Sulfameth/trimeth 400-80mg Tab
It is used to treat or prevent bacterial infections.
Drug Class
Antibiotic
Pharmacologic Class
Folic acid antagonist; Sulfonamide antibiotic; Dihydrofolate reductase inhibitor
Pregnancy Category
Category D
FDA Approved
Aug 1973
DEA Schedule
Not Controlled
Overview
What is this medicine?
Sulfamethoxazole and trimethoprim is an antibiotic combination used to treat various bacterial infections, including urinary tract infections, ear infections, bronchitis, and a specific type of pneumonia. It works by stopping the growth of bacteria.
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 instructed by your doctor or healthcare provider, even if you start feeling better.
Staying Hydrated
Drink plenty of non-caffeinated fluids, 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 the best way to dispose of your medication. 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 dose.
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 instructed by your doctor or healthcare provider, even if you start feeling better.
Staying Hydrated
Drink plenty of non-caffeinated fluids, 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 the best way to dispose of your medication. 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 dose.
Lifestyle & Tips
- Drink plenty of fluids (6-8 glasses of water daily) to prevent kidney stones and help the medication work effectively.
- Avoid prolonged sun exposure, tanning beds, and sunlamps, as this medication can make your skin more sensitive to sunlight (photosensitivity). Use sunscreen and wear protective clothing when outdoors.
- Take the medication exactly as prescribed, even if you start feeling better. Do not skip doses or stop taking it early, as this can lead to antibiotic resistance.
- This medication may interfere with certain lab tests, such as creatinine levels. Inform your doctor or lab personnel that you are taking SMX/TMP.
Available Forms & Alternatives
Dosing & Administration
Adult Dosing
Standard Dose:
800 mg sulfamethoxazole/160 mg trimethoprim (DS tablet) orally every 12 hours for 10-14 days for most infections (e.g., UTI). Dosing varies significantly by indication.
Dose Range:
400 - 1600 mg
Condition-Specific Dosing:
uncomplicated_uti:
400 mg sulfamethoxazole/80 mg trimethoprim (SS tablet) orally every 12 hours for 3-7 days or 800 mg sulfamethoxazole/160 mg trimethoprim (DS tablet) orally every 12 hours for 3 days.
pneumocystis_pneumonia_treatment:
15-20 mg/kg trimethoprim and 75-100 mg/kg sulfamethoxazole per day orally or IV, divided into 3-4 doses for 14-21 days.
pneumocystis_pneumonia_prophylaxis:
800 mg sulfamethoxazole/160 mg trimethoprim (DS tablet) orally once daily or 3 times per week.
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: 6-12 mg/kg/day trimethoprim and 30-60 mg/kg/day sulfamethoxazole, divided every 12 hours. Max 320 mg trimethoprim/1600 mg sulfamethoxazole per day. Dosing varies by indication (e.g., UTI, AOM, PCP).
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 well studied, generally avoid or use with extreme caution and monitoring.
Hepatic Impairment:
Mild:
No specific adjustment recommended.
Moderate:
Use with caution; monitor for signs of toxicity.
Severe:
Contraindicated in patients with marked hepatic damage or severe hepatic impairment.
Pharmacology
Mechanism of Action
Sulfamethoxazole inhibits bacterial dihydrofolate synthesis by competing with para-aminobenzoic acid (PABA). Trimethoprim inhibits bacterial dihydrofolate reductase, blocking the production of tetrahydrofolic acid. This sequential blockade of two enzymes in the folic acid pathway results in a synergistic bactericidal effect.
Pharmacokinetics
Absorption:
Bioavailability:
90-100% (oral)
Tmax:
Sulfamethoxazole: 3-4 hours; Trimethoprim: 1-4 hours
FoodEffect:
Absorption is not significantly affected by food, but may delay Tmax.
