Updated: 2 August, 2019

Bactrim is a medication used to treat various bacterial infections. This drug is made up of two synthesized antibiotics; sulfamethoxazole and trimethoprim. It is the brand name for the generic drug named after these two major ingredients but commonly referred to as co-trimoxazole. These two ingredients combine in the ratio of 5:1 with sulfamethoxazole taking up five out of the six parts and trimethoprim taking up only one part. This antibiotic tablet is usually round and white, made up of 400 mg of sulfamethoxazole and 80 mg of trimethoprim. Bactrim double strain (DS), another brand name for this drug is oval shaped and white. It contains 800 mg of sulfamethoxazole and 160mg of trimethoprim. Bactrim was approved by the FDA in 1973. Other brand names include Sulfatrim, Septra, etc.


Bactrim is used to treat bacterial infections. It lowers the ability of certain bacteria to use folic acid for their growth. Sulfamethoxazole stops the body from making dihydrofolic acid. At the same time trimethoprim also stops the body from making tetrahydrofolic acid, by reducing the acting power of the enzyme used to synthesize this acid from dihydrofolic acid. Human cells and bacteria use these folic acids to make the protein required for metabolic reactions. The combination of sulfamethoxazole and trimethoprim is more effective against bacterial strains than when they are used separately to combat the microorganism. They cut short important steps that would have made the production of protein inevitable, therefore giving bacteria what to thrive on.

Pneumonia, chronic bronchitis, infections affecting the middle ear (caused by Haemophilus influenza), lung, intestine and urinary tract infections are common bacterial infections treated with bactrim medication. Viral diseases like cold and flu cannot be treated with this antibiotic. Travellers’ diarrhoea, caused by enterotoxin, E. coli can also be treated with this drug. AIDS patients take bactrim to prevent toxoplasma encephalitis.

Do not use this drug if you have liver or kidney disease, anaemia (caused by folic acid deficiency), low blood platelets (caused by trimethoprim or any other sulphate drug). Children under 2 months should not be given this drug

Let your doctor know if you fall into any of these categories before using this drug to treat your bacterial infection:

  • If you are asthmatic (or have any form of allergy.)
  • If you have kidney or liver problem.
  • If you have a thyroid disorder.
  • If you are suffering from folic acid deficiency.
  • If you have a genetic enzyme disorder that affects your skin and nervous system (porphyria.)
  • If you are malnourished.
  • If you are deficient in glucose-6-phosphate dehydrogenase. (G6PD)
  • If you are pregnant (as it can harm the unborn foetus.)
  • If you are breastfeeding.

How to use Bactrim Medication

Bactrim: Uses, Dosage and Side Effects 1 bac2 205x300


Take bactrim by mouth (follow your doctor’s directives), wash down with a full glass of water. Drink lots of water while on this medication (unless you are told otherwise by your doctor). It will help reduce your chances of developing kidney stone. Take this drug at regular intervals, be consistent in using it (as directed by your doctor). You are to complete your medication. Continue taking your drug even if you feel better. If you stop taking it before completing the total medication as prescribed by your doctor, there is a great chance of bacteria regrowth. This will definitely cause a relapse, making you experience the sickness again.

Do not take bactrim with alcohol. While it is true that alcohol will not reduce its effectiveness, it will however lead to unwanted side effects. You might feel drowsy, dizzy and nauseous if you take alcohol while using this drug. It can also upset your stomach and lead to frequent vomiting making the drug ineffective. If you experience stomach upset anytime you take this drug with water, try taking it with food or milk to hold the contents of your stomach.

Bactrim can be given to dogs but must first be approved by the veterinary doctor. The weight of the dog to use bactrim medication should be put into consideration before administering the drug.

Bactrim Dosage

Read the prescription label very well and understand it before using this drug. This is a prescription drug, follow your doctor’s advice to the latter. For urinary tract infection, double strength bactrim (bactrim ds) is usually prescribed. Take one tablet, once daily. If you are using single strength bactrim, take 2 tablets every 12 hours. You are to continue medication for about 10-14 days. The same routine is used for flares of chronic bronchitis. Medication for this usually takes up to 14 days. Your doctor may adjust your dosage to suit you personally. The recommended dosage by your doctor may be different from what is written on the package label of the drug. Discuss any confusion you feel with your doctor and understand why your dosage was adjusted. The dosage your doctor will recommend for you largely depends on the following:

  • The severity of your condition
  • Your age
  • Other medical conditions you might have
  • Your body size (area of your body surface)
  • Your weight
  • The state of your kidney
  • Other medications you are currently taking
  • Your response to the medication

Make sure you are not allergic or react to any of the ingredients used to make bactrim. Do not reduce or increase your dosage by yourself. Keep taking your drugs until you complete the prescribed dosage. Do not extend the days you are to take this medication by yourself. Discontinue use after the time given by your doctor elapses. Make sure you shake the containing bottle before taking the liquid (oral suspension) type of bactrim. You should have a special dose measuring spoon or medicine cup to measure out the prescribed quantity. If you do not have any of the measuring devices, ask your pharmacist for one. Do not use an ordinary spoon to measure out the quantity. The dimensions differ and doing that will definitely alter your dosage.

Be careful not to skip any dose. Skipping doses will interfere with your treatment. It will most likely decrease the effectiveness of the drug and will make you more susceptible to other similar infections that are resistant to antibiotics. If you are to undergo any medical test during the period you are using this drug, tell your doctor. The drug may interfere with your test results.

