC Code

L01AB01


L01AB01


L01AB01

S76 | LUXPHARMA | Pharmaceuticals Marketed in Luxembourg | Pharmaceuticals marketed in Luxembourg, as published by d'Gesondheetskeess (CNS, la caisse nationale de sante, www.cns.lu), mapped by name to structures using CompTox by R. Singh et al. (in prep.). List downloaded from https://cns.public.lu/en/legislations/textes-coordonnes/liste-med-comm.html. Dataset DOI:10.5281/zenodo.4587355


L - Antineoplastic and immunomodulating agents

L01 - Antineoplastic agents

L01A - Alkylating agents

L01AB - Alkyl sulfonates

L01AB01 - Busulfan


5.5 Absorption, Distribution and Excretion

Absorption

Completely absorbed from the gastrointestinal tract. Busulfan is a small, highly lipophilic molecule that crosses the blood-brain-barrier. The absolute bioavailability, if a single 2 mg IV bolus injection is given to adult patients, is 80% 20%. In children (1.5 - 6 years old), the absolute bioavailability was 68% 31%. When a single oral dose is given to patients, the area under the curve (AUC) was 130 nghr/mL. The peak plasma concentration when given orally is 30 ng/mL (after dose normalization to 2 mg). It takes 0.9 hours to reach peak plasma concentration after dose normalization to 4 mg.


Route of Elimination

Following administration of 14C- labeled busulfan to humans, approximately 30% of the radioactivity was excreted into the urine over 48 hours; negligible amounts were recovered in feces. Less than 2% of the administered dose is excreted in the urine unchanged within 24 hours. Elimination of busulfan is independent of renal function.


Clearance

2.52 ml/min/kg [Following an infusion of dose of 0.8 mg/kg every six hours, for a total of 16 doses over four days]


The pharmacokinetic disposition of busulfan differs in children versus adults. The mean bioavailability of busulfan is lower in children than in adults; the interindividual variation in bioavailability for oral busulfan is large, particularly in children. In a pharmacokinetic study in children receiving IV busulfan (0.8 or 1 mg/kg based on actual body weight), an estimated volume of distribution of 0.64 L/kg (with an interpatient variability of 11%) was reported.

American Society of Health System Pharmacists. AHFS Drug Information 2008. Bethesda, Maryland 2008, p. 956


Busulfan, a small and highly lipophilic molecule, easily crosses the blood-brain barrier. Busulfan concentrations in the cerebrospinal fluid (CSF) are approximately equal to concurrent busulfan plasma concentrations. It is not known whether the drug is distributed into milk.

American Society of Health System Pharmacists. AHFS Drug Information 2008. Bethesda, Maryland 2008, p. 956


For adults receiving busulfan 2, 4, or 6 mg orally as a single dose on consecutive days, the drug exhibits linear kinetics for both the maximum plasma concentration and the area under the concentration-time curve (AUC); a mean peak plasma concentration (normalized to a dose of 2 mg) of about 30 ng/mL was observed. In a study of 12 patients receiving single oral busulfan doses of 4-8 mg, a mean peak plasma concentration (normalized to a dose of 4 mg) of about 68 ng/mL was reported; the time to peak plasma concentration was about 0.9 hours.

American Society of Health System Pharmacists. AHFS Drug Information 2008. Bethesda, Maryland 2008, p. 956


Busulfan is rapidly and completely absorbed from the GI tract after oral administration of the drug. The effect of food on the bioavailability of busulfan is not known.

American Society of Health System Pharmacists. AHFS Drug Information 2008. Bethesda, Maryland 2008, p. 956


For more Absorption, Distribution and Excretion (Complete) data for BUSULFAN (11 total), please visit the HSDB record page.