Distribution:
Vd:
Sulfamethoxazole: 0.16 L/kg; Trimethoprim: 1.3-1.8 L/kg
ProteinBinding:
Sulfamethoxazole: 66%; Trimethoprim: 44%
CnssPenetration:
Yes (good penetration into CSF, sputum, vaginal fluid, middle ear fluid)
Elimination:
HalfLife:
Sulfamethoxazole: 9-11 hours; Trimethoprim: 8-10 hours
Clearance:
Primarily renal
ExcretionRoute:
Renal (glomerular filtration and tubular secretion)
Unchanged:
Sulfamethoxazole: 20%; Trimethoprim: 50-60%
Pharmacodynamics
OnsetOfAction:
Rapid (within 1-2 hours)
PeakEffect:
Within 2-4 hours
DurationOfAction:
Approximately 12 hours (allows for twice-daily dosing)
Safety & Warnings
BLACK BOX WARNING
FATALITIES ASSOCIATED WITH THE ADMINISTRATION OF SULFONAMIDES, ALTHOUGH RARE, HAVE OCCURRED DUE TO SEVERE REACTIONS INCLUDING STEVENS-JOHNSON SYNDROME, TOXIC EPIDERMAL NECROLYSIS, FULMINANT HEPATIC NECROSIS, AGRANULOCYTOSIS, APLASTIC ANEMIA, AND OTHER BLOOD DYSCRASIAS. SULFONAMIDE-RELATED DEATHS HAVE ALSO BEEN REPORTED FROM HYPERSENSITIVITY OF THE RESPIRATORY TRACT. Sulfamethoxazole and trimethoprim should be discontinued at the first appearance of skin rash or any sign of adverse reaction. Clinical signs such as rash, sore throat, fever, arthralgia, pallor, purpura or jaundice may be early indications of serious reactions. Cough, shortness of breath, and pulmonary infiltrates are also reported as hypersensitivity reactions of the respiratory tract. The more common adverse effects are nausea, vomiting, anorexia, and allergic skin reactions such as rash and urticaria.
Side Effects
Urgent Side Effects: Seek Medical Help 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, contact your doctor immediately or seek emergency medical attention:
Allergic Reaction: 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, drowsiness, 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.
Other Serious Side Effects: Muscle or joint pain, purple patches on the skin or mouth, hallucinations (seeing or hearing things that are not there), depression or mood changes, abnormal burning, numbness, or tingling sensations, ringing in the ears, swollen glands, chest pain, pale skin, severe dizziness, or fainting.
Antibiotic-Related Side Effects:
Diarrhea is a common side effect of antibiotics. However, a rare but severe form called C. diff-associated diarrhea (CDAD) may occur. If you experience stomach pain, cramps, or loose, watery, or bloody stools, contact your doctor immediately.
Before treating diarrhea, consult your doctor.
Rare but Serious Side Effects:
Sulfa Drug Reactions: Rarely, severe and potentially life-threatening effects have occurred with sulfa drugs, including liver problems, blood disorders, and severe skin reactions (Stevens-Johnson syndrome/toxic epidermal necrolysis). If you experience a rash, red, swollen, blistered, or peeling skin, red or irritated eyes, mouth, throat, nose, or eye sores, fever, chills, sore throat, new or worsening cough, fatigue, weakness, bruising, or bleeding, or signs of liver problems (dark urine, tiredness, decreased appetite, nausea, vomiting, light-colored stools, or yellow skin and eyes), contact your doctor immediately.
Aseptic Meningitis: This medication may increase the risk of a severe brain problem called aseptic meningitis. If you experience a headache, fever, chills, severe nausea and vomiting, stiff neck, rash, sensitivity to light, drowsiness, or confusion, contact your doctor immediately.
Hemophagocytic Lymphohistiocytosis (HLH): A rare but potentially life-threatening immune system problem called HLH has occurred with this medication. If you experience fever, swollen glands, rash, seizures, confusion, balance changes, or new or worsening difficulty walking, contact your doctor immediately.
Other Side Effects:
Most people do not experience side effects or only have mild side effects. However, if you notice any of the following, contact your doctor or seek medical attention:
+ Diarrhea, stomach pain, nausea, vomiting, or decreased appetite.
This is not an exhaustive list of side effects. If you have questions or concerns, contact your doctor.
To report side effects, call your doctor or the FDA at 1-800-332-1088, or visit 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, contact your doctor immediately or seek emergency medical attention:
Allergic Reaction: 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, drowsiness, 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.
Other Serious Side Effects: Muscle or joint pain, purple patches on the skin or mouth, hallucinations (seeing or hearing things that are not there), depression or mood changes, abnormal burning, numbness, or tingling sensations, ringing in the ears, swollen glands, chest pain, pale skin, severe dizziness, or fainting.
Antibiotic-Related Side Effects:
Diarrhea is a common side effect of antibiotics. However, a rare but severe form called C. diff-associated diarrhea (CDAD) may occur. If you experience stomach pain, cramps, or loose, watery, or bloody stools, contact your doctor immediately.
Before treating diarrhea, consult your doctor.
