Cotrimoxazole: What It Is And How It Works

Cotrimoxazole is a drug made by combining two different antibiotics. Therefore, this drug is capable of fighting infections that have a bacterial origin such as pneumonia or bronchitis, among others. At present, its use is widely accepted in the field of medicine.

Like all drugs, it should not be used without a prescription. Regarding its administration, it is important to always follow the advice of the specialist. However, we are going to see below how it works in our body, what effects it can have and what it is used for.

Chemical synthesis of cotrimoxazole

As we have said and in accordance with the article Trimethoprim Sulfamethoxazole published in 2019, cotrimoxazole is formed from the union of two other antibiotics:

• Sulfamethoxazole: a sulfonamide.
• Trimethoprim: an inhibitor of the enzyme dihydrofolate reductase.

As a general rule, the combination used is 5: 1 ; that is, 5 parts of sulfamethoxazole for each part of trimethoprim. This is so, in part, due to the toxicity of the latter compound and its high risk of causing side effects.

However, in low doses these compounds work effectively to treat bacterial infections. However, it is important to supervise the doctor when using it.

There are various presentations of this drug on the market. The pharmaceutical industry prepares cotrimoxazole both in tablet form and in liquid formula for children, for example.

How does cotrimoxazole work?

Cotrimoxazole kills the bacteria that cause various infections. Its two components act synergistically ; that is, the effects that they present when used in combination are greater than those that each substance has separately. That is why this association is used.

Both compounds are involved in the synthesis of folic acid. They prevent bacteria from synthesizing this compound that they need for their DNA:

• Sulfamethoxazole inhibits the formation of dihydrofolic acid because it has a similar structure to that of p-aminobutyric acid (PABA) used in its synthesis and competes with it.

• Trimethoprim binds to the enzyme dihydrofolate reductase. In this way, it prevents the formation of tetrahydrofolic acid from dihydrofolate.

Through these mechanisms, cotrimoxazole is effective against a wide variety of infection- causing bacteria, including the following:

• Staphylococcus epidermidis and S. aureus.
• Streptococuus pneumoniae and S. viridans.
• Numerous Enterobacteriaceae such as Salmonella or Shigella.
• Haemophilus influenzae, Moraxella catarrhalis, and Stenotrophomonas maltophilia.
• Enterococci .
• Neisseria gonorrhoeae and Pseudomonas aeruginosa.

It must be taken into account that the process of synthesis of folic acid also occurs in our cells and inhibiting it would have toxic consequences. However, bacteria have a higher affinity for trimethoprim than our cells and this prevents the drug from acting on the latter.

Uses of cotrimoxazole

The administration of this compound is recommended in the treatment of infections caused by staphylococci and streptococci. These are two families of bacteria responsible for diseases such as the following:

• Bronchitis.
• Resistant acne, which persists despite being treated with other antibiotics.
• Urinary tract, ear, and intestinal infections.
• Traveler’s diarrhea.

It is important to note that, although it belongs to the group of antibiotics, cotrimoxazole is not effective for all bacterial infections. Therefore, as we have said, it cannot be used without a prescription. Sometimes, before prescribing it, you have to do a sensitivity culture for the specific germ.

Side effects

Consistent with the article published in 2011 in the Canadian Medical Association Journal , the most common side effects or adverse effects of this drug include the following:

• Nausea and vomiting
• Frequent headaches or headaches.
• Diarrhea
• Eruption.
• Photosensitivity: it is an allergic reaction to sunlight. It is characteristic that small red bumps appear all over the skin surface that has been exposed to the sun.
• Anemia: the patient usually presents general fatigue even if he does not perform physical activities that require great effort. This is due to the lower supply of oxygen to the body.

• Hypoglycemia or low blood glucose levels.
• Depression, hallucinations and seizures : these are side effects that appear less frequently than those mentioned above. They occur in those patients with predisposition or in treatment with psychotropic drugs.

Contraindications

The use of this chemical compound must be adapted to the patient in question. Specifically, its use is not recommended in the following circumstances:

• Liver diseases: if the patient suffers from any disease, such as liver failure or hepatitis, poisoning is more likely to appear. This is because the liver metabolizes toxic substances.
• Kidney diseases: in those patients with kidney failure it is necessary to take extreme precautions since their kidneys do not filter the blood well. They are the people most vulnerable to poisoning.

• Pregnancy: the effects that it could have on babies throughout their embryonic development have not yet been studied. It is believed that these chemicals could cause some alteration in the baby, both in the womb and in newborns.
• Porphyria: the body has problems synthesizing the heme group found in the hemoglobin of red blood cells, responsible for transporting oxygen throughout the body.
• Other serious hematological disorders: Conditions that affect blood cells, including diseases that affect clotting, white blood cells, and red blood cells.

Things to consider before taking cotrimoxazole

Do not use this drug if you do not have a medical prescription and always follow the advice and instructions given by the specialist. Consult your doctor or pharmacist about its side effects and, above all, tell him or her if you have a history of allergic reactions to this drug or any other drug.

Also, inform the professional if you are taking other prescription or non-prescription medications, including vitamins, supplements, or over-the-counter drugs. Do not forget that there can be interactions.