The mean ±SD melphalan peak plasma concentration is 1.2 ± 0.4 following an intravenous dosage of 10 mg/m2 (0.62 times the approved recommended dosage) and 2.8 ± 1.9 mcg/mL following an intravenous dosage of 20 mg/m2 (1.25 times the approved recommended dosage) in myeloma patients.
Distribution
The melphalan steady-state volume of distribution is 0.5 L/kg. Melphalan penetration into cerebrospinal fluid (CSF) is low.
The mean melphalan plasma protein binding ranges from 53% to 92% with approximately 30% irreversible (covalent). Serum albumin accounts for approximately 40% to 60% and α1-acid glycoprotein approximately 20% of the plasma protein binding.
Elimination
The melphalan elimination half-life is approximately 75 minutes. Mean total body melphalan clearance varied among studies, but typical values of approximately 7 to 9 mL/min/kg (250 to 325 mL/min/m2) were observed.
Metabolism
Melphalan primarily metabolized by hydrolysis to monohydroxymelphalan and dihydroxymelphalan, which are inactive.
Excretion
Following a radiolabeled dose of intravenous melphalan in 9 patients with cancer, the mean (± SD) excretion of melphalan over 24 hours was 13% ± 5.4% of the total dose.
Specific Populations
Patients with renal Impairment
Although melphalan renal clearance appears to be low, one study reported an increase in the occurrence of severe leukopenia in patients with BUN levels ≥30 mg/dL after 10 weeks of therapy. A 50% reduction in the IV melphalan dosage decreased the incidence of severe bone marrow suppression in the latter portion of this study.
Drug Interaction Studies
Cyclosporine
Patients treated with a single dose of intravenous melphalan followed by standard oral doses of cyclosporine were reported to develop severe renal failure.
Immunoglobulins
Interactions between melphalan and immunoglobulins are negligible.