Bactrim DS (800-160mg) Tablets
It is used to treat or prevent bacterial infections.
Drug Class
Antibiotic
Pharmacologic Class
Sulfonamide and Dihydrofolate Reductase Inhibitor Combination
Pregnancy Category
D
FDA Approved
Aug 1973
DEA Schedule
Not Controlled
Overview
What is this medicine?
Bactrim DS is an antibiotic that combines two medicines, sulfamethoxazole and trimethoprim, to fight bacterial infections. It works by stopping bacteria from making a substance they need to grow and multiply. It's commonly used for urinary tract infections, certain types of pneumonia, and other bacterial infections.
How to Use This Medicine
Taking Your Medication
To get the most benefit from your medication, follow these steps:
Take your medication exactly as directed by your doctor.
Read all the information provided with your medication and follow the instructions carefully.
You can take your medication with or without food. If it causes stomach upset, take it with food.
Swallow your medication with a full glass of water.
Take your medication at the same time every day to establish a routine.
Continue taking your medication as prescribed by your doctor or healthcare provider, even if you start feeling well.
Staying Hydrated
Drink plenty of non-caffeinated liquids, unless your doctor advises you to limit your fluid intake.
Storing and Disposing of Your Medication
Store your medication at room temperature, away from light and moisture.
Keep your medication in a dry place, such as a closet or drawer. Avoid storing it in a bathroom.
Keep all medications out of the reach of children and pets.
Dispose of unused or expired medications properly. Do not flush them down the toilet or pour them down the drain unless instructed to do so by your doctor or pharmacist.
Check with your pharmacist for guidance on disposing of medications. You may also have access to drug take-back programs in your area.
Missing a Dose
If you miss a dose, take it as soon as you remember.
If it's close to the time for your next dose, skip the missed dose and resume your regular schedule.
* Do not take two doses at the same time or take extra doses to make up for a missed one.
To get the most benefit from your medication, follow these steps:
Take your medication exactly as directed by your doctor.
Read all the information provided with your medication and follow the instructions carefully.
You can take your medication with or without food. If it causes stomach upset, take it with food.
Swallow your medication with a full glass of water.
Take your medication at the same time every day to establish a routine.
Continue taking your medication as prescribed by your doctor or healthcare provider, even if you start feeling well.
Staying Hydrated
Drink plenty of non-caffeinated liquids, unless your doctor advises you to limit your fluid intake.
Storing and Disposing of Your Medication
Store your medication at room temperature, away from light and moisture.
Keep your medication in a dry place, such as a closet or drawer. Avoid storing it in a bathroom.
Keep all medications out of the reach of children and pets.
Dispose of unused or expired medications properly. Do not flush them down the toilet or pour them down the drain unless instructed to do so by your doctor or pharmacist.
Check with your pharmacist for guidance on disposing of medications. You may also have access to drug take-back programs in your area.
Missing a Dose
If you miss a dose, take it as soon as you remember.
If it's close to the time for your next dose, skip the missed dose and resume your regular schedule.
* Do not take two doses at the same time or take extra doses to make up for a missed one.
Lifestyle & Tips
- Drink plenty of fluids (6-8 glasses of water daily) to prevent kidney stones and help the medicine work.
- Avoid prolonged exposure to sunlight or tanning beds, as this medication can make your skin more sensitive to the sun. Use sunscreen and wear protective clothing.
- Take the medication exactly as prescribed, even if you start feeling better. Do not skip doses or stop early, as this can lead to antibiotic resistance.
- Take with food or milk if stomach upset occurs.
Available Forms & Alternatives
Available Strengths:
Generic Alternatives:
Dosing & Administration
Adult Dosing
Standard Dose:
1 Bactrim DS tablet (800 mg SMX / 160 mg TMP) orally every 12 hours for 10-14 days for most infections (e.g., UTI). For Pneumocystis pneumonia (PCP) treatment: 15-20 mg TMP/kg/day and 75-100 mg SMX/kg/day in 3-4 divided doses.
