Gemcitabine is a nucleoside analog used as chemotherapy. It is marketed as Gemzar® by Eli Lilly and Company. As with fluorouracil and other analogues of pyrimidines, the drug replaces one of the building blocks of nucleic acids, in this case cytidine, during DNA replication. The process arrests tumor growth, as new nucleosides cannot be attached to the “faulty” nucleoside, resulting in apoptosis (cellular “suicide”). Gemcitabine is used in various carcinomas: non-small cell lung cancer, pancreatic cancer, bladder cancer and breast cancer. It is being investigated for use in oesophageal cancer, and is used experimentally in lymphomas and various other tumor types.
Antineoplastic Agents Antiviral Agents Immunosuppressive Agents Enzyme Inhibitors Antimetabolites Antimetabolites, Antineoplastic Radiation-Sensitizing Agents Antineoplastic and Immunomodulating Agents Pyrimidine Analogues
Gemcitabine 200 GM
Gemcitabine is indicated for the treatment of advanced ovarian cancer that has relapsed at least 6 months after completion of platinum-based therapy; metastatic ovarian cancer; inoperable, locally advanced (Stage IIIA or IIIB), or metastatic (Stage IV) non-small cell lung cancer; and locally advanced (nonresectable Stage II or Stage III) or metastatic (Stage IV) adenocarcinoma of the pancreas.
Gemcitabine is an antineoplastic anti-metabolite. Anti-metabolites masquerade as purine or pyrimidine - which become the building blocks of DNA. They prevent these substances becoming incorporated in to DNA during the "S" phase (or DNA synthesis phase of the cell cycle), stopping normal development and division. Gemcitabine blocks an enzyme which converts the cytosine nucleotide into the deoxy derivative. In addition, DNA synthesis is further inhibited because Gemcitabine blocks the incorporation of the thymidine nucleotide into the DNA strand. It demonstrates dose-dependent synergistic activity with cisplatin in vitro. In vivo, gemcitabine showed activity in combination with cisplatin against the LX-1 and CALU-6 human lung xenografts, but minimal activity was seen with the NCI-H460 or NCI-H520 xenografts. Gemcitabine was synergistic with cisplatin in the Lewis lung murine xenograft. Sequential exposure to gemcitabine 4 hours before cisplatin produced the greatest interaction.
Gemcitabine inhibits thymidylate synthetase, leading to inhibition of DNA synthesis and cell death. Gemcitabine is a prodrug so activity occurs as a result of intracellular conversion to two active metabolites, gemcitabine diphosphate and gemcitabine triphosphate by deoxycitidine kinase. Gemcitabine diphosphate also inhibits ribonucleotide reductase, the enzyme responsible for catalyzing synthesis of deoxynucleoside triphosphates required for DNA synthesis. Finally, Gemcitabine triphosphate (diflurorodeoxycytidine triphosphate) competes with endogenous deoxynucleoside triphosphates for incorporation into DNA.
The pharmacokinetics of gemcitabine are described by a 2-compartment model.
50 L/m^2 [infusions lasting <70 minutes] 370 L/m^2 [long infusions]
Transformed via nucleoside kinases to two active metabolites, gemcitabine diphosphate and gemcitabine triphosphate. Can also undergo deamination via cytidine deaminase to an inactive uracil metabolite (dFdU).
Within one (1) week, 92% to 98% of the dose was recovered, almost entirely in the urine. Gemcitabine (<10%) and the inactive uracil metabolite, 2´-deoxy-2´,2´-difluorouridine (dFdU), accounted for 99% of the excreted dose.
Gemcitabine half-life for short infusions ranged from 42 to 94 minutes, and the value for long infusions varied from 245 to 638 minutes, depending on age and gender, reflecting a greatly increased volume of distribution with longer infusions.
Myelosuppression, paresthesias, and severe rash were the principal toxicities, LD50=500 mg/kg (orally in mice and rats)
Anemia, low white blood cell count, and low platelet count. Chance of getting an infection. Wash hands often. Stay away from people with infections, colds, or flu. Flu-like signs. These include headache, weakness, fever, shakes, aches, pains, and sweating. Mild pain drugs may help. Upset stomach or throwing up. Many small meals, good mouth care, sucking hard, sugar-free candy, or chewing sugar-free gum may help. Loose stools (diarrhea). Chance of bleeding. Mouth irritation or sores. Using a soft toothbrush or cotton swabs and rinsing the mouth may help. Do not use mouth rinses that have alcohol in them. Fever. Hair loss. Swelling in the arms or legs. Feeling tired or weak. Harm to the kidneys may rarely happen. Harm to the liver may rarely happen.