If you accidentally miss your dose, take it immediately you remember. If you remember and it’s almost time for your next dose, wait till the time for the next dose and take a single dose. Do not double your dose because you missed the previous dose. Try to take your drug at the same time, daily. It will help you remember to always take them and also enhance the effectiveness of the drug. In any case of drug overdose, contact your doctor immediately or call the poison control centre.

Bactrim Side Effects

Ask your doctor to enlighten you on the side effects of this drug before you start using the medication. Skin reactions (hives, itch), diarrhoea, nausea, vomiting and anorexia are common side effects of bactrim. Severe side effects in the following categories have been reported by patients taking this drug.

Severe Diarrhoea: This is a common effect of antibiotics on most people. It usually stops at the end of the medication. Most people taking antibiotics have watery stools that might come with stomach cramps. Do not take any other drug for the diarrhoea if it occurs. Talk to your doctor first. Sometimes diarrhoea may continue up to 2 months after using antibiotics. If diarrhoea is severe, tell your doctor. Only use diarrhoea medication caused by antibiotics when your doctor tells you to.

Severe Reaction (hypersensitivity): Bactrim medication may lead to the following reactions:

  • Breathing problem
  • Difficulty swallowing substances
  • Chest pain
  • Swelling of various parts of the body like eye, face, lips, tongue, arms or legs
  • Body rash
  • Fainting

High level of potassium in the body (hyperkalaemia): Too much potassium in the body may cause sharp breaths. It is a severe effect of antibiotic usage. Tell your doctor if you notice these symptoms:

  • Chest pain
  • Dizziness
  • Profuse sweating
  • Fast or slow heartbeat
  • Shortness of breath
  • Skipping heartbeat

Abnormal bleeding: Thrombocytopenia may occur when your blood platelet count level is decreased. You might experience the following symptoms as a result; skin discoloration (red or purple spots on skin), easy bruising unlike before using the medication, bruising that is very slow to heal. Contact your doctor as soon as you notice these symptoms.

Kidney stones: You are advised to take lots of liquid while using bactrim medication. This is to reduce any risk of having kidney stone. The following are symptoms you might experience if you are in danger of having kidney stone as a result of this medication;

  • Cloudy urine with foul smell
  • Burning sensation while urinating
  • Fever and cold
  • Blood in the urine
  • Regular vomiting
  • Severe back or side pain that persists over time

Let your doctor know if you have any of these symptoms. They are sign of a serious medical condition. Side Effects of  Bactrim.

Drug Interactions

Let your doctor know about all the supplements, vitamins, herbal substances, prescription and non-prescription drugs you are taking. Do not withhold any information about any drug you are on. Some drugs might not go well with bactrim, this is why you need to discuss this with your doctor.

Some of the drugs that may likely react with bactrim include:

  • Warfarin
  • Methotrexate
  • Phenytoin
  • Cyclosporine
  • Digoxin
  • Thiazide diuretic (hydrochlorothiazide, chlorothalidone)
  • Indomethacin
  • Leucovorin
  • Pyrimethamine
  • Metformin
  • Medications that make use of CYP2C9 enzyme like glipizide and glyburide
  • Medications that make use of the enzyme CYP2C8 such as ploglitazone, repaglinide and rosiglitazone


FAD usually place drugs in categories based on how risky they are to pregnant women and their unborn babies. This is a five category grouping ranging from A, B, C, D and X. A is safe while X is extremely unsafe for pregnant women and the foetus they are carrying. Bactrim is categorized as D, it is strongly not recommended for use during pregnancy. This is because sulfonamides move across the placental barrier and put the unborn child at a high risk of brain damage. Sulfamethoxazole and trimethoprim, the active ingredients of this drug may likely interfere with the activity of folic acid in the body. This will cause more negative effect on the baby. Bactrim should not be used by pregnant women except the doctor feels the benefit of the drug to the mother-to-be is more than any effect it might have on her.

Let your doctor know if you are breastfeeding or planning to breastfeed. The constituents of bactrim can pass into the breast milk and get into the baby’s system. This is very dangerous as it can cause brain damage to the baby.

Your doctor will monitor you to know if this drug is actually improving your health condition. Tell your doctor if you still have symptoms of infection after using this medication. Do not let any other person use your drug. If they express the same symptoms as you, tell them to see a doctor. Experiencing the same symptoms does not mean they have the same sickness as you. It’s better they get checked by a doctor so that they can be fully diagnosed. This prescription may not be refillable so if you are to continue using it, get a fresh prescription.

Your medication should be kept in the container it came with. Make sure the lid is tightly closed so air cannot gain entrance and spoil the drug. Do not store in the bathroom. Store in a cool dry place away from excess heat and moisture (extreme temperatures will definitely spoil the drug). Keep drugs out of reach of children and pets. Ensure that the safety cap is always on.

Dispose any of your unused medication properly, away from people. It is best to dispose any unused drug through the medicine take-back program. Ask your pharmacist how best to go about this disposal or contact the recycling department in your area.

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Table Of Contents

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Chapter 1 – Uses

Chapter 2 – How to use Bactrim Medication

Chapter 3 – Bactrim Dosage

Chapter 4 – Bactrim Side Effects

Chapter 5 – Drug Interactions

Chapter 6 – Precautions



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