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What is Bactrim (sulfamethoxazole and trimethoprim)?
Bactrim (sulfamethoxazole and trimethoprim) is a combination of antibiotics used to treat infections due to susceptible bacteria. Examples include urinary tract infections, flares of chronic bronchitis due to bacteria, middle ear infections, for prevention of infections due to pneumococcus in organ transplant recipients, for the treatment or prevention of Pneumocystis carinii pneumonia, chancroid, and prevention of toxoplasma encephalitis in patients with AIDS.
Sulfamethoxazole is an anti-bacterial sulfonamide (a “sulfa” drug) that disrupts the production of dihydrofolic acid, while trimethoprim disrupts the production of tetrahydrofolic acid. Dihydrofolic acid and tetrahydrofolic acid are forms of folic acid that bacteria and human cells use for producing proteins. Trimethoprim inhibits production of tetrahydrofolic acid by inhibiting the enzyme responsible for making tetrahydrofolic acid from dihydrofolic acid.
By combining both drugs, two important steps required in the production of bacterial proteins are interrupted, and the combination is more effective than either drug alone.
Common side effects of Bactrim include:
Serious side effects of Bactrim include:
Sulfonamides such as sulfamethoxazole can add to the kidney damage caused by cyclosporines. All sulfonamides can crystallize in urine when the urine is acidic. Since methenamine causes an acidic urine, it should not be used with sulfonamides.
Blood levels of phenytoin may be increased by treatment with Bactrim and can lead to dizziness and reduced attention. Bactrim also may increase blood levels of digoxin and possibly lead to serious toxic effects.
Increased blood levels of potassium may occur when Bactrim is combined with ACE inhibitors.
Use of sulfonamides may cause bilirubin to be displaced from proteins in the infant’s blood. Displacement of bilirubin can lead to jaundice and a dangerous condition called kernicterus in the infant. For this reason, Bactrim should not be used near term (late in pregnancy) among women.
What are the important side effects of Bactrim (sulfamethoxazole and trimethoprim)?
Common side effects of sulfamethoxazole/trimethoprim are:
Other side effects include:
- liver damage,
- low white blood cell count,
- low platelet count (thrombocytopenia), and
Bactrim (sulfamethoxazole and trimethoprim) side effects list for healthcare professionals
The following serious adverse reactions are described elsewhere in the labeling:
- Embryo-fetal Toxicity
- Hypersensitivity and Other Fatal Reactions
- Clostridium difficile-Associated Diarrhea
- Sulfite Sensitivity
- Risk Associated with Concurrent Use of Leucovorin for Pneumocystis jirovecii Pneumonia
- Infusion Reactions
- Electrolyte Abnormalities
Clinical Trials Experience
Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.
Table 3: Adverse Reactions Reported with Bactrim
|Body System||Adverse Reactions|
|Metabolic and Nutritional||
The following adverse reactions have been identified during post-approval use of Bactrim. Because these reactions were reported voluntarily from a population of uncertain size, it is not possible to reliably estimate their frequency or establish a causal relationship to drug exposure:
- Thrombotic thrombocytopenia purpura
- Idiopathic thrombocytopenic purpura
- QT prolongation resulting in ventricular tachycardia and torsade de pointes
What drugs interact with Bactrim (sulfamethoxazole and trimethoprim)?
Potential For Bactrim To Affect Other Drugs
Trimethoprim is an inhibitor of CYP2C8 as well as OCT2 transporter. Sulfamethoxazole is an inhibitor of CYP2C9. Avoid coadministration of Bactrim with drugs that are substrates of CYP2C8 and 2C9 or OCT2.