5.6 Metabolism/Metabolites

Busulfan is extensively metabolizes in the hepatic. Busulfan is predominantly metabolized by conjugation with glutathione, both spontaneously and by glutathione S-transferase (GST) catalysis. GSTA1 is the primary GST isoform that facilitates the the metabolism of busulfan. Other GST isoforms that are also involved are GSTM1 and GSTP1. At least 12 metabolites have been identified among which tetrahydrothiophene, tetrahydrothiophene 12-oxide, sulfolane, and 3-hydroxysulfolane were identified. These metabolites do not have cytotoxic activity.


After IP injections of 2:3-(14)C-Myleran in the rat, rabbit and mouse, 60% of the urinary radioactivity was found to be in the form of the 3-hydroxy tetrahydrothiophene-1,1-dioxide, a sulphone. It is suggested that in vivo Myleran undergoes a reaction with cysteine or a cysteinyl moiety to form a cyclic sulphonium ion, which in turn undergoes cleavage to the tetrahydrothiophene, oxidation to the 1,1-dioxide and biological hydroxylation to the 3-hydroxy compound.

IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: https://monographs.iarc.fr/ENG/Classification/index.php, p. V4 250 (1974)


In the rat and mouse 50-60% of a single dose of Myleran-(35)S (10 mg/kg bw) injected intraperitoneally in arachis oil was excreted within 24 to 48 hours, mainly as methane sulphonic acid; a small amount of unchanged Myleran and two unidentified components were present. In the rabbit, methane sulphonic acid was the only metabolite found in the urine.

IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work). Available at: https://monographs.iarc.fr/ENG/Classification/index.php, p. V4 250 (1974)


The metabolic fate of busulfan has been studied in rats and humans using (14)C- and (35)S-labeled materials. In humans, as in the rat, almost all of the radioactivity in (35)S-labeled busulfan is excreted in the urine in the form of (35)S-methanesulfonic acid. /It was/ demonstrated that the formation of methanesulfonic acid in vivo in the rat is not due to a simple hydrolysis of busulfan to 1,4-butanediol, since only about 4% of 2,3-(14)C-busulfan was excreted as carbon dioxide, whereas 2,3-(14)C-1,4-butanediol was converted almost exclusively to carbon dioxide. The predominant reaction of busulfan in the rat is the alkylation of sulfhydryl groups (particularly cysteine and cysteine-containing compounds) to produce a cyclic sulfonium compound which is the precursor of the major urinary metabolite of the 4-carbon portion of the molecule, 3-hydroxytetrahydrothiophene-1,1-dioxide. This has been termed a "sulfur-stripping" action of busulfan and it may modify the function of certain sulfur-containing amino acids, polypeptides, and proteins; whether this action makes an important contribution to the cytotoxicity of busulfan is unknown.

Thomson Health Care Inc.; Physicians' Desk Reference 62 ed., Montvale, NJ 2008, p. 1525


(14)C busulfan was administered ip (15 mg/kg) to 5 male Sprague-Dawley rats. For 72 hours, the urinary recovery of (14)C was approximately 70% of the total dose, while the fecal excretion was within the range 1.5-2%. The pattern of the urinary metabolites of busulfan was studied by HPLC in combination with radioactivity detection of the pooled urine. At least eight radioactive fractions could be separated. Three major metabolite peaks were identified by GC/MS and NMR spectroscopy: 3-hydroxysulfolane (39% of total urine radioactivity), tetrahydrothiophene 1- oxide (20%), and sulfolane (13%). Busulfan (6%) and tetrahydrofuran (2%) were also identified. A sulfonium ion glutathione conjugate was hypothesised as another metabolite, but was not isolated because it was very unstable. However, another compound was observed. This metabolite co-eluted with the sulfonium ion obtained of the reaction of busulfan with N-acetyl-L-cysteine and produced tetrahydrothiophene when hydrolyzed. Finally, busulfan and the three main metabolites were tested for cytotoxicity on Chinese V79 hamster cells in vitro. Cell toxicity was induced only by busulfan, which indicates that the cytotoxicity in vivo is mediated by the parent compound, as expected.