Rare but Serious Side Effects:
Sulfa Drug Reactions: Rarely, severe and potentially life-threatening effects have occurred with sulfa drugs, including liver problems, blood disorders, and severe skin reactions (Stevens-Johnson syndrome/toxic epidermal necrolysis). If you experience a rash, red, swollen, blistered, or peeling skin, red or irritated eyes, mouth, throat, nose, or eye sores, fever, chills, sore throat, new or worsening cough, fatigue, weakness, bruising, or bleeding, or signs of liver problems (dark urine, tiredness, decreased appetite, nausea, vomiting, light-colored stools, or yellow skin and eyes), contact your doctor immediately.
Aseptic Meningitis: This medication may increase the risk of a severe brain problem called aseptic meningitis. If you experience a headache, fever, chills, severe nausea and vomiting, stiff neck, rash, sensitivity to light, drowsiness, or confusion, contact your doctor immediately.
Hemophagocytic Lymphohistiocytosis (HLH): A rare but potentially life-threatening immune system problem called HLH has occurred with this medication. If you experience fever, swollen glands, rash, seizures, confusion, balance changes, or new or worsening difficulty walking, contact your doctor immediately.
Other Side Effects:
Most people do not experience side effects or only have mild side effects. However, if you notice any of the following, contact your doctor or seek medical attention:
+ Diarrhea, stomach pain, nausea, vomiting, or decreased appetite.
This is not an exhaustive list of side effects. If you have questions or concerns, contact your doctor.
To report side effects, call your doctor or the FDA at 1-800-332-1088, or visit https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- Severe skin rash, blistering, peeling skin, or sores in the mouth, nose, throat, or eyes (signs of Stevens-Johnson syndrome or toxic epidermal necrolysis)
- Sore throat, fever, chills, body aches, unusual tiredness, or flu-like symptoms (signs of serious blood problems)
- Yellowing of the skin or eyes (jaundice), dark urine, severe stomach pain, nausea, vomiting (signs of liver problems)
- Easy bruising or unusual bleeding (signs of low platelets)
- Sudden severe diarrhea (watery or bloody) that does not stop, with or without fever and stomach cramps (signs of Clostridioides difficile-associated diarrhea)
- Swelling of the face, lips, tongue, or throat, difficulty breathing (signs of severe allergic reaction)
- Muscle weakness, irregular heartbeat, numbness or tingling (signs of high potassium levels)
- New or worsening cough, shortness of breath, or difficulty breathing (signs of lung hypersensitivity reaction)
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 circumstances to ensure safe treatment:
Any known allergies to this medication, its components, or other substances, including foods and drugs. Describe the allergic reaction and its symptoms.
A history of anemia caused by a lack of folic acid.
Presence of kidney disease or liver disease.
Certain health conditions, including:
+ Asthma
+ Porphyria
+ Thyroid disease
+ Folate deficiency
+ Malabsorption
+ Poor nutrition
Long-term alcohol consumption or current use of antiseizure medications.
Previous experience with low platelet counts while taking trimethoprim or sulfa (sulfonamide) drugs.
Concurrent use of the following medications:
+ Amantadine
+ Cyclosporine
+ Dofetilide
+ Indomethacin
+ Leucovorin
+ Methotrexate
+ Pyrimethamine
Recent or current use of the following drugs:
+ Benazepril
+ Captopril
+ Enalapril
+ Fosinopril
+ Lisinopril
+ Moexipril
+ Perindopril
+ Quinapril
+ Ramipril
+ Trandolapril
Use of diuretics (water pills).
For pediatric patients: 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.
This list is not exhaustive, and it is crucial to disclose all your medications (prescription, over-the-counter, natural products, and vitamins) and health conditions to your doctor and pharmacist. They will help you determine the safety of taking this medication with your existing treatments and health status. 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 circumstances to ensure safe treatment:
Any known allergies to this medication, its components, or other substances, including foods and drugs. Describe the allergic reaction and its symptoms.
A history of anemia caused by a lack of folic acid.
Presence of kidney disease or liver disease.
Certain health conditions, including:
+ Asthma
+ Porphyria
+ Thyroid disease
+ Folate deficiency
+ Malabsorption
+ Poor nutrition
Long-term alcohol consumption or current use of antiseizure medications.
Previous experience with low platelet counts while taking trimethoprim or sulfa (sulfonamide) drugs.
Concurrent use of the following medications:
+ Amantadine
+ Cyclosporine
+ Dofetilide
+ Indomethacin
+ Leucovorin
+ Methotrexate
+ Pyrimethamine
Recent or current use of the following drugs:
+ Benazepril
+ Captopril
+ Enalapril
+ Fosinopril
+ Lisinopril
+ Moexipril
+ Perindopril
+ Quinapril
+ Ramipril
+ Trandolapril
Use of diuretics (water pills).
For pediatric patients: 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.