Dose Range:
160 - 320 mg
Condition-Specific Dosing:
Uncomplicated UTI:
1 DS tablet every 12 hours for 3-7 days
Pneumocystis Pneumonia (PCP) Treatment:
15-20 mg/kg/day (TMP component) orally or IV in 3-4 divided doses for 14-21 days
Pneumocystis Pneumonia (PCP) Prophylaxis:
1 DS tablet orally once daily or 3 times per week
Acute Exacerbation of Chronic Bronchitis:
1 DS tablet every 12 hours for 10-14 days
Traveler's Diarrhea:
1 DS tablet every 12 hours for 5 days
Pediatric Dosing
Neonatal:
Contraindicated in infants less than 2 months of age due to risk of kernicterus.
Infant:
Not established for infants < 2 months. For infants > 2 months, dosing is weight-based.
Child:
Based on Trimethoprim component: 8-10 mg TMP/kg/day orally in 2 divided doses for general infections. For PCP treatment: 15-20 mg TMP/kg/day in 3-4 divided doses. For PCP prophylaxis: 5-10 mg TMP/kg/day in 2 divided doses or once daily, 3 times per week.
Adolescent:
Same as adult dosing for most indications.
Dose Adjustments
Renal Impairment:
Mild:
CrCl 30-50 mL/min: Reduce dose by 50% or administer standard dose every 24 hours.
Moderate:
CrCl 15-30 mL/min: Reduce dose by 50% or administer standard dose every 24 hours.
Severe:
CrCl < 15 mL/min: Not recommended unless plasma concentrations can be monitored. If used, reduce dose by 75% or administer standard dose every 48 hours.
Dialysis:
Hemodialysis: Administer 50% of the usual dose after each dialysis session. Peritoneal Dialysis: Not recommended due to insufficient data, but generally avoid or use with extreme caution.
Hepatic Impairment:
Mild:
No specific dose adjustment recommended, but use with caution.
Moderate:
Use with caution; monitor for signs of toxicity. Consider lower doses.
Severe:
Contraindicated in patients with marked hepatic damage or severe hepatic insufficiency.
Pharmacology
Mechanism of Action
Sulfamethoxazole (SMX) inhibits bacterial dihydrofolate synthesis by competing with para-aminobenzoic acid (PABA). Trimethoprim (TMP) inhibits bacterial dihydrofolate reductase, blocking the conversion of dihydrofolate to tetrahydrofolate. This sequential blockade of two enzymes in the folic acid synthesis pathway results in a synergistic bactericidal effect.
Pharmacokinetics
Absorption:
Bioavailability:
SMX: 90-100%, TMP: 90-100%
Tmax:
SMX: 2-4 hours, TMP: 1-4 hours
FoodEffect:
Absorption is not significantly affected by food, but may delay Tmax.
Distribution:
Vd:
SMX: 0.16-0.2 L/kg, TMP: 1.3-1.8 L/kg (higher due to lipophilicity)
ProteinBinding:
SMX: 66%, TMP: 44%
CnssPenetration:
Yes (both cross blood-brain barrier, TMP more readily)
Elimination:
HalfLife:
SMX: 9-11 hours, TMP: 8-10 hours
Clearance:
SMX: 1.5-2.5 L/hr, TMP: 3.5-5 L/hr
ExcretionRoute:
Renal (glomerular filtration and tubular secretion)
Unchanged:
SMX: 20-30%, TMP: 50-60%
Pharmacodynamics
OnsetOfAction:
Rapid (within 1-2 hours of oral administration)
PeakEffect:
Within 2-4 hours (correlates with Tmax)
DurationOfAction:
Approximately 12 hours (allows for twice-daily dosing)
Safety & Warnings
BLACK BOX WARNING
FATALITIES ASSOCIATED WITH THE ADMINISTRATION OF SULFAMETHOXAZOLE AND TRIMETHOPRIM HAVE OCCURRED DUE TO SEVERE ADVERSE REACTIONS INCLUDING STEVENS-JOHNSON SYNDROME, TOXIC EPIDERMAL NECROLYSIS, FULMINANT HEPATIC NECROSIS, AGRANULOCYTOSIS, APLASTIC ANEMIA, AND OTHER BLOOD DYSCRASIAS. CLINICAL SIGNS SUCH AS RASH, SORE THROAT, FEVER, ARTHRALGIA, PALLOR, PURPURA OR JAUNDICE MAY BE EARLY INDICATIONS OF SERIOUS REACTIONS. CAUTION SHOULD BE EXERCISED WHEN ADMINISTERING SULFAMETHOXAZOLE AND TRIMETHOPRIM TO PATIENTS WITH IMPAIRED RENAL OR HEPATIC FUNCTION, TO THOSE WITH POSSIBLE FOLATE DEFICIENCY (E.G., THE ELDERLY, CHRONIC ALCOHOLICS, PATIENTS RECEIVING ANTICONVULSANT THERAPY, PATIENTS WITH MALNUTRITION), AND TO THOSE WITH SEVERE ALLERGY OR BRONCHIAL ASTHMA. IN GLUCOSE-6-PHOSPHATE DEHYDROGENASE DEFICIENCY, HEMOLYSIS MAY OCCUR. THIS DRUG IS NOT RECOMMENDED FOR USE IN INFANTS LESS THAN 2 MONTHS OF AGE.
