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Trimetoprima para infecciones

Trimethoprim is an antibacterial medicine prescribed for treating infections, mainly chest or urine infections. It is sometimes prescribed to prevent an infection.

Space out your doses evenly throughout the day, and remember to finish the full course of treatment.

The most common side-effects are feeling sick (nausea), and a mild itchy rash.

At a glance

  • Trimethoprim is an antibacterial medicine used to treat bacterial infections like urine infections.

  • It is available as tablets and oral liquid medicine.

  • Take trimethoprim exactly as your doctor tells you, usually for 3-14 days.

  • Common side-effects include feeling sick, diarrhoea, headache, and an itchy skin rash.

  • Tell your doctor if you have a fever, sore throat, skin rash, mouth ulcers, or unexplained bruising or bleeding.

  • Before taking trimethoprim, tell your doctor if you are pregnant, breastfeeding, or have kidney or liver problems.

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About trimethoprim

Tipo de medicamento

An antibacterial medicine

Usado para

Bacterial infections (in adults and children)

Disponible como

Tabletas y medicina líquida oral

Trimethoprim is given to treat a bacterial infection. It is mainly prescribed for urine infections, but it is also prescribed for chest infections and some other types of infection. It works by killing the germs (bacteria) responsible for the infection.

A urine infection is often called a urinary tract infection (UTI) by doctors. Most urine infections are caused by bacteria that come from your own bowel. They are usually easily treated with a short course of trimethoprim. Occasionally, longer-term treatment may be needed to prevent the infection from recurring.

Some medicines are not suitable for people with certain conditions, and sometimes a medicine can only be used if extra care is taken. For these reasons, before you start taking trimethoprim it is important that your doctor knows:

  • Si estás embarazada, intentando tener un bebé o amamantando.

  • If you know you have low amounts of the vitamin folic acid.

  • Si tienes problemas con el funcionamiento de tus riñones.

  • Si tienes problemas con el funcionamiento de tu hígado.

  • If you have a blood disorder, or if you have a rare inherited blood disorder called porphyria.

  • Si está tomando otros medicamentos. Esto incluye cualquier medicamento que se pueda comprar sin receta, así como medicamentos herbales y complementarios.

  • Si alguna vez has tenido una reacción alérgica a un medicamento.

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  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about trimethoprim and will provide you with a full list of the side-effects which you could experience from taking it.

  • Take trimethoprim tablets exactly as your doctor tells you to. Your dose will depend upon whether you are being treated because you have an infection, or to prevent an infection. As a guide, the dose for adults with an infection is 200 mg twice daily, taken morning and evening. The adult dose to prevent an infection is 100 mg at night. If trimethoprim has been prescribed for a child, it is likely that you will be supplied a liquid medicine - the dose will depend upon the age of the child, so read the directions on the label carefully to make sure you give the correct dose.

  • Space your doses out evenly throughout the day - this means that tablets/medicine prescribed twice daily should be taken every 12 hours. Swallow the tablet with a drink of water. You can take trimethoprim either with or without food.

  • Even if you feel your infection has cleared up, keep taking trimethoprim until the full course is finished (unless a doctor tells you to stop). This is to prevent the infection from coming back. A normal course of tratamiento is likely to last 3-14 days. The course will be for longer than this if you are taking trimethoprim to prevenir recurrent infections.

  • If you forget to take a dose at the correct time, take one as soon as you remember. Try to take the correct number of doses each day. Do not take two doses at the same time to make up for a forgotten dose.

  • Most people improve within a few days of starting treatment. If your symptoms do not improve despite taking trimethoprim, go back to see your doctor, as you may need an alternative medicine. This is because some bacteria are resistant to some types of antibiotics.

  • If you are taking the contraceptive 'pill' at the same time as this antibacterial medicine, the effectiveness of the 'pill' can be reduced if you have a bout of being sick (vomiting) or diarrhoea which lasts for more than 24 hours. If this should happen, ask your doctor or pharmacist for advice about what additional contraceptive precautions to use over the following few days. There is no need to use additional precautions for any bouts of sickness or diarrhoea which last for less than 24 hours.

  • Trimethoprim can stop the oral typhoid vaccine from working. If you are due to have any vaccinations, make sure the person treating you knows that you are taking it.

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Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the most common ones associated with trimethoprim. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.

Very common trimethoprim side-effects (these affect more than 1 in 10 people)

¿Qué puedo hacer si experimento esto?

Sentirse mal (náuseas) o estar enfermo (vómitos)

Stick to simple foods - avoid fatty or spicy meals. If you are not already doing so, try taking trimethoprim after food

Common trimethoprim side-effects (these affect fewer than 1 in 10 people)

¿Qué puedo hacer si experimento esto?

