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Melphalan


ACCESSION NB: DB01042 (APRD00118)


TYPE: small molecule


GROUP: approved


DESCRIPTION:
An alkylating nitrogen mustard that is used as an antineoplastic in the form of the levo isomer – melphalan, the racemic mixture – merphalan, and the dextro isomer – medphalan; toxic to bone marrow, but little vesicant action; potential carcinogen. [PubChem]

VOLUME OF DISTRIBUTION: 0.5 L/kg

CATEGORIES:
Antineoplastic Agents, Alkylating Myeloablative Agonists

ABSORPTION: Incomplete, variable, 25-89% post oral dose

INDICATION:
For the palliative treatment of multiple myeloma and for the palliation of non-resectable epithelial carcinoma of the ovary. Has also been used alone or as part of various chemotherapeutic regimens as an adjunct to surgery in the treatment of breast cancer, alone or in combination regimens for palliative treatment of locally recurrent or unresectable in-transit metastatic melanoma of the extremities, as well as for the treatment of amyloidosis with prednisone.

PHARMACODYNAMICS:
Melphalan 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 inhibits their correct utilization by base pairing and causes a miscoding of DNA. Alkylating agents are cell cycle-nonspecific. Alkylating agents work by three different mechanisms all of which achieve the same end result - disruption of DNA function and cell death.

MECHANISM OF ACTION:
Alkylating agents work by three different mechanisms: 1) attachment of alkyl groups to DNA bases (primarily at the N-7 position of guanine and to a lesser extent, at the N-3 position of adenine), forming monoadducts and resulting in the DNA being fragmented by repair enzymes in their attempts to replace the alkylated bases, preventing DNA synthesis and RNA transcription from the affected DNA, 2) DNA damage via the formation of cross-links (bonds between atoms in the DNA) which prevents DNA from being separated for synthesis or transcription, and 3) the induction of mispairing of the nucleotides leading to mutations.

PROTEIN BINDING:
Moderate to high (60 to 90%), primarily to albumin and, to a lesser extent, alpha 1-acid glycoprotein. 30% is irreversibly bound.

METABOLISM:
Melphalan is not actively metabolised, it spontaneously degrades to mono and dihydroxy products.

TOXICITY:
Vomiting, ulceration of the mouth, diarrhea, and hemorrhage of the gastrointestinal tract; The principal toxic effect is bone marrow suppression. LD50=11.2 mg/kg (orally in rat)

AFECTED ORGANISMS:
Humans and other mammals