Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
PEMETREXED DISODIUM vs ALFENTA
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Pemetrexed is a folate analog metabolic inhibitor that disrupts folate-dependent metabolic processes essential for cell replication. It inhibits thymidylate synthase (TS), dihydrofolate reductase (DHFR), and glycinamide ribonucleotide formyltransferase (GARFT), thereby inhibiting de novo synthesis of thymidine and purine nucleotides.
μ-opioid receptor agonist that activates G-protein coupled receptors to inhibit adenylate cyclase, decreasing c AMP production, leading to reduced neuronal excitability and pain transmission.
Mesothelioma: In combination with cisplatin for treatment of malignant pleural mesothelioma in patients who are not candidates for curative surgery.,Non-small cell lung cancer: First-line treatment in combination with cisplatin for locally advanced or metastatic nonsquamous NSCLC.,Non-small cell lung cancer: Maintenance monotherapy for locally advanced or metastatic nonsquamous NSCLC with stable disease after 4 cycles of platinum-based chemotherapy.,Non-small cell lung cancer: Second-line treatment as monotherapy for locally advanced or metastatic nonsquamous NSCLC after prior chemotherapy.
Induction and maintenance of anesthesia,Analgesic supplement during surgical procedures,Intravenous use for monitored anesthesia care (MAC)
500 mg/m2 intravenously over 10 minutes on Day 1 of each 21-day cycle, with vitamin B12 and folic acid supplementation.
Intravenous: Initial dose 8-20 mcg/kg (0.5-1 min) then 0.5-3 mcg/kg/min or 3-5 mcg/kg q5-20min. For short procedures: 8-20 mcg/kg. For longer procedures: 50-75 mcg/kg followed by 0.5-3 mcg/kg/min.
Terminal half-life is 3.5 hours in patients with normal renal function. Increases in renal impairment (up to 20 hours if Cr Cl <45 m L/min).
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours); prolonged in hepatic impairment.
Pemetrexed is primarily eliminated unchanged in urine. It undergoes minimal hepatic metabolism. The drug is a substrate for multidrug resistance-associated proteins (MRPs) and possibly other transporters.
Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive).
Primarily renal excretion (70-90% as unchanged drug within 24 hours). Biliary/fecal excretion accounts for <5%.
Primarily renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces.
~81% bound primarily to albumin.
Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin.
Vd = 0.2 L/kg (approximately 16 L in adults). Indicates limited distribution to extravascular spaces.
0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly.
Intravenous: 100% (only route of administration).
Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration).
Cr Cl ≥45 m L/min: No adjustment. Cr Cl <45 m L/min: Not recommended. For Cr Cl 40-59 m L/min, no adjustment; Cr Cl <40 m L/min, not recommended based on clinical trial criteria.
No specific dose adjustment is recommended for renal impairment; however, alfentanil is primarily metabolized in the liver and its pharmacokinetics are not significantly altered in renal failure.
No specific dose adjustment guidelines for hepatic impairment. Use caution with bilirubin >1.5 times ULN and/or AST/ALT >3 times ULN. Child-Pugh classification not formally studied.
In hepatic impairment (Child-Pugh class A, B, C): Reduce dose by 50% and titrate carefully due to prolonged elimination half-life. Consider lower initial doses and extended dosing intervals.
Safety and efficacy not established in pediatric patients. No recommended dosing.
Children (1-12 years): Induction of anesthesia: 10-20 mcg/kg IV; maintenance: 5-10 mcg/kg IV or infusion 0.5-1 mcg/kg/min. For neonates and infants: Dose individualization required; titrate to effect.
No specific dose adjustment recommended based on age alone. Monitor renal function closely as elderly patients may have reduced Cr Cl.
Elderly patients (>65 years): Reduce initial dose by 30-50% and administer slowly. Due to decreased clearance and increased sensitivity, lower infusion rates (e.g., 0.3-0.5 mcg/kg/min) may be needed.
Pemetrexed can cause severe myelosuppression, which may lead to infection and bleeding. Patients must be monitored for bone marrow suppression. Adequate folic acid and vitamin B12 supplementation is required to reduce toxicity.
Risk of respiratory depression, particularly in elderly or debilitated patients. Concomitant use with benzodiazepines or other CNS depressants may cause profound sedation, respiratory depression, coma, and death.
Bone marrow suppression: Monitor blood counts regularly; dose adjust or hold for severe neutropenia, thrombocytopenia, or anemia.,Renal toxicity: Avoid in creatinine clearance <45 m L/min; monitor renal function.,Gastrointestinal toxicity: Severe diarrhea, mucositis may occur; manage with supportive care.,Dermatologic toxicity: Severe rash may occur; premedicate with corticosteroids.,Radiation recall: Risk of severe radiation recall in patients who have received prior radiotherapy.,Folic acid and vitamin B12 supplementation: Required to reduce hematologic and gastrointestinal toxicity.,Pregnancy: Can cause fetal harm; advise women of reproductive potential to use effective contraception.
