NIPENT® (pentostatin for injection)
Rx only
WARNING
NIPENT should be administered under the supervision of a physician qualified and experienced in the use of cancer chemotherapeutic agents. The use of higher doses than those specified (see DOSAGE AND ADMINISTRATION) is not recommended. Dose-limiting severe renal, liver, pulmonary, and CNS toxicities occurred in Phase 1 studies that used NIPENT at higher doses (20-50 mg/m2 in divided doses over 5 days) than recommended.

In a clinical investigation in patients with refractory chronic lymphocytic leukemia using NIPENT at the recommended dose in combination with fludarabine phosphate, 4 of 6 patients entered in the study had severe or fatal pulmonary toxicity. The use of NIPENT in combination with fludarabine phosphate is not recommended.

DESCRIPTION
NIPENT® (pentostatin for injection) is supplied as a sterile, apyrogenic, lyophilized powder in single-dose vials for intravenous administration. Each vial contains 10 mg of pentostatin and 50 mg of Mannitol, USP. The pH of the final product is maintained between 7.0 and 8.5 by addition of sodium hydroxide or hydrochloric acid.

Pentostatin, also known as 2’-deoxycoformycin (DCF), is a potent inhibitor of the enzyme adenosine deaminase and is isolated from fermentation cultures of Streptomyces antibioticus. Pentostatin is known chemically as (R)-3-(2-deoxy-ß-D-erythropentofuranosyl)3,6,7,8 tetrahydroimidazo[4,5d][1,3]diazepin-8-ol with a molecular formula of C11H16N4O4 and a molecular weight of 268.27. The molecular structure of pentostatin is:
Pentostatin is a white to off-white solid, freely soluble in distilled water.

CLINICAL PHARMACOLOGY
Mechanism of Action

Pentostatin is a potent transition state inhibitor of the enzyme adenosine deaminase (ADA). The greatest activity of ADA is found in cells of the lymphoid system with T-cells having higher activity than B-cells, and T-cell malignancies having higher ADA activity than B-cell malignancies. Pentostatin inhibition of ADA, particularly in the presence of adenosine or deoxyadenosine, leads to cytotoxicity, and this is believed to be due to elevated intracellular levels of dATP which can block DNA synthesis through inhibition of ribonucleotide reductase. Pentostatin can also inhibit RNA synthesis as well as cause increased DNA damage. In addition to elevated dATP, these mechanisms may also contribute to the overall cytotoxic effect of pentostatin. The precise mechanism of pentostatin’s antitumor effect, however, in hairy cell leukemia is not known.

Pharmacokinetics/Drug Metabolism

A tissue distribution and whole-body autoradiography study in the rat revealed that radioactivity concentrations were highest in the kidneys with very little central nervous system penetration.

In man, following a single dose of 4 mg/m2 of pentostatin infused over 5 minutes, the distribution half-life was 11 minutes, the mean terminal half-life was 5.7 hours, the mean plasma clearance was 68 mL/min/m2, and approximately 90% of the dose was excreted in the urine as unchanged pentostatin and/or metabolites as measured by adenosine deaminase inhibitory activity. The plasma protein binding of pentostatin is low, approximately 4%.

A positive correlation was observed between pentostatin clearance and creatinine clearance (CrCl) in patients with creatinine clearance values ranging from 60 mL/min to 130 mL/min.1 Pentos