FLUDARABINE PHOSPHATE

Clinical safety rating: avoid

Contraindicated (not allowed)

How it works

Fludarabine phosphate is a purine analog that inhibits DNA synthesis by interfering with ribonucleotide reductase and DNA polymerase, leading to apoptosis in lymphocytes.

What the body does with it

Metabolism	Fludarabine phosphate is dephosphorylated in serum to 2-fluoro-ara-A, which is then phosphorylated intracellularly to the active triphosphate. Metabolism is primarily hepatic via deamination by adenosine deaminase to 2-fluoro-ara-hypoxanthine.
Excretion	Renal excretion of the active metabolite 2-fluoro-ara-A accounts for approximately 60% of drug elimination. Biliary/fecal elimination is minimal (<5%).
Half-life	Terminal half-life of 2-fluoro-ara-A is approximately 20 hours (range 10–30 hours). Clinical context: accumulation occurs with repeated dosing, requiring dose adjustment in renal impairment (CrCl <30 mL/min).
Protein binding	Fludarabine phosphate is approximately 19–29% bound to plasma proteins, primarily albumin.
Volume of Distribution	Vd is approximately 2.2 L/kg (range 1.5–3.0 L/kg), indicating extensive tissue distribution, including accumulation in lymphocytes and bone marrow.
Bioavailability	Oral bioavailability is approximately 55–75% (mean 65%) compared to IV administration. Bioavailability is highly variable and increased when taken with food.
Onset of Action	IV administration: Onset of antineoplastic effect is typically observed within 1–2 weeks, with maximal response after several cycles. Oral bioavailability: Onset similar to IV but delayed due to absorption time.
Duration of Action	Myelosuppression persists for 2–4 weeks. Lymphocyte depletion may last for 6–12 months post-treatment.

Classification & Brands

Dosing & administration

25 mg/m2 intravenously over 30 minutes daily for 5 consecutive days every 28 days.

Dosage form	INJECTABLE
Renal impairment	For CrCl 30-70 mL/min: reduce dose by 20% and monitor closely. For CrCl <30 mL/min: contraindicated.
Liver impairment	No specific dose adjustment for Child-Pugh class A or B; use caution in severe hepatic impairment (Child-Pugh class C) with dose reduction based on bilirubin and transaminases.
Pediatric use	Not established; safety and efficacy have not been determined in pediatric patients.
Geriatric use	Increased risk of severe toxicity (myelosuppression, neurotoxicity); consider dose reduction based on renal function (CrCl) and overall status. No specific adjustment by age alone.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Other bone marrow suppressants may have additive effects Can cause severe myelosuppression and neurotoxicity.

Breastfeeding	No human data on excretion in breast milk. M/P ratio unknown. Based on molecular weight (less than 500 Da), likely excreted. Advise against breastfeeding during therapy and for at least 1 week after last dose due to potential infant toxicity (myelosuppression, immunosuppression).
Teratogenic Risk	FDA Pregnancy Category D. First trimester: Known to cause fetal harm, including congenital malformations (e.g., skeletal, cardiac) and embryolethality based on animal studies and case reports. Second and third trimesters: Risk of myelosuppression, intrauterine growth restriction, and potential neurodevelopmental effects. Avoid use during pregnancy unless no safer alternative.

Warnings & precautions

■ FDA Black Box Warning

Fludarabine phosphate can cause severe neurologic effects including blindness, coma, and death, especially at higher doses. Dose-dependent severe bone marrow suppression (anemia, thrombocytopenia, neutropenia) and autoimmune hemolytic anemia have been reported.

Side Effect Profile

Common Effects	Myelosuppression
Serious Effects

Absolute Contraindications

Hypersensitivity to fludarabine or any component of the formulation; severe renal impairment (creatinine clearance <30 mL/min); decompensated hemolytic anemia.

Clinical Precautions

Precautions

Severe bone marrow suppression, particularly neutropenia, thrombocytopenia, and anemia; autoimmune hemolytic anemia; neurotoxicity including delayed blindness, coma, and death; tumor lysis syndrome; pulmonary toxicity; and increased risk of opportunistic infections.

Clinical Tips & Counseling

Drug interactions

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