Prescription medication · Dihydrofolate Reductase Inhibitor
trimethoprim
Also sold as Primsol. This medicine can treat urinary tract infections, ear infections in children, and bronchitis in adults.
Data updated 2026-05-15
- 11,380
- FDA reportsModerately reported
- 22
- InteractionsSeveral interactions
- 1
- Recall record
What the data shows
trimethoprim (Primsol) is a prescription Dihydrofolate Reductase Inhibitor, reported less often than most tracked drugs (11,380 FDA reports), with 22 documented drug interactions.
Reporting volume reflects how widely a drug is used and studied, not how dangerous it is, a FAERS report documents a temporal association, never proof of cause.
trimethoprim (Primsol) is a prescription Dihydrofolate Reductase Inhibitor. This medicine can treat urinary tract infections, ear infections in children, and bronchitis in adults.
This medicine contains sulfamethoxazole and trimethoprim. It is an antibiotic that fights bacteria in your body.
Verify with FDA → · CMS NADAC pricing →
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.
The sections below are summarized in plain English from trimethoprim's FDA-approved prescribing information. They describe what the official label says, and are not personal medical advice.
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.
Side Effects (from patient reports)
Based on 11,380 FDA adverse event reports.
Most-reported reactions
Adverse reactions in FAERS for trimethoprim, by number of reports
- Nausea
Nausea
945 reports
- Diarrhoea
Diarrhoea
848 reports
- Headache
Headache
835 reports
- Malaise
Malaise
816 reports
- Pyrexia
Pyrexia
721 reports
- Dyspnoea
Dyspnoea
712 reports
- Vomiting
Vomiting
708 reports
- Fatigue
Fatigue
641 reports
- Pain
Pain
605 reports
- Rash
Rash
605 reports
What this shows Bars show how often each reaction was reported, not how likely it is to happen, a report records a temporal association, never proof that the drug caused it.
Reports over time
Adverse-event reports filed for trimethoprim each year to the FDA Adverse Event Reporting System (FAERS).
Year-to-year volume tracks usage, prescribing, and scrutiny, not a change in per-patient risk. Source: FDA FAERS.
Where trimethoprim sits
trimethoprim has more FDA adverse-event reports than 42% of the drugs FAERS tracks. A high position reflects how widely a drug is used and watched, not how dangerous it is.
Percentile across all drugs PlainMeds tracks by FAERS report volume. The dot is trimethoprim; the line is the median (50th percentile).
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
Reports Mentioning Death
1,472
12.9% of reports — not proof of cause
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 |
| 3 | DIARRHOEA | 848 |
| 4 | HEADACHE | 835 |
| 5 | MALAISE | 816 |
| 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 |
| 16 | ARTHRALGIA | 549 |
| 17 | ABDOMINAL PAIN | 496 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: 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,...
Mechanism: This medication has been shown to have no important effect on how quickly theophylline is cleared from your body.
• 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.
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.
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.
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.
This is a plain-language summary of FDA-label interaction records and does not provide individual medication-combination directions.
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?
What pregnancy or breastfeeding source fields are listed for trimethoprim?
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
Other drugs grouped near trimethoprim - same-class peers and common alternatives.
amikacin
Amikin
Amikacin is an antibiotic medicine.
Compare with trimethoprim →
amoxicillin
Amoxil
Amoxicillin and Clavulanate Potassium is a combination medicine used to fight bacterial infections.
Compare with trimethoprim →
amoxicillin/clavulanate
Augmentin
Augmentin is a combination of two medicines, amoxicillin and clavulanate.
Compare with trimethoprim →
ampicillin/sulbactam
Unasyn
Unasyn is a combination of two antibiotics that fights bacteria in your body.
Compare with trimethoprim →
azithromycin
Zithromax, Z-Pack
Azithromycin is an antibiotic that fights bacteria.
Compare with trimethoprim →
Compare beyond drug class
Nationwide peers by FAERS volume & death-report share
Two PlainMeds-derived comparison paths for trimethoprim: nearest FDA FAERS report volume and nearest death-report share among drugs with at least 1,000 logged reports, excluding same-class neighbors listed above. Counts reflect reporting volume, not proven individual harm.
Similar FAERS report volume
Nearest drugs by total FAERS reports. This record: 11,380.
Similar death-report share
Nearest drugs by FAERS death-report share. This record: 12.93%.
- ranolazine Δ 0.00 pts · 10,014 reports · Late Sodium Current Inhibitor (Antianginal) 12.93%death share
- ondansetron Δ 0.05 pts · 103,354 reports · 5-HT3 Receptor Antagonist (Antiemetic) 12.99%death share
- candesartan Δ 0.07 pts · 33,477 reports · Angiotensin II Receptor Blocker (ARB) 12.87%death share
- docusate Δ 0.10 pts · 55,963 reports · Stool Softener 13.04%death share
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
FDA bioequivalence and label-record context for narrow therapeutic index medicines
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
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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 11,380 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 are separate source-record fields. This page is a public FDA/CMS registry and does not provide medical, treatment, substitution, or medication-change directions.
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. This registry does not provide medication decisions.
Last updated: December 17, 2024
PlainMeds is rendered directly from FDA openFDA/FAERS extracts, DailyMed labels, and CMS drug-pricing files, no number is typed in by an editor. FAERS counts, recalls, shortages, and price figures on this page are queried live from those federal extracts. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-05-15. Primary sources: openFDA / FAERS, DailyMed and CMS Part B ASP.
Read our methodology - how this data is sourced, computed, and verified.
Data currency: FDA FAERS adverse-event reports through 2025, CMS NADAC acquisition-cost pricing effective December 2024, compiled from the source snapshot dated . See our methodology for per-source dates and refresh cadence. Spot a figure that looks wrong? Report a data issue.
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