Pralatrexate (PDX or 10-propargyl-10-deazaaminopterin) is a folate analogue that is internalised by the reduced folate carrier 1 (RFC-1) protein, and polyglutamylated by the enzyme folylpolyglutamyl synthetase (FPGS), resulting in accumulation of the antifolate. Pralatrexate, a methotrexate analogue, is intended as an inhibitor of dihydrofolate reductase (DHFR), an enzyme which catalyses the reduction of dihydrofolic acid to tetrahydrofolic acid. Inhibition of DHFR leads to a depletion of intracellular reduced folate stores, thereby leading to a disruption of DNA synthesis. Preclinical studies in vitro and in models of B-cell lymphomas, T-cell lymphomas and NSCLC indicated that pralatrexate exhibited antitumor activity that was superior to the activity of other antifolates. FOLOTYN (pralatrexate injection) is indicated for the treatment of patients with relapsed or refractory peripheral T-cell lymphoma.

Pemetrexed is a new-generation antifolate, approved for the treatment of mesothelioma and non-small cell lung cancer, currently being evaluated for the treatment of a variety of other solid tumors. Pemetrexed, is a folate analog metabolic inhibitor that exerts its action by disrupting folate-dependent metabolic processes essential for cell replication. In vitro studies have shown that pemetrexed inhibits thymidylate synthase (TS), dihydrofolate reductase (DHFR), glycinamide ribonucleotide formyltransferase (GARFT) and and to a lesser extent aminoimidazole carboxamide ribonucleotide formyltransferase (AICARFT), which are folate-dependent enzymes involved in the de novo biosynthesis of thymidine and purine nucleotides. Pemetrexed is taken into cells by membrane carriers such as the reduced folate carrier and membrane folate binding protein transport systems. Once in the cell, pemetrexed is converted to polyglutamate forms by the enzyme folylpolyglutamate synthetase. The polyglutamate forms are retained in cells and are inhibitors of TS and GARFT. Polyglutamation is a time- and concentration-dependent process that occurs in tumor cells and, is thought to occur to a lesser extent, in normal tissues. Polyglutamated metabolites are thought to have an increased intracellular half-life resulting in prolonged drug action in malignant cells.

Methotrexate is an antineoplastic anti-metabolite. Anti-metabolites masquerade as purine or pyrimidine - which become the building blocks of DNA. They prevent these substances becoming incorporated in to DNA during the "S" phase (of the cell cycle), stopping normal development and division. Methotrexate inhibits folic acid reductase which is responsible for the conversion of folic acid to tetrahydrofolic acid. At two stages in the biosynthesis of purines and at one stage in the synthesis of pyrimidines, one-carbon transfer reactions occur which require specific coenzymes synthesized in the cell from tetrahydrofolic acid. Tetrahydrofolic acid itself is synthesized in the cell from folic acid with the help of an enzyme, folic acid reductase. Methotrexate looks a lot like folic acid to the enzyme, so it binds to it quite strongly and inhibits the enzyme. Thus, DNA synthesis cannot proceed because the coenzymes needed for one-carbon transfer reactions are not produced from tetrahydrofolic acid because there is no tetrahydrofolic acid. Methotrexate selectively affects the most rapidly dividing cells (neoplastic and psoriatic cells). Methotrexate is indicated in the treatment of gestational choriocarcinoma, chorioadenoma destruens and hydatidiform mole. In acute lymphocytic leukemia, methotrexate is indicated in the prophylaxis of meningeal leukemia and is used in maintenance therapy in combination with other chemotherapeutic agents. Methotrexate is also indicated in the treatment of meningeal leukemia. Methotrexate is used alone or in combination with other anticancer agents in the treatment of breast cancer, epidermoid cancers of the head and neck, advanced mycosis fungoides (cutaneous T cell lymphoma), and lung cancer, particularly squamous cell and small cell types. Methotrexate is also used in combination with other chemotherapeutic agents in the treatment of advanced stage non-Hodgkin’s lymphomas. Methotrexate is indicated in the symptomatic control of severe, recalcitrant, disabling psoriasis. Methotrexate is indicated in the management of selected adults with severe, active rheumatoid arthritis (ACR criteria), or children with active polyarticular-course juvenile rheumatoid arthritis.

Pyrimethamine, sold under the trade name Daraprim, is one of the folic acid antagonists that is used as an antimalarial or with a sulfonamide to treat toxoplasmosis. In addition it was approved in Chemoprophylaxis of Malaria. However, resistance to pyrimethamine is prevalent worldwide. It is not suitable as a prophylactic agent for travelers to most areas. Pyrimethamine is well absorbed with peak levels occurring between 2 to 6 hours following administration. It is eliminated slowly and has a plasma half-life of approximately 96 hours. Pyrimethamine is 87% bound to human plasma proteins. Pyrimethamine acts by selectively inhibiting malarial dihydrofolate reductase-thymidylate synthase and the rationale for its therapeutic action is based on the differential requirement between host and parasite for nucleic acid precursors involved in growth. This activity is highly selective against plasmodia and Toxoplasma gondii. Pyrimethamine possesses blood schizonticidal and some tissue schizonticidal activity against malaria parasites of humans. The action of pyrimethamine against Toxoplasma gondii is greatly enhanced when used in conjunction with sulfonamides.

