- Also called:
- sulfonamide
- Key People:
- Daniel Bovet
- Related Topics:
- sulfonamide
- Prontosil
- sulfanilamide
- sulfathiazole
- mafenide
- On the Web:
- National Center for Biotechnology Information - Sulfonamides (Nov. 04, 2026)
sulfa drug
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What are sulfa drugs?
Sulfa drugs are synthetic antibiotics containing the sulfanilamide molecular structure and were the first chemical substances used to treat and prevent bacterial infections in humans. Sulfa drugs inhibit the growth and multiplication of bacteria by interfering with the synthesis of folic acid.
Though relatively safe, allergic reactions to sulfa drugs such as skin rashes, fever, nausea, vomiting, and even mental confusion were common. Because of increased instances of drug resistance and the availability of safer, more effective antibiotics, their use has diminished. Today, they are largely used for treating urinary tract infections and preventing infection of burns, as well as in the treatment of certain forms of malaria.
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What are sulfa drugs used for in medicine?
Sulfa drugs, the first antibiotics systematically used in humans, treat and prevent bacterial infections. Though their use has decreased with the emergence of more effective antibiotics, they are still used to treat urinary tract infections and prevent infection of burns. They can also be used in treating some forms of malaria.
Sulfa drugs work by inhibiting the growth and multiplication of bacteria by interfering with the synthesis of folic acid. Because humans get folic acid from their diet, sulfa drugs can target microorganisms without harming the host.
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How do sulfa drugs work to fight infections?
Sulfa drugs are synthetic antibiotics that contain the sulfanilamide molecular structure. They stop bacteria from growing and multiplying, but they don't kill them. Sulfa drugs work by disrupting the synthesis of folic acid, a B vitamin that all living cells have. Because bacteria must produce their own folic acid while humans get it from their diet, sulfa drugs can stop microorganisms from growing without hurting the host. Sulfa drugs can cause allergic reactions, and bacteria can become resistant to them.
Doctors prescribe sulfa drugs to treat urinary tract infections, prevent burn infections, and treat some types of malaria. Sometimes, sulfa drugs are combined with other antibiotics to treat conditions ranging from skin burns, to malaria, to pneumonia in HIV/AIDS patients.
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What kinds of illnesses are commonly treated with sulfa drugs?
Sulfa drugs treat bacterial infections by impeding folic acid synthesis in microorganisms, without harming the host. While their use has decreased due to more effective antibiotics and increased resistance, sulfonamides remain relevant in treating urinary tract infections and preventing burn infections. They are also used to treat some forms of malaria. Additionally, a combination of sulfa drugs with antibiotics can address conditions from skin burns to pneumonia in HIV/AIDS patients. Sulfones, related to sulfonamides, treat leprosy.
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What are some possible side effects of sulfa drugs?
Sulfa drugs, the first antibiotics systematically used to treat bacterial infections in humans, can have side effects, including allergic reactions like skin rashes, fever, nausea, vomiting, and even mental confusion. Less-toxic derivatives have been developed to counter these effects. Some patients may be hypersensitive to sulfa drugs, leading to fever and skin eruptions. Intoxication from sulfa drugs can cause anemia (destruction of red blood cells) and leukopenia (destruction of white blood cells). Kidney irritation and obstructed urine flow are also possible but preventable reactions.
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Why are some people allergic to sulfa drugs, and what happens if they take them?
Sulfa drugs, the first chemical substances used to treat bacterial infections in humans, can cause allergic reactions in some individuals. These reactions can manifest as skin rashes, fever, nausea, vomiting, and, in rare cases, mental confusion.
Drug allergies, in general, are hypersensitivity reactions that occur upon re-exposure to a drug against which an individual has already produced antibodies. After a drug allergy is confirmed, lifelong avoidance of the drug and its derivatives is typically necessary. Although sulfa drugs are still used today, mainly for urinary tract infections and burn treatments, their use has decreased due to more effective and safer antibiotics becoming available.
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sulfa drug, any member of a group of synthetic antibiotics containing the sulfanilamide molecular structure. Sulfa drugs were the first chemical substances systematically used to treat and prevent bacterial infections in humans. Their use has diminished because of the availability of antibiotics that are more effective and safer and because of increased instances of drug resistance. Sulfonamides are still used, but largely for treating urinary tract infections and preventing infection of burns. They are also used in the treatment of certain forms of malaria.
The antibacterial effects of sulfonamides were first observed in 1932, when German bacteriologist and pathologist Gerhard Domagk noted the effects of the red dye Prontosil on Streptococcus infections in mice. It was later proved by French researchers that the active agent of Prontosil was sulfanilamide, or para-aminobenzenesulfonamide, a product of the body’s metabolism of Prontosil. By the 1940s sulfanilamide was a widely used drug. During World War II white sulfanilamide powders became standard in first-aid kits for the treatment of open wounds, and sulfanilamide tablets were taken to fight intestinal infections. Though the medicine was relatively safe, allergic reactions such as skin rashes, fever, nausea, vomiting, and even mental confusion were common. With the introduction of less-toxic derivatives and especially with the mass production of penicillin, its use declined.
Many other sulfa drugs were derived from sulfanilamide in the 1940s, including sulfathiazole (systemic bacterial infections), sulfadiazine (urinary tract and intestinal tract infections), and sulfamethazine (urinary tract infections). However, all sulfa drugs induced some of the side effects listed above, and bacteria developed resistant strains after exposure to the drugs. Within a few decades many of the sulfa drugs had lost favour to more-effective and less-toxic antibiotics.
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Trisulfapyrimidine (triple sulfa), a combination of sulfadiazine, sulfamerazine, and sulfamethazine, is used in the treatment of vaginal infections, and several sulfa drugs are used in combination with antibiotics to treat a wide range of conditions, from skin burns to malaria to pneumonia in HIV/AIDS patients.
Sulfa drugs are bacteriostatic; i.e., they inhibit the growth and multiplication of bacteria but do not kill them. They act by interfering with the synthesis of folic acid (folate), a member of the vitamin B complex present in all living cells. Most bacteria make their own folic acid from simpler starting materials; humans and other higher animals, however, must obtain folic acid in the diet. Thus, sulfa drugs can inhibit the growth of invading microorganisms without harming the host.
When trimethoprim (a dihydrofolate reductase inhibitor) is given with sulfamethoxazole, the sequential blockage of the pathway produced by the two drugs achieves markedly greater inhibition of folic acid synthesis. As a result, this combination is valuable in treating urinary tract infections and some systemic infections.
The sulfones are related to the sulfonamides and are inhibitors of folic acid synthesis. They tend to accumulate in skin and inflamed tissue and are retained in the tissue for long periods. Thus, sulfones such as dapsone are useful in treatment of leprosy.
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