Table 4: Drug Interactions with Bactrim
|Diuretics||Avoid concurrent use||In elderly patients concurrently receiving certain diuretics, primarily thiazides, an increased incidence of thrombocytopenia with purpura has been reported.|
|Warfarin||Monitor prothrombin time and INR||It has been reported that Bactrim may prolong the prothrombin time in patients who are receiving the anticoagulant warfarin (a CYP2C9 substrate). This interaction should be kept in mind when Bactrim is given to patients already on anticoagulant therapy, and the coagulation time should be reassessed.|
|Phenytoin||Monitor serum phenytoin levels||Bactrim may inhibit the hepatic metabolism of phenytoin (a CYP2C9 substrate). Bactrim, given at a common clinical dosage, increased the phenytoin half-life by 39% and decreased the phenytoin metabolic clearance rate by 27%. When administering these drugs concurrently, one should be alert for possible excessive phenytoin effect.|
|Methotrexate||Avoid concurrent use||Sulfonamides can also displace methotrexate from plasma protein binding sites and can compete with the renal transport of methotrexate, thus increasing free methotrexate concentrations.|
|Cyclosporine||Avoid concurrent use||There have been reports of marked but reversible nephrotoxicity with coadministration of Bactrim and cyclosporine in renal transplant recipients.|
|Digoxin||Monitor serum digoxin levels||Increased digoxin blood levels can occur with concomitant Bactrim therapy, especially in elderly patients|
|Indomethacin||Avoid concurrent use||Increased sulfamethoxazole blood levels may occur in patients who are also receiving indomethacin.|
|Pyrimethamine||Avoid concurrent use||Occasional reports suggest that patients receiving pyrimethamine as malaria prophylaxis in doses exceeding 25 mg weekly may develop megaloblastic anemia if Bactrim is prescribed.|
|Tricyclic Antidepressants (TCAs)||Monitor therapeutic response and adjust dose of TCA accordingly||The efficacy of tricyclic antidepressants can decrease when coadministered with Bactrim.|
|Oral hypoglycemics||Monitor blood glucose more frequently||Like other sulfonamide-containing drugs, Bactrim potentiates the effect of oral hypoglycemic that are metabolized by CYP2C8 (e.g., pioglitazone, repaglinide, and rosiglitazone) or CYP2C9 (e.g., glipizide and glyburide) or eliminated renally via OCT2 (e.g., metformin). Additional monitoring of blood glucose may be warranted.|
|Amantadine||Avoid concurrent use||In the literature, a single case of toxic delirium has been reported after concomitant intake of Bactrim and amantadine (an OCT2 substrate). Cases of interactions with other OCT2 substrates, memantine and metformin, have also been reported.|
|Angiotensin Converting Enzyme Inhibitors||Avoid concurrent use||In the literature, three cases of hyperkalemia in elderly patients have been reported after concomitant intake of Bactrim and an angiotensin converting enzyme inhibitor.6,7|
|Zidovudine||Monitor for hematologic toxicity||Zidovudine and Bactrim are known to induce hematological abnormalities. Hence, there is potential for an additive myelotoxicity when coadministered.8|
|Dofetilide||Concurrent administration is contraindicated||Elevated plasma concentrations of dofetilide have been reported following concurrent administration of trimethoprim and dofetilide. Increased plasma concentrations of dofetilide may cause serious ventricular arrhythmias associated with QT interval prolongation, including torsade de pointes.2,3|
|Procainamide||Closely monitor for clinical and ECG signs of procainamide toxicity and/or procainamide plasma concentration if available||Trimethoprim increases the plasma concentrations of procainamide and its active N-acetyl metabolite (NAPA) when trimethoprim and procainamide are coadministered. The increased procainamide and NAPA plasma concentrations that resulted from the pharmacokinetic interaction with trimethoprim are associated with further prolongation of the QTc interval.9|
Interactions With Laboratory Or Diagnostic Testing
Bactrim, specifically the trimethoprim component, can interfere with a serum methotrexate assay as determined by the competitive binding protein technique (CBPA) when a bacterial dihydrofolate reductase is used as the binding protein. No interference occurs, however, if methotrexate is measured by a radioimmunoassay (RIA).
The presence of Bactrim may also interfere with the Jaffé alkaline picrate reaction assay for creatinine, resulting in overestimations of about 10% in the range of normal values.
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Related Disease Conditions
Inner Ear Infection (Symptoms, Signs, Treatments, Home Remedies)
An inner ear infection or otitis interna is caused by viruses or bacteria and can occur in both adults and children. An inner ear infection can cause symptoms and signs, for example, a severe ear, dizziness, vertigo, nausea and vomiting, and vertigo. An inner ear infection also may cause inflammation of the inner ear or labyrinthitis. Inner ear infections are not contagious; however, the bacteria and viruses that cause the infection can be transmitted to other people. Good hygiene practices will help decrease the chances of the infection spreading to others. Inner ear infection symptoms and signs like ear pain and nausea may be relieved with home remedies or over the counter (OTC) medication. Some inner ear infections will need to be treated and cured with antibiotics or prescription pain or antinausea medication.
Ear Infection Home Treatment
Infections of the outer, middle, and inner ear usually are caused by viruses. Most outer (swimmer's ear) and middle ear (otitis media) infections can be treated at home with remedies like warm compresses for ear pain relief, tea tree, ginger, or garlic oil drops. Symptoms of an outer ear (swimmer's ear) and middle ear infection include mild to severe ear pain, pus draining from the ear, swelling and redness in the ear, and hearing problems. Middle and inner ear infections may cause fever, and balance problems. Inner ear infections also may cause nausea, vomiting, vertigo, ringing in the ear, and labyrinthitis (inflammation of the inner ear). Most outer and middle ear infections do not need antibiotics. Inner ear infections should be treated by a doctor specializing in ear and hearing problems.
