Trimethoprim
Trimethoprim is an antibiotic used to treat cystitis, an infection that occurs when bacteria are introduced into the urinary tract. It may also be used for other types of bacterial infections, such as bronchitis, pneumonia or traveller’s diarrhoea. Antibiotics are only used for bacterial infections and are ineffective on viral infections such as colds and flu.
How Does Trimethoprim Work?
Trimethoprim works in two ways: by killing bacteria and by blocking an important step in bacterial growth. Bacteria need folate, or folic acid, to produce DNA and thus increase in number. Trimethoprim prevents bacteria from producing folic acid so that the spread of the infection is halted.
Trimethoprim Dosage
This oral medication comes in tablet form and can be taken either on an empty stomach or with food if stomach upset occurs. You should take each dose with a full glass of water and drink eight glasses of water per day while using this medication. Carefully follow dosing instructions on the prescription label, and always take the entire course of medication as prescribed by your doctor, even if your symptoms have cleared up. Stopping your medication early can create an antibiotic-resistant strain of bacteria, which will lead to a relapse of cystitis that may be more difficult to treat.
How Effective is Trimethoprim?
Trimethoprim is the most frequently prescribed antibiotic for cystitis and has a success rate of 90 percent. In most cases, symptoms improve within 24 hours of starting treatment and are completely gone after three days.
Trimethoprim Side Effects
Common minor side effects include vomiting, diarrhoea and upset stomach. If any of these side effects persist or become intolerable, talk to your doctor.
Trimethoprim occasionally causes serious side effects. Discontinue your medication and contact your doctor immediately if you experience any of the following:
- skin rash or itching
- fever or chills
- difficulty breathing or swallowing
- sore throat
- mouth ulcers
- bruising or bleeding
- jaundice
- joint aches
- bluish colored skin, lips or fingernails
Avoid prolonged exposure to the sun while taking Trimethoprim, as it can cause skin photosensitivity and lead to severe sunburn.
What Other Medications Affect Trimethoprim?
Always tell your doctor if you are taking any other medications, including over-the- counter medicines, herbal treatments and vitamin supplements. Medicines known to interact with Trimethoprim include:
- cyclosporine
- antimalarial pyrimethamine
- dapsone
- digoxin
- phenytoin
- procainamide
- azathioprine
- clozapine
- mercaptopurine
- methotrexate
- warfarin
If you are taking oral contraceptives, Trimethoprim may decrease their effectiveness at preventing pregnancy. Talk to your doctor about backup contraceptive methods you can use during your course of treatment.
Who Should Not Take Trimethoprim?
Do not take Trimethoprim if you are
- allergic to any of the ingredients in Trimethoprim, diuretics or sulfa drugs
- pregnant, especially in the first trimester
- breastfeeding
Trimethoprim should be used with caution in the elderly and newborns, as well as anyone with the following conditions:
- decreased kidney function
- liver disease
- folic acid deficiency
- anaemia
- hereditary blood disorders
If you have any of these conditions, discuss them with your doctor to determine if Trimethoprim is right for you.
