IMATINIB MESYLATE
Clinical safety rating: avoid
Contraindicated (not allowed)
Imatinib mesylate is a tyrosine kinase inhibitor that selectively inhibits BCR-ABL, c-KIT, and PDGFR tyrosine kinases, thereby blocking signal transduction pathways involved in cellular proliferation and survival.
| Metabolism | Primarily metabolized by CYP3A4 to the active metabolite N-desmethylimatinib (CGP74588). Minor contributions from CYP1A2, CYP2D6, CYP2C9, and CYP2C19. Excreted mostly via feces (68%) and urine (13%). |
| Excretion | Primarily fecal (68% of dose) as metabolites; renal excretion accounts for approximately 13% of dose (5% as unchanged drug and 8% as metabolites). |
| Half-life | Terminal elimination half-life is approximately 18 hours (range 13–22 hours) for the parent drug; the active metabolite N-desmethyl imatinib has a half-life of about 40 hours. Clinically, this supports once-daily dosing. |
| Protein binding | Approximately 95% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | Apparent volume of distribution is about 4.0 L/kg (range 3.2–4.8 L/kg), indicating extensive tissue distribution. |
| Bioavailability | Oral bioavailability is approximately 98% after a 400 mg dose, with minimal first-pass metabolism. |
| Onset of Action | Oral: Clinical response (e.g., hematologic improvement in CML) typically observed within 2–4 weeks; maximum plasma concentrations reached 2–4 hours post-dose. |
| Duration of Action | Duration of action relates to continuous target inhibition; with daily dosing, trough concentrations maintain effective inhibition of BCR-ABL tyrosine kinase. Clinical effect persists as long as therapy is continued; missed doses may allow reactivation of signaling. |
| Molecular Weight | 589.7 Da (calculated) |
400 mg orally once daily, with a meal and a large glass of water. Dose escalation to 600 mg or 800 mg daily may be considered in cases of disease progression.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment (CrCl >20 mL/min). For severe renal impairment (CrCl <20 mL/min), use with caution; a 50% dose reduction (200 mg daily) is recommended. |
| Liver impairment | Child-Pugh A (mild): no adjustment; Child-Pugh B (moderate): reduce dose by 25% (300 mg daily); Child-Pugh C (severe): reduce dose by 50% (200 mg daily). |
| Pediatric use | For chronic myeloid leukemia (CML): 340 mg/m²/day orally (maximum 600 mg/day) as a single daily dose; for Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL): 340 mg/m²/day (maximum 600 mg/day). Dosing based on body surface area. |
| Geriatric use | No specific dose adjustment based solely on age. Monitor renal function and hepatic function due to age-related decline; consider starting at 300 mg daily if significant comorbidities or intolerance expected. |
| 1st trimester | Avoid use during first trimester unless potential benefit justifies risk to fetus. Imatinib is teratogenic in animals; human data limited but suggests increased risk of spontaneous abortion and congenital anomalies. |
| 2nd trimester | Use only if clearly needed. May cause fetal harm; consider alternative therapy if possible during organogenesis (weeks 14-27). |
| 3rd trimester | Avoid in third trimester if possible; may cause neonatal hepatotoxicity or myelosuppression. Monitor newborn for adverse effects if exposed late in pregnancy. |
Clinical note
Strong CYP3A4 inducers may decrease efficacy Can cause fluid retention and myelosuppression.
| Placental transfer | Imatinib crosses the placenta; detectable in cord blood from placental transfer. Animal studies show high transfer with fetal tissue levels similar to maternal. |
| Breastfeeding | Imatinib is excreted into breast milk in low concentrations; however, potential for serious adverse reactions in nursing infants exists. The manufacturer recommends discontinuing breastfeeding due to unknown risks. Consider using a formula or alternative treatment. |
■ FDA Black Box Warning
None. Imatinib does not have a boxed warning in the FDA prescribing information.