European Medicines Agency (EMEA), Committee for Medicinal Products for Human Use; European Public Assessment Report (EPAR) (Science Discussion); Busilvex, p.10 (2005). Available from, as of July 15, 2008: https://www.emea.europa.eu/humandocs/PDFs/EPAR/busilvex/168603en6.pdf


5.7 Biological Half-Life

2.6 hours


The terminal half life /in children from < 6 months up to 17 years old/ ranged from 2.26 to 2.52 hr.

European Medicines Agency (EMEA), Committee for Medicinal Products for Human Use; European Public Assessment Report (EPAR) (Annex I: Summary of Product Characteristics); Busilvex, p.12 (2005). Available from, as of July 15, 2008: https://www.emea.europa.eu/humandocs/PDFs/EPAR/busilvex/H-472-PI-en.pdf


The elimination half-life is about 2.6 hours in adults receiving oral busulfan.

American Society of Health System Pharmacists. AHFS Drug Information 2008. Bethesda, Maryland 2008, p. 956


Following intravenous administration, the mean half life of busulfan ranged from 2.83 hours to 3.90 hours ... . Oral busulfan had a mean half life of 3.87 hours.

European Medicines Agency (EMEA), Committee for Medicinal Products for Human Use; European Public Assessment Report (EPAR) (Science Discussion); Busilvex, p.15 (2005). Available from, as of July 15, 2008: https://www.emea.europa.eu/humandocs/PDFs/EPAR/busilvex/168603en6.pdf


5.8 Mechanism of Action

Busulfan is an alkylating agent that contains 2 labile methanesulfonate groups attached to opposite ends of a 4-carbon alkyl chain. Once busulfan is hydrolyzed, the methanesulfonate groups are released and carbonium ions are produced. These carbonium ions alkylate DNA, which results in the interference of DNA replication and RNA transcription, ultimately leading to the disruption of nucleic acid function. Specifically, its mechanism of action through alkylation produces guanine-adenine intrastrand crosslinks. These crosslinks occur through a SN2 reaction guanine N7 nucleophilically attacks the carbon adjacent to the mesylate leaving group. This kind of damage cannot be repaired by cellular machinery and thus the cell undergoes apoptosis.


The primary molecular action of busulfan is alkylation of intracellular nucleophiles. Both proteins and nucleic acids are affected. With regard to DNA, busulfan reacts with guanine residues to form a fourcarbon di-guanine DNA cross-linkage with release of methylsulfonate. The DNA cross-linkage causes misreading of the DNA code and single-strand breakage. The degree of DNA cross-linkage has been shown to be proportional to the dose and cytotoxicity of the compound. Busulfan-induced crosslinkages of DNA to nuclear proteins may also occur and is considered a cytotoxic mechanism. Busulfan has also been reported to esterify phosphate groups of chromosomal DNA, accounting for the fragmentation of chromosomes seen in various cell types after treatment. Chromosomal damage further contributes to the overall cytotoxic effect.

European Medicines Agency (EMEA), Committee for Medicinal Products for Human Use; European Public Assessment Report (EPAR) (Science Discussion); Busilvex, p.6 (2005). Available from, as of July 15, 2008: https://www.emea.europa.eu/humandocs/PDFs/EPAR/busilvex/168603en6.pdf


Studies of cloned tumour and normal cells indicate that busulfan interrupts certain parts of the cell mitotic cycle. While busulfan can act on cells at any stage of mitosis, similar to other alkylating agents, in vitro studies with tumour cell lines indicate that replicating cells are most sensitive to busulfan in the late G1 phase and that progression through the cell cycle is blocked in the G2 phase. Cultured cells in the S-phase, which involves DNA synthesis, are not as affected because the DNA repair systems are active at this stage. Clinically, busulfan is cytotoxic to proliferating tissues, especially granulopoietic cells in the bone marrow.

European Medicines Agency (EMEA), Committee for Medicinal Products for Human Use; European Public Assessment Report (EPAR) (Science Discussion); Busilvex, p.6 (2005). Available from, as of July 15, 2008: https://www.emea.europa.eu/humandocs/PDFs/EPAR/busilvex/168603en6.pdf