Leucovorin is a compound similar to folic acid, which is a necessary vitamin. It has been around and in use for many decades. Leucovorin is a medication frequently used in combination with the chemotherapy drugs fluoruracil and methotrexate. Leucovorin is not a chemotherapy drug itself, however it is used in addition to these chemotherapy drugs to enhance anticancer effects (with fluorouracil) or to help prevent or lessen side effects (with methotrexate). Leucovorin is also used by itself to treat certain anemia problems when folic acid deficiency is present.

4-AMINOSALICYLIC ACID (Paser) is an anti-tuberculosis drug used to treat tuberculosis in combination with other active agents. 4-AMINOSALICYLIC ACID (Paser) is most commonly used in patients with Multi-drug Resistant TB (MDR-TB) or when isoniazid and rifampin use is not possible due to a combination of resistance and/or intolerance. There are two mechanisms responsible for aminosalicylic acid's bacteriostatic action against Mycobacterium tuberculosis. Firstly, aminosalicylic acid inhibits folic acid synthesis (without potentiation with antifolic compounds). The binding of para-aminobenzoic acid to pteridine synthetase acts as the first step in the folic acid synthesis. Aminosalicylic acid binds pteridine synthetase with greater affinity than para-aminobenzoic acid, effectively inhibiting the synthesis of folic acid. As bacteria are unable to use external sources of folic acid, cell growth and multiplication slow. Secondly, the aminosalicylic acid may inhibit the synthesis of the cell wall component, mycobactin, thus reducing iron uptake by M. tuberculosis.

Proguanil is a prophylactic antimalarial drug, which works by stopping the malaria parasite, Plasmodium falciparum and Plasmodium vivax, from reproducing once it is in the red blood cells. Proguanil in combination with atovaquone are marked under the brand name malarone, which is indicated for the treatment of acute, uncomplicated P. falciparum malaria and for the prophylaxis of Plasmodium falciparum malaria, including in areas where chloroquine resistance has been reported. Atovaquone and proguanil, interfere with 2 different pathways involved in the biosynthesis of pyrimidines required for nucleic acid replication. Atovaquone is a selective inhibitor of parasite mitochondrial electron transport. Proguanil hydrochloride primarily exerts its effect by means of the metabolite cycloguanil, a dihydrofolate reductase inhibitor. Inhibition of dihydrofolate reductase in the malaria parasite disrupts deoxythymidylate synthesis. Recently were done experiments, which confirmed the hypothesis that proguanil might act on another target than dihydrofolate reductase. In addition, was made conclusion, that effectiveness of malarone was due to the synergism between atovaquone and proguanil and may not require the presence of cycloguanil.

Edatrexate (10-ethyl-10-deazaaminopterin or 10-EDAM) is an analog of methotrexate with improved pre-clinical antitumor activity, more selective cellular uptake, and with the more extensive formation of intracellular polyglutamate metabolites. This drug is a new dihydrofolate reductase inhibitor, which was studied in phase II clinical trial for the patients with different cancers. The studies were discontinued, for example, in advanced renal cell carcinoma edatrexate in the investigated dose and schedule had minimal activity and was toxic. In case of non-small-cell lung cancer, the dosing schedule of edatrexate did not appear to be improved compared to other chemotherapeutic regimens. In addition, edatrexate was involved in the experiment for the treatemnt of rheumatoid arthritis, but this study was also discontinued.

Iodophthalein was used as an iodine-containing X-ray contrast agent in icteric subjects. There is also existed mention, that iodophthalein has also been used as a wound treatment, and for the treatment of intestinal catarrhs. But nowadays more modern drugs are being used.

Piritrexim is a synthetic antifolate agent with antiparasitic, antipsoriatic and antitumor properties. Piritrexim inhibits the enzyme dihydrofolate reductase, thereby disrupting folate metabolism and DNA synthesis and cell division. A theoretical advantage of piritrexim over trimetrexate is a lack of any known effects on histamine metabolism, which may lower the risk of hypersensitivity reactions. Piritrexim is a nonclassical antifolate for antitumor and parasitic chemotherapy that passively diffuses into cells and hence do not have to depend on folylpoly-gamma-glutamate synthetase or the reduced folate carrier. Because piritrexim is not a substrate for polyglutamation, the drug is not selectively retained within cells for prolonged periods. Piritrexim has a reliably high oral bioavailability of about 75%, which has led to its development as an oral lipophilic antifolate. Most commonly, it has been administered in oral daily doses of 75 to 150 mg bid or tid every 5 days, with cycles repeated every 3 weeks. Oral absorption is rapid, with peak plasma levels appearing at 1.5 hours after ingestion. Elimination occurs primarily via hepatic metabolism of the drug to active metabolites, and the terminal half-life of the parent compound is about 1.5 to 4.5 hours. Single-agent oral piritrexim has clinical activity in melanoma, urothelial cancers, and head and neck cancers. Tolerable combinations of piritrexim with cisplatin, fluorouracil, and leucovorin have been tested, with promising results achieved in head and neck cancer. An interesting attempt to alternate piritrexim with methotrexate did not have any greater activity than methotrexate alone.