Side Effects
Important Side Effects to Report to Your Doctor Right Away
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, seek medical attention immediately:
Allergic reactions: Rash, hives, itching, red, swollen, blistered, or peeling skin with or without fever, wheezing, tightness in the chest or throat, trouble breathing, swallowing, or talking, unusual hoarseness, or swelling of the mouth, face, lips, tongue, or throat.
High potassium levels: Abnormal heartbeat, confusion, weakness, lightheadedness, dizziness, numbness or tingling, or shortness of breath.
Low blood sugar: Dizziness, headache, sleepiness, weakness, shaking, rapid heartbeat, confusion, hunger, or sweating.
Kidney problems: Inability to urinate, changes in urine output, blood in the urine, or significant weight gain.
Low sodium levels: Headache, difficulty focusing, memory problems, confusion, weakness, seizures, or balance changes.
Lung or breathing problems: Shortness of breath, trouble breathing, cough, or fever.
Pancreas problems (pancreatitis): Severe stomach pain, severe back pain, or severe nausea and vomiting.
Musculoskeletal issues: Muscle or joint pain.
Skin and mucous membrane issues: Purple patches on the skin or mouth.
Neurological issues: Hallucinations (seeing or hearing things that are not there), depression, or mood changes.
Numbness or tingling: Abnormal burning, numbness, or tingling sensations.
Hearing issues: Ringing in the ears.
Swollen glands: Enlarged lymph nodes.
Cardiovascular issues: Chest pain or pale skin.
Severe dizziness or fainting: Sudden loss of balance or consciousness.
Antibiotic-Associated Diarrhea
Diarrhea is a common side effect of antibiotics. However, a severe form called C. difficile-associated diarrhea (CDAD) may occur, which can lead to life-threatening bowel problems. If you experience stomach pain, cramps, or loose, watery, or bloody stools, seek medical attention immediately. Do not treat diarrhea without consulting your doctor.
Rare but Serious Side Effects
Sulfa drugs, like this medication, can cause rare but severe side effects, including:
Liver problems: Dark urine, tiredness, decreased appetite, nausea, vomiting, light-colored stools, or yellow skin and eyes.
Blood problems: Unusual bruising or bleeding.
Severe skin reactions: Stevens-Johnson syndrome or toxic epidermal necrolysis, characterized by rash, red, swollen, blistered, or peeling skin, red or irritated eyes, mouth, throat, or nose sores, fever, chills, or sore throat.
Aseptic meningitis: A severe brain problem that can cause headache, fever, chills, nausea, vomiting, stiff neck, rash, sensitivity to light, sleepiness, or confusion.
Hemophagocytic lymphohistiocytosis (HLH): A life-threatening immune system problem that can cause fever, swollen glands, rash, seizures, confusion, balance changes, or difficulty walking.
Other Side Effects
Most people do not experience significant side effects or only have mild ones. However, if you notice any of the following side effects, consult your doctor:
Diarrhea
Stomach pain
Nausea
Vomiting
* Decreased appetite
This is not an exhaustive list of side effects. If you have questions or concerns, discuss them with your doctor. You can also report side effects to the FDA at 1-800-332-1088 or https://www.fda.gov/medwatch.
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, seek medical attention immediately:
Allergic reactions: Rash, hives, itching, red, swollen, blistered, or peeling skin with or without fever, wheezing, tightness in the chest or throat, trouble breathing, swallowing, or talking, unusual hoarseness, or swelling of the mouth, face, lips, tongue, or throat.
