Bosutinib (Bosulif): Understanding Its Mechanism, Dosing, Clinical Uses, and Role in Chronic Myeloid Leukemia

Bosutinib (Bosulif) is an oral BCR::ABL1 and SRC-family tyrosine kinase inhibitor (TKI) used for the treatment of Philadelphia chromosome-positive chronic myeloid leukemia (Ph+ CML). It is approved for newly diagnosed chronic-phase CML and for patients with chronic, accelerated, or blast-phase disease that is resistant or intolerant to prior therapy. As of the current U.S. prescribing information revised in March 2026, bosutinib is also approved for children aged 1 year and older with chronic-phase Ph+ CML.

Unlike some other second-generation TKIs, bosutinib has a toxicity profile dominated by gastrointestinal adverse effects, particularly diarrhea, and hepatic toxicity, while clinically significant arterial vascular toxicity and pleural effusion are generally less prominent than with some alternative TKIs. Its selection in CML is therefore strongly influenced by the patient’s prior TKI exposure, comorbidities, treatment goals, and tolerance profile.

Key Facts

• Generic name: Bosutinib
• Brand name: Bosulif
• Drug class: BCR::ABL1/SRC-family tyrosine kinase inhibitor
• Major targets: BCR::ABL1, SRC, Lyn, Hck
• Route: Oral
• Initial U.S. approval: 2012
• Newly diagnosed adult CP-CML dose: 400 mg once daily
• Resistant/intolerant adult CML dose: 500 mg once daily
• Administration: With food
• Pediatric newly diagnosed CP-CML: 300 mg/m² once daily
• Pediatric resistant/intolerant CP-CML: 400 mg/m² once daily
• Maximum adult/pediatric dose after escalation: 600 mg once daily
• Most characteristic toxicity: Diarrhea
• Other important risks: Hepatotoxicity, myelosuppression, cardiovascular toxicity, fluid retention, renal toxicity
• Major interaction pathway: CYP3A4
• Important absorption interaction: Proton-pump inhibitors can reduce bosutinib exposure.

What Is Bosutinib?

Bosutinib is an orally administered small-molecule kinase inhibitor designed primarily to suppress signaling from the abnormal:

BCR::ABL1 fusion tyrosine kinase

that drives Philadelphia chromosome-positive CML.

The Philadelphia chromosome results from:

t(9;22) → BCR::ABL1

The constitutively active BCR::ABL1 kinase promotes:

• Leukemic-cell proliferation
• Survival
• Reduced apoptosis
• Expansion of the malignant myeloid clone

Bosutinib also inhibits several SRC-family kinases, including:

• SRC
• Lyn
• Hck

In preclinical testing, bosutinib inhibited 16 of 18 imatinib-resistant BCR::ABL1 variants, but it does not adequately inhibit:

• T315I
• V299L.

What Is the Mechanism of Action of Bosutinib?

1. Constitutive BCR::ABL1 Signaling

The Philadelphia chromosome generates the BCR::ABL1 fusion protein, which has continuously active tyrosine kinase activity.

This drives downstream pathways such as:

• RAS–RAF–MEK–ERK
• PI3K–AKT
• JAK/STAT-associated signaling

These pathways support leukemic-cell proliferation and survival.

2. Bosutinib Binds the BCR::ABL1 Kinase

Bosutinib binds to and inhibits the BCR::ABL1 kinase domain.

It also inhibits SRC-family kinases, particularly:

• SRC
• Lyn
• Hck.

3. Kinase Phosphorylation Is Suppressed

Blocking kinase activity prevents phosphorylation of downstream signaling proteins.

4. Oncogenic Signaling Declines

The inhibition of BCR::ABL1 and SRC-family signaling reduces:

• Proliferative signaling
• Leukemic-cell survival
• Malignant clone expansion

5. Leukemic-Cell Growth Is Suppressed

Overall:

Bosutinib → BCR::ABL1 + SRC inhibition → ↓ oncogenic phosphorylation → ↓ proliferation and survival → increased leukemic-cell death

Bosutinib retains activity against many imatinib-resistant mutations but is not effective against T315I or V299L.

What Is the Recommended Dose of Bosutinib?

Newly Diagnosed Adult Chronic-Phase Ph+ CML

The recommended starting dose is:

400 mg orally once daily with food. 

Resistant or Intolerant Adult Ph+ CML

For adult patients with:

• Chronic-phase CML
• Accelerated-phase CML
• Blast-phase CML

that is resistant or intolerant to prior therapy:

500 mg orally once daily with food. 

Pediatric Newly Diagnosed Chronic-Phase CML

For children aged ≥1 year:

300 mg/m² orally once daily with food.

