Pyrimidine | Health Encyclopedia: Pyrimidine

Pyrimidine: From 1 Different Sources

n. a nitrogen-containing compound with a ring molecular structure. The commonest pyrimidines are cytosine, thymine, and uracil, which form the *nucleotides of nucleic acids.

Health Source: Oxford | Concise Colour Medical Dictionary
Author: Jonathan Law, Elizabeth Martin

Methotrexate

One of the ANTIMETABOLITES used to treat certain forms of malignant disease. Acting to inhibit the ENZYME dihydrofolate reductase, which is essential for purine and pyrimidine synthesis, it is given orally, intravenously, intramuscularly or intrathecally. Methotrexate is used as maintenance therapy for childhood acute lymphoblastic LEUKAEMIA, while other uses include CHORIOCARCINOMA, nonHodgkin’s LYMPHOMA, and various solid tumours. Intrathecally, it is used in the prophylaxis of childhood acute lymphoblastic leukaemia, and as treatment for established meningeal cancer or lymphoma.

Side-effects include suppression of myelocytes in bone marrow, in?ammation of mucous membranes, and, rarely, PNEUMONITIS. It should be avoided whenever signi?cant renal impairment is present, while signi?cant pleural e?usion or ascites is also a contraindication. Blood counts should be carefully monitored whenever intrathecal methotrexate is given. Oral or parenteral folinic acid helps to prevent, or to speed recovery from, myelosuppression or mucositis.

Methotrexate is used in dermatology, where it may be indicated for cases of severe uncontrolled PSORIASIS unresponsive to conventional therapy; it may also be indicated for severe active RHEUMATOID ARTHRITIS. Because of its potentially severe haematological, pulmonary, gastrointestinal, and other toxicities it should be used only by specialists and appropriate renal and liver function tests carried out before and during treatment. It should be avoided in pregnancy, and conception should be avoided for at least six months after stopping, as should breast feeding. Concurrent administration of aspirin or other NONSTEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDS) reduces methotrexate excretion, increasing its toxicity, and should therefore be avoided whenever possible.... methotrexate

Nucleic Acid

A substance constructed out of units known as nucleotides which consist of a purine or pyrimidine base linked to a pentose sugar, which in turn is esteri?ed with phosphoric acid. Two types of nucleic acid occur in nature: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).... nucleic acid

Cytarabine

n. an *antimetabolite that interferes with pyrimidine synthesis and is used to suppress the symptoms of acute myeloblastic leukaemia and lymphomatous meningitis. It can damage the normal bone marrow, leading to various blood cell disorders. Other side-effects are nausea, vomiting, mouth ulcers, and diarrhoea.... cytarabine

Cytosine

n. one of the nitrogen-containing bases (see pyrimidine) that occurs in the nucleic acids DNA and RNA.... cytosine

Nucleoside

n. a compound consisting of a nitrogen-containing base (a *purine or *pyrimidine) linked to a sugar. Examples are *adenosine, *guanosine, *cytidine, *thymidine, and uridine.... nucleoside

Nucleotide

n. a compound consisting of a nitrogen-containing base (a *purine or *pyrimidine) linked to a sugar and a phosphate group. Nucleic acids (DNA and RNA) are long chains of linked nucleotides (polynucleotide chains), which in DNA contain the purine bases adenine and guanine and the pyrimidines thymine and cytosine; in RNA, thymine is replaced by uracil.... nucleotide