Gemcitabine

Absorption

Peak plasma concentrations of gemcitabine range from 10 to 40 mg/L following a 30-minute intravenous infusion, and are reached at 15 to 30 minutes. One study showed that steady-state concentrations of gemcitabine showed a linear relationship to dose over the dose range 53 to 1000 mg/m2. Gemcitabine triphosphate, the active metabolite of gemcitabine, can accumulate in circulating peripheral blood mononuclear cells. In one study, the Cmax of gemcitabine triphosphate in peripheral blood mononuclear cells occurred within 30 minutes of the end of the infusion period and increased increased proportionally with gemcitabine doses of up to 350 mg/m2.

Toxicity

The oral LD50 is 333 mg/kg in mice and >500 mg/kg in rats. The dermal LD50 in rabbits is >1000 mg/kg.
There is no known antidote for gemcitabine overdose. In a dose-escalation study, patients were administered a single dose of gemcitabine as high as 5700 mg/m2 administered by intravenous infusion over 30 minutes every two weeks: main observed toxicities were myelosuppression, paresthesia, and severe rash. In the event of a suspected drug overdose, blood counts should be monitored, and patients should be provided with supportive therapy, as necessary.

Description

Gemcitabine is an anticancer nucleoside analog that inhibits the growth of HL-60 promyelocytic leukemia cells with an LC₅₀ value of 40 nM. It inhibits the growth of MX-1 mammary, CX-1, HC-1, GC3, and VRC5 colon, LX-1, Calu-6, and NCI-H460 lung, and HS766T, PaCa-2, PANC-1, and BxPC-3 pancreatic cancer tumors in mouse xenograft models (45-93% inhibition). Gemcitabine is a prodrug that is metabolized to a diphosphate and triphosphate form in cells. The triphosphate form is incorporated into DNA which induces masked chain termination and cell death. By specifically inhibiting growth arrest and DNA damage inducible protein 45 a (Gadd45a), a key mediator of active DNA demethylation, gemcitabine, at concentrations ranging from 34 to 134 nM, inhibits repair-mediated DNA demethylation in a methylation-sensitive reporter assay. Gemcitabine also has broad antiretroviral activity, decreasing MuLV cell infectivity, a murine AIDS model, in cell culture (EC₅₀ = ~1.5 nM) and inhibits the progression of murine AIDS in vivo at a dose of 1-2 mg/kg per day.

The Uses of Gemcitabine

Gemcitabine(Gemzar) belongs to the group of medicines called antimetabolites. It is used alone or in combination with other medicines to treat cancer of the breast, ovary, pancreas, and lung. Gemcitabine interferes with the growth of cancer cells, which a

Background

Gemcitabine is a nucleoside analog and a chemotherapeutic agent. It was originally investigated for its antiviral effects, but it is now used as an anticancer therapy for various cancers. Gemcitabine is a cytidine analog with two fluorine atoms replacing the hydroxyl on the ribose. As a prodrug, gemcitabine is transformed into its active metabolites that work by replacing the building blocks of nucleic acids during DNA elongation, arresting tumour growth and promoting apoptosis of malignant cells. The structure, metabolism, and mechanism of action of gemcitabine are similar to cytarabine, but gemcitabine has a wider spectrum of antitumour activity.
Gemcitabine is marketed as Gemzar and it is available as intravenous injection. It is approved by the FDA to treat advanced ovarian cancer in combination with carboplatin, metastatic breast cancer in combination with paclitaxel, non-small cell lung cancer in combination with cisplatin, and pancreatic cancer as monotherapy. It is also being investigated in other cancer and tumour types.

Indications

Gemcitabine is a chemotherapeutic agent used as monotherapy or in combination with other anticancer agents.
In combination with carboplatin, it is indicated for the treatment of advanced ovarian cancer that has relapsed at least 6 months after completion of platinum-based therapy.
Gemcitabine in combination with paclitaxel is indicated for the first-line treatment of patients with metastatic breast cancer after failure of prior anthracycline-containing adjuvant chemotherapy, unless anthracyclines were clinically contraindicated.
In combination with cisplatin, gemcitabine is indicated for the first-line treatment of patients with inoperable, locally advanced (Stage IIIA or IIIB) or metastatic (Stage IV) non-small cell lung cancer (NSCLC). Dual therapy with cisplatin is also used to treat patients with Stage IV (locally advanced or metastatic) transitional cell carcinoma (TCC) of the bladder.
Gemcitabine is indicated as first-line treatment for patients with locally advanced (nonresectable Stage II or Stage III) or metastatic (Stage IV) adenocarcinoma of the pancreas. Gemcitabine is indicated for patients previously treated with fluorouracil.

What are the applications of Application

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Pharmacokinetics

Gemcitabine is a nucleoside analog that mediates its antitumour effects by promoting apoptosis of malignant cells undergoing DNA synthesis. More specifically, it blocks the progression of cells through the G1/S-phase boundary. Gemcitabine demonstrated cytotoxic effects against a broad range of cancer cell lines in vitro. It displayed schedule-dependent antitumour activity in various animal models and xenografts from human non-small cell lung cancer (NSCLC) and pancreatic cancer. Therefore, the antineoplastic effects of gemcitabine are enhanced through prolonged infusion time rather than higher dosage. Gemcitabine inhibited the growth of human xenografts from carcinoma of the lung, pancreas, ovaries, head and neck, and breast. In mice, gemcitabine inhibited the growth of human tumour xenografts from the breast, colon, lung or pancreas by 69 to 99%. In clinical trials of advanced NSCLC, gemcitabine monotherapy produced objective response rates ranging from 18 to 26%, with a median duration of response ranging from 3.3 to 12.7 months. Overall median survival time was 6.2 to 12.3 months. The combined use of cisplatin and gemcitabine produced better objective response rates compared to monotherapy. In patients with advanced pancreatic cancer, objective response rates in patients ranged from 5.to 12%, with a median survival duration of 3.9 to 6.3 months. In Phase II trials involving patients with metastatic breast cancer, treatment with gemcitabine alone or with adjuvant chemotherapies resulted in response rate ranging from 13 to 42% and median survival duration ranging from 11.5 to 17.8 months. In metastatic bladder cancer, gemcitabine has a response rate 20 to 28%. In Phase II trials of advanced ovarian cancer, patients treated with gemcitabine had response rate of 57.1%, with progression free survival of 13.4 months and median survival of 24 months.
Gemcitabine causes dose-limiting myelosuppression, such as anemia, leukopenia, neutropenia, and thrombocytopenia; however, events leading to discontinuation tend to occur less than 1% of the patients. Gemcitabine can elevate ALT, AST and alkaline phosphatase levels.

Metabolism

Following administration and uptake into cancer cells, gemcitabine is initially phosphorylated by deoxycytidine kinase (dCK), and to a lower extent, the extra-mitochondrial thymidine kinase 2 to form gemcitabine monophosphate (dFdCMP). dFdCMP is subsequently phosphorylated by nucleoside kinases to form active metabolites, gemcitabine diphosphate (dFdCDP) and gemcitabine triphosphate (dFdCTP). Gemcitabine is also deaminated intracellularly and extracellularly by cytidine deaminase to its inactive metabolite 2′,2′-difluorodeoxyuridine or 2′-deoxy-2′,2′-difluorouridine (dFdU). Deamination occurs in the blood, liver, kidneys, and other tissues, and this metabolic pathway accounts for most of drug clearance.