Pediatric Resistant or Intolerant Chronic-Phase CML
Recommended dose:

400 mg/m² orally once daily with food.

Pediatric doses are adjusted according to body surface area, with the approved label providing specific dose bands.

Can the Dose Be Increased?

Yes.

For adults who do not achieve or maintain an adequate:

• Hematologic response
• Cytogenetic response
• Molecular response

and who do not have Grade ≥3 adverse reactions, dose escalation may be considered in:

100 mg increments

to a maximum of:

600 mg once daily. 

Pediatric dose escalation may also be considered after insufficient response, using smaller increments depending on body surface area.

How Should Bosutinib Be Taken?

Bosutinib should be taken:

• Once daily
• With food
• At approximately the same time each day

Bosutinib tablets should be swallowed whole.

Do not:

• Cut
• Crush
• Break
• Chew

the tablets.

Bosulif capsules can be swallowed whole.

For patients who cannot swallow capsules, the capsule contents may be mixed with:

• Applesauce
• Yogurt

and consumed immediately without chewing.

Importantly, mixing the capsule with applesauce or yogurt does not replace the requirement to take bosutinib with a proper meal. 

What Should You Do If You Miss a Dose of Bosutinib?

If the missed dose is remembered within approximately 12 hours, follow the prescribed schedule.

If the dose has been missed by more than 12 hours:

• Skip the missed dose
• Take the normal prescribed dose the following day
• Do not double the dose.

How Are Bosutinib Dose Reductions Managed?

Dose interruption or reduction may be necessary for:

• Diarrhea
• Hepatotoxicity
• Neutropenia
• Thrombocytopenia
• Other clinically significant toxicities

Severe Diarrhea

For Grade 3–4 diarrhea:

• Withhold bosutinib until recovery to Grade ≤1
• Treatment may then be resumed at 400 mg once daily.

Hepatic Toxicity

If ALT or AST rises to:

>5 × ULN

bosutinib should be withheld until recovery to ≤2.5 × ULN.

Treatment may then be resumed at:

400 mg once daily.

If recovery takes more than 4 weeks, discontinuation is recommended.

Bosutinib should be discontinued for laboratory findings compatible with Hy’s law.

Other Nonhematologic Toxicities

For clinically significant moderate or severe toxicity:

• Withhold bosutinib
• Allow recovery
• Consider restarting at a dose reduced by 100 mg once daily

Re-escalation may be considered if clinically appropriate.

Myelosuppression

If:

ANC <1,000 × 10⁶/L

or:

platelets <50,000 × 10⁶/L

withhold treatment until recovery.

If recovery occurs within 2 weeks, treatment may resume at the same dose.

If cytopenia persists for >2 weeks:

reduce the dose by 100 mg.

If cytopenia recurs, reduce by another:

100 mg. 

What Drug Interactions Are Important With Bosutinib?

Strong or Moderate CYP3A Inhibitors

Bosutinib is a:

CYP3A substrate.

Strong or moderate CYP3A inhibitors can significantly increase bosutinib exposure.

Examples include:

• Ketoconazole
• Itraconazole
• Clarithromycin
• Ritonavir
• Certain azole antifungals and antivirals

Concomitant use should generally be avoided.

Ketoconazole increased bosutinib:

• Cmax approximately 5.2-fold
• AUC approximately 8.6-fold.

Strong CYP3A Inducers

Strong CYP3A inducers can markedly reduce bosutinib exposure.

Examples include:

• Rifampin
• Carbamazepine
• Phenytoin
• Phenobarbital
• St. John’s wort

Rifampin reduced:

• Cmax by 86%
• AUC by 94%.

These combinations should generally be avoided.

Proton-Pump Inhibitors

Bosutinib has pH-dependent solubility.

PPIs can therefore decrease bosutinib absorption.

Lansoprazole reduced bosutinib:

• Cmax by 46%
• AUC by 26%.

Instead of PPIs, consider:

• Short-acting antacids
• H2 blockers

These should be separated from bosutinib by:

more than 2 hours. 

Does Bosutinib Require Dose Adjustment in Renal or Hepatic Impairment?

Renal Impairment

For newly diagnosed chronic-phase CML:

• CrCl 30–50 mL/min: 300 mg once daily
• CrCl <30 mL/min: 200 mg once daily

For resistant/intolerant CML:

• CrCl 30–50 mL/min: 400 mg once daily
• CrCl <30 mL/min: 300 mg once daily.

Bosutinib has not been adequately studied in patients undergoing hemodialysis.

Hepatic Impairment

For patients with:

• Child-Pugh A
• Child-Pugh B
• Child-Pugh C

the recommended starting dose is:

200 mg once daily

for both newly diagnosed and resistant/intolerant adult CML.

