Infectious Disease Compendium

Trimethoprim/Sulfamethoxisole (Bactrim®, Cotrim®, Septra®)


CrCl Formula

CrCl > 80: 3-5 mg/kg iv q 6-12 h; oral is 1 - 2 po bid or tid of single or double strength.

CrCl 80-50: q 18 h iv.

CrCl 50-10: q 24 h iv.

CrCl < 10: avoid.

Oral therapy varies greatly depending on disease and CrCl. For MRSA I suggest 2 DS po tid for a mythical 70 lb human, increasing as the Vd increases. No clinical data to support this.

Hemodialysis: 4 -5 mg/kg after hd.

Peritoneal dialysis:

Important side effects

Anorexia, nausea, vomiting, stevens-johnson syndrome, toxic epidermal necrolysis, aplastic anemia, agranulocytosis, other blood dyscrasias, fulminant hepatic necrosis, rash, urticaria.

In the elderly it can lead to hyperkalemia severe enough to warrent hospitalization.

Sudden death is most likely if the patient is on an ARB or an ACE (Pubmed), perhaps due to hyperkalemia.

"Trimethoprim is associated with a greater risk of acute kidney injury and hyperkalaemia compared with other antibiotics used to treat UTIs, but not a greater risk of death. The relative risk increase is similar across population groups, but the higher baseline risk among those taking renin-angiotensin system blockers and potassium-sparing diuretics translates into higher absolute risks of acute kidney injury and hyperkalaemia in these groups (PubMed).

Important drug interactions

DEATH when combined with spironolactone (PubMed).

Acenocoumarol, acetohexamide, anisindione, antipsychotics, arsenic trioxide, astemizole, bepridil, chloral hydrate, chloroquine, chlorpropamide, cisapride, clarithromycin, class i antiarrhythmic agents, class ia antiarrhythmic agents, class iii antiarrhythmic agents, cyclosporine, dapsone, dicumarol, digoxin, dofetilide, dolasetron, droperidol, enalapril maleate, enalaprilat, enflurane, erythromycin, fluconazole, fluoxetine, foscarnet, fosphenytoin, gemifloxacin, glipizide, glyburide, halofantrine, halothane, isoflurane, isradipine, levomethadyl, lidoflazine, mefloquine, mesoridazine, metformin, methotrexate, octreotide, para-aminobenzoic acid (paba) and paba derivatives, pentamidine, phenothiazines, phenprocoumon, phenytoin, pimozide, porfimer, probucol, pyrimethamine, quinapril, rosiglitazone, spiramycin, telithromycin, terfenadine, thioridazine, tolazamide, tolbutamide, tricyclic antidepressants, vasopressin, venlafaxine, warfarin, ziprasidone, zolmitriptan.

Rants and Screeds


If E. coli resistance is > 10-15% in your community can't be relied on for the empirical treatment if UTI.

Treatment of choice


Use for

Susceptible gram negative aerobes (such as E. coli). In our community, where MRSA rates are 66%, I recommend 2 ds po tid to treat MRSA soft tissue infections. Actinomyces, Aeromonas hydrophilia, Bronchitis, Cholera, Cyclospora, Diverticulosis/itis, Isospora beli, keratitis, Listeria monocytogenes, Meningitis, MRSA, Moraxella catarrhalis, Neutropenic fever, Nocardia, Otitis media, Pneumonia, Peritonitis, Pneumocystis, Prostatitis, Salmonella, Sinusitis, Stenotrophomonas maltophilia, Toxoplasma, travelers' Diarrhea, Typhoid fever, UTI, Wegener's granulomatosis, Whipples disease, Yersinia enterocolitica.

Don't use for


Curious Cases

Relevant links to my Medscape blog

A quick overreaction

Say Yes to the DRSS

Last Update: 04/03/18.