One extremely long-acting sulfa medication is sulphadoxine. Pyrimethamine and sulfadoxine are frequently used together to treat or prevent malaria. Both medications are antifolates; they prevent the parasite from producing the enzymes needed for folate synthesis. Because P. falciparum may be able to exploit exogenous folate, or folate that is present in the parasite's environment, either medication by itself would only be moderately successful in treating malaria, but when combined, the two substances have an over-equilibrium synergistic effect. This capacity [1, 2].

[1]. http://www.malaria-ipca.com/sulphadoxine_pyrimethamine.html.

[2]. http://en.wikipedia.org/wiki/Sulfadoxine/pyrimethamine.

[3]. The Use of Antimalarial Drugs against Viral Infection. Microorganisms. 2020 Jan 8;8(1). pii: E85.

Sulfadoxine is a sulfonamide consisting of pyrimidine having methoxy substituents at the 5- and 6-positions and a 4-aminobenzenesulfonamido group at the 4-position. In combination with the antiprotozoal pyrimethamine (CHEBI:8673) it is used as an antimalarial. It has a role as an antibacterial drug and an antimalarial. It is a sulfonamide and a member of pyrimidines.
A long acting sulfonamide that is used, usually in combination with other drugs, for respiratory, urinary tract, and malarial infections.
Sulfadoxine is a Sulfonamide.
Sulfadoxine is a broad-spectrum sulfanilamide and a synthetic analog of para-aminobenzoic acid (PABA) with bacteriostatic and antimalarial properties. Sulfadoxine competes with PABA for the bacterial enzyme dihydropteroate synthase, thereby preventing the incorporation of PABA into dihydrofolic acid, the immediate precursor of folic acid. This leads to an inhibition of parasitic folic acid synthesis and de novo synthesis of purines and pyrimidines, ultimately resulting in cell growth arrest and cell death.
A long acting sulfonamide that is used, usually in combination with other drugs, for respiratory, urinary tract, and malarial infections.

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Drug Indication
Sulfadoxine is used in combination with pyrimethamine for the treatment or prevention of malaria. It can also be used to treat various infections in livestock as well. Sulfadoxine and pyrimethamine is indicated for the treatment of Plasmodium falciparum malaria in those patients in whom chloroquine resistance is suspected.

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Mechanism of Action
Sulfadoxine is a sulfa drug, often used in combination with pyrimethamine to treat malaria. This medicine may also be used to prevent malaria in people who are living in, or will be traveling to, an area where there is a chance of getting malaria. Sulfadoxine targets Plasmodium dihydropteroate synthase and dihydrofolate reductase. Sulfa drugs or Sulfonamides are antimetabolites. They compete with para-aminobenzoic acid (PABA) for incorporation into folic acid. The action of sulfonamides exploits the difference between mammal cells and other kinds of cells in their folic acid metabolism. All cells require folic acid for growth. Folic acid (as a vitamin) diffuses or is transported into human cells. However, folic acid cannot cross bacterial (and certain protozoan) cell walls by diffusion or active transport. For this reason bacteria must synthesize folic acid from p-aminobenzoic acid.

C12H14N4O4S

310.328

310.073

2447-57-6

Sulfadoxine-d4;1330266-05-1;Sulfadoxine-d3;1262770-70-6

17134

White to off-white solid powder

1.4±0.1 g/cm3

522.8±60.0 °C at 760 mmHg

190-194ºC

270.0±32.9 °C

0.0±1.4 mmHg at 25°C

1.623

0.34

2

8

5

21

420

0

PJSFRIWCGOHTNF-UHFFFAOYSA-N

InChI=1S/C12H14N4O4S/c1-19-10-11(14-7-15-12(10)20-2)16-21(17,18)9-5-3-8(13)4-6-9/h3-7H,13H2,1-2H3,(H,14,15,16)

4-amino-N-(5,6-dimethoxypyrimidin-4-yl)benzenesulfonamide

WR 4873; WR4873; WR-4873

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ≥ 100 mg/mL (~322.24 mM)
H2O : ~0.1 mg/mL (~0.32 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (8.06 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (8.06 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (8.06 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)