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Sulfonamides – Effect, Application & Risks


Sulfonamides are synthetic chemical antibiotics that prevent bacteria from multiplying . Today they are only rarely used in humans due to their rather weak mode of action and many side effects . In order to prevent resistance, combination preparations of sulfonamides with diaminopyrimidines are usually used.

What are sulfonamides?

Sulfonamides are used as antibiotics because of their antimicrobial effect. Today they have largely been superseded by penicillins , which are more effective. Nevertheless, they are still often used in uncomplicated urinary tract diseases. They are still used particularly frequently in veterinary medicine.

Sulfonamides have the characteristic atomic group SO2NHR. With the help of this group of atoms, they unfold their effect against bacteria. Of the large number of sulfonamides, only a few are still used in humans today. These include the drugs sulfamethoxazole, sulfamerazine, silver sulfadiazine, or sulfadiazine.

The effectiveness of sulfanilamide against bacteria was discovered by the pathologist Gerhard Domagk in 1935. Sulfanilamide came onto the market as an antibiotic under the brand name Prontosil®. However, Prontosil only worked in vivo (in the organism) because it could only be converted into its active form in the organism.

Already in the Second World War, the first sulfonamides were replaced by the more effective penicillins. However, they were not completely supplanted and are still used today for certain infections .

Pharmacological action

The effectiveness of the sulfonamides is based on the disruption of the formation of folic acid. They occupy important active centers in the corresponding enzymes , which are responsible for the formation of folic acid. The folic acid in turn takes care of the synthesis of nucleotides . This reaction occurs in all organisms. The nucleotides are required for the construction of the nucleic acids .

In contrast to eukaryotic cells, bacteria produce folic acid as part of their metabolism. However, eukaryotic organisms, including humans, must ingest folic acid through food. This explains the specific toxic effect of sulfonamides against bacteria.

However, there are also bacteria that do not produce folic acid. These bacterial strains are resistant to sulfonamides. However, the sulfonamides alone do not kill the bacteria. However, by inhibiting the formation of nucleic acids, they prevent the formation of new bacteria through cell division. The organism’s immune system now destroys the existing bacteria. This shortens the duration of infection.

Medical Application & Use

The sulfonamides are effective against various strains of bacteria, such as the intestinal bacteria Pseudomonas , Escherichia coli , Shigella or Salmonella . Furthermore, they are effective against streptococci , staphylococci , Pneumocystis jirovecii, Neisseria , Toxoplasma gondii, Plasmodium or Neospora caninum.

The drug cotrimoxazole is used to treat uncomplicated urinary tract infections. Co-trimoxazole is a combination of sulfamethoxazole with trimethoprim. The drug is used as a combination drug to prevent resistance to sulfonamides. Both the sulfonamides and trimethoprim block the formation of folic acid. However, they intervene at different points in the same metabolic pathway. The combination of both active ingredients also produces a synergistic, bactericidal effect, which means that the bacteria are even killed.

However, sulfamethoxazole is used alone to treat Pneumocystis jirovecii. It is also used for other respiratory infections and gastrointestinal infections . Silver sulfadiazine is used in the antibiotic treatment of wounds and burns . It is applied on the spot.

In turn, sulfadiazine is administered orally for Plasmodium, Toxoplasma gondii or Pneumocystis jiroveci. The drug sulfamerazine is used for respiratory diseases, diseases of the ear, nose and throat area and urinary tract infections. Sulfamerazine is also usually used here in combination with trimethoprim. It is administered in the form of tablets or by infusion .

While sulfonamides are rarely used in humans, they are common antibiotics in veterinary medicine. There they are often used against gastrointestinal infections, respiratory tract infections and urinary tract infections. In the poultry sector, they have long been used to combat coccidia.

Risks & side effects

As already mentioned, sulfonamides are only rarely used in humans today. One reason, in addition to the higher effectiveness of penicillins, is also the occurrence of side effects. When used, skin rashes , nausea , vomiting , loss of appetite , diarrhea , depression or even psychoses can occur.

Sulfonamide use is dangerous during pregnancy . The breakdown of bilirubin in the fetus is disturbed, which can lead to dangerous hyperbilirubinemia in the newborn . Sulfonamides often produce an allergy on the skin . In combination with sunlight, a phototoxic reaction can be triggered. The skin reacts with itching , reddening , scaling and drying out .

Blood count changes can also occur. Severe hemolytic crises can be triggered under certain circumstances in the case of hereditary methemoglobinemia . A side effect is also the lowering of the aqueous humor pressure in the eye . Therefore, glaucoma is today often treated with eye drops containing modified sulfonamides.

Sulfonamides must not be administered together with some medications because of undesirable interactions. For example, if sulfonamides are used concurrently with local anesthetics such as procaine or tetracaine, their effects will be reversed. There are also undesirable interactions with urotropin, which is used as a food preservative. Undesirable interactions also take place with phenylbutazone , an antirheumatic agent . There is a risk of kidney damage if sulfonamides are used concomitantly with cyclosporine A.

Clear contraindications exist in the case of intolerance to sulfonamides, kidney diseases and the so-called long QT syndrome . Long QT syndrome is a heart disease caused by ion channel dysfunction. It is characterized by cardiac arrhythmias that can lead to ventricular fibrillation . Antibiotics such as sulfonamides can cause or worsen the disease.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.