What Is the Pharmacokinetic Profile of Bosutinib?

Absorption

After oral administration with food, median time to maximum concentration is approximately:

6 hours.

Absolute bioavailability is approximately:

34%.

Effect of Food

Food substantially increases bosutinib exposure.

With a high-fat meal, bosutinib tablets showed approximately:

• 1.8-fold higher Cmax
• 1.7-fold higher AUC

compared with fasting administration.

This is why Bosulif should be taken:

with food.

Protein Binding

Bosutinib is highly protein bound:

• Approximately 94% in vitro
• Approximately 96% ex vivo.

Half-Life

The mean terminal elimination half-life is approximately:

22.5 hours. 

This supports once-daily dosing.

Metabolism

Bosutinib is primarily metabolized by:

CYP3A4.

Excretion

Following radiolabeled administration:

• Approximately 91.3% was recovered in feces
• Approximately 3.3% was recovered in urine.

What Are the Clinical Uses of Bosutinib?

Newly Diagnosed Chronic-Phase Ph+ CML

Bosutinib is FDA approved for adults and children aged ≥1 year with:

newly diagnosed chronic-phase Philadelphia chromosome-positive CML. 

Chronic-Phase CML Resistant or Intolerant to Prior Therapy

Bosutinib is also approved for:

chronic-phase Ph+ CML after resistance or intolerance to prior therapy.

This applies to both adults and pediatric patients aged ≥1 year.

Advanced-Phase CML

In adults, bosutinib is approved for:

• Accelerated-phase Ph+ CML
• Blast-phase Ph+ CML

after resistance or intolerance to previous therapy.

What Did the Pivotal Clinical Trials Show?

BFORE

The phase III BFORE trial established bosutinib as a first-line treatment for newly diagnosed chronic-phase CML.

A total of:

536 patients

were randomized to:

• Bosutinib 400 mg once daily
• Imatinib 400 mg once daily.

At 12 months:

Major Molecular Response

• Bosutinib: 47.2%
• Imatinib: 36.9%

P = 0.02

Complete Cytogenetic Response

• Bosutinib: 77.2%
• Imatinib: 66.4%

P = 0.0075.

Bosutinib therefore produced faster and deeper molecular responses than imatinib.

Five-Year BFORE Results

At 5 years, cumulative:

MMR

• Bosutinib: 73.9%
• Imatinib: 64.6%

MR4

• Bosutinib: 58.2%
• Imatinib: 48.1%

MR4.5

• Bosutinib: 47.4%
• Imatinib: 36.6%.

These final results confirmed the durability of bosutinib as a first-line CML treatment.

BYOND

The phase IV BYOND trial evaluated bosutinib in patients who were resistant or intolerant to previous TKIs.

A total of:

163 patients

with previously treated CML received bosutinib, generally beginning at:

500 mg once daily.

At final analysis, among evaluable patients with Ph+ chronic-phase CML:

• MMR achieved or maintained: 71.8%
• MR4 achieved or maintained: 59.7%
• 48-month overall survival: 88.3%.

The probability of maintaining response at 36 months was:

• MMR: 87.2%
• MR4: 80.7%

Importantly, dose reduction for toxicity could improve tolerability without necessarily compromising efficacy.

Long-Term Second-Line Bosutinib Study

A 2026 final analysis provides the longest follow-up yet reported for bosutinib after imatinib failure.

Among:

284 patients

with chronic-phase CML receiving second-line bosutinib, cumulative:

• Complete cytogenetic response: 49.6%
• MMR: 42.1%
• MR4: 37.1%

At year 11:

• Overall survival was 70.5%
• No new long-term safety signals emerged.

This mature dataset supports durable efficacy of bosutinib as a long-term second-line therapy.

Is Bosutinib FDA Approved?

Yes.

Current FDA-approved indications include:

Adults

• Newly diagnosed chronic-phase Ph+ CML
• Chronic-phase Ph+ CML resistant or intolerant to prior therapy
• Accelerated-phase Ph+ CML resistant or intolerant to prior therapy
• Blast-phase Ph+ CML resistant or intolerant to prior therapy

Pediatrics ≥1 Year

• Newly diagnosed chronic-phase Ph+ CML
• Chronic-phase Ph+ CML resistant or intolerant to prior therapy.

What Is the Current Clinical Role of Bosutinib in 2026?

First-Line Chronic-Phase CML

Bosutinib remains an established second-generation TKI for newly diagnosed chronic-phase CML.

Compared with imatinib, BFORE demonstrated:

• Faster molecular responses
• Higher cumulative MMR
• Higher MR4 and MR4.5 rates.

