Pharmacokinetics

Following injection, drug plasma concentrations declined rapidly in a biexponential manner with distribution phase and terminal elimination phase half-lives of approximately 10 and 75 minutes, respectively. Estimates of average total body clearance varied among studies, but typical values of approximately 7 to 9 mL/min/kg (250 to 325 mL/min/m2) were observed. One study has reported that on repeat dosing of 0.5 mg/kg every 6 weeks, the clearance of melphalan decreased from 8.1 mL/min/kg after the first course, to 5.5 mL/min/kg after the third course, but did not decrease appreciably after the third course. Mean (±SD) peak melphalan plasma concentrations in myeloma patients given IV melphalan at doses of 10 or 20 mg/m2 were 1.2 ± 0.4 and 2.8 ± 1.9 mcg/mL, respectively.

The steady-state volume of distribution of melphalan is 0.5 L/kg. Penetration into cerebrospinal fluid (CSF) is low. The average melphalan binding to plasma proteins is highly variable (range: 53% to 92%). Serum albumin is the major binding protein, accounting for approximately 40% to 60% of the plasma protein binding, while α1-acid glycoprotein accounts for about 20% of the plasma protein binding. Approximately 30% of melphalan is (covalently) irreversibly bound to plasma proteins. Interactions with immunoglobulins have been found to be negligible.

Melphalan is eliminated from plasma primarily by chemical hydrolysis to monohydroxymelphalan and dihydroxymelphalan. Aside from these hydrolysis products, no other melphalan metabolites have been observed in humans. Although the contribution of renal elimination to melphalan clearance appears to be low, one study noted an increase in the occurrence of severe leukopenia in patients with elevated BUN after 10 weeks of therapy.

Clinical Trial

A randomized trial compared prednisone plus IV melphalan to prednisone plus oral melphalan in the treatment of myeloma. As discussed below, overall response rates at week 22 were comparable; however, because of changes in trial design, conclusions as to the relative activity of the 2 formulations after week 22 are impossible to make.

Both arms received oral prednisone starting at 0.8 mg/kg/day with doses tapered over 6 weeks. Melphalan doses in each arm were:

Arm 1: Oral melphalan 0.15 mg/kg/day x 7 followed by 0.05 mg/kg/day when WBC began to rise.

Arm 2: IV melphalan 16 mg/m2 q 2 weeks x 4 (over 6 weeks) followed by the same dose every 4 weeks.

Doses of melphalan were adjusted according to the following criteria:

Table 1. Criteria for Dosage Adjustment in a Randomized Clinical Trial

One hundred seven patients were randomized to the oral melphalan arm and 203 patients to the IV melphalan arm. More patients had a poor-risk classification (58% versus 44%) and high tumor load (51% versus 34%) on the oral compared to the IV arm (P<0.04). Response rates at week 22 are shown in the following table:

Table 2. Response Rates at Week 22

Because of changes in protocol design after week 22, other efficacy parameters such as response duration and survival cannot be compared.

Severe myelotoxicity (WBC ≤1,000 and/or platelets ≤25,000) was more common in the IV melphalan arm (28%) than in the oral melphalan arm (11%).

An association was noted between poor renal function and myelosuppression; consequently, an amendment to the protocol required a 50% reduction in IV melphalan dose if the BUN was ≥30 mg/dL. The rate of severe leukopenia in the IV arm in the patients with BUN over 30 mg/dL decreased from 50% (8/16) before protocol amendment to 11% (3/28) (P = 0.01) after the amendment.

Before the dosing amendment, there was a 10% (8/77) incidence of drug-related death in the IV arm. After the dosing amendment, this incidence was 3% (3/108). This compares to an overall 1% (1/100) incidence of drug-related death in the oral arm.