Middle Ear Infection (Otitis Media)
Middle ear infection (otitis media) is inflammation of the middle ear. There are two forms of this type of ear infection, acute and chronic. Acute otitis media is generally short in duration, and chronic otitis media generally lasts several weeks. Babies, toddlers, and children with a middle ear infection may be irritable, pull and tug at their ears, and experience numerous other symptoms and signs. Treatment depends upon the type of ear infection.
Urinary Tract Infection (UTI)
A urinary tract infection (UTI) is an infection of the bladder, kidneys, ureters, or urethra. E. coli, a type of bacteria that lives in the bowel and near the anus, causes most UTIs. UTI symptoms include pain, abdominal pain, mild fever, urinary urgency and frequency. Treatment involves a course of antibiotics.
Inner Ear Infection (Labyrinthitis)
Labyrinthitis is inflammation of the labyrinth (the part of the ear responsible for balance and hearing). Doctors do not know the exact cause of labyrinthitis; however, they often are associated viral infections of the inner ear. Symptoms of labyrinthitis are ear pain or earache, ear discharge, problems with balance and walking, ringing in the ears, dizziness, nausea, vomiting, and vertigo. Viral infections associated with labyrinthitis are contagious. Home remedies may help labyrinthitis symptoms and signs. Over-the-counter (OTC) and prescription medication may treat inner ear infections, labyrinthitis symptoms like vertigo and nausea, and help ear pain.
Bronchitis is inflammation of the airways in the lung. Acute bronchitis is short in duration (10-20 days) in comparison with chronic bronchitis, which lasts for months to years. Causes of acute bronchitis include viruses and bacteria, which means it can be contagious. Acute bronchitis caused by environmental factors such as pollution or cigarette smoke is not contagious. Common symptoms for acute bronchitis include nasal congestion, cough, headache, sore throat, muscle aches, and fatigue. Acute bronchitis in children also my include runny nose, fever, and chest pain. Treatment for acute bronchitis are OTC pain relievers, cough suppressants (although not recommended in children), and rest. Infrequently antibiotics may be prescribed to treat acute bronchitis.
Is a Urinary Tract Infection (UTI) Contagious?
Bacteria such as E. coli or Pseudomonas can cause a urinary tract infection (UTI). The incubation period for a UTI ranges from three to eight days.
Chronic bronchitis is a cough that occurs daily with production of sputum that lasts for at least 3 months, 2 years in a row. Causes of chronic bronchitis include cigarette smoking, inhaled irritants, and underlying disease processes (such as asthma, or congestive heart failure). Symptoms include cough, shortness of breath, and wheezing. Treatments include bronchodilators and steroids. Complications of chronic bronchitis include COPD and emphysema.
Urinary Tract Infections in Children
Urinary tract infections (UTIs) are very common in children. Symptoms and signs include fever and abdominal pain. Associated symptoms and signs include flank pain, vomiting, and blood in the urine. Treatment for a UTI involves antibiotic therapy.
There are many types of urinary incontinence (UI), which is the accidental leakage of urine. These types include stress incontinence, urge incontinence, and overflow incontinence. Urinary incontinence in men may be caused by prostate or nerve problems. Treatment depends upon the type and severity of the UI and the patient's lifestyle.
Urinary Tract Infection in Adults
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Sex, Urinary, and Bladder Problems of Diabetes
Having diabetes can mean early onset and increased severity of bladder symptoms (urinary incontinence and urinary tract infections) and changes in sexual function. Men may have erectile dysfunction; and women may have problems with sexual response and vaginal lubrication. Keep your diabetes under control, and you can lower your risk of sexual and urologic problems.
Yeast Infection vs. Urinary Tract Infection (UTI)
Candida albicans typically causes vaginal yeast infections. Bacterial infections typically cause urinary tract infections (UTIs). Thick white cottage-cheese like vaginal discharge characterizes vaginal yeast infections. Painful, frequent urination characterize urinary tract infections. Antifungal medications treat yeast infections while prescription antibiotics treat UTIs.
Emphysema, Chronic Bronchitis, and Colds
If you have a COPD such as emphysema, avoiding chronic bronchitis and colds is important to avoid a more severe respiratory infection such as pneumonia. Avoiding cigarette smoking, practice good hygeine, stay away from crowds, and alerting your healthcare provider if you have a sinus infection or cold or cough that becomes worse. Treatment options depend upon the severity of the emphysema, bronchitis, or cold combination.
Treatment & Diagnosis
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Medications & Supplements
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
Professional side effects and drug interactions sections courtesy of the U.S. Food and Drug Administration.
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9. Kosoglou T, Rocci ML Jr, Vlasses PH. Trimethoprim alters the disposition of procainamide and Nacetylprocainamide. Clin Pharmacol Ther. Oct 1988;44(4):467-77.