High potassium levels: Abnormal heartbeat, confusion, weakness, lightheadedness, dizziness, numbness or tingling, or shortness of breath.
Low blood sugar: Dizziness, headache, sleepiness, weakness, shaking, rapid heartbeat, confusion, hunger, or sweating.
Kidney problems: Inability to urinate, changes in urine output, blood in the urine, or significant weight gain.
Low sodium levels: Headache, difficulty focusing, memory problems, confusion, weakness, seizures, or balance changes.
Lung or breathing problems: Shortness of breath, trouble breathing, cough, or fever.
Pancreas problems (pancreatitis): Severe stomach pain, severe back pain, or severe nausea and vomiting.
Musculoskeletal issues: Muscle or joint pain.
Skin and mucous membrane issues: Purple patches on the skin or mouth.
Neurological issues: Hallucinations (seeing or hearing things that are not there), depression, or mood changes.
Numbness or tingling: Abnormal burning, numbness, or tingling sensations.
Hearing issues: Ringing in the ears.
Swollen glands: Enlarged lymph nodes.
Cardiovascular issues: Chest pain or pale skin.
Severe dizziness or fainting: Sudden loss of balance or consciousness.
Antibiotic-Associated Diarrhea
Diarrhea is a common side effect of antibiotics. However, a severe form called C. difficile-associated diarrhea (CDAD) may occur, which can lead to life-threatening bowel problems. If you experience stomach pain, cramps, or loose, watery, or bloody stools, seek medical attention immediately. Do not treat diarrhea without consulting your doctor.
Rare but Serious Side Effects
Sulfa drugs, like this medication, can cause rare but severe side effects, including:
Liver problems: Dark urine, tiredness, decreased appetite, nausea, vomiting, light-colored stools, or yellow skin and eyes.
Blood problems: Unusual bruising or bleeding.
Severe skin reactions: Stevens-Johnson syndrome or toxic epidermal necrolysis, characterized by rash, red, swollen, blistered, or peeling skin, red or irritated eyes, mouth, throat, or nose sores, fever, chills, or sore throat.
Aseptic meningitis: A severe brain problem that can cause headache, fever, chills, nausea, vomiting, stiff neck, rash, sensitivity to light, sleepiness, or confusion.
Hemophagocytic lymphohistiocytosis (HLH): A life-threatening immune system problem that can cause fever, swollen glands, rash, seizures, confusion, balance changes, or difficulty walking.
Other Side Effects
Most people do not experience significant side effects or only have mild ones. However, if you notice any of the following side effects, consult your doctor:
Diarrhea
Stomach pain
Nausea
Vomiting
* Decreased appetite
This is not an exhaustive list of side effects. If you have questions or concerns, discuss them with your doctor. You can also report side effects to the FDA at 1-800-332-1088 or https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- New or worsening skin rash, blistering, peeling skin, or sores in the mouth, nose, eyes, or genitals (signs of severe skin reactions like SJS/TEN).
- Fever, chills, body aches, sore throat, unusual tiredness, or easy bruising/bleeding (signs of blood problems).
- Yellowing of the skin or eyes (jaundice), dark urine, or pale stools (signs of liver problems).
- Severe, watery diarrhea that does not stop, especially if it contains blood or mucus (may be C. difficile infection).
- Sudden muscle weakness, numbness or tingling, or a slow heart rate (signs of high potassium).
- Signs of kidney stones (severe pain in your side or back, blood in urine).
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following conditions and situations to ensure safe treatment with this medication:
Any allergies you have, including allergies to this drug, its components, or other substances, such as foods or medications. Describe the allergic reactions you have experienced.
A diagnosis of anemia caused by a lack of folic acid.
Presence of kidney disease or liver disease.
History of asthma, porphyria, thyroid disease, or conditions characterized by low folate levels, poor absorption, or poor nutrition.
Long-term alcohol consumption or current treatment with antiseizure medications.
Previous episodes of low platelet count associated with the use of trimethoprim or sulfa (sulfonamide) drugs.
Concurrent use of the following medications: amantadine, cyclosporine, dofetilide, indomethacin, leucovorin, methotrexate, or pyrimethamine.
