Pemetrexed, a chemotherapy drug used to treat certain types of cancer, was developed in the 1980s and approved for medical use in the early 2000s. Its history is marked by its effectiveness in treating malignant pleural mesothelioma and non-small cell lung cancer, but also by careful monitoring of hematologic toxicities that led to the recommendation of vitamin supplementation to reduce side effects. Pemetrexed, an antifolate antimetabolite used in cancer therapy, was approved in the United States in 2004 and is included in multiple combination chemotherapy regimens. Its development featured accelerated clinical trials and a notable expanded access program (EAP) that permitted early use and observation of the drug’s safety profile.
BRAND NAMES
For pemetrexed, the main brand names are:
Alimta – the most widely known brand for pemetrexed.
Pemfexy is a ready-to-use injectable formulation.
In some markets, it may also be marketed as generic pemetrexed disodium.
PHARMACOKINETICS
Absorption:
Pemetrexed is administered intravenously, so it bypasses the gastrointestinal tract and is completely available in systemic circulation. Because it is given directly into the bloodstream, oral absorption is not relevant, and peak plasma concentrations are achieved rapidly at the end of the infusion.
Distribution
After intravenous administration, pemetrexed distributes widely into body tissues. It has a moderate volume of distribution, approximately 16 L, and is about 81% bound to plasma proteins, primarily albumin. It shows limited penetration into the central nervous system.
Elimination
In patients with normal renal function (creatinine clearance of 90 mL/min), pemetrexed has a total systemic clearance of 91.8 mL/min and an elimination half-life of 3.5 hours. When renal function declines, pemetrexed clearance is reduced, leading to increased drug exposure (AUC).
Metabolism
The majority of the drug remains unchanged, with only a small fraction undergoing hepatic transformation. This limited metabolism reduces the potential for drug–drug interactions compared to agents extensively metabolized by the liver.
Excretion
Pemetrexed is primarily excreted unchanged by the kidneys through renal clearance. About 70–90% of the administered dose is recovered in the urine within 24 hours. Its elimination half-life is approximately 3.5 hours in patients with normal renal function.
PHARMACODYNAMICS
Pemetrexed is an antifolate antimetabolite that inhibits multiple enzymes involved in folate-dependent nucleotide synthesis, including thymidylate synthase, dihydrofolate reductase, and glycinamide ribonucleotide formyltransferase. This blocks DNA and RNA synthesis, leading to cancer cell death.
ADMINISTRATION
Pemetrexed is administered as an intravenous (IV) infusion. It is typically given over about 10 minutes in a clinical setting under medical supervision.
DOSAGE AND STRENGTH
Pemetrexed is available as a sterile lyophilized powder for reconstitution in vials, commonly in strengths of 100 mg and 500 mg. These are diluted before intravenous administration.
DRUG INTERACTIONS
NSAIDs such as ibuprofen may reduce the renal clearance of pemetrexed, increasing its toxicity. Caution is advised, especially in patients with impaired kidney function.
FOOD INTERACTIONS
Adequate dietary intake or supplementation of folic acid is important during pemetrexed therapy, as it helps reduce the risk of severe toxicity. Patients are usually advised to take folic acid supplements regularly.
CONTRAINDICATIONS
Pemetrexed is contraindicated in patients with known severe hypersensitivity to the drug or any of its components, as this may result in serious allergic reactions. It is also contraindicated in individuals with severe renal impairment (creatinine clearance < 45 mL/min) due to reduced drug elimination and increased risk of toxicity. Additionally, pemetrexed should not be used during breastfeeding because of the potential for harmful effects on the nursing infant.
SIDE EFFECTS
Pemetrexed commonly causes fatigue, nausea, vomiting, loss of appetite, and mucositis (inflammation of the mouth). Skin rash and mild gastrointestinal disturbances are also frequently reported.
TOXICITY
Pemetrexed toxicity primarily involves bone marrow suppression, leading to severe neutropenia, anemia, and thrombocytopenia, which increase the risk of infections and bleeding. Gastrointestinal toxicity such as severe mucositis, diarrhea, and vomiting may also occur. Renal toxicity can develop, particularly in patients with pre-existing kidney impairment or when used with nephrotoxic drugs. Without proper supplementation of folic acid and vitamin B12, the risk of severe and potentially life-threatening toxicity is significantly increased.
