Trimethoprim
Trimethoprim is an oral antibiotic used to treat first-time, uncomplicated urinary tract infections caused by susceptible bacteria.
🧬 Where this information comes from Click to expand
The clinical label records used on this page are FDA-filed Structured Product Labeling (SPL) retrieved through openFDA. We identified 5 clinical label sets within the page’s selected clinical scope after exact ingredient or ingredient-combination matching and applicable route/form matching. Forms, routes, brands, labelers, strengths, and NDC product-record counts are built separately from matching FDA National Drug Code Directory records. The linked DailyMed document is a representative official source for verification, not the page’s only clinical source. View the linked label on DailyMed →
Trimethoprim is an older antibiotic for first-time, uncomplicated urinary tract infections that stops bacteria by blocking an enzyme they need to build their DNA. It is the same ingredient in the sulfamethoxazole combination (Bactrim), minus the sulfa, and it has been on the U.S. market since about 1973 and is available as a generic. Most people handle the short course well, with upset stomach, nausea or an itchy rash the usual complaints. The one thing to watch for is a rash, fever, sore throat, unusual paleness or purple spots on the skin, which can signal an allergic reaction or a rare blood problem, plus any diarrhea, even weeks after the last dose.
Clinical pearls
- Tell every prescriber if you take phenytoin, because trimethoprim slows its clearance and can make its effect too strong.
- Mention kidney problems first, since the dose is lowered for moderately reduced function and avoided when function is severely reduced.
- It can make skin react to sunlight, so use sunscreen and cover up outdoors during the course.
- It is not for anyone whose anemia comes from low folate, and it crosses the placenta and passes into breast milk.
Patient information guide A plain-language walkthrough of Trimethoprim, written from its FDA label.
What Trimethoprim is used for
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Trimethoprim is an antibiotic used for one main purpose:
- Trimethoprim tablets (oral) treat initial episodes of uncomplicated urinary tract infections caused by susceptible strains of Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, Enterobacter species, and coagulase-negative Staphylococcus species, including S. saprophyticus.
How Trimethoprim works
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Trimethoprim blocks an enzyme called dihydrofolate reductase. Bacteria need this enzyme to make folate-related building blocks for their DNA and proteins. The drug binds far more tightly to the bacterial enzyme than to the human one, so it mostly affects the bacteria.
Bacteria can become resistant in several ways. Some species, such as Pseudomonas aeruginosa, are naturally resistant. Enterococcus may look sensitive in the lab but does not respond well in real infections.
Trimethoprim dosage
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Trimethoprim tablets are taken by mouth. Adults usually take them either twice a day or once a day for 10 days, as directed by the prescriber.
- Follow your prescriber's directions and the pharmacy label.
- People with moderately reduced kidney function take a lower dose.
- It is not recommended with severely reduced kidney function.
Dosing details from the FDA-approved label
From the Trimethoprim prescribing information (“Dosage and Administration”). Doses are set by your prescriber for your product, condition, kidney function and age — never change a dose on your own.
- Usual oral adult dosage
- 100 mg of trimethoprim every 12 hours or 200 mg of trimethoprim every 24 hours, each for 10 days
- Patients with a creatinine clearance of 15 to 30 mL/min
- 50 mg every 12 hours
- Kidney adjustment: creatinine clearance 15 to 30 mL/min
- Patients with a creatinine clearance of less than 15 mL/min
- Use of trimethoprim is not recommended
- Creatinine clearance of less than 15 mL/min
Read the label’s full dosing text
DOSAGE AND ADMINISTRATION The usual oral adult dosage is 100 mg of trimethoprim every 12 hours or 200 mg of trimethoprim every 24 hours, each for 10 days. The use of trimethoprim in patients with a creatinine clearance of less than 15 mL/min is not recommended. For patients with a creatinine clearance of 15 to 30 mL/min, the dose should be 50 mg every 12 hours.
Read the full Dosage and Administration section on DailyMed →
Trimethoprim side effects
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The most common side effects are skin-related.
Common side effects
- Rash
- Itching
- Upset stomach or pain in the upper belly
- Nausea
- Vomiting
- Sore, swollen tongue (glossitis)
- Sensitivity of the skin to sunlight (phototoxic skin reactions)
When to get medical help
- Get help right away for signs of a severe allergic reaction, such as trouble breathing, swelling, or a widespread, blistering or peeling rash.
- Call your doctor if you develop a sore throat, fever, unusual paleness, or purple or red spots on the skin. These can be early signs of a blood disorder.
- Call your doctor if you have a skin rash that is severe or spreading.
- Tell your doctor if you have diarrhea during or after treatment, even weeks later. It can be a sign of C. difficile infection.
- Report yellowing of the skin or eyes (jaundice).
- Report severe headache with stiff neck, which can be a sign of aseptic meningitis (a rare inflammation around the brain).
