trimethoprim
Brand names: Primsol
This medicine contains sulfamethoxazole and trimethoprim. It is an antibiotic that fights bacteria in your body.
Drug Pricing (NADAC)
Generic Price
$1.36/unit
Generic Available
Yes (2 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
This medicine can treat urinary tract infections, ear infections in children, and bronchitis in adults.
Common side effects
Nausea, Vomiting, Loss of appetite
Key warnings
Rarely, sulfonamide drugs like this one have caused severe reactions.
How It Works
This medicine works by stopping bacteria from making folic acid. Bacteria need folic acid to grow and multiply. By blocking folic acid production, the medicine kills the bacteria.
How to Take It
Take this medicine exactly as your doctor tells you. For adults with urinary tract infections, the usual dose is 1 double-strength tablet or 2 regular tablets every 12 hours for 10 to 14 days. For children, the dose is based on weight. You can take this medicine with or without food.
Pregnancy & Breastfeeding
Tell your doctor if you are pregnant or plan to become pregnant. This medicine may not be safe for your baby. Talk to your doctor about the risks and benefits of taking this medicine while breastfeeding.
Missed Dose
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule.
Storage
Store this medicine at room temperature, away from heat and light.
Side Effects (from patient reports)
Based on 7,838 FDA adverse event reports.
FDA Adverse Event Report Analysis
Detailed analysis of 11,380 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2001–2025.
Total Reports
11,380
Death-Related Reports
1,472
Hospitalization Reports
4,968
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | NAUSEA | 945 |
| 2 | OFF LABEL USE | 868 |
| 3 | DIARRHOEA | 848 |
| 4 | HEADACHE | 835 |
| 5 | MALAISE | 816 |
| 6 | DRUG INEFFECTIVE | 746 |
| 7 | PYREXIA | 721 |
| 8 | DYSPNOEA | 712 |
| 9 | VOMITING | 708 |
| 10 | FATIGUE | 641 |
| 11 | PAIN | 605 |
| 12 | RASH | 605 |
| 13 | DIZZINESS | 599 |
| 14 | ACUTE KIDNEY INJURY | 594 |
| 15 | URINARY TRACT INFECTION | 555 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
Rarely, sulfonamide drugs like this one have caused severe reactions. These include Stevens-Johnson syndrome, toxic epidermal necrolysis, liver damage, and blood problems. Tell your doctor right away if you have a fever, rash, blisters, mouth sores, or signs of infection.
Known Drug Interactions
albuterol, systemic and inhaled mebendazole amoxicillin medroxyprogesterone ampicillin, with or without sulbactam methylprednisolone atenolol metronidazole azithromycin metoprolol caffeine, dietary ingestion nadolol cefaclor nifedipine co-trimoxazole (trimethoprim and sulfamethoxazole) nizatidine diltiazem norfloxacin dirithromycin ofloxacin enflurane omeprazole famotidine prednisone, prednisolone felodipine ranitidine finasteride rifabutin hydrocortisone roxithromycin isoflurane Sorbitol (purgative doses do not inhibit theophylline absorption) isoniazid sucralfate isradipine terbutaline, s...
Mechanism: This medication has been shown to have no important effect on how quickly theophylline is cleared from your body.
What to do: You can take these together safely without a dose change, but tell your doctor if you feel any new side effects like nausea or jitters.
• L-dopa, triamterene, colchicine, and trimethoprim may decrease plasma folate levels. Caution should be exercised with the concomitant use of folinic acid and trimethoprim- sulfamethoxazole for the acute treatment of Pneumocystis carinii pneumonia in patients with HIV infection as it is associated with increased rates of treatment failure and mortality in a placebo-controlled study.
Mechanism: Trimethoprim can lower the amount of folate, an important B-vitamin, in your blood. This can make the folate in your prenatal vitamin less effective.
What to do: Your doctor should use caution when prescribing these together and may need to monitor your vitamin levels.
Examples of drugs that can increase potassium include: ACE inhibitors angiotensin receptor blockers non-steroidal anti-inflammatory drugs (NSAIDs) heparin and low molecular weight heparin trimethoprim 7.2 Lithium Like other diuretics, spironolactone reduces the renal clearance of lithium, thus increasing the risk of lithium toxicity.
Mechanism: Both of these medications can cause your body to hold onto potassium. Taking them together increases the risk of having too much potassium in your blood.
What to do: Your doctor may need to monitor your potassium levels closely or adjust your doses.
Examples of drugs that can increase potassium include: • ACE inhibitors • angiotensin receptor blockers • non-steroidal anti-inflammatory drugs (NSAIDs) • heparin and low molecular weight heparin • trimethoprim 7.2 Lithium Like other diuretics, ALDACTONE reduces the renal clearance of lithium, thus increasing the risk of lithium toxicity.
Mechanism: Both medications can cause potassium to build up in your body. This combination increases the risk of a condition called hyperkalemia, or high potassium.
What to do: Your doctor should monitor your potassium levels and may need to adjust your treatment plan.
Sulfamethoxazole and trimethoprim potentiates the effect of oral hypoglycemics 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). Cases of interactions with other OCT2 substrates, memantine and metformin, have also been reported.
Mechanism: Trimethoprim can stop your kidneys from clearing metformin out of your body as fast as they should.
What to do: Your doctor may need to check your blood sugar more often or adjust your metformin dose.
Common Questions
Can children take this medicine?
What if I have kidney problems?
Can this medicine interact with other drugs?
What should I avoid while taking this medicine?
What are the symptoms of an allergic reaction?
Can this medicine cause diarrhea?
How long does it take for this medicine to work?
What if I have liver problems?
Can this medicine cause anemia?
What do the tablet markings mean?
What are the common side effects of trimethoprim?
Does trimethoprim interact with other medications?
What drug class is trimethoprim?
Is trimethoprim safe during pregnancy?
Has trimethoprim been recalled?
Active Recalls
Presence of a foreign substance.A specific lot of auxiliary polyester coil, used in product packaging was detected with presence of a micro-organism. No micro-organism was detected on any tablets.
Amneal Pharmaceuticals, LLC
Related Medications in Dihydrofolate Reductase Inhibitor
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Medication Guides
Understanding Drug Interactions
How CYP450 enzymes, inhibitors, and inducers affect your medications
Generic vs Brand Name Drugs
FDA requirements, cost savings, and when the difference matters
Narrow Therapeutic Index Drugs
Why some drugs demand precise dosing and monitoring
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
Related Health & Safety Data
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What the FDA Data Shows for trimethoprim
The FDA label for trimethoprim (sold under brand names such as Primsol) classifies it as a prescription-only medication in the Dihydrofolate Reductase Inhibitor class. This medicine can treat urinary tract infections, ear infections in children, and bronchitis in adults. Official labeling lists 5 commonly reported side effects, including Nausea, Vomiting, Loss of appetite.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 7,838 voluntary reports. The database also lists 22 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated major severity. NADAC pricing from CMS shows a generic unit cost of $1.36.
Report counts do not establish causation — a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history (currently 1 recall record on file), and patent information further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice — always consult a licensed healthcare provider before starting, stopping, or changing any medication.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. Always consult a healthcare professional before making medication decisions.
Last updated: December 17, 2024
Read our methodology — how this data is sourced, computed, and verified.
All federal data sources used on this page
- FDA Orange Book — approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed — NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) — post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm — standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files — federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database — current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages