Microplastics and Misinformation: What Science Really Says
November 12, 2025
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Brand Name :
Bactrim
(United States) [Available] ,Bactrim DS
(United States) [Available] ,Sulfatrim Pediatric
(United States) [Available]Synonyms :
trimethoprim (Rx)
Class :
Urinary anti-infectives
Brand Name :
Bactrim
(United States) [Available] ,Bactrim DS
(United States) [Available] ,Sulfatrim Pediatric
(United States) [Available]Synonyms :
trimethoprim (Rx)
Class :
Urinary anti-infectives
Dosage Forms and Strengths: Â
oral solution  Â
50 mg/5 ml Â
oral tablet  Â
100 mg Â
100
mg
Orally
every 12 hrs
The maximum duration of therapy is 10 days
Dosage Forms and Strengths: Â
oral solution  Â
50 mg/5 ml Â
oral tablet  Â
100 mg Â
Age: >12 years
100 mg orally every 12 hours
The maximum duration of therapy is 10 days
Age: >6 months
5 mg/kg orally every 12 hours
The maximum duration of therapy is 10 days
The maximum dose is 200 mg
trimethoprim: they may increase the neutropenic effect of amodiaquine
trimethoprim: they may enhance the serum concentration of phenytoin
trimethoprim may increase serum concentrations of procainamide
fosphenytoin: they may diminish the serum concentration of trimethoprim
trimethoprim: they may enhance the serum concentration of dofetilide
may enhance the toxic effect of methotrexate, avoid combination
may enhance the toxic effect of trimetrexate, avoid combination
it may diminish the excretion rate when combined with permethrin, resulting in an enhanced serum level
trimethoprim: they may increase the toxic effect of amantadine
trimethoprim: they may increase the myelosuppressive effect of azathioprine
trimethoprim: they may enhance the serum concentration of dapsone
trimethoprim: they may enhance the serum concentration of digoxin
trimethoprim: they may increase the hyperkalemic effect of eplerenone
trimethoprim: they may enhance the serum concentration of lamivudine
trimethoprim: they may increase the toxic effect of memantine
trimethoprim: they may increase the myelosuppressive effect of mercaptopurine
trimethoprim: they may enhance the serum concentration of pralatrexate
trimethoprim: they may diminish the serum concentration of sapropterin
trimethoprim: they may increase the hyperkalemic effect of spironolactone
trimethoprim: they may increase the hyperkalemic effect of Angiotensin II Receptor Blockers
trimethoprim: they may increase the hyperkalemic effect of Angiotensin II Receptor Blockers
trimethoprim: they may increase the hyperkalemic effect of Angiotensin II Receptor Blockers
trimethoprim: they may increase the hyperkalemic effect of Angiotensin II Receptor Blockers
trimethoprim: they may increase the hyperkalemic effect of Angiotensin II Receptor Blockers
isoxicam may increase the risk or severity of hyperkalemia when combined with trimethoprim
may decrease trimethoprim elimination, raising serum levels
may increase the toxic effect of amantadine
may increase the CNS depressant effect of CNS Depressants
rifampin: they may diminish the serum concentration of trimethoprim
zidovudine: they may enhance the neutropenic effect of trimethoprim
lamivudine serum concentration is increased with trimethoprim when used in combination
The excretory rate of ancestim may be reduced with trimethoprim, resulting in higher levels of serum
the risk of hyperkalemia may be increased
may enhance the effect of the other by cationic drug competition for renal tubular clearance
Trimethoprim works by reversibly blocking the bacterial enzyme dihydrofolate reductase, which is essential for producing tetrahydrofolic acid—a key component needed for bacterial DNA and protein synthesis. This selective inhibition disrupts bacterial growth without significantly affecting human cells, as trimethoprim binds bacterial enzymes much more strongly than mammalian ones.Â
When used alone, trimethoprim has a bacteriostatic effect. However, when combined with sulfamethoxazole—which blocks an earlier step in the same folic acid pathway—the two drugs together inhibit successive steps in nucleic acid and protein production, resulting in bactericidal activity.Â
Adverse drug reactions:  Â
Frequency definedÂ
1-10% Â
Rash Â
Urticaria Â
<0.01% Â