Its selection should take into account:

• CML risk
• Comorbidities
• Molecular response goals
• Mutation profile
• Prior gastrointestinal disease
• Liver function
• Renal function
• Cardiovascular risk
• Previous TKI intolerance

Read more: Choice of Frontline TKI for CML-CP by OncoDaily reviews the approved frontline TKIs, including bosutinib, and highlights treatment selection based on molecular goals, comorbidities, and toxicity patterns such as diarrhea, renal dysfunction, and liver dysfunction.

Watch more: Bosutinib: a new, safer TKI for frontline CML — Michael Mauro, MD, discusses bosutinib as a frontline option for chronic myeloid leukemia and the BFORE trial.

After Prior TKI Therapy

Bosutinib is particularly valuable after intolerance or resistance to:

• Imatinib
• Dasatinib
• Nilotinib

and can provide durable molecular responses after multiple prior TKIs.

Mutation Considerations

Bosutinib retains activity against many BCR::ABL1 mutations.

However, it should not be relied upon for:

• T315I
• V299L.

Treatment-Free Remission

Compared with imatinib, nilotinib, and dasatinib, prospective treatment-free remission data for bosutinib remain comparatively limited.

Small datasets suggest that TFR after bosutinib can be feasible in selected patients with sustained deep molecular response, but this is not yet the defining clinical role of bosutinib.

What Are the Major Side Effects of Bosutinib?

Common adverse reactions include:

• Diarrhea
• Abdominal pain
• Nausea
• Vomiting
• Rash
• Fatigue
• Headache
• Pyrexia
• Decreased appetite
• Hepatic dysfunction
• Respiratory tract infections
• Constipation.

Important clinically significant toxicities include:

• Severe diarrhea
• Hepatotoxicity
• Myelosuppression
• Cardiovascular toxicity
• Fluid retention
• Pleural effusion
• Renal toxicity
• Pancreatic enzyme elevations
• Rare pancreatitis

Gastrointestinal Toxicity

Diarrhea is the characteristic toxicity of bosutinib.

In BFORE, diarrhea occurred in approximately:

75%

of bosutinib-treated patients, compared with 40% receiving imatinib.

Grade 3/4 diarrhea occurred in approximately:

9% versus 1%, respectively.

In newly diagnosed patients, the median time to onset was only:

4 days

and individual episodes typically lasted approximately:

3 days. 

Management includes:

• Antidiarrheal therapy
• Oral or IV fluid replacement when needed
• Treatment interruption
• Dose reduction for severe toxicity

Hepatotoxicity

Bosutinib frequently causes elevations in:

• ALT
• AST

In newly diagnosed patients:

• ALT elevation occurred in approximately 68%
• AST elevation in approximately 56%.

Most first elevations occurred within the first:

3 months.

Liver enzymes should therefore be monitored closely early in therapy.

Myelosuppression

Bosutinib may cause:

• Thrombocytopenia
• Neutropenia
• Anemia

CBC should be performed:

• Weekly during the first month
• Then monthly
• Or more frequently when clinically indicated.

Cardiovascular Toxicity

Bosutinib can cause:

• Cardiac failure
• Left ventricular dysfunction
• Cardiac ischemic events

In the first-line randomized study:

• Cardiac failure: 1.9%
• Cardiac ischemic events: 4.9%.

Patients with established cardiovascular disease or risk factors should be monitored closely.

Fluid Retention

Bosutinib can cause:

• Peripheral edema
• Pleural effusion
• Pericardial effusion
• Pulmonary edema

Severe fluid retention was uncommon in newly diagnosed patients but occurred more often in previously treated populations.

Renal Toxicity

A progressive reduction in:

eGFR

has been observed during bosutinib therapy.

Renal function should therefore be assessed:

• At baseline
• Periodically during treatment
• More frequently in patients with pre-existing renal impairment or renal risk factors.

What Monitoring Is Required During Bosutinib Treatment?

Monitoring should include:

• CBC
• BCR::ABL1 quantitative PCR
• ALT
• AST
• Bilirubin
• Serum creatinine
• eGFR
• Electrolytes
• Lipase when clinically indicated
• Gastrointestinal symptoms
• Hydration status
• Fluid retention
• Cardiac symptoms
• Blood pressure
• Medication interactions
• Use of CYP3A inhibitors or inducers
• Use of proton-pump inhibitors
• Pregnancy status when relevant

CBC

• Weekly during the first month
• Monthly thereafter

Liver Function

• At least monthly during the first 3 months
• Then as clinically indicated.

Molecular Monitoring

Serial:

BCR::ABL1 quantitative PCR

should be performed according to standard CML molecular monitoring recommendations.