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
Keflex
Macrobid vs. Keflex Dosage
Macrobid
Keflex
| 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 |
| 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
| 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
| 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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