Myleran2 mg

Myleran is a cytotoxic alkylating agent used only under the direction of a specialized hematology-oncology/transplant team. Its indications are classified below by strength of evidence.

Established / FDA-approved uses

• Conditioning regimen before allogeneic hematopoietic stem cell transplantation (HSCT): Intravenous Myleran, in combination with cyclophosphamide, is indicated as part of a preparative (conditioning) regimen prior to allogeneic HSCT for chronic myelogenous leukemia (CML).
• Chronic myelogenous leukemia (CML), palliative treatment: Oral Myleran is indicated for the palliative treatment of CML, historically used to reduce white blood cell counts and induce hematologic remission.

Guideline-supported / adjunct transplant use (requires combination therapy)

• Myleran-containing conditioning regimens (e.g., combined with cyclophosphamide or fludarabine) are used per institutional transplant protocols as conditioning for HSCT in other hematologic malignancies (such as acute myeloid leukemia and myelodysplastic syndrome) and in select non-malignant conditions requiring stem cell transplantation. This broader conditioning use is standard practice in transplant centers though it extends beyond the narrowest label wording, and must always be directed by a specialized transplant physician.

Historical / largely superseded use

• As monotherapy for long-term CML control, oral Myleran has been largely replaced by tyrosine kinase inhibitors (e.g., imatinib), which are now first-line; Myleran is reserved for specific transplant-conditioning or select second-line scenarios.

Each formulation contains Busulfan as the sole active ingredient. Busulfan is available as an oral tablet (2 mg) and as a sterile concentrated solution for intravenous infusion (6 mg/mL), which must be diluted before administration.

Myleran is a bifunctional alkylating agent of the alkyl sulfonate chemical class. It has been used for decades in the management of chronic myelogenous leukemia and, more prominently today, as a key component of high-dose myeloablative conditioning regimens administered before hematopoietic stem cell transplantation. Myleran is administered only in a hospital or specialized oncology/transplant setting under close medical supervision, never as a routine outpatient prescription.

Antineoplastic agent - Alkylating agent (alkyl sulfonate class)

Busulfan is a bifunctional alkylating agent that covalently binds (alkylates) the N7 position of guanine in DNA, forming intra-strand and inter-strand DNA cross-links. This cross-linking disrupts DNA replication and transcription, ultimately triggering apoptosis in rapidly dividing cells. Busulfan has a relatively selective cytotoxic effect on early and late hematopoietic progenitor and stem cells, which accounts for its profound, dose-dependent myelosuppressive (myeloablative) activity - an effect that is unwanted in the treatment of CML but is the intended therapeutic goal when used for transplant conditioning, where it eradicates the recipient's marrow to allow donor stem cell engraftment.

Intravenous: The diluted Myleran solution is infused through a central venous catheter using a controlled infusion (syringe or volumetric) pump over approximately 2 hours; it must not be given as a rapid infusion or IV push. Oral: Tablets are swallowed whole with water, generally on an empty stomach with a consistent relationship to meals as directed by the prescriber, and should not be crushed or chewed without specific instruction. All administration of Myleran takes place under direct medical supervision.

• Acetaminophen (paracetamol): May reduce clearance of Myleran, raising plasma levels and increasing toxicity risk; avoid acetaminophen for at least 72 hours before and during high-dose Myleran administration unless specifically directed otherwise.
• Metronidazole: Significantly increases Myleran plasma concentrations, raising the risk of severe toxicity; concurrent use should generally be avoided during Myleran therapy.
• Itraconazole: Can increase Myleran exposure; closer monitoring is warranted if co-administration is unavoidable.
• Phenytoin: Increases the metabolic clearance of Myleran, which can lower drug levels; this is relevant because phenytoin is also commonly used prophylactically for seizure prevention during high-dose Myleran conditioning, so pharmacokinetic monitoring accounts for this interaction.
• Fludarabine and other myelosuppressive or hepatotoxic agents: Combination with Myleran in conditioning regimens can increase the risk of additive bone marrow suppression and hepatic veno-occlusive disease; used only within specialist-directed protocols with close monitoring.

Profound and prolonged bone marrow suppression is an expected, dose-related effect of Myleran (and the intended effect in transplant conditioning) rather than an unpredictable adverse reaction; other effects include:

• Very common: Neutropenia, thrombocytopenia, anemia (myelosuppression); nausea, vomiting, mucositis/stomatitis, diarrhea, anorexia.
• Common: Skin hyperpigmentation, alopecia, fatigue, fever, headache, insomnia, elevated liver enzymes.
• Serious/less common: Hepatic veno-occlusive disease (sinusoidal obstruction syndrome), seizures, interstitial pulmonary fibrosis ("Myleran lung"), cataracts with long-term use, gonadal suppression/infertility and amenorrhea, secondary malignancies in long-term survivors, engraftment syndrome.

See Precautions and Warnings for detail on the serious risks above.

Myleran is contraindicated in pregnancy: it is cytotoxic and has demonstrated teratogenic and embryo-fetal toxic potential in animal and human data. Women and men of reproductive potential should use effective contraception during and for a period after treatment with Myleran, and pregnancy should be excluded before starting therapy. Myleran is not recommended during breastfeeding because of the potential for serious adverse effects in a nursing infant; breastfeeding should be discontinued before and during treatment. Use only under the direct guidance of a specialist physician, who will weigh any exceptional circumstance individually.

