Can fosfomycin cause vision side effects?

Fosfomycin and Vision Side Effects

Fosfomycin can cause vision-related adverse effects, specifically unilateral optic neuritis, though this is an extremely rare occurrence documented in clinical trials. 1

Documented Ocular Adverse Effects

The FDA-approved prescribing information for fosfomycin explicitly states that one patient developed unilateral optic neuritis during clinical trials, an event considered possibly related to fosfomycin tromethamine therapy. 1 This represents the only documented vision-related adverse effect directly attributed to fosfomycin in the clinical trial database.

Frequency and Clinical Significance

• The incidence of optic neuritis with fosfomycin is exceptionally low, occurring in less than 1% of patients in clinical trials 1
• Among 1,233 fosfomycin-treated patients in controlled studies, only a single case of optic neuritis was identified 1
• This contrasts sharply with other antimicrobials like ethambutol, where retrobulbar neuritis is a well-established, dose-dependent adverse effect occurring in up to 3% of patients at higher doses 2

Common Non-Ocular Side Effects

The most frequently reported adverse effects of fosfomycin are gastrointestinal and gynecologic, not ophthalmologic:

• Diarrhea occurs in 9-10% of patients 2, 1
• Vaginitis affects 5.5-7.6% of patients 2, 1
• Nausea occurs in 4-5% of patients 2, 1
• Headache affects 3.9-10.3% of patients 2, 1

Clinical Context and Comparison

Fosfomycin does not carry the same level of ocular toxicity concern as medications with well-established vision-threatening effects. For comparison:

• Ethambutol causes dose-related retrobulbar neuritis with red/green color blindness and central scotomata, requiring visual acuity monitoring before and during treatment 2
• Azole antifungals like voriconazole cause neurologic and ophthalmic adverse events as recognized toxicities 2
• Bisphosphonates can cause serious ocular effects including uveitis, scleritis, and episcleritis that may lead to blindness if untreated 2

Clinical Recommendations

Routine ophthalmologic monitoring is not indicated for patients receiving fosfomycin based on the extremely low incidence of ocular adverse effects. 1

• If patients report visual symptoms (pain, vision changes, color perception changes) while taking fosfomycin, evaluate these symptoms promptly, though a causal relationship is unlikely given the rarity of documented cases 1
• The single-dose administration regimen for uncomplicated UTIs (3g once) further minimizes any theoretical risk of cumulative ocular toxicity 2, 3, 4
• Fosfomycin remains well-tolerated overall with a low incidence of adverse events, predominantly mild and self-limiting gastrointestinal symptoms 3, 5, 4

Important Caveat

The post-marketing surveillance data for fosfomycin has not identified vision problems as a recurring safety signal, supporting that the single case of optic neuritis in clinical trials represents an isolated event rather than a class effect 1, 5