PEMETREXED DITROMETHAMINE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PEMETREXED DITROMETHAMINE (PEMETREXED DITROMETHAMINE).
Pemetrexed inhibits thymidylate synthase (TS), dihydrofolate reductase (DHFR), and glycinamide ribonucleotide formyltransferase (GARFT), enzymes involved in folate-dependent purine and pyrimidine synthesis, leading to disruption of DNA synthesis and cell death.
| Metabolism | Pemetrexed is primarily excreted unchanged in the urine. It undergoes minimal hepatic metabolism; less than 5% is metabolized by the liver. |
| Excretion | Primarily renal excretion: 70-90% of the dose is eliminated unchanged in urine within 24 hours. Fecal excretion accounts for <5%. |
| Half-life | Terminal half-life 3.5 hours (range 2.5-5.0 hours) in patients with normal renal function; prolonged to 5-10 hours in moderate renal impairment. Clinical context: Half-life is dose-independent; clearance correlates with creatinine clearance. |
| Protein binding | 81% bound primarily to albumin; minimal binding to alpha-1-acid glycoprotein. |
| Volume of Distribution | Vd at steady state = 16.1 L/m² (approximately 0.4 L/kg in adults). Clinical meaning: Indicates distribution into total body water with limited tissue binding; low Vd suggests minimal extravascular distribution. |
| Bioavailability | Intravenous only; bioavailability is 100% by IV route. Not orally available due to poor absorption and extensive first-pass metabolism. |
| Onset of Action | Intravenous administration: Onset of effect within 1-2 hours post-dose, based on antifolate activity (timing of cellular uptake and polyglutamation). |
| Duration of Action | Duration of pharmacodynamic effect approximately 1-2 weeks, corresponding to the dosing interval (every 21 days). Clinical notes: Cell cycle phase-specific (S-phase); prolonged duration due to polyglutamation in tumor cells. |
500 mg/m2 intravenously over 10 minutes every 21 days.
| Dosage form | POWDER |
| Renal impairment | CrCl ≥45 mL/min: 500 mg/m2; CrCl 30-44 mL/min: 375 mg/m2; CrCl <30 mL/min: not recommended. |
| Liver impairment | No dose adjustment recommended for Child-Pugh A or B. Child-Pugh C: no data. |
| Pediatric use | Not established; safety and efficacy not determined in pediatric patients. |
| Geriatric use | No specific dose adjustment; monitor renal function closely due to age-related decline in CrCl. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PEMETREXED DITROMETHAMINE (PEMETREXED DITROMETHAMINE).
| Breastfeeding | There are no data on the presence of pemetrexed in human milk, its effects on the breastfed infant, or milk production. Due to the potential for serious adverse reactions in nursing infants (e.g., myelosuppression, gastrointestinal toxicity), breastfeeding is not recommended during pemetrexed therapy and for at least one week after the last dose. The M/P ratio is unknown. |
| Teratogenic Risk | Pemetrexed is a folate analog metabolic inhibitor that is teratogenic in animals. In humans, it is contraindicated in pregnancy due to its mechanism of action interfering with DNA synthesis and cell division. First trimester exposure carries the highest risk of major congenital malformations (e.g., neural tube defects, craniofacial anomalies). Second and third trimester exposure may cause fetal growth restriction, oligohydramnios, and potential fetal demise. Use in pregnant women is not recommended unless no safer alternative exists. |
■ FDA Black Box Warning
Pemetrexed can cause severe or fatal hypersensitivity reactions, including anaphylaxis. It also causes severe myelosuppression, which may require dose modification or discontinuation. Patients must be pretreated with corticosteroids and vitamin supplementation to reduce toxicity.
| Serious Effects |
["History of severe hypersensitivity reaction to pemetrexed or any excipients.","Concurrent yellow fever vaccine (risk of systemic fatal disease).","Severe renal impairment (CrCl <45 mL/min) not meeting criteria for dose adjustment."]
| Precautions | ["Myelosuppression: Dose-dependent, monitor blood counts regularly.","Renal toxicity: Excreted renally; adjust dose in renal impairment (CrCl <45 mL/min).","Gastrointestinal toxicity: Nausea, vomiting, diarrhea; may require antiemetics.","Hypersensitivity reactions: Premedicate with corticosteroids.","Folic acid and vitamin B12 deficiency: Supplement to reduce hematologic toxicity.","Third-space fluid accumulation: Consider drainage before treatment."] |
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| Fetal Monitoring | Complete blood count (CBC) with differential and platelets prior to each dose; renal function (serum creatinine) and hepatic function tests. Monitor for signs of myelosuppression, fatigue, nausea, and skin reactions. In pregnancy, fetal ultrasound for growth and amniotic fluid volume, and consider fetal echocardiography if first-trimester exposure. |
| Fertility Effects | Pemetrexed may impair fertility in both males and females. In males, it may cause oligospermia or azoospermia; in females, it may cause amenorrhea and premature ovarian failure. The effects may be irreversible. Patients should be counseled on fertility preservation options before treatment. |