Ophthalmic Antibiotics

Concise summaries of common ophthalmic antibiotic eye drops and ointments used in optometric practice in Singapore, including practical guidance on drug class, dosing, patient selection, antimicrobial stewardship, and referral thresholds.

Last updated: March 2026

What are ophthalmic antibiotics?

Ophthalmic antibiotics are pharmaceutical preparations — drops, ointments, or gels — applied topically to the ocular surface to treat or prevent bacterial infections of the eye and its adnexa. They deliver bactericidal or bacteriostatic drug concentrations directly to the conjunctiva, cornea, and lid margin, achieving local levels that far exceed the minimum inhibitory concentrations (MICs) of common ocular pathogens without the systemic burden of oral antibiotics.

In Singapore's tropical climate, the high ambient humidity and warmth favour gram-negative organisms in the environment, while one of the world's highest contact lens wearing rates creates a significant burden of contact lens-associated microbial keratitis. Most critically, Pseudomonas aeruginosa keratitis — a potentially sight-threatening emergency — is strongly associated with contact lens wear, particularly extended overnight wear and poor lens hygiene, and requires prompt treatment with an anti-pseudomonal fluoroquinolone or aminoglycoside.^[1,2]

Drug classes

Fluoroquinolones — broad-spectrum bactericidal agents; dual inhibition of DNA gyrase and topoisomerase IV; excellent gram-negative and gram-positive coverage; first-line for bacterial keratitis and CL-related infections (e.g., ciprofloxacin, moxifloxacin).
Aminoglycosides — bactericidal; 30S ribosomal subunit inhibitors; strong gram-negative including Pseudomonas coverage; may be combined with a gram-positive agent for empirical broad-spectrum cover (e.g., tobramycin, gentamicin).
Fusidic acid — narrow-spectrum; primarily gram-positive (staphylococcal) bacteriostatic/cidal agent; first-line for staphylococcal blepharoconjunctivitis with excellent tolerability and BD dosing convenience.
Chloramphenicol — broad-spectrum bacteriostatic; 50S ribosomal inhibitor; historically widely used first-line agent for bacterial conjunctivitis in Singapore; available as drops and ointment.
Macrolides — bacteriostatic; 50S ribosomal inhibitors with gram-positive and atypical organism coverage; erythromycin ointment for neonatal prophylaxis; azithromycin drops for short-course chlamydial conjunctivitis treatment.
Polymyxin combinations — synergistic gram-negative coverage combined with trimethoprim (folate synthesis inhibitor); appropriate for uncomplicated bacterial conjunctivitis when fluoroquinolone stewardship is a priority.

Who are they for?

Ophthalmic antibiotics are indicated for patients with confirmed or clinically suspected bacterial infections of the external eye and adnexa. In Singapore, the most frequently encountered conditions in primary eye care are acute bacterial conjunctivitis, staphylococcal blepharoconjunctivitis, and contact lens-associated microbial keratitis. Lim et al. identified sleeping in contact lenses as the most significant independent risk factor for CL-related keratitis in Singapore — a pattern seen across the city-state's large young, urban contact lens-wearing population.^[2,3]

Patient profiles — common conditions

Acute bacterial conjunctivitis

Mucopurulent discharge, lid crusting, conjunctival injection; gram-positive organisms (Staphylococcus aureus, Streptococcus pneumoniae) predominate; most cases self-limit in healthy adults but antibiotic therapy shortens course and reduces community transmission.

Staphylococcal blepharoconjunctivitis

Chronic lid margin inflammation with secondary conjunctival involvement; coagulase-negative Staphylococcus spp. most common; fusidic acid or chloramphenicol first-line; lid hygiene (warm compresses, lid scrubs) is an essential adjunct.

Contact lens-related microbial keratitis (CLMK)

Singapore's high CL-wearing population makes this a priority presentation; Pseudomonas aeruginosa is the most dangerous organism — associated with extended wear, poor hygiene, swimming in lenses; urgent same-day ophthalmology referral mandatory; any corneal sign in a CL wearer = emergency.

Neonatal conjunctivitis (ophthalmia neonatorum)

Chlamydia trachomatis and Neisseria gonorrhoeae are the most serious causes; erythromycin ointment prophylaxis at birth and systemic treatment mandatory; refer all neonates with purulent eye discharge urgently to paediatric ophthalmology for culture, treatment, and maternal partner notification.

Caution — contact lens wearers

Any contact lens wearer presenting with a red, painful, or photophobic eye must be treated as microbial keratitis until proven otherwise — cease lens wear immediately. Most ophthalmic antibiotic preparations contain benzalkonium chloride (BAK) as preservative, which adsorbs onto soft contact lenses and causes toxic keratopathy. Do not instil BAK-preserved drops with lenses in situ. Where intensive therapy is required, preservative-free formulations (e.g., Vigamox) are preferable. Refer any case with corneal involvement urgently — the same day — to ophthalmology.

When should they be prescribed?

