Amoxicillin vs. Bactrim

See how Amoxicillin and Bactrim compare on approved uses, dosing, side effects, and cost.

Key Takeaways

  • Amoxicillin, a penicillin-class antibiotic, treats ear, throat, and respiratory infections, while Bactrim, a sulfa combination, treats UTIs, PCP pneumonia, and traveler's diarrhea.

  • Both are inexpensive generic antibiotics, but Bactrim carries added warnings for severe skin reactions, hemolytic anemia in G6PD deficiency, and use in young infants.

  • Amoxicillin is often chosen first for common childhood and respiratory infections, while Bactrim is used when broader gram-negative coverage or PCP prevention is needed.

Amoxicillin vs. Bactrim Drug Summary

Amoxicillin

Amoxicillin is an aminopenicillin antibiotic used to treat infections of the ear, nose, throat, lungs, skin, and urinary tract, along with H. pylori and gonorrhea as part of combination therapy. It has been available since 1974 and is typically taken as a tablet, capsule, chewable, or oral suspension every 8 to 12 hours.

Bactrim

Bactrim combines sulfamethoxazole and trimethoprim to block two steps in bacterial folate production, treating conditions such as urinary tract infections, Pneumocystis pneumonia, shigellosis, and traveler's diarrhea. Approved since 1973, it is taken orally or by injection, usually every 12 hours depending on the infection.

Amoxicillin vs. Bactrim Side Effects

Amoxicillin

Most common
Vomiting (greater than 1%)
Nausea (greater than 1%)
Rash (greater than 1%)
Diarrhea (greater than 1%)

Bactrim

Most common
Vomiting (rate not quantified)
Nausea (rate not quantified)
Rash (rate not quantified)
Anorexia (rate not quantified)

Amoxicillin vs. Bactrim Dosage

Amoxicillin

Dosage
Dosage Table
STAGE DOSE WHEN
Starting dose 250 mg every 8 hours At the start
Maximum dose 1 g three times daily If needed
Dose changes 4 increases As tolerated

Bactrim

Dosage
Dosage Table
STAGE DOSE WHEN
Starting dose 800 mg/160 mg every 12h At the start
Maximum dose 8-10 mg/kg/day div q6-12h If needed
Dose changes 3 increases As tolerated

Amoxicillin vs. Bactrim Indications

Amoxicillin

Amoxicillin is FDA-approved for a wide range of common bacterial infections, including those of the ear, nose, throat, and lower respiratory tract. It also treats skin infections and uncomplicated urinary tract infections, and it is used with other drugs to eradicate H. pylori or treat gonorrhea.

  • Ear, nose, and throat infections

  • Lower respiratory tract infections

  • Skin and skin structure infections

  • Urinary tract infections

  • H. pylori eradication (combination therapy)

Bactrim

Bactrim is FDA-approved for urinary tract infections, Pneumocystis jirovecii pneumonia, shigellosis, and acute otitis media in children. It also treats bronchitis flare-ups in adults and traveler's diarrhea, and it is commonly used off-label for MRSA skin infections.

  • Urinary tract infections

  • Pneumocystis pneumonia (treatment and prevention)

  • Shigellosis

  • Acute otitis media in children

  • MRSA skin infections (off-label use)

Amoxicillin vs. Bactrim Pros and Cons

Amoxicillin

Amoxicillin has a long safety record and works well for common infections in children and adults, with a relatively low rate of serious side effects. It is not effective against many resistant bacteria and can trigger a distinctive rash in people with mononucleosis.

Pros

  • Long-standing safety record since 1974

  • Well tolerated in children and during pregnancy

  • Effective first-line option for ENT and respiratory infections

  • Fewer severe cutaneous reaction warnings than Bactrim

Cons

  • Not effective against MRSA or many resistant bacteria

  • Can cause severe rash if given during mononucleosis

  • Cross-reactivity risk in patients with penicillin allergy

  • Not effective against Pneumocystis pneumonia

Bactrim

Bactrim offers broader coverage against resistant bacteria and is the standard treatment for Pneumocystis pneumonia. It carries more serious warnings, including severe skin reactions, hemolytic anemia risk, and contraindications in pregnancy and early infancy.

Pros

  • Effective for Pneumocystis pneumonia treatment and prevention

  • Covers MRSA and many resistant gram-negative bacteria

  • Useful for traveler's diarrhea and shigellosis

  • Broader spectrum against resistant organisms

Cons

  • Contraindicated in infants under two months old

  • Should be avoided during pregnancy and breastfeeding

  • Higher risk of severe skin reactions like Stevens-Johnson syndrome

  • Risk of hemolytic anemia in G6PD-deficient patients

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