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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Strong CYP3A4 inducers may decrease efficacy Can cause fluid retention and myelosuppression.
| Breastfeeding | No adequate human data on imatinib excretion in breast milk. M/P ratio unknown. Animal studies show distribution into milk. Potential for serious adverse reactions in breastfed infant (e.g., neutropenia, growth retardation). Discontinue breastfeeding or discontinue drug, considering importance of drug to mother. |
| 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. |
■ 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 formulation"]
| 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)"] |
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| 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. |