Chemotherapy BSA Dose Calculator — Oncology Drug Dosing by Body Surface Area

How to Use This Calculator

1. Enter height (cm) and weight (kg) — BSA calculates via Mosteller formula.
2. Select the chemotherapy drug from the list.
3. Dose in mg displays with BSA capping note.
4. Use the Dose Adjustments tab for renal/hepatic modifications.
5. Use the Anthracycline Limit tab to track cumulative doxorubicin exposure.

Formula

Example

Frequently Asked Questions

• Why is chemotherapy dosed by body surface area? ▼
  Chemotherapy has been dosed by body surface area (BSA) since the late 1950s, when Freifeld and colleagues observed that BSA correlated better with drug toxicity and clearance than body weight alone in animal studies. The theoretical rationale is that BSA correlates with cardiac output, glomerular filtration rate, and hepatic blood flow — the primary determinants of drug distribution and elimination. By normalising dose to BSA, the goal is to achieve comparable drug exposure (area under the plasma concentration-time curve, or AUC) across patients of different sizes. In practice, BSA dosing reduces — but does not eliminate — inter-patient pharmacokinetic variability. The coefficient of variation in drug clearance is approximately 3–6 fold even after BSA adjustment, reflecting the importance of genetic polymorphisms in metabolising enzymes (particularly CYP450 and UGT1A1), organ function, drug interactions, and other patient-specific factors. Despite well-documented limitations, BSA dosing remains the standard for most cytotoxic agents because the infrastructure for therapeutic drug monitoring (TDM) is not routinely available for most drugs, and switching away from BSA dosing without robust alternatives risks introducing new dosing errors.
• When is BSA capped for chemotherapy dosing? ▼
  BSA capping is the practice of using a maximum BSA value — typically 2.0 or 2.2 m² — for dose calculation in obese patients, regardless of their actual BSA. This is controversial and not universally supported by evidence. The rationale for capping is that obese patients may have disproportionately high BSA relative to lean body mass, and drug distribution in adipose tissue differs from lean tissue for many agents; using actual BSA in morbidly obese patients could lead to overdosing. However, multiple retrospective analyses and ASCO guidelines have challenged this practice. For many drugs — particularly carboplatin (where AUC-based dosing is used instead), paclitaxel, and several targeted agents — using actual body weight and actual BSA is associated with similar toxicity rates in obese patients and potentially improved efficacy compared to capped dosing. ASCO's 2012 guideline on chemotherapy dosing in obese adults recommends using actual body weight for most agents, with BSA uncapped or capped at 2.0–2.2 m² for select regimens where evidence supports capping. Institutional practices vary, and clinical pharmacists should be consulted when BSA exceeds 2.0 m².
• What is dose-dense chemotherapy? ▼
  Dose-dense chemotherapy refers to delivering standard cumulative doses in shortened intervals compared to conventional scheduling — typically every 2 weeks instead of every 3 weeks — while maintaining full dose per cycle. The biological rationale is based on the Norton-Simon hypothesis of tumour growth kinetics: delivering cytotoxic agents more frequently prevents rapid tumour re-growth between cycles in fast-proliferating cancers. The CALGB 9741 trial by Citron et al. (2003) demonstrated that dose-dense AC-T (doxorubicin/cyclophosphamide followed by paclitaxel every 2 weeks) significantly improved disease-free survival and overall survival in node-positive breast cancer compared to every 3-week dosing. Dose-dense regimens require mandatory granulocyte colony-stimulating factor (G-CSF) support to prevent prolonged neutropenia from the shortened cycle interval. Without G-CSF, dose-dense scheduling would produce unacceptably high rates of febrile neutropenia. ANC must be adequate (≥1,000–1,500 cells/μL depending on protocol) before each cycle. Dose-dense strategies are also used in aggressive lymphomas and germ cell tumours, where rapid cycling provides therapeutic advantage against rapidly proliferating tumour cells.
• How does renal or hepatic impairment affect chemotherapy dosing? ▼
  Renal and hepatic impairment affect chemotherapy dosing through their effects on drug elimination and metabolism. Renally cleared drugs require dose reduction when creatinine clearance (CrCl) falls below threshold values. Cisplatin is the classic example — it is directly nephrotoxic and primarily renally eliminated; most protocols hold cisplatin if CrCl falls below 50–60 mL/min. Carboplatin dose is calculated using the Calvert formula, which incorporates GFR directly, so renal function automatically modulates the dose. Other renally cleared agents requiring adjustment include bleomycin, methotrexate, and etoposide. Hepatically metabolised drugs require adjustment when liver function is compromised. Taxanes (paclitaxel, docetaxel), anthracyclines (doxorubicin), and vinca alkaloids (vincristine, vinblastine) are predominantly hepatically metabolised and excreted in bile. Standard practice uses bilirubin and transaminase thresholds to guide dose reductions: mild hepatic impairment (bilirubin 1–1.5× ULN) typically warrants 75–80% dosing; moderate (bilirubin 1.5–3× ULN) warrants 50–75%; severe (bilirubin >3× ULN) typically contraindicates therapy or requires extreme reduction. Specific adjustments vary by drug and should be verified against AHFS Drug Information, FDA labelling, or institutional pharmacy protocols.
• Is flat dosing replacing BSA-based dosing in oncology? ▼
  There is growing interest in flat (fixed) dosing — giving all patients the same absolute dose regardless of BSA — for certain oncology drugs, particularly targeted therapies, immunotherapy, and antibody-drug conjugates. Flat dosing offers practical advantages: simpler preparation and dispensing, reduced pharmacy burden, easier dose rounding, and elimination of BSA calculation errors. The scientific rationale comes from pharmacokinetic modelling showing that for agents with wide therapeutic indices, pharmacogenomic variability in drug metabolism far exceeds the inter-patient variability that BSA accounts for. Anti-PD-1 and anti-PD-L1 immunotherapy agents (pembrolizumab, nivolumab, atezolizumab) are all now approved with flat fixed doses rather than mg/kg or mg/m² dosing. Several targeted oral agents have always been given as fixed doses. For cytotoxic chemotherapy, the case for flat dosing is weaker — platinum drugs, taxanes, and anthracyclines have narrow therapeutic indices where even modest overdosing causes serious toxicity. The FDA's Project Optimus initiative is encouraging oncology drug developers to better characterise dose-response and dose-toxicity relationships to support optimal dosing strategies, which may lead to more fixed-dose approvals. In practice, BSA-based dosing remains dominant for cytotoxic agents while flat dosing is standard for immunotherapy.

Related Calculators