Rashes are usually mild to moderate and tend to start 7 to 14 days after beginning treatment. Seek help for severe skin reactions, signs of allergic reaction, fever, sore throat, unusual bruising, jaundice, or lasting diarrhea.
Trimethoprim warnings and precautions
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- Serious allergic reactions are rare but possible, including severe skin reactions.
- Blood problems can rarely occur, especially with high doses or long use. Watch for sore throat, fever, paleness, or purple spots.
- C. difficile diarrhea can happen with antibiotics, even more than two months later.
- Other reported effects include high potassium, low sodium, and liver test changes.
Trimethoprim interactions
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One interaction is highlighted on the label.
- Phenytoin: trimethoprim can slow its breakdown in the liver, which may make phenytoin's effects stronger.
Interactions listed in the FDA-approved label
From the Trimethoprim prescribing information (“Drug Interactions”): what the manufacturer studied or reported to the FDA.
- Phenytoin: Trimethoprim may inhibit the hepatic metabolism of phenytoin; at a common clinical dosage it increased the phenytoin half-life by 51% and decreased the phenytoin metabolic clearance rate by 30%. When administering these drugs concurrently, be alert for possible excessive phenytoin effect.
Read the label’s full interactions text
Drug Interactions Trimethoprim may inhibit the hepatic metabolism of phenytoin. Trimethoprim, given at a common clinical dosage, increased the phenytoin half-life by 51% and decreased the phenytoin metabolic clearance rate by 30%. When administering these drugs concurrently, one should be alert for possible excessive phenytoin effect.
Not a complete list. The label covers the interactions the manufacturer studied or reported, and our own interaction database does not cover every medicine either. Bring your full medication list, including vitamins and herbal products, to your pharmacist.
Before taking Trimethoprim
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- Do not use it if you are allergic to trimethoprim.
- Do not use it if you have megaloblastic anemia from folate deficiency.
- Tell your doctor about kidney problems, since dosing changes or avoidance may be needed.
- Tell your doctor if you are pregnant or breastfeeding, since the drug crosses the placenta and passes into breast milk.
- Tell your doctor if you take phenytoin.
Trimethoprim overdose
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Signs of a large overdose, about 1 gram or more, include nausea, vomiting, dizziness, headache, depression, confusion, and bone marrow suppression. Treatment involves stomach emptying and supportive care. Long-term high doses can lower blood cell counts, and the medicine may need to be stopped and leucovorin given.
What Trimethoprim does in the body
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Trimethoprim interferes with bacteria's ability to make nucleic acids and proteins, which stops their growth. It is active against common urinary bacteria such as E. coli, Proteus mirabilis, and Klebsiella pneumoniae. It reaches high levels in urine and vaginal secretions, and enough is excreted in feces to markedly reduce susceptible organisms in the gut flora.
How your body processes Trimethoprim
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Trimethoprim is absorbed rapidly after you swallow it, with blood levels peaking in 1 to 4 hours. About 10 to 20 percent is broken down, mainly in the liver. The rest leaves unchanged in the urine, where levels are much higher than in the blood.
The half-life is 8 to 10 hours and is longer in severe kidney impairment. Steady levels are reached within 2 to 3 days.
How to store Trimethoprim
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Store at 20° to 25°C (68° to 77°F); excursions permitted to 15° to 30°C (59° to 86°F) . Dispense in a tight, light-resistant container as defined in the USP with a child-resistant closure (as required).
Written from the FDA-approved label with AI and reviewed by our pharmacy team. How we use AI →
Supplements & herbs that interact with Trimethoprim
59 supplements and herbal products have documented interactions with Trimethoprim in the licensed clinical database we use. Most are manageable — but your pharmacist should know about everything you take, including vitamins and herbals.
- Major · 7
- Moderate · 41
- Minor · 11
Educational information from a licensed clinical database (Natural Medicines) — see our data sources & update cadence. Not medical advice: an interaction being documented does not mean it will happen to you; do not start or stop medications or supplements without professional guidance.
Nutrient depletion considerations
Trimethoprim has been associated with lower levels of 7 nutrients in the clinical literature. This does not mean a deficiency will occur — it means these may be worth discussing with your pharmacist or healthcare provider, especially with long-term use.
- Higher significance · 6
- Moderate · 1
Educational information from a licensed clinical database (Natural Medicines) — not medical advice. Do not start or stop medications or supplements without professional guidance.
Trimethoprim: pharmacist answers to common questions
Quick, plain-English answers to the questions patients ask most about Trimethoprim — the kind of thing our pharmacy team would talk through with you at the counter.
What am I taking this for?
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How should I take it?
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What side effects are normal?
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When should I call my doctor?
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Does it interact with other medicines?
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Is it safe if I have kidney problems or am pregnant?
