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Why a clear melphalan guide matters
High‑dose Melphalan is a nitrogen‑mustard alkylating agent used in the curative treatment of several blood cancers. A small miscalculation in **melphalan dosing** can mean the difference between a successful transplant and life‑threatening toxicity. This guide walks you through the facts you need to prescribe, prepare, and monitor melphalan safely.
Pharmacology at a glance
Melphalan works by cross‑linking DNA strands, preventing replication and ultimately triggering cell death. Its pharmacokinetics are dose‑dependent, with a half‑life of 90‑120 minutes after intravenous (IV) administration. The drug is primarily eliminated unchanged by the kidneys, making renal function the most critical factor for dose adjustments.
Key clinical indications
Although melphalan is approved for multiple conditions, two scenarios dominate daily practice:
- Multiple Myeloma is a plasma‑cell malignancy that often requires high‑dose melphalan as part of an autologous stem cell transplant (ASCT) conditioning regimen.
- Lymphoma (particularly Hodgkin and certain non‑Hodgkin subtypes) may be treated with melphalan in combination protocols or as a salvage agent.
Dosage calculations - the core of safe practice
Melphalan dosing is expressed in milligrams per square meter (mg/m²) of body surface area (BSA). The most common formulas are:
- Calculate BSA using the DuBois formula: BSA (m²) = 0.007184 × weight^0.425 (kg) × height^0.725 (cm).
- Multiply the BSA by the indication‑specific dose.
Typical regimens:
| Indication | Usual dose (mg/m²) | Frequency | Route |
|---|---|---|---|
| High‑dose conditioning for ASCT (multiple myeloma) | 200 mg/m² | Single dose | IV infusion |
| Lymphoma salvage | 100 mg/m² | Days 1 and 2 | IV infusion |
| Oral maintenance (low‑dose) | 0.25 mg/kg (rounded to nearest 2 mg) | Daily | Oral tablet |
Always round to the nearest 5 mg for IV and the nearest 2 mg for oral tablets, unless a specific protocol dictates otherwise.
Administration routes and practical tips
Melphalan is supplied as a sterile lyophilised powder for reconstitution (IV) and as 2 mg and 4 mg oral tablets. Follow these steps:
- IV infusion: Melphalan must be reconstituted with sterile water for injection to a concentration of 1 mg/mL. Dilute the solution further in 0.9% NaCl or D5W to a final volume of 250 mL for infusion over 30 minutes.
- Administer through a dedicated central line (preferably a tunneled catheter) to avoid extravasation.
- Perform the infusion in a negative‑pressure isolation room if the patient is neutropenic.
- Oral tablets should be swallowed with water; do not crush or chew as this increases mucosal toxicity.
Preparation, handling, and safety precautions
Melphalan is a hazardous drug. Pharmacy staff must use certified biological safety cabinets (Class II) and wear double gloves, a gown, and a mask. After reconstitution, keep the solution protected from light and use within 2 hours. Dispose of all waste according to local hazardous drug guidelines.
Monitoring parameters and managing toxicities
Key labs should be drawn before dosing and daily for 7 days post‑infusion:
- Complete blood count (CBC) - watch for nadir neutrophils < 0.5 × 10⁹/L.
- Serum creatinine and blood urea nitrogen - adjust dose if creatinine clearance < 40 mL/min.
- Liver enzymes (AST, ALT, bilirubin) - especially in patients with hepatic metastases.
- Electrolytes - melphalan can cause hyponatremia.
Common toxicities:
- Myelosuppression: anticipate a 10‑14 day aplastic phase; provide growth‑factor support (e.g., G‑CSF) as needed.
- Mucositis: prophylactic oral rinses (saline or chlorhexidine) reduce severity.
- Renal toxicity: maintain adequate hydration (≥2 L / day) and monitor urine output.
- Secondary malignancies: counsel patients on long‑term risk, especially after high‑dose regimens.
Dose adjustments for organ dysfunction
Because melphalan is renally cleared, dose reductions are essential for impaired kidneys:
- Creatinine clearance 30‑50 mL/min: reduce dose to 75% of calculated amount.
- Clearance < 30 mL/min: reduce to 50% or consider alternative conditioning.
Hepatic impairment (bilirubin > 2 × ULN) also warrants a 25‑30% dose reduction, though data are less robust than for renal function.
Practical checklist for the clinical team
- Confirm indication and target dose (mg/m²).
- Calculate patient BSA accurately; double‑check with a second clinician.
- Review latest labs - creatinine, bilirubin, CBC.
- Adjust dose per renal/hepatic guidelines.
- Order melphalan vials, sterile water, diluent, and infusion set.
- Pharmacy staff reconstitutes under hood, labels with patient ID, dose, and expiration time.
- Nurse verifies dose, checks line integrity, and starts infusion over 30 minutes.
- Provide anti‑emetic prophylaxis (e.g., ondansetron) and oral care kit.
- Monitor vitals and labs per protocol; document any adverse events.
- Post‑infusion, arrange for stem‑cell rescue (if applicable) and discharge planning.
Frequently Asked Questions
How is melphalan different from other alkylating agents?
Melphalan adds a phenylalanine side chain, which increases its lipophilicity. This allows better penetration into bone marrow and solid tumors, making it especially useful for high‑dose conditioning before stem‑cell transplant.
Can melphalan be given orally for high‑dose regimens?
No. Oral melphalan is limited to low‑dose maintenance (typically 0.25 mg/kg). High‑dose regimens require IV infusion to achieve the plasma concentrations needed for effective myeloablation.
What pre‑hydration protocol reduces renal toxicity?
Give 1 L of normal saline 30 minutes before infusion, then another 1 L during the infusion, followed by 500 mL over the next 6 hours. Adjust for cardiac status.
How long after melphalan can stem cells be reinfused?
Typically 24 hours after the high‑dose infusion, once the melphalan plasma level has fallen below 10 µg/mL. Exact timing depends on the conditioning protocol.
What are the signs of extravasation and how should they be managed?
Pain, erythema, and swelling at the infusion site indicate extravasation. Stop the infusion immediately, aspirate any residual drug, elevate the limb, and apply cold compresses for the first 24 hours. Consult the oncology pharmacy for antidote protocols.
Bottom line
When you nail the three pillars-accurate BSA‑based dosing, vigilant organ‑function adjustment, and disciplined infusion technique-melphalan can be a life‑saving weapon with manageable side effects. Keep this guide at hand, double‑check every calculation, and involve the multidisciplinary team early. Your attention to detail translates directly into better transplant outcomes and fewer complications.