Recent or current use of the following drugs: benazepril, captopril, enalapril, fosinopril, lisinopril, moexipril, perindopril, quinapril, ramipril, or trandolapril.
* Use of diuretics (water pills).
Special Considerations for Children:
If your child is under 2 months of age, do not administer this medication, as it is not recommended for infants younger than 2 months old.
To ensure your safety, it is crucial to disclose all your medications, including prescription and over-the-counter drugs, natural products, and vitamins, as well as any health problems you have, to your doctor and pharmacist. This will help determine whether it is safe to take this medication with your other treatments. Never start, stop, or adjust the dosage of any medication without consulting your doctor.
It is essential to inform your doctor about the following conditions and situations to ensure safe treatment with this medication:
Any allergies you have, including allergies to this drug, its components, or other substances, such as foods or medications. Describe the allergic reactions you have experienced.
A diagnosis of anemia caused by a lack of folic acid.
Presence of kidney disease or liver disease.
History of asthma, porphyria, thyroid disease, or conditions characterized by low folate levels, poor absorption, or poor nutrition.
Long-term alcohol consumption or current treatment with antiseizure medications.
Previous episodes of low platelet count associated with the use of trimethoprim or sulfa (sulfonamide) drugs.
Concurrent use of the following medications: amantadine, cyclosporine, dofetilide, indomethacin, leucovorin, methotrexate, or pyrimethamine.
Recent or current use of the following drugs: benazepril, captopril, enalapril, fosinopril, lisinopril, moexipril, perindopril, quinapril, ramipril, or trandolapril.
* Use of diuretics (water pills).
Special Considerations for Children:
If your child is under 2 months of age, do not administer this medication, as it is not recommended for infants younger than 2 months old.
To ensure your safety, it is crucial to disclose all your medications, including prescription and over-the-counter drugs, natural products, and vitamins, as well as any health problems you have, to your doctor and pharmacist. This will help determine whether it is safe to take this medication with your other treatments. Never start, stop, or adjust the dosage of any medication without consulting your doctor.
Precautions & Cautions
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication. Your doctor will likely recommend regular blood tests and other laboratory evaluations to monitor your condition. Be aware that this drug may interfere with certain lab tests, so it is crucial to notify all your healthcare providers and laboratory personnel that you are taking this medication.
Do not exceed the prescribed duration of treatment, as this may increase the risk of a second infection. If you have a deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD), you may be more susceptible to anemia. Individuals of African, South Asian, Middle Eastern, and Mediterranean descent are more likely to have low G6PD levels.
If you have diabetes (high blood sugar), it is vital to closely monitor your blood sugar levels while taking this medication. Before consuming alcohol, consult with your doctor to discuss any potential risks. This drug may increase your sensitivity to the sun, making you more prone to sunburn. Take necessary precautions when exposed to sunlight, and inform your doctor if you experience excessive sunburning while taking this medication.
In rare cases, this drug can cause a severe and potentially life-threatening reaction, characterized by symptoms such as fever, rash, swollen glands, and problems affecting various organs, including the liver, kidney, blood, heart, muscles and joints, or lungs. If you have any concerns or questions, discuss them with your doctor.
If you are 65 years or older, use this medication with caution, as you may be more susceptible to side effects. Women who are pregnant or become pregnant while taking this drug should contact their doctor immediately, as it may harm the unborn baby. If you are breastfeeding, consult with your doctor to discuss any potential risks to your baby and determine the best course of action.
Do not exceed the prescribed duration of treatment, as this may increase the risk of a second infection. If you have a deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD), you may be more susceptible to anemia. Individuals of African, South Asian, Middle Eastern, and Mediterranean descent are more likely to have low G6PD levels.
If you have diabetes (high blood sugar), it is vital to closely monitor your blood sugar levels while taking this medication. Before consuming alcohol, consult with your doctor to discuss any potential risks. This drug may increase your sensitivity to the sun, making you more prone to sunburn. Take necessary precautions when exposed to sunlight, and inform your doctor if you experience excessive sunburning while taking this medication.
In rare cases, this drug can cause a severe and potentially life-threatening reaction, characterized by symptoms such as fever, rash, swollen glands, and problems affecting various organs, including the liver, kidney, blood, heart, muscles and joints, or lungs. If you have any concerns or questions, discuss them with your doctor.
