Fosfomycin for Recurrent Postcoital Cystitis
Fosfomycin is not a first-line agent for recurrent postcoital cystitis; nitrofurantoin or trimethoprim-sulfamethoxazole taken as postcoital prophylaxis are the preferred options, with fosfomycin reserved as an alternative when first-line agents cannot be used. 1
Evidence for Postcoital Prophylaxis
The most effective strategy for recurrent postcoital cystitis is postcoital antibiotic prophylaxis rather than treatment of acute episodes. 1
Nitrofurantoin (50-100 mg as a single dose within 2 hours after intercourse) significantly reduces recurrent cystitis episodes and is equally effective as continuous daily prophylaxis. 1
Ciprofloxacin (125 mg postcoital) has been shown in randomized trials to be as effective as continuous prophylaxis, though fluoroquinolones should be reserved for cases where first-line agents cannot be used due to resistance concerns and adverse effects. 1
Trimethoprim-sulfamethoxazole postcoital dosing is also effective, but should only be used if local E. coli resistance rates are <20%. 1
Why Fosfomycin Is Not First-Line for This Indication
Fosfomycin has inferior efficacy compared to standard short-course regimens for acute uncomplicated cystitis, with microbiological cure rates of approximately 78-80% versus 86-91% for nitrofurantoin. 1
The IDSA/ESCMID guidelines explicitly state that fosfomycin "appears to have inferior efficacy compared with standard short-course regimens" based on FDA data. 1
While fosfomycin is listed as a first-line option for acute uncomplicated cystitis due to minimal resistance and collateral damage, this recommendation does not extend to prophylactic use for recurrent postcoital cystitis. 1, 2
No high-quality evidence supports fosfomycin for postcoital prophylaxis specifically, whereas nitrofurantoin and fluoroquinolones have demonstrated efficacy in this setting. 1
Recommended Prophylactic Regimen
For women with recurrent cystitis clearly associated with sexual intercourse:
First choice: Nitrofurantoin 50-100 mg as a single dose within 2 hours after intercourse. 1
Alternative: Trimethoprim-sulfamethoxazole 40/200 mg (half of a single-strength tablet) postcoital, only if local resistance <20%. 1
Reserve option: Ciprofloxacin 125 mg postcoital if first-line agents are contraindicated or ineffective, recognizing FDA warnings about serious adverse effects. 1
When to Consider Fosfomycin
Fosfomycin may be appropriate in the following scenarios:
Treatment of acute breakthrough episodes during prophylaxis, where a single 3-g dose can be used. 1, 2
Patients with contraindications to nitrofurantoin (creatinine clearance <30 mL/min) or trimethoprim-sulfamethoxazole (sulfa allergy, high local resistance). 1, 3
Intermittent prophylaxis regimen: One study showed fosfomycin 3 g every 10 days reduced recurrence to 0.14 episodes/year versus 3 episodes with placebo, though this requires 18 times the antibiotic exposure of treating acute episodes. 4
Critical Clinical Pitfalls
Do not use fosfomycin for suspected pyelonephritis or upper tract symptoms (fever, flank pain), as it does not achieve adequate renal tissue concentrations. 1, 3
Avoid treating asymptomatic bacteriuria between symptomatic episodes, as this increases resistance and subsequent symptomatic infection risk. 1
The lowest antibiotic exposure strategy is postcoital prophylaxis rather than continuous daily prophylaxis or treating each acute episode, making nitrofurantoin postcoital dosing the optimal approach. 1, 4
Fluoroquinolones should not be first-line for prophylaxis due to FDA warnings about disabling adverse effects (tendon rupture, peripheral neuropathy, aortic dissection) and rising resistance rates of approximately 24%. 1, 3