Diarrea

Drink plenty of water to replace lost fluids. Stick to simple foods

Dolor de cabeza

Bebe mucha agua y pide a tu farmacéutico que te recomiende un analgésico adecuado. Si los dolores de cabeza continúan, informa a tu médico

Itchy skin rash

Try applying a gentle, fragrance-free skin moisturiser. If the rash becomes troublesome or severe, speak with your doctor

Importante: if trimethoprim is taken over a long period of time (such as when it is taken long-term to prevent an infection), it can occasionally cause problems. If you develop a high temperature (fever), sore throat, skin rash, mouth ulcers or any bruising or bleeding which you can't explain, you should let your doctor know about this straightaway. These may be signs of a blood disorder.

Si experimenta otros síntomas que cree que pueden deberse a este medicamento, hable con su médico o farmacéutico.

  • Mantenga todos los medicamentos fuera del alcance y la vista de los niños.

  • Almacenar en un lugar fresco y seco, lejos del calor y la luz directos.

Información importante sobre todos los medicamentos

Nunca tome más de la dosis prescrita. Si sospecha que usted u otra persona podría haber tomado una sobredosis de este medicamento, acuda de inmediato al departamento de accidentes y emergencias de su hospital local. Lleve el envase con usted, incluso si está vacío.

Este medicamento es para ti. Nunca lo des a otras personas, incluso si su condición parece ser la misma que la tuya.

Si compras algún medicamento, consulta con un farmacéutico que sea seguro tomarlo junto con tus otros medicamentos.

Si vas a someterte a una operación o a un tratamiento dental, informa a la persona que realiza el tratamiento sobre los medicamentos que estás tomando.

No guardes medicamentos caducados o no deseados. Llévalos a tu farmacia local, que se encargará de desecharlos por ti.

Si tienes alguna pregunta sobre este medicamento, consulta a tu farmacéutico.

Informar efectos secundarios de un medicamento o vacuna

Si experimenta efectos secundarios, puede reportarlos en línea a través de Yellow Card website.

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Verifica posibles interacciones entre medicamentos, suplementos y alimentos antes de tomarlos juntos.

Preguntas frecuentes

Can I take trimethoprim if I'm pregnant or breastfeeding?

It's important to let your doctor know if you are pregnant, trying for a baby, or breastfeeding, as some medicines are not suitable in these situations or may require extra care.

What should I do if my symptoms don't get better after starting trimethoprim?

Most people improve within a few days of starting treatment. If your symptoms do not improve despite taking trimethoprim, you should go back to see your doctor. You might need a different medicine because some bacteria are resistant to certain types of antibiotics.

Does trimethoprim affect other medications I might be taking regularly?

Yes, trimethoprim can interact with other medicines. For example, if you are taking the contraceptive 'pill' and experience vomiting or diarrhoea for more than 24 hours, the 'pill's effectiveness can be reduced. Also, trimethoprim can stop the oral typhoid vaccine from working. Always inform your doctor about all medicines you are taking, including over-the-counter, herbal, and complementary medicines.

What are the common side-effects of trimethoprim and how can I manage them?

Common side-effects include feeling sick (nausea) or being sick (vomiting), diarrhoea, headache, and an itchy skin rash. For nausea/vomiting, stick to simple foods and try taking trimethoprim after food. For diarrhoea, drink plenty of water and eat simple foods. For headaches, drink water and consider a painkiller, but if they continue, tell your doctor. For an itchy rash, try a gentle, fragrance-free moisturiser; if it's troublesome or severe, speak to your doctor. These often improve as your body adjusts.

What should I do if I forget to take a dose of trimethoprim?

If you forget a dose, take it as soon as you remember. Try to take the correct number of doses each day. Do not take two doses at the same time to make up for a missed dose.

How long will I need to take trimethoprim for?

The length of your course depends on why you're taking it. A normal course for an existing infection is likely to last 3-14 days. If you are taking it to prevent recurrent infections, the course will be for longer. It's important to continue taking it until the full course is finished, even if you feel better, unless your doctor tells you to stop.

Are there any serious signs I should watch out for if I'm taking trimethoprim for a long time?

Yes, if trimethoprim is taken over a long period, it can occasionally cause problems. You should immediately tell your doctor if you develop a high temperature (fever), a sore throat, a skin rash, mouth ulcers, or any bruising or bleeding that you cannot explain. These could be signs of a blood disorder.

Lecturas adicionales y referencias

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About the authorView full bio

Author image

Michael Stewart, MRPharmS

Medicine Leaflet Review Manager – Contractor, Pharmacist

BPharm (Hons), MRPharmS

Michael is a community pharmacist practicing in the Midlands and South Yorkshire with more than 20 years’ experience advising on medicines and medical conditions. He has a strong background in healthcare training, having produced and delivered training courses for pharmacy teams and staff of residential care settings, including nurses. He has also contributed to pharmacy advisory boards for the management of low acuity conditions in the community.

About the reviewer

Author image

Sid Dajani

Sultan Dajani qualified at the London School of Pharmacy in 1994 and became the youngest elected member of the Royal Pharmaceutical Society council since its founding in 1842.

Historial del artículo

La información en esta página está escrita y revisada por pares por clínicos calificados.

  • Next review due: 5 May 2028
  • 5 May 2025 | Última versión

    Última actualización por

    Michael Stewart, MRPharmS

    Revisado por pares por

    Sid Dajani
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