Carcinogenesis

Secondary malignancies, including acute nonlymphocytic leukemia, myeloproliferative syndrome, and carcinoma, have been reported in patients with cancer treated with alkylating agents (including melphalan). Some patients also received other chemotherapeutic agents or radiation therapy. Precise quantitation of the risk of acute leukemia, myeloproliferative syndrome, or carcinoma is not possible. Published reports of leukemia in patients who have received melphalan (and other alkylating agents) suggest that the risk of leukemogenesis increases with chronicity of treatment and with cumulative dose. In one study, the 10-year cumulative risk of developing acute leukemia or myeloproliferative syndrome after oral melphalan therapy was 19.5% for cumulative doses ranging from 730 to 9,652 mg. In this same study, as well as in an additional study, the 10-year cumulative risk of developing acute leukemia or myeloproliferative syndrome after oral melphalan therapy was less than 2% for cumulative doses under 600 mg. This does not mean that there is a cumulative dose below which there is no risk of the induction of secondary malignancy. The potential benefits from melphalan therapy must be weighed on an individual basis against the possible risk of the induction of a second malignancy.

Adequate and well-controlled carcinogenicity studies have not been conducted in animals. However, intraperitoneal (IP) administration of melphalan in rats (5.4 to 10.8 mg/m2) and in mice (2.25 to 4.5 mg/m 2) 3 times per week for 6 months followed by 12 months post-dose observation produced peritoneal sarcoma and lung tumors, respectively.

Mutagenesis

Melphalan has been shown to cause chromatid or chromosome damage in humans. Intramuscular administration of melphalan at 6 and 60 mg/m 2 produced structural aberrations of the chromatid and chromosomes in bone marrow cells of Wistar rats.

Impairment of Fertility

Melphalan causes suppression of ovarian function in premenopausal women, resulting in amenorrhea in a significant number of patients. Reversible and irreversible testicular suppression have also been reported.

Pregnancy

General

In all instances where the use of melphalan hydrochloride for injection is considered for chemotherapy, the physician must evaluate the need and usefulness of the drug against the risk of adverse events. Melphalan should be used with extreme caution in patients whose bone marrow reserve may have been compromised by prior irradiation or chemotherapy or whose marrow function is recovering from previous cytotoxic therapy.

Dose reduction should be considered in patients with renal insufficiency receiving IV melphalan. In one trial, increased bone marrow suppression was observed in patients with BUN levels ≥30 mg/dL. A 50% reduction in the IV melphalan dose decreased the incidence of severe bone marrow suppression in the latter portion of this study.

Administration of live vaccines to immunocompromised patients should be avoided.

Information for Patients

Patients should be informed that the major acute toxicities of melphalan are related to bone marrow suppression, hypersensitivity reactions, gastrointestinal toxicity, and pulmonary toxicity. The major long-term toxicities are related to infertility and secondary malignancies. Patients should never be allowed to take the drug without close medical supervision and should be advised to consult their physicians if they experience skin rash, signs or symptoms of vasculitis, bleeding, fever, persistent cough, nausea, vomiting, amenorrhea, weight loss, or unusual lumps/masses. Women of childbearing potential should be advised to avoid becoming pregnant.

Laboratory Tests

Periodic complete blood counts with differentials should be performed during the course of treatment with melphalan. At least 1 determination should be obtained prior to each dose. Patients should be observed closely for consequences of bone marrow suppression, which include severe infections, bleeding, and symptomatic anemia (see WARNINGS).

Drug Interactions

The development of severe renal failure has been reported in patients treated with a single dose of IV melphalan followed by standard oral doses of cyclosporine. Cisplatin may affect melphalan kinetics by inducing renal dysfunction and subsequently altering melphalan clearance. IV melphalan may also reduce the threshold for BCNU lung toxicity. When nalidixic acid and IV melphalan are given simultaneously, the incidence of severe hemorrhagic necrotic enterocolitis has been reported to increase in pediatric patients.

Carcinogenesis, Mutagenesis, Impairment of Fertility

See WARNINGS section.

Pregnancy

Nursing Mothers

It is not known whether this drug is excreted in human milk. IV melphalan should not be given to nursing mothers.

Pediatric Use

The safety and effectiveness in pediatric patients have not been established.

Geriatric Us

Clinical studies of Melphalan Hydrochloride for Injection did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

Hematologic

The most common side effect is bone marrow suppression leading to leukopenia, thrombocytopenia, and anemia. White blood cell count and platelet count nadirs usually occur 2 to 3 weeks after treatment, with recovery in 4 to 5 weeks after treatment. Irreversible bone marrow failure has been reported.

Gastrointestinal

Gastrointestinal disturbances such as nausea and vomiting, diarrhea, and oral ulceration occur infrequently. Hepatic disorders ranging from abnormal liver function tests to clinical manifestations such as hepatitis and jaundice have been reported. Hepatic veno-occlusive disease has been reported.

Hypersensitivity

Acute hypersensitivity reactions including anaphylaxis were reported in 2.4% of 425 patients receiving Melphalan Hydrochloride for Injection for myeloma (see WARNINGS). These reactions were characterized by urticaria, pruritus, edema, skin rashes, and in some patients, tachycardia, bronchospasm, dyspnea, and hypotension. These patients appeared to respond to antihistamine and corticosteroid therapy. If a hypersensitivity reaction occurs, IV or oral melphalan should not be readministered since hypersensitivity reactions have also been reported with oral melphalan. Cardiac arrest has also been reported rarely in association with such reports.

Miscellaneous

Other reported adverse reactions include skin hypersensitivity, skin ulceration at injection site, skin necrosis rarely requiring skin grafting, maculopapular rashes, vasculitis, alopecia, hemolytic anemia, allergic reaction, pulmonary fibrosis (including fatal outcomes), and interstitial pneumonitis. Temporary significant elevation of the blood urea has been seen in the early stages of therapy in patients with renal damage. Subjective and transient sensation of warmth and/or tingling.

Administration Precautions

As with other toxic compounds, caution should be exercised in handling and preparing the solution of melphalan hydrochloride for injection. Skin reactions associated with accidental exposure may occur. The use of gloves is recommended. If the solution of melphalan hydrochloride for injection contacts the skin or mucosa, immediately wash the skin or mucosa thoroughly with soap and water.

Procedures for proper handling and disposal of anticancer drugs should be considered. Several guidelines on this subject have been published. 1-4 There is no general agreement that all of the procedures recommended in the guidelines are necessary or appropriate.

Parenteral drug products should be visually inspected for particulate matter and discoloration prior to administration whenever solution and container permit. If either occurs, do not use this product.

Care should be taken to avoid possible extravasation of melphalan hydrochloride for injection and in cases of poor peripheral venous access, consideration should be given to use of a central venous line (see WARNINGS).

Preparation for Administration/Stability

1. Melphalan Hydrochloride for Injection must be reconstituted by rapidly injecting 10 mL of the supplied diluent directly into the vial of lyophilized powder using a sterile needle (20-gauge or larger needle diameter) and syringe. Immediately shake vial vigorously until a clear solution is obtained. This provides a 5-mg/mL solution of melphalan. Rapid addition of the diluent followed by immediate vigorous shaking is important for proper dissolution.
2. Immediately dilute the dose to be administered in 0.9% Sodium Chloride Injection, USP, to a concentration not greater than 0.45 mg/mL.
3. Administer the diluted product over a minimum of 15 minutes.
4. Complete administration within 60 minutes of reconstitution.

The time between reconstitution/dilution and administration of Melphalan Hydrochloride for Injection should be kept to a minimum because reconstituted and diluted solutions of Melphalan Hydrochloride for Injection are unstable. Over as short a time as 30 minutes, a citrate derivative of melphalan has been detected in reconstituted material from the

reaction of Melphalan Hydrochloride for Injection with Sterile Diluent for Melphalan Hydrochloride for Injection. Upon further dilution with saline, nearly 1% label strength of melphalan hydrolyzes every 10 minutes.

A precipitate forms if the reconstituted solution is stored at 5°C. DO NOT REFRIGERATE THE RECONSTITUTED PRODUCT.