Trimethoprim

In New Zealand, trimethoprim is available as tablets (300 mg).

• To treat an infection: The usual dose for adults with an infection is 1 tablet (300mg), each night. Your doctor or pharmacist will advise you how long to take trimethoprim for (usually 3 to 7 days).
• To prevent an infection: The dose to prevent infection is half a tablet (150mg) at night. If you have frequent urine infections, you will have to take trimethoprim each night for a few months to prevent recurrent infections.
• Always take your trimethoprim exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much trimethoprim to take, how often to take it, and any special instructions.

• Timing of your dose: You can take trimethoprim with or without food. If you get stomach upset, try taking it with food. Trimethoprim is best taken before bedtime. Take trimethoprim at the same time each day. 
• Splitting tablets: If your dose is half a tablet, you can split the tablet into two by either breaking the tablet along a scored line, or using a tablet cutter. You can buy a tablet cutter from your pharmacy. If you have trouble splitting your tablets, talk to your pharmacist, they can do this for you. It’s important to halve tablets correctly because uneven splitting or crumbling, changes the dose.
• Missed dose: If you forget to take trimethoprim, take it as soon as you remember. But, if it is nearly time for your next dose, just take the next dose at the right time. Do not take double the dose.
• Finish the course: It is best to take the whole course of antibiotics for the number of days your doctor has told you to. Do not stop taking it, even if you feel your infection has cleared up.  

Here are some things to know when you're taking trimethoprim. Other things may be important as well, so ask your healthcare provider what you should know about.

• Trimethoprim does not have direct interaction with alcohol. This means that most people could have the occasional drink while taking it without any serious problems. However, if trimethoprim makes you feel sick (nausea), do not drink alcohol as it will make you feel worse.
• If you are taking the contraceptive pill, you do not usually need to use additional contraception if you're taking trimethoprim. But if the antibiotic or the illness they're treating cause diarrhoea or vomiting, lasting more than 24 hours, absorption of the contraceptive pill may be affected. If this happens, ask your doctor or pharmacist for advice about contraception over the following few days.

Like all medicines, trimethoprim can cause side effects, although not everyone gets them. Often side effects improve as your body adjusts to the new medicine