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Is Trimethoprim available over the counter?
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When was Trimethoprim first available?
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Who makes Trimethoprim?
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Answers drafted from the FDA-approved label with AI and reviewed by our pharmacy team. How we use AI →
More about Trimethoprim on HelloPharmacist
Trimethoprim forms and strengths (how it comes)
Trimethoprim is available in 1 form. Different forms and brands can have different approved uses, doses, schedules, and directions. Follow the instructions for your exact product, and do not switch forms without guidance from your prescriber or pharmacist.
Need a version that does not list lactose, a gluten source, a dye or gelatin? Inactive ingredients differ by manufacturer: see Trimethoprim inactive ingredients by manufacturer.
Tablet
How this form is used
- Trimethoprim tablets treat initial episodes of uncomplicated urinary tract infections caused by susceptible bacteria.
- Trimethoprim tablets are taken by mouth, either every 12 hours or once every 24 hours, for 10 days in adults.
- Trimethoprim tablets are not recommended in people with severely reduced kidney function, and the dose is lowered for moderately reduced kidney function.
Trimethoprim on the U.S. market: products, makers and brands
How Trimethoprim appears in the FDA’s National Drug Code Directory — including its dosage forms, strengths, brand names, manufacturers, and FDA-listed product records. These are directory records, not sales or prescription volume.
5 companies list 5 Trimethoprim product records with the FDA, mostly as tablet; the earliest marketing or approval year on record is 1973. Brand names on the directory include Primsol, Proloprim, Trimpex; the rest are generics.
Also listed with the FDA, not a patient dose form: Powder (10) — bulk drug substance sold to compounders/manufacturers and multi-item kits. These aren’t counted in the dose-form total above.
Share of FDA-listed product records by manufacturer — FDA National Drug Code Directory. Record counts are not sales or prescription volume.
How widely Trimethoprim is used (Medicaid data)
A general measure of how commonly Trimethoprim is prescribed, based on Medicaid — one of the largest public drug programs. The figure below is prescriptions filled in Q1–Q4 2025, summed across every form and brand of the drug.
Think of this as a proxy for how widely Trimethoprim is used, drawn from freely available public data. Medicaid is just one program — these numbers don’t include Medicare, other government coverage, or commercial and cash-pay prescriptions, so real-world use is higher than what’s shown here.
How commonly is Trimethoprim prescribed? Of the 1,601 medications we measure, Trimethoprim ranks #982 by Medicaid prescriptions — more than 39% of them.
Utilization by Trimethoprim product
Pick a product to see its own Medicaid numbers. Each chip is one clinical product — a specific strength & dosage form as defined by RxNorm — with brand-name and generic versions combined.
trimethoprim 100 MG Oral Tablet
Summed across the 2 of 7 listed NDC products with Medicaid activity — every brand and generic of this exact strength & form. RxNorm 198332
Shares are of the Medicaid prescriptions shown here. Product grouping follows RxNorm (the National Library of Medicine’s drug terminology), so “one product” means one strength & dosage form regardless of manufacturer. Dollar figures are gross Medicaid reimbursement before mandatory rebates — rebates (often large, especially for brand-name drugs) are confidential, so actual net cost to Medicaid is lower than shown.
Source: Medicaid State Drug Utilization Data (CMS), aggregated by generic ingredient — summed across every NDC (all brands, strengths, salt forms and dosage forms) of Trimethoprim, and across all states and both fee-for-service and managed-care claims. A general popularity signal; it excludes Medicare, commercial insurance and cash prescriptions, so it is not total U.S. use. Based on the 2 of 7 listed Trimethoprim NDCs with Medicaid activity.
Compare Trimethoprim products
A representative set of FDA-listed product records for Trimethoprim — across manufacturers, strengths, and dosage forms, grouped by form with each product’s manufacturer and how the FDA approved it. The same medicine may be made and packaged by different companies, so a single drug can have many directory entries. (It’s also why a refill can look different — a new shape, color, or box — even though it contains the same medication.)
| Strength | Route | Manufacturer / Labeler | Category ⓘ | Details |
|---|---|---|---|---|
| 💊Tablet | ||||
| 100 mg | Oral | Dr. Reddy's Labratories Inc. | NDA | View NDC → |
| 100 mg | Oral | Golden State Medical Supply, Inc. | ANDA | View NDC → |
| 100 mg | Oral | Lupin Pharmaceuticals,Inc. | ANDA | View NDC → |
| 100 mg | Oral | Novel Laboratories, Inc. | ANDA | View NDC → |
| 100 mg | Oral | Novitium Pharma LLC | ANDA | View NDC → |
Showing 5 of 5 products — FDA National Drug Code Directory. See every product, package size and price: browse all 5 Trimethoprim NDCs →
Trimethoprim side effects reported to the FDA (FAERS)
After a medicine reaches the market, patients, doctors and drugmakers can send the FDA reports of problems they think may be linked to it. Here’s what’s been reported for Trimethoprim — a signal of what to watch for, not proof the drug caused it.