If you are 65 years or older, use this medication with caution, as you may be more susceptible to side effects. Women who are pregnant or become pregnant while taking this drug should contact their doctor immediately, as it may harm the unborn baby. If you are breastfeeding, consult with your doctor to discuss any potential risks to your baby and determine the best course of action.
Overdose Information
Overdose Symptoms:
- Nausea, vomiting, diarrhea
- Dizziness, headache
- Drowsiness, confusion
- Bone marrow depression (manifesting as fever, sore throat, pallor, easy bruising/bleeding)
- Jaundice
- Crystalluria, hematuria, anuria (kidney problems)
- Hyperkalemia
What to Do:
Seek immediate medical attention or call Poison Control at 1-800-222-1222. Treatment is supportive and may include gastric lavage, forced diuresis, alkalinization of urine (for SMX), and administration of leucovorin (for TMP overdose).
Drug Interactions
Contraindicated Interactions
- Dofetilide (risk of QT prolongation and Torsades de Pointes)
- Methotrexate (high-dose, due to increased bone marrow suppression)
Major Interactions
- Warfarin (increased INR and bleeding risk)
- Phenytoin (increased phenytoin levels and toxicity)
- Digoxin (increased digoxin levels, especially in elderly)
- Potassium-sparing diuretics (e.g., spironolactone, amiloride, triamterene - increased risk of hyperkalemia)
- ACE inhibitors/ARBs (increased risk of hyperkalemia)
- Cyclosporine (decreased cyclosporine levels, increased nephrotoxicity)
- Azathioprine, Mercaptopurine (increased myelosuppression)
- Oral hypoglycemics (sulfonylureas - increased risk of hypoglycemia)
- Procainamide (increased procainamide levels)
- Amantadine (increased amantadine levels and toxicity)
Moderate Interactions
- Rifampin (decreased TMP levels)
- Thiazide diuretics (increased risk of thrombocytopenia with purpura in elderly)
- Tricyclic antidepressants (increased TCA levels)
- Pyrimethamine (increased risk of megaloblastic anemia)
- Zidovudine (increased myelosuppression)
Minor Interactions
- Not available
Monitoring
Baseline Monitoring
Complete Blood Count (CBC) with differential
Rationale: To establish baseline hematologic parameters and identify pre-existing cytopenias, as Bactrim can cause blood dyscrasias.
Timing: Prior to initiation of therapy.
Renal Function (BUN, Creatinine, eGFR)
Rationale: To assess baseline kidney function, as the drug is primarily renally eliminated and dose adjustments are required in renal impairment.
Timing: Prior to initiation of therapy.
Serum Electrolytes (especially Potassium)
Rationale: To establish baseline potassium levels, as TMP can cause hyperkalemia.
Timing: Prior to initiation of therapy.
Liver Function Tests (ALT, AST, Bilirubin)
Rationale: To assess baseline hepatic function, as severe hepatotoxicity is a rare but serious adverse effect.
Timing: Prior to initiation of therapy.
Routine Monitoring
Complete Blood Count (CBC) with differential
Frequency: Weekly for patients on high-dose or prolonged therapy (e.g., PCP treatment/prophylaxis), or every 2-4 weeks for standard therapy.
Target: Within normal limits; monitor for significant decreases in WBC, platelets, or hemoglobin.
Action Threshold: Discontinue if significant cytopenias develop (e.g., severe neutropenia < 500/mm³, thrombocytopenia < 50,000/mm³).
Renal Function (BUN, Creatinine)
Frequency: Weekly for patients on high-dose or prolonged therapy, or every 2-4 weeks for standard therapy, especially in elderly or those with pre-existing renal impairment.
Target: Stable or within acceptable limits.
Action Threshold: Significant increase in BUN/Creatinine (e.g., >25% increase from baseline) may warrant dose adjustment or discontinuation.
Serum Potassium
Frequency: Weekly for patients on high-dose or prolonged therapy, or those at risk for hyperkalemia (e.g., elderly, renal impairment, concomitant ACE inhibitors/ARBs, potassium-sparing diuretics).
Target: 3.5-5.0 mEq/L
Action Threshold: Potassium > 5.5 mEq/L warrants intervention (e.g., dose reduction, discontinuation, hyperkalemia management).