Boxed warnings

• Severe myelosuppression: Myleran causes profound and prolonged suppression of bone marrow function in essentially all patients; this is an expected and, in the transplant-conditioning setting, intended effect, but it requires specialized supportive care (blood product support, growth factors, infection prophylaxis, and monitoring) throughout treatment and recovery.
• Hepatic veno-occlusive disease (sinusoidal obstruction syndrome): A serious, potentially fatal liver toxicity associated particularly with high-dose intravenous Myleran conditioning. Adequate hydration and close monitoring are required during and after high-dose administration for signs including sudden weight gain, jaundice, right-upper-quadrant pain, and ascites; report these immediately.
• Specialist supervision required: Myleran must be prescribed and administered only by, or under the direct supervision of, a physician experienced in the chemotherapy of hematologic malignancies and hematopoietic stem cell transplantation; it is not an outpatient or general-practice medication.

Other important warnings

• Seizures: Seizures have been reported with Myleran, particularly with high-dose conditioning regimens; prophylactic anticonvulsant therapy (commonly phenytoin) is standard practice during high-dose Myleran administration.
• Pulmonary toxicity ("Myleran lung"): A rare but recognized long-term complication historically associated with prolonged Myleran use, less relevant to modern short-course conditioning regimens but still noted; presents as interstitial pulmonary fibrosis.
• Secondary malignancies: Long-term survivors of Myleran-containing regimens carry an increased risk of secondary cancers; periodic long-term follow-up is advised.
• Individualized dosing: Administration and dosing of Myleran for transplant conditioning often requires therapeutic drug monitoring/pharmacokinetic dose adjustment, performed by a specialized hematology/oncology/transplant team.
• Cataracts and gonadal effects: Long-term use has been associated with cataract formation and gonadal suppression/infertility; discuss fertility preservation options before starting Myleran where feasible.

Overdose with Myleran is a medical emergency. There is no specific antidote; management is supportive, focusing on aggressive treatment of profound bone marrow suppression (blood product transfusion, growth factors, infection prophylaxis/treatment) and monitoring for hepatic veno-occlusive disease and other organ toxicity. Hemodialysis has been used in reported cases of significant overexposure to help lower drug levels. Anyone who has received or may have received an excessive dose of Myleran should seek immediate medical attention or contact emergency services/poison control without delay; do not attempt home management.

Oral Myleran tablets: store at room temperature (below 30°C), away from light and moisture, and keep out of reach of children. The intravenous concentrate for infusion should be stored under refrigeration (2-8°C) prior to dilution, protected from light, and used per the diluted-solution stability window specified by the manufacturer/pharmacy; it is handled and stored by hospital pharmacy and nursing staff, not by patients at home.

Renal impairment: No well-established formal dosing guideline exists; use with caution and enhanced monitoring. Hepatic impairment: Use with caution given the risk of hepatic veno-occlusive disease with Myleran; baseline and ongoing liver function assessment is recommended. Elderly: Limited specific data; comorbidities and organ reserve should be carefully assessed before high-dose Myleran conditioning. Pediatric and adolescent patients: see Pediatric Uses.

For transplant conditioning, intravenous Myleran is given as a fixed, short intensive course (typically over 4 consecutive days) immediately before stem cell infusion, as part of a defined protocol. For CML, oral Myleran treatment duration is individualized by the treating hematologist based on blood count response, and may range from several weeks to longer maintenance dosing, with the drug reduced or stopped once target counts are reached; today, its CML use is largely confined to specific transplant or second-line scenarios rather than long-term first-line therapy.

The intravenous concentrate must be diluted before use: the calculated dose is added to either 0.9% Sodium Chloride Injection or 5% Dextrose Injection to achieve a final Myleran concentration of approximately 0.5 mg/mL, following the manufacturer's preparation instructions, and infused via a central venous line using an infusion pump over about 2 hours. It must never be given undiluted or as a rapid injection. Oral tablets require no reconstitution.

Alkylating agents; Alkyl sulfonates; Antineoplastic (cytotoxic chemotherapy) agents

Busulfan acts as a bifunctional DNA-alkylating agent, forming covalent cross-links between DNA strands (primarily at the N7 position of guanine). This prevents proper DNA replication and transcription, activating apoptotic pathways in dividing cells. Hematopoietic stem and progenitor cells are particularly sensitive to this mechanism, which underlies both the antileukemic effect of Busulfan and its use as a myeloablative conditioning agent that empties the bone marrow space to permit donor stem cell engraftment.

D

Myleran is used in pediatric patients as part of conditioning regimens before hematopoietic stem cell transplantation, with dosing calculated on a weight or body-surface-area basis. Pharmacokinetics of Myleran are more variable in children than adults, so therapeutic drug monitoring (pharmacokinetic-guided dose adjustment) is strongly recommended to reduce the risk of under- or over-exposure. Safety and efficacy of oral Myleran specifically for chronic myelogenous leukemia have not been well established in children, as pediatric CML is rare; when used, it is only under specialist hematology-oncology direction.