The effects most often named in FDA reports that mention Trimethoprim are pyrexia, fatigue, diarrhoea; about 84% of the reports were classed as serious. These are voluntary reports, so they show what people report, not how often it happens.
Source: openFDA, from the FDA Adverse Event Reporting System (FAERS). These are voluntary reports — they don’t prove the drug caused the effect, and counts reflect how often something was reported, not how often it actually happens. Reports also often name the very problem the medicine is taken for — a common reason to file one is that the drug didn’t help — so for a pain reliever you may see “pain” high on the list; that points to why the report was filed, not to the drug causing the symptom. This counts every report that lists Trimethoprim in any role, so the total runs higher than the FDA’s official dashboard, which counts only cases where the drug is the suspect. For the authoritative figures, see the FDA FAERS Public Dashboard. Always talk to your pharmacist or doctor.
Trimethoprim FDA approval history
How Trimethoprim went from FDA review to the pharmacy shelf — the key milestones in its regulatory journey.
Trimethoprim was first approved by the FDA in 1973 (Brand: SEPTRA · Monarch Pharms); the first generic version was approved in 1984. It remains available in U.S. pharmacies today.
Source: Drugs@FDA.
Trimethoprim recall history
A recall is when a specific batch of a medicine is pulled from the market — usually a manufacturing issue, not a problem with the drug itself. Class I is most serious, Class III least.
The FDA’s enforcement reports list no Trimethoprim recalls since July 2021.
✅No Trimethoprim recalls on record since July 2021Source: FDA enforcement (recall) reports, via openFDA; our copy was last updated Sep 24, 2026.
RxNorm Concept Web — From Ingredient to Every Form and Strength
This page starts with one ingredient concept (IN). The branches below show its dose-form concepts (SCDF), then the available clinical drug and strength concepts (SCD). Combination products remain separate concepts with their own pages.
RxCUI 10829 4 dose forms · 6 strengths
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Dose form (SCDF) Injectable Solution RxCUI 378828No current FDA listingClinical drug / strength (SCD) 20 MG/MLRxCUI 141843 -
Dose form (SCDF) Oral Solution RxCUI 375982No current FDA listingClinical drug / strength (SCD) 10 MG/MLRxCUI 562707 -
Dose form (SCDF) Oral Suspension RxCUI 374229No current FDA listingClinical drug / strength (SCD) 10 MG/MLRxCUI 108449 -
Dose form (SCDF) Oral Tablet RxCUI 374230In current FDA listings
Look up RxCUI 10829 in the RxCUI Atlas →
RxNorm is the U.S. National Library of Medicine’s normalized drug vocabulary. Its concept hierarchy can include forms that are not currently marketed; the status on each branch compares that concept with current FDA listings. RxCUIs identify vocabulary concepts, not individual packages or manufacturers.
Trimethoprim supply and shortage status
Whether Trimethoprim is in short supply in the U.S. right now, plus any shortage history the FDA has on record. A shortage usually reflects a manufacturing or demand issue — not a safety problem with the drug.
Source: openFDA, from the FDA Drug Shortages database.
Trimethoprim brand names
Trimethoprim is sold under 3 brand names in the FDA directory — Primsol, Proloprim, Trimpex. A brand and its generic contain the same active ingredient; the brand name belongs to one company's product.
Who makes Trimethoprim: manufacturers and labelers
5 companies list Trimethoprim products with the FDA. By number of product records, the largest are Dr. Reddy's Labratories Inc., Golden State Medical Supply, Inc., Lupin Pharmaceuticals,Inc.. Labelers include manufacturers and repackagers; the product in your bottle depends on which one your pharmacy stocks.
Trimethoprim drug class (RxNorm)
Trimethoprim belongs to the Dihydrofolate Reductase Inhibitor Antibacterial class.
Classified by RxNorm RxClass — the U.S. National Library of Medicine's standardized drug-classification service (Established Pharmacologic Class from the FDA, the ATC drug family from the WHO, and mechanism of action). Reference only, not medical advice.
Sources for this Trimethoprim page
Core label, product, RxNorm, safety, and utilization data on this page come from the sources identified below. AI-written, editorial, and licensed sections are labeled separately.
How this page is built
HelloPharmacist combines public FDA and NLM records and does not author the underlying clinical facts. The plain-language sections are written with AI from the FDA-approved label text and reviewed by our pharmacy team before publication. Dr. Reddy's Labratories Inc. is the representative DailyMed label linked for verification and dates. This is general education, not medical advice: always talk to your doctor or pharmacist about your own medicines. How we build and review drug pages →