This list is not exhaustive, and it is crucial to disclose all your medications (prescription, over-the-counter, natural products, and vitamins) and health conditions to your doctor and pharmacist. They will help you determine the safety of taking this medication with your existing treatments and health status. 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. Regular blood tests and other laboratory assessments, as directed by your doctor, are crucial to monitor your condition.
This medication may interfere with certain lab tests, so it is vital to notify all your healthcare providers and laboratory personnel that you are taking this drug. 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 crucial to closely monitor your blood sugar levels. Before consuming alcohol, consult with your doctor to discuss any potential risks. This medication 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 sunburn while taking this medication.
In rare cases, this medication 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. This medication can harm an unborn baby if taken during pregnancy. If you become pregnant or suspect you are pregnant while taking this medication, contact your doctor immediately.
If you are breastfeeding, consult with your doctor to discuss any potential risks to your baby and determine the best course of action.
This medication may interfere with certain lab tests, so it is vital to notify all your healthcare providers and laboratory personnel that you are taking this drug. 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 crucial to closely monitor your blood sugar levels. Before consuming alcohol, consult with your doctor to discuss any potential risks. This medication 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 sunburn while taking this medication.
In rare cases, this medication 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. This medication can harm an unborn baby if taken during pregnancy. If you become pregnant or suspect you are pregnant while taking this medication, contact your doctor immediately.
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 (e.g., anemia, leukopenia, thrombocytopenia)
- Fever
- Jaundice
- Crystalluria, hematuria, anuria (kidney problems)
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 (to increase sulfamethoxazole excretion), and administration of leucovorin (folinic acid) for trimethoprim overdose.
Drug Interactions
Contraindicated Interactions
- Dofetilide (increased dofetilide levels, risk of Torsades de Pointes)
- Methotrexate (increased methotrexate levels, increased toxicity, especially myelosuppression)
Major Interactions
- Warfarin (potentiates anticoagulant effect, increased INR/bleeding risk)
- Phenytoin (increased phenytoin levels, risk of toxicity)
- Digoxin (increased digoxin levels, especially in elderly)
- Potassium-sparing diuretics (e.g., spironolactone, amiloride), ACE inhibitors, ARBs (increased risk of hyperkalemia)
- Cyclosporine (decreased cyclosporine levels, increased risk of nephrotoxicity)
- Oral hypoglycemics (sulfonylureas) (increased hypoglycemic effect)
- Amantadine (increased amantadine levels, risk of toxicity)
- Procainamide (increased procainamide levels)
- Lamivudine (increased lamivudine levels)
Moderate Interactions
- Rifampin (decreased trimethoprim levels)
- Thiazide diuretics (increased risk of thrombocytopenia with purpura in elderly)
- Tricyclic antidepressants (increased TCA levels)
- Pyrimethamine (increased risk of megaloblastic anemia)
- Zidovudine (increased risk of hematologic toxicity)
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 SMX/TMP can cause bone marrow suppression.
Timing: Prior to initiation of therapy.
Renal function (BUN, creatinine, eGFR)
Rationale: To assess baseline kidney function, as SMX/TMP is primarily renally eliminated and dose adjustments are necessary in renal impairment.
Timing: Prior to initiation of therapy.
Liver function tests (ALT, AST, bilirubin)
Rationale: To assess baseline hepatic function, as SMX/TMP can cause hepatotoxicity.
Timing: Prior to initiation of therapy, especially in patients with pre-existing liver disease.
Serum Potassium
Rationale: To establish baseline potassium levels, as trimethoprim can cause hyperkalemia.
Timing: Prior to initiation of therapy, especially in patients at risk for hyperkalemia (e.g., renal impairment, concomitant medications).
Routine Monitoring
Complete Blood Count (CBC) with differential
Frequency: Weekly or bi-weekly, especially during prolonged therapy (e.g., PCP treatment/prophylaxis) or in patients at risk for myelosuppression.
Target: Within normal limits; monitor for significant drops in cell counts.
Action Threshold: Discontinue if significant decrease in any blood count occurs (e.g., platelet count < 50,000/mm³, neutrophil count < 1,000/mm³).
Renal function (BUN, creatinine)
Frequency: Weekly or bi-weekly during prolonged therapy, or as clinically indicated.
Target: Stable or within acceptable limits.
Action Threshold: Significant increase in creatinine or BUN may necessitate dose adjustment or discontinuation.
Serum Potassium
Frequency: Weekly or bi-weekly during prolonged therapy, especially in patients at risk for hyperkalemia.
Target: 3.5-5.0 mEq/L
Action Threshold: Potassium > 5.5 mEq/L may require intervention (e.g., discontinuation, potassium-lowering agents).
