Reviewed by Patrick Moser, FNP-BC
Information last reviewed 08/20/19
Trimethoprim is a type of antibiotic. Its main purpose is to treat urinary tract infections (UTIs) but might also be given for chest infections or acne.
Trimethoprim works by stopping the bacteria that causes the infection from being able to multiply and survive, resulting in the disappearance of the bacterial infection.
Your symptoms will usually start to ease off after a few days of starting Trimethoprim. Always complete the full course of the treatment to ensure the infection is properly treated.
The symptoms of a UTI commonly include:
An urgent need to urinate
Frequent urination
Burning feeling or pain while urinating
Urine that's cloudy, smelly or bloody
Lower abdominal pain
Tiredness
In elderly people, they may experience behavioral changes such as confusion and agitation.
The antibiotic is most commonly used for bacterial infections like UTIs. It can also be given to prevent UTIs from recurring in people who get them frequently. Aside from this, the medication can also be useful in the treatment of chest infections and acne.
The active ingredient in Trimethoprim is trimethoprim.
The inactive ingredients in Trimethoprim are colloidal silicon dioxide, lactose, macrogol, magnesium stearate, povidone, sodium starch glycollate, stearic acid, and microcrystalline cellulose (E460). (Please note: inactive ingredients may vary across different manufacturers).
This medication does not contain any active or inactive ingredients associated with causing an allergic reaction in users. However, if you are using the medication for the first time, please lookout for signs of anaphylaxis (facial swelling, difficulty breathing, dizziness, and rash) or a severe skin reaction (burning eyes, sore throat, and fever). If you notice any of these symptoms, please seek immediate medical attention.
If you take too many doses of Trimethoprim, seek immediate medical attention.
You need to take all the doses of Trimethoprim that you have been given otherwise, the infection may not be fully cleared. This leaves you at risk of a repeat UTI.
The dosage may vary depending on your symptoms and the nature of your infection. Always take the dose prescribed by your doctor.
Trimethoprim should be taken at the same time each day, and usually twice daily. Ensure you spread out the doses, taking one pill in the morning and the other in the evening. Each one should be swallowed whole with water.
If you forget a dose of Trimethoprim, take it as soon as you can. If it's nearly time for your second dose then leave the missed one. You should never double up a dose.
Take Trimethoprim for as long as your doctor tells you to. This will vary from one individual to another.
Common side effects include:
Heightened levels of potassium in the blood
Nausea
Vomiting
Diarrhea
Headache
Rash
Urticaria
Anemia
Sore throat
Mouth ulcers
Thrush
Rare side effects may include:
Constipation
Severe diarrhoea
Coughing
Altered behaviour
Aggression
Aseptic meningitis (signs of this include stiff neck, headache, fever, feeling generally unwell, tiredness and sensitivity to light)
Kidney problems
Dizziness
Tiredness
Convulsions
Pins and needles
Shakiness or tremors
Vertigo and tinnitus
Pain or redness in the eyes
Photosensitivity
Low blood sugar
Low sodium
Anorexia
Depression
Anxiety
Insomnia
Confusion
Jaundice
Aching muscles and joints
Shortness of breath
Wheezing
Nosebleeds
Lupus erythematosus
Skin discoloration
Fever
Severe side effects which need immediate medication attention include:
Swollen face, lips, tongue or throat
Difficulty breathing
Chest pain
Fainting or shock
Peeling or blistering of the skin
Lesions or skin eruptions
Pancreatitis
Trimethoprim is not suitable for individuals who:
Are allergic to any of the ingredients in the medicine
Are pregnant
Have a blood disorder
Have severe kidney or liver disease
Tell your doctor if:
You are deficient in folic acid
You have kidney disease
You are having dialysis treatment
The following medications might interact with Trimethoprim:
Other antibiotics
Anticoagulants
Digoxin
Phenytoin
Pyrimethamine
Dapsone
Immunosuppressant drugs
Bone marrow depressants
Spironolactone
Repaglinide
Diuretics
Procainamide
Both Trimethoprim and Nitrofurantoin are antibiotics used to treat UTIs. Nitrofurantoin is used solely for this function as the medicine is filtered straight to the urine. If you have low levels of folic acid in your blood or you are pregnant, then Nitrofurantoin is more suitable. Trimethoprim is likely to be prescribed if you have diabetes or a vitamin B deficiency.
There are several types of antibiotics that treat urinary tract infections. Quinolone types like Nitrofurantoin, Ciprofloxacin, Norfloxacin and Ofloxacin are the first choice of medicines to treat UTIs. Trimethoprim may be prescribed if these types of antibiotics are not suitable, or prove ineffective.
There is no evidence to suggest that alcohol interacts with Trimethoprim. It is considered generally safe to consume alcohol in moderation while taking Trimethoprim.
Other than treating urinary tract infections, Trimethoprim is sometimes used to treat skin and soft tissue infections, Staph infections, certain forms of traveler’s diarrhea, and for the routine prevention of infection in immunocompromised patients.
Trimethoprim is rated as pregnancy category C and is not recommended during the initial 12 weeks of pregnancy, also known as the first trimester. Trimethoprim decreases folic acid levels. Folic acid is very important for the fetus during the first trimester. Lack of folic acid during this time can lead to problems with the unborn baby’s neurological system, known as neural tube defects. Trimethoprim is generally safe after the first trimester.
There are no specific dietary restrictions while taking Trimethoprim. You can take Trimethoprim with or without food. Taking Trimethoprim with food or milk can help ease upset stomach sometimes associated with Trimethoprim and other antibiotics.
No. Although they are both antibiotic pills, they are used to treat different things. They can both be used to treat the common urinary tract infections. Trimethoprim is a “sulfa” antibiotic and works by inhibiting DNA synthesis via a folic acid blocking mechanism. Nitrofurantoin works by blocking bacterial ribosomal function, which blocks their ability to grow.
Disclaimer: This is not medical advice. You and your physician will determine if and how you should take any medication prescribed to you following a medical consultation.
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