Keflex Dose for UTI in Pregnancy
For uncomplicated cystitis in pregnancy, administer cephalexin (Keflex) 500 mg orally every 12 hours for 7 to 14 days. 1
Dosing Recommendations
Standard Treatment Regimen
- Dose: 500 mg orally every 12 hours 1
- Duration: 7 to 14 days for cystitis 1
- Alternative dosing: 250 mg every 6 hours can also be used, though the every 12-hour regimen is more convenient 1
The FDA-approved labeling specifically states that for uncomplicated cystitis in patients over 15 years of age, 500 mg may be administered every 12 hours, with therapy continued for 7 to 14 days 1. This dosing applies to pregnant women, as cephalexin is considered safe during pregnancy.
Clinical Efficacy in Pregnancy
Cephalexin has demonstrated excellent efficacy for UTI prevention and treatment during pregnancy. In a study of 33 pregnant women with recurrent UTIs, postcoital prophylaxis with cephalexin 250 mg single dose reduced UTI episodes from 130 infections (pre-prophylaxis) to only 1 infection during pregnancy—a highly significant reduction 2. This effectiveness is attributed to cephalexin achieving high bactericidal concentrations in the urinary tract while inducing minimal resistance in gram-negative flora 2.
Pharmacokinetic Considerations
Cephalexin achieves urinary concentrations of 500-1000 mcg/mL following 250-500 mg oral doses, which far exceeds the minimum inhibitory concentration for typical urinary pathogens 3. The drug is:
- Rapidly and completely absorbed in the upper intestine 3
- 70-100% excreted unchanged in urine within 6-8 hours 3
- Not metabolized during its passage through the body 3
Safety Profile in Pregnancy
Cephalexin is a first-generation cephalosporin with an established safety record during pregnancy 4. A comparative trial in 80 pregnant women with bacteriuria showed no fetal toxicity attributable to cephalexin, with cure rates of 74% at 2 weeks and 60% at 6 weeks 4.
Important Caveats
- Local resistance patterns matter: Know your local susceptibility patterns for E. coli to cephalexin, as geographic variability exists 5
- Not for pyelonephritis: Cephalexin should not be used as monotherapy for acute pyelonephritis in pregnancy, as oral cephalosporins achieve lower blood concentrations than parenteral agents 5
- Renal adjustment: Patients with creatinine clearance <30 mL/min require dosage reduction proportional to reduced renal function 3
- Follow-up cultures: Repeat urine cultures 7 days after completing therapy to confirm cure 6
Alternative Considerations
If cephalexin is ineffective or contraindicated, amoxicillin-clavulanate (500 mg three times daily for 3-7 days) or nitrofurantoin (avoid in third trimester) are reasonable alternatives 6, 4. However, cephalexin remains a preferred first-line agent due to its safety profile, convenient dosing, and minimal disruption of bowel flora 3.