Liver function tests (ALT, AST, bilirubin)
Frequency: Periodically during prolonged therapy or if symptoms of hepatotoxicity develop.
Target: Within normal limits.
Action Threshold: Significant elevation (e.g., >3x ULN) may warrant discontinuation.
Symptom Monitoring
- Skin rash (e.g., Stevens-Johnson syndrome, toxic epidermal necrolysis)
- Sore throat, fever, pallor, easy bruising, unusual bleeding (signs of blood dyscrasias)
- Jaundice, dark urine, abdominal pain (signs of hepatotoxicity)
- Severe diarrhea, abdominal cramps (Clostridioides difficile-associated diarrhea)
- Signs of hyperkalemia (e.g., muscle weakness, fatigue, paresthesias, palpitations)
- Signs of kidney stones (e.g., flank pain, hematuria)
Special Patient Groups
Pregnancy
Generally avoided, especially in the first trimester and near term. Category D. Use only if the potential benefit justifies the potential risk to the fetus.
Trimester-Specific Risks:
First Trimester:
Potential for teratogenicity (e.g., neural tube defects, cardiovascular defects, oral clefts) due to folate antagonism, especially if folic acid supplementation is inadequate. Avoid unless no safer alternative.
Second Trimester:
Generally considered safer than first or third trimester, but still used with caution and only if clearly needed.
Third Trimester:
Contraindicated near term (last few weeks of pregnancy) due to the risk of kernicterus in the newborn (sulfamethoxazole displaces bilirubin from albumin binding sites).
Lactation
Generally not recommended, especially in infants with hyperbilirubinemia, G6PD deficiency, or who are ill/premature. L3 (Moderately Safe).
Infant Risk:
Sulfamethoxazole and trimethoprim are excreted into breast milk. Risk of kernicterus in jaundiced, premature, or G6PD-deficient infants due to sulfamethoxazole. Risk of hemolytic anemia in G6PD-deficient infants. Monitor breastfed infants for rash, diarrhea, or jaundice.
Pediatric Use
Contraindicated in infants less than 2 months of age due to the risk of kernicterus. Use with caution and appropriate weight-based dosing in children older than 2 months. Close monitoring for adverse effects is crucial.
Geriatric Use
Increased risk of adverse effects, particularly hyperkalemia, bone marrow suppression, and severe skin reactions. More susceptible to renal impairment, requiring careful dose adjustment. Increased risk of drug interactions (e.g., with ACE inhibitors, ARBs, diuretics). Close monitoring of renal function, potassium, and CBC is essential.
Clinical Information
Clinical Pearls
- Always inquire about sulfa allergy before prescribing. Cross-reactivity with non-antibiotic sulfonamides (e.g., furosemide, hydrochlorothiazide, sulfonylureas) is low, but caution is advised.
- Ensure adequate hydration to prevent crystalluria and kidney stone formation.
- Trimethoprim can cause a reversible increase in serum creatinine by inhibiting tubular secretion of creatinine, without necessarily indicating a true decrease in GFR. However, true renal impairment can also occur.
- Be vigilant for hyperkalemia, especially in patients with renal impairment, diabetes, or those on ACE inhibitors, ARBs, or potassium-sparing diuretics.
- Consider folic acid supplementation in patients on long-term therapy or those at risk for folate deficiency (e.g., elderly, malnourished, HIV patients) to mitigate hematologic side effects, though this may theoretically reduce efficacy.
- The 400-80mg tablet is often referred to as 'single strength' (SS) and the 800-160mg tablet as 'double strength' (DS).
Alternative Therapies
- For UTIs: Nitrofurantoin, Fosfomycin, Fluoroquinolones (e.g., Ciprofloxacin, Levofloxacin), Beta-lactams (e.g., Amoxicillin/Clavulanate, Cephalexin)
- For PCP: Pentamidine, Atovaquone, Clindamycin + Primaquine
- For other bacterial infections: Various other classes of antibiotics depending on the specific pathogen and site of infection.
Cost & Coverage
Average Cost:
$10 - $50 per 30 tablets (generic DS)
Generic Available:
Yes
Insurance Coverage:
Tier 1 (Generic)
General Drug Facts
If your symptoms or health issues persist or worsen, it is essential to contact your doctor promptly. To ensure safe and effective treatment, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so it is a good idea to consult with your pharmacist. If you have any questions or concerns about this medication, do not hesitate to discuss them with 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 reporting the incident, be prepared to provide detailed information, including the name of the medication taken, the amount, and the time it occurred.