Respiratory depression; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use.
History of severe hypersensitivity reaction to pemetrexed or any excipient.,Patients with creatinine clearance <45 m L/min (contraindicated for use in combination with cisplatin due to increased toxicity).
Hypersensitivity to alfentanil or any component; significant respiratory insufficiency; severe asthma; paralytic ileus; concurrent use of MAOIs (or within 14 days); acute or postoperative pain management in children (except for procedural sedation).
No known food interactions. Avoid folic acid-containing supplements beyond prescribed dose as they may interfere with pemetrexed activity. Maintain adequate hydration.
No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption.
Pemetrexed is contraindicated in pregnancy. It is an antifolate antimetabolite that inhibits thymidylate synthase and other folate-dependent enzymes, essential for DNA synthesis and cell division. Based on its mechanism of action and animal studies, it is expected to cause fetal harm when administered to a pregnant woman. First trimester: High risk of teratogenicity (neural tube defects, craniofacial, cardiovascular malformations) due to folate antagonism. Second and third trimesters: Risk of fetal growth restriction, oligohydramnios, and fetal death. Embryofetal toxicity and teratogenicity have been demonstrated in mice and rats at doses lower than the human therapeutic dose.
Alfentanil, a short-acting opioid analgesic, is classified as FDA Pregnancy Category C. No well-controlled studies in pregnant women exist. In animal studies, no teratogenic effects were observed at clinically relevant doses; however, high doses caused embryotoxicity and increased fetal mortality. Trimester-specific risks: First trimester - potential for minor malformations based on limited human data; second trimester - possible risk if used chronically; third trimester - prolonged use may lead to neonatal respiratory depression, withdrawal syndrome, or opioid dependence. Use only if benefits outweigh risks.
No data available on the presence of pemetrexed in human milk, its effects on the breastfed infant, or on milk production. Due to the potential for serious adverse reactions in the breastfed infant (including myelosuppression, gastrointestinal toxicity, and carcinogenesis), breastfeeding is not recommended during therapy and for at least 1 week after the last dose. The M/P ratio is unknown.
Alfentanil is excreted into human breast milk in low concentrations. The milk-to-plasma (M/P) ratio is approximately 0.3. Estimated infant dose is <1% of maternal weight-adjusted dose, which is considered clinically insignificant. However, due to potential for neonatal opioid effects, caution is advised; monitor infant for drowsiness, respiratory depression, and feeding difficulties. Consider alternative analgesics with established safety profiles, such as acetaminophen or ibuprofen, for lactation.
No specific dose adjustment guidelines exist for pemetrexed in pregnancy because its use is contraindicated. However, pregnancy may alter the pharmacokinetics of pemetrexed due to increased renal clearance (increased glomerular filtration rate) and expanded plasma volume, potentially reducing drug exposure. No formal studies have been conducted. Given the high risk of fetal harm, pemetrexed should not be used in pregnant women. If treatment is deemed necessary for a life-threatening condition, the risks versus benefits must be considered, and dosing adjustments cannot be recommended due to lack of data.
Pregnancy can alter pharmacokinetics of alfentanil. Increased plasma volume and distribution may require higher doses to achieve same effect, while decreased plasma protein binding may increase free fraction, potentiating effects. Alpha-1-acid glycoprotein levels change in pregnancy, affecting binding. In third trimester, clearance may be increased by up to 50% due to enhanced hepatic metabolism. Therefore, dose adjustments may be needed: consider starting at low dose and titrating to effect, with close monitoring. For intravenous administration, typical adult doses (5-20 μg/kg) may need adjustments; no standard pregnancy-specific dosing exists. Use the lowest effective dose for the shortest duration. In labor, avoid high doses prior to delivery due to risk of neonatal respiratory depression.
Administer folic acid 350-1000 mcg orally daily beginning 7 days before first dose and continuing throughout therapy. Administer vitamin B12 1000 mcg IM 1 week before first dose and every 3 cycles thereafter. Premedicate with dexamethasone 4 mg orally twice daily the day before, day of, and day after each dose to reduce cutaneous reactions. Monitor for myelosuppression, especially neutropenia; dose reduce as needed. Contraindicated in patients with creatinine clearance <45 m L/min. Avoid NSAIDs 2-5 days before and 2 days after pemetrexed due to increased toxicity.