Photosensitivity Â
Angioedema Â
Exfoliative dermatitis Â
fixed drug eruption Â
Erythema multiforme Â
Erythema nodosum Â
Stevens-Johnson syndrome Â
toxic epidermal necrolysis (Lyell’s Syndrome) Â
bullous dermatitis Â
Purpura Â
Allergic vasculitis Â
There is no blackbox warningÂ
Contraindication/CautionÂ
ContraindicationÂ
 HypersensitivityÂ
CautionsÂ
 Trimethoprim may raise potassium levels, especially in patients with kidney issues or when combined with other drugs that increase potassium. High doses or prolonged use can suppress blood cell production, so signs like fever or unusual bruising should be checked promptly. Extended treatment may also lead to serious secondary infections, including C. difficile-associated diarrhea.Â
Use trimethoprim cautiously in people with kidney or liver problems and those at risk of folate deficiency; folic acid can be given if needed. Some forms contain benzyl alcohol, which should not be used in newborns. It should not be used to prevent or long-term treat ear infections.Â
Pregnancy warnings:    Â
AU TGA pregnancy category: B3
US FDA pregnancy category: Not assigned.Â
Breastfeeding warnings: Â
The release of the drug into the human breastmilk is unknownÂ
Pregnancy Categories:     Â
Category A: Satisfactory and well-controlled studies show no risk to the fetus in the first or later trimester.     Â
Category B: No evidence shown of risk to the fetus found in animal reproduction studies, and there are not enough studies on pregnant women     Â
Category C: Adverse effects on the fetus found with evidence in animal reproduction studies and no adequate evidence for a result in humans must take care of potential risks in pregnant women     Â
Category D: There is adequate data available with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits     Â
Category X: Drugs listed in this category outweigh risks over benefits. Hence these categories of drugs need to be avoided by pregnant women.     Â
Category N: There is no data available for the drug under this category
Trimethoprim is an antimicrobial agent that works by blocking bacterial dihydrofolate reductase (DHFR), an enzyme essential for producing tetrahydrofolate, which bacteria need to make DNA, RNA, and proteins. This disruption stops bacteria from growing and multiplying. It is most used with sulfamethoxazole, combining two steps of folate pathway inhibition to treat infections like urinary tract infections and Pneumocystis jirovecii pneumonia.Â
PharmacokineticsÂ
 AbsorptionÂ
Trimethoprim is well absorbed from the gastrointestinal tract, reaching peak blood levels within 1 to 4 hours.Â
DistributionÂ
It distributes widely throughout the body, including the middle ear, prostate, bile, aqueous humor, and cerebrospinal fluid. It crosses the placenta and is also present in breast milk. About 42–46% is bound to plasma proteins.Â
MetabolismÂ
The drug undergoes partial metabolism in the liver.Â
Elimination/ExcretionÂ
Trimethoprim has a half-life of about 8 to 14 hours, which can be prolonged in patients with kidney impairment. Most of the drug (60–80%) is excreted unchanged in the urine.Â
PharmacodynamicsÂ
 Trimethoprim works by blocking a key step in bacterial DNA and protein production and is active against various gram-negative bacteria and coagulase-negative staphylococci. Resistance can develop through different bacterial adaptations, like enzyme changes or cell wall alterations. Rarely, it may cause blood disorders, so patients should be monitored for warning signs like sore throat or bruising. Because resistance patterns vary by region, local antibiograms should be checked before prescribing.Â
Trimethoprim is taken orally, usually as tablets or suspension, and is often given with sulfamethoxazole. It should be taken exactly as prescribed, with or without food, and patients should complete the full course even if symptoms improve. Dosage adjustments may be needed in patients with kidney impairment.
Generic Name: trimethoprim (Rx)Â
Pronunciation: trye-METH-oh-primÂ
Why do we use trimethoprim?Â
trimethoprim is an antibiotic drug used to treat bladder, renal infections, or ear infections that are caused by certain bacteria. Â
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