Liver Function Tests (ALT, AST)
Frequency: Periodically for patients on prolonged therapy or with pre-existing liver disease.
Target: Within normal limits.
Action Threshold: Significant elevation (e.g., >3x ULN) may warrant discontinuation.
Symptom Monitoring
- Skin rash (especially severe, blistering, or spreading)
- Fever, sore throat, mouth sores (signs of blood dyscrasias or severe skin reactions)
- Unusual bleeding or bruising
- Yellowing of skin or eyes (jaundice)
- Dark urine, pale stools
- Severe or persistent diarrhea (may indicate C. difficile infection)
- Signs of hyperkalemia (muscle weakness, fatigue, paresthesias, bradycardia)
- Signs of kidney stones (flank pain, hematuria)
Special Patient Groups
Pregnancy
Category D. Avoid during the first trimester due to potential teratogenicity (folate antagonism) and during the third trimester (especially near term) due to risk of kernicterus in the newborn.
Trimester-Specific Risks:
First Trimester:
Potential risk of neural tube defects and other malformations due to folate antagonism. Use only if potential benefit justifies the potential risk to the fetus.
Second Trimester:
Generally considered safer than first or third trimester, but still Category D. Use with caution and only if clearly needed.
Third Trimester:
Contraindicated near term (last few weeks of pregnancy) due to risk of kernicterus in the newborn, as sulfonamides can displace bilirubin from albumin binding sites.
Lactation
L3 (Moderate risk). Both SMX and TMP are excreted into breast milk. Avoid in infants < 2 months of age, premature infants, jaundiced infants, or infants with G6PD deficiency due to risk of kernicterus or hemolysis.
Infant Risk:
Risk of kernicterus (especially in jaundiced or premature infants) and hemolytic anemia (in G6PD deficient infants). Monitor breastfed infants for rash, diarrhea, and jaundice.
Pediatric Use
Contraindicated in infants less than 2 months of age due to the risk of kernicterus. Use with caution in children with G6PD deficiency due to risk of hemolytic anemia. Dosing is weight-based for children > 2 months.
Geriatric Use
Increased risk of severe adverse reactions, including hyperkalemia, severe skin reactions (SJS/TEN), bone marrow suppression, and renal impairment. Monitor renal function, electrolytes, and CBC closely. Use lower doses and longer dosing intervals in patients with impaired renal function.
Clinical Information
Clinical Pearls
- Always ensure adequate hydration to prevent crystalluria and kidney stone formation.
- Counsel patients on photosensitivity and advise sun protection.
- Be vigilant for signs of severe skin reactions (SJS/TEN) and blood dyscrasias; discontinue immediately if suspected.
- Monitor potassium levels, especially in elderly patients, those with renal impairment, or those on concomitant medications that increase potassium (e.g., ACE inhibitors, ARBs, potassium-sparing diuretics).
- Contraindicated in patients with G6PD deficiency due to risk of hemolytic anemia.
- Not effective against Pseudomonas aeruginosa or anaerobes.
- Consider alternative agents for patients with a history of severe sulfa allergy.
- For PCP prophylaxis, adherence is crucial, and alternative regimens exist for intolerant patients.
Alternative Therapies
- Fluoroquinolones (e.g., Ciprofloxacin, Levofloxacin for UTIs, respiratory infections)
- Beta-lactam antibiotics (e.g., Amoxicillin-clavulanate, Cephalexin for UTIs, skin infections)
- Tetracyclines (e.g., Doxycycline for skin infections, respiratory infections)
- Macrolides (e.g., Azithromycin for respiratory infections)
- Clindamycin (for PCP treatment/prophylaxis in combination with primaquine)
- Atovaquone (for PCP treatment/prophylaxis)
Cost & Coverage
Average Cost:
$10 - $50 per 30 tablets (generic)
Generic Available:
Yes
Insurance Coverage:
Tier 1 (Generic)
General Drug Facts
If your symptoms or health issues persist or worsen, it's essential to contact your doctor for further guidance. To ensure your safety, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so be sure to check with your pharmacist for more information. If you have any questions or concerns about your medication, don't hesitate to reach out to your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek emergency medical attention. When seeking help, be prepared to provide details about the medication taken, the amount, and the time it happened.