Alfentanil is a potent, rapid-onset, short-acting opioid analgesic used primarily for induction and maintenance of anesthesia. Due to its high protein binding (90%) and rapid redistribution, it has a shorter duration of action than fentanyl, making it suitable for brief, painful procedures. It undergoes hepatic metabolism via CYP3A4, so concomitant use with CYP3A4 inhibitors like ketoconazole or erythromycin can prolong its effects. Use caution in elderly or hypovolemic patients due to increased risk of hypotension. Naloxone reverses respiratory depression. Alfentanil is 5-10 times less potent than fentanyl.
Take folic acid supplements daily, starting 7 days before your first treatment and continuing until your doctor stops it.,You will receive vitamin B12 injections before your first dose and then every 9 weeks.,Take a steroid medication (dexamethasone) as prescribed the day before, day of, and day after each infusion to prevent skin reactions.,Avoid taking NSAIDs (like ibuprofen or naproxen) for at least 2-5 days before and 2 days after your pemetrexed infusion.,Report any signs of infection (fever, chills, sore throat), unusual bleeding or bruising, or severe fatigue immediately.,Drink plenty of fluids unless otherwise instructed. There are no specific dietary restrictions, but maintain a balanced diet.,Use effective contraception during treatment and for at least 6 months after the last dose (females) or 3 months (males). Do not breastfeed during treatment.
This medication is given only by a healthcare professional in a hospital or surgical setting.,You may feel drowsy, dizzy, or nauseated after receiving this drug.,Report any difficulty breathing or slow heart rate to your healthcare provider immediately.,Avoid alcohol and sedatives for 24 hours after administration, as they can increase side effects.,Do not drive or operate machinery until the effects have fully worn off.
"The risk or severity of adverse effects can be increased when Pemetrexed is combined with Leflunomide."
"Pemetrexed may decrease the cardiotoxic activities of Acetyldigitoxin."
"Pemetrexed may increase the immunosuppressive activities of Fingolimod."
"Propantheline, an anticholinergic agent, can competitively antagonize muscarinic acetylcholine receptors, potentially reducing gastrointestinal motility and secretion. Alfentanil, a mu-opioid receptor agonist, also decreases gastrointestinal motility through central and peripheral opioid receptors. Concomitant use may synergistically inhibit peristalsis, leading to severe constipation, paralytic ileus, or delayed gastric emptying, which can increase the risk of aspiration and complicate anesthesia recovery."
"Alfentanil, a potent opioid analgesic, can cause significant hypotension and respiratory depression. When combined with furosemide, a loop diuretic that reduces blood volume and vascular resistance, there is a synergistic decrease in blood pressure, which may precipitate cardiovascular collapse, especially in patients with compromised circulatory reserves. Additionally, furosemide may enhance the sedative and respiratory depressant effects of alfentanil, leading to increased risk of respiratory acidosis and altered mental status."
"Alfentanil, a potent mu-opioid receptor agonist, can enhance the bradycardic effects of nebivolol, a beta-1 selective blocker with additional nitric oxide-mediated vasodilation. The combination may lead to excessive slowing of heart rate, reduced cardiac output, and potential hemodynamic instability, particularly in patients with underlying cardiac conduction abnormalities or hypovolemia."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about PEMETREXED DISODIUM vs ALFENTA, answered by our medical review team.
PEMETREXED DISODIUM is a Antineoplastic Antifolate that works by Pemetrexed is a folate analog metabolic inhibitor that disrupts folate-dependent metabolic processes essential for cell replication. It inhibits thymidylate synthase (TS), dihydrofolate reductase (DHFR), and glycinamide ribonucleotide formyltransferase (GARFT), thereby inhibiting de novo synthesis of thymidine and purine nucleotides.. ALFENTA is a Opioid Analgesic that works by μ-opioid receptor agonist that activates G-protein coupled receptors to inhibit adenylate cyclase, decreasing c AMP production, leading to reduced neuronal excitability and pain transmission.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between PEMETREXED DISODIUM and ALFENTA depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of PEMETREXED DISODIUM is: 500 mg/m2 intravenously over 10 minutes on Day 1 of each 21-day cycle, with vitamin B12 and folic acid supplementation.. The standard adult dose of ALFENTA is: Intravenous: Initial dose 8-20 mcg/kg (0.5-1 min) then 0.5-3 mcg/kg/min or 3-5 mcg/kg q5-20min. For short procedures: 8-20 mcg/kg. For longer procedures: 50-75 mcg/kg followed by 0.5-3 mcg/kg/min.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between PEMETREXED DISODIUM and ALFENTA in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. PEMETREXED DISODIUM is classified as Category C. Pemetrexed is contraindicated in pregnancy. It is an antifolate antimetabolite that inhibits thymidylate synthase and other folate-dependent enzymes, essential for DNA synthesis an. ALFENTA is classified as Category C. Alfentanil, a short-acting opioid analgesic, is classified as FDA Pregnancy Category C. No well-controlled studies in pregnant women exist. In animal studies, no teratogenic effect. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.