| Common Effects | Edema swelling Nausea Vomiting Muscle cramp Musculoskeletal bone muscle or joint pain Diarrhea Rash Fatigue Abdominal pain Bleeding Breathing problems Cough Weight gain Dry eye Dizziness Hemorrhage |
| Serious Effects |
Hypersensitivity to imatinib or any component of the formulationSevere hepatic impairment (Child-Pugh class C) unless dose adjustedConcurrent use with strong CYP3A4 inducers such as rifampin (avoid if possible)Pregnancy (category D; avoid unless benefit outweighs risk)
| Precautions | Fluid retention (e.g., pleural effusion, pericardial effusion, severe edema), Hepatotoxicity (elevated liver enzymes, bilirubin; can be severe), Cardiovascular effects (e.g., QT prolongation, congestive heart failure, left ventricular dysfunction), Cytopenias (neutropenia, thrombocytopenia, anemia) requiring dose reduction or interruption, Hemorrhage (especially in GIST patients), Gastrointestinal perforation, Hypothyroidism in patients undergoing thyroidectomy, Growth retardation in children, Tumor lysis syndrome, Fetal harm (pregnancy category D) |
Loading safety data…
| Lactation Rating | L4 (Possibly Hazardous) |
| Teratogenic Risk | Imatinib mesylate is teratogenic in animal studies. First trimester exposure is associated with increased risk of major congenital malformations (e.g., exencephaly, encephalocele, skeletal anomalies) based on animal data. Second and third trimester exposure may cause fetal growth restriction, oligohydramnios, and preterm birth. Human data are limited; however, cases of spontaneous abortion and fetal abnormalities have been reported. Use only if maternal benefit outweighs fetal risk. |
| Fetal Monitoring | Monitor complete blood counts (CBC) with differential monthly, hepatic function (ALT, AST, bilirubin), and renal function (serum creatinine, BUN) every 2-3 months. Assess fetal growth by ultrasound every 4-6 weeks from 20 weeks gestation. Monitor amniotic fluid volume due to risk of oligohydramnios. Perform fetal echocardiography for potential cardiac effects. Monitor maternal thyroid function if on concomitant levothyroxine. |
| Fertility Effects | Imatinib may impair male and female fertility. In males, it can cause oligospermia and reduced testosterone levels; in females, it may cause menstrual irregularities, amenorrhea, and decreased ovarian reserve. Reversibility is uncertain. Preclinical studies show impaired spermatogenesis and ovarian follicular development. Counsel patients on potential impact and consider fertility preservation before treatment. |
| Food/Dietary | Avoid grapefruit, grapefruit juice, Seville oranges, and pomelos due to CYP3A4 inhibition increasing imatinib levels. Avoid St. John's wort as it induces CYP3A4 and may reduce efficacy. Take with food and ample water to minimize gastrointestinal irritation. No other specific dietary restrictions; maintain consistent intake of vitamin K-containing foods if on warfarin (imatinib may alter warfarin metabolism). |
| Clinical Pearls | Monitor for fluid retention, especially pleural effusion and peripheral edema. Obtain baseline LFTs, CBC, and renal function; repeat monthly for first 3 months. Avoid concurrent strong CYP3A4 inducers/inhibitors. Imatinib is a major substrate of CYP3A4 and P-glycoprotein. QT prolongation possible; monitor ECG if risk factors present. Dose reduction for severe hepatic impairment. In chronic myeloid leukemia, assess molecular response (BCR-ABL1 transcript levels) every 3 months. Grapefruit increases imatinib exposure. Advise patients to take with food and a large glass of water to reduce GI upset. |
| Patient Advice | Take exactly as prescribed, usually once or twice daily with a meal and full glass of water. · Do not stop taking this medication without consulting your doctor, even if you feel well. · Report any signs of fluid retention such as swelling of ankles/legs, sudden weight gain, or shortness of breath. · Avoid grapefruit, grapefruit juice, and Seville oranges while on this medication. · Use effective contraception during treatment and for at least 14 days after stopping. · Do not become pregnant or father a child while taking this drug; discuss fertility preservation options. · Avoid St. John's wort as it may decrease effectiveness. · Common side effects include nausea, muscle cramps, diarrhea, and rash; contact doctor if severe or persistent. · Check with doctor before taking any new medications, including over-the-counter drugs and supplements. · Attend all scheduled blood tests and appointments to monitor response and side effects. |