Macrobid vs. Keflex

See how Macrobid and Keflex compare on approved uses, dosing, side effects, and cost.

Key Takeaways

  • Macrobid is a narrow-spectrum antibiotic approved specifically for uncomplicated bladder infections, while Keflex treats a much broader range of infections including skin, bone, and respiratory illness.

  • Macrobid stays concentrated in urine with minimal systemic absorption, which limits side effects but also limits its use to lower urinary tract infections only.

  • Macrobid is taken twice daily for 7 days for a UTI, while Keflex dosing varies by infection type and can require dosing up to four times daily.

Macrobid vs. Keflex Drug Summary

Macrobid

Macrobid (nitrofurantoin) is a urinary anti-infective used specifically to treat uncomplicated bladder infections caused by E. coli or S. saprophyticus. It's taken as a capsule twice daily for 7 days and concentrates almost entirely in urine, which limits its use to lower urinary tract infections.

Keflex

Keflex (cephalexin) is a first-generation cephalosporin antibiotic used for a wide range of bacterial infections, including skin, bone, respiratory, and urinary tract infections. Dosing varies by infection type and severity, ranging from 250 mg twice daily up to 500 mg every 12 hours for more serious cases.

Macrobid vs. Keflex Side Effects

Macrobid

Most common
nausea (up to 8%)
headache (up to 6%)
flatulence (up to 1.5%)

Keflex

Most common
nausea (rate not specified)
diarrhea (rate not specified)
vomiting (rate not specified)

Macrobid vs. Keflex Dosage

Macrobid

Dosage
Dosage Table
STAGE DOSE WHEN
Starting dose 100 mg every 12 hours Days 1-7
Maximum dose 100 mg every 12 hours Same as starting
Dose changes None Fixed dose

Keflex

Dosage
Dosage Table
STAGE DOSE WHEN
Starting dose 25-50 mg/kg/day divided At the start
Maximum dose Up to 4 g/day divided If needed
Dose changes 3 increases As tolerated

Macrobid vs. Keflex Indications

Macrobid

Macrobid is FDA-approved only for acute, uncomplicated bladder infections caused by susceptible bacteria like E. coli. It is also used off-label at low doses for long-term prevention of recurrent UTIs, but it is not approved for kidney infections or use in young children.

  • FDA-approved for uncomplicated bladder infections (cystitis)

  • Effective against E. coli and S. saprophyticus

  • Used off-label for long-term UTI prevention

  • Not indicated for kidney infections (pyelonephritis)

  • Not approved for children under 12

Keflex

Keflex is FDA-approved for a much wider variety of bacterial infections, including respiratory, ear, skin, bone, and urinary tract infections. It is also used off-label to prevent infection after certain surgeries, reflecting its broader spectrum of activity.

  • FDA-approved for skin and soft tissue infections

  • Also approved for respiratory and ear infections

  • Covers bone infections and urinary tract infections

  • Used off-label for surgical infection prevention

  • Available in liquid form for pediatric dosing

Macrobid vs. Keflex Pros and Cons

Macrobid

Macrobid is a narrow-spectrum option reserved specifically for uncomplicated bladder infections, which helps limit antibiotic resistance. It's covered by most insurance plans as a first-line UTI treatment, though it isn't an option for patients with reduced kidney function.

Pros

  • Stays concentrated in urine, causing fewer systemic side effects

  • Preferred first-line choice for uncomplicated UTIs per guidelines

  • Simple twice-daily dosing for a short 7-day course

  • Narrow spectrum helps limit broader antibiotic resistance

Cons

  • Contraindicated in reduced kidney function (CrCl under 60)

  • Not effective for kidney infections or systemic infections

  • Rare but serious risk of lung and liver toxicity with prolonged use

  • Typically costs more than Keflex, roughly $80 to $200 a month without insurance

Keflex

Keflex treats a much wider range of infections, from skin to bone to respiratory illness, making it a versatile choice when the infection site is uncertain. It's an older, well-established antibiotic with predictable dosing, though its broad use contributes more to general antibiotic resistance than UTI-specific drugs.

Pros

  • Broad spectrum covers many infection types beyond UTIs

  • Long safety record since 1971 as a widely prescribed antibiotic

  • Available in liquid suspension form for children

  • Typically costs less than Macrobid, roughly $53 to $95 per course without insurance

Cons

  • Not UTI-specific, so broader use raises resistance concerns

  • Dosing regimens can require up to four doses a day

  • Carries risk of C. difficile-associated diarrhea

  • Seizure risk if dose isn't reduced in kidney impairment

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