Acute bacterial conjunctivitis

In immunocompetent adults with classic mucopurulent conjunctivitis — no corneal involvement, no contact lens wear — topical antibiotic therapy shortens the clinical course and reduces person-to-person transmission. Fucithalmic (fusidic acid BD) or chloramphenicol drops (every 2–4 hours) are appropriate first-line choices. Avoid fluoroquinolones as empirical first-line therapy for uncomplicated conjunctivitis — reserve this antibiotic class for corneal disease, Pseudomonas cover, and cases where first-line agents fail, in line with antimicrobial stewardship principles.^[4]

Prophylactic use

Prophylactic ophthalmic antibiotics are routinely used post-operatively — following cataract surgery, pterygium excision, and other anterior segment procedures — and for neonatal ophthalmia neonatorum prevention. Erythromycin 0.5% ointment is the standard neonatal prophylactic agent in most Singapore hospital protocols. Post-operative antibiotic regimens are prescribed by the operating ophthalmologist and are frequently incorporated into antibiotic-steroid combination preparations (see antibiotic-steroid combinations page) for streamlined post-operative care.

Escalation and urgent referral

Any case with corneal infiltrate, stromal haze, reduced visual acuity, significant pain, photophobia, hypopyon, or contact lens association must be referred urgently — the same day — to an ophthalmologist or hospital eye emergency service. Do not initiate antibiotic therapy and observe: bacterial keratitis can progress to corneal perforation within 24–48 hours without appropriate intensive treatment. If referral is unavoidably delayed and corneal ulcer is strongly suspected, a loading dose of a fluoroquinolone (ciprofloxacin or moxifloxacin) may be initiated after consulting the receiving clinician.

Severity / Presentation	Recommended agent	Duration / Referral
Mild bacterial conjunctivitis (no corneal signs, no CL wear)	Fucithalmic BD or Chloramphenicol drops every 2–4 h	5–7 days; reassess at 48 h if not improving
Moderate mucopurulent conjunctivitis or non-response to first-line	Chloramphenicol drops every 2 h or Tobramycin QID	7–10 days; culture if no response after 48 h
CL-associated red eye with any corneal sign	Cease lenses immediately — urgent same-day referral to ophthalmology	Emergency referral; do not manage in community
Suspected bacterial keratitis / corneal ulcer	Urgent referral — fluoroquinolone (ciprofloxacin or moxifloxacin) intensive loading	Same-day referral to SNEC / NUH / TTSH eye emergency; specialist-directed

Where are they available in Singapore?

In Singapore, ophthalmic antibiotics are regulated by the Health Sciences Authority (HSA) under the Medicines Act. The vast majority are classified as Prescription-Only Medicines (POM), reflecting the need for professional diagnosis to guide appropriate agent selection, ensure culture and sensitivity testing in severe cases, and prevent the emergence of antimicrobial resistance through inappropriate self-treatment and over-the-counter use.

Scope of practice — Singapore optometrists

Under the Optometrists and Opticians Act (Cap. 213A), Singapore-registered optometrists are authorised to examine eyes, assess visual function, and prescribe optical appliances (spectacles and contact lenses). They do not have the authority to prescribe, supply, or administer therapeutic medications, including prescription antibiotic eye drops or ointments. Any patient requiring antibiotic therapy must be referred to a registered medical practitioner — an ophthalmologist, general practitioner, or hospital emergency department, as appropriate to the clinical urgency. Optometrists play a critical role in early identification of bacterial infections, appropriate triaging, and recognition of the red flags that mandate emergency referral.^[5,6]

Prescription-only (POM): All ophthalmic fluoroquinolones (Ciloxan, Vigamox), aminoglycosides (Tobrex, Gentamicin), fusidic acid (Fucithalmic), chloramphenicol drops and ointment, macrolides (erythromycin ointment, Azyter), and Polytrim are classified as POMs in Singapore — requiring a prescription from a registered medical practitioner before dispensing.
General practitioners: GPs may prescribe fusidic acid (Fucithalmic) or chloramphenicol for uncomplicated bacterial conjunctivitis without corneal involvement. More severe presentations — any corneal sign, CL-associated keratitis, immunocompromised patients, or non-response after 48 hours — require referral to an ophthalmologist.
Ophthalmologists (primary prescribers for keratitis): Fluoroquinolones at intensive loading doses for bacterial keratitis are prescribed and managed by ophthalmologists at SNEC (Singapore National Eye Centre), NUH Eye Institute, TTSH, and private eye surgery centres. Hospital compounded fortified antibiotics (vancomycin 5%, ceftazidime 5%) for severe keratitis are available through hospital pharmacies under ophthalmologist direction.
Public hospital formularies: SNEC, NUH Eye Institute, and TTSH routinely stock chloramphenicol, tobramycin (Tobrex), gentamicin, ciprofloxacin (Ciloxan), and moxifloxacin (Vigamox). Erythromycin ointment is a standard neonatal pharmacy item in all Singapore restructured hospitals.
HSA product verification: Current registration status and supply schedule for all products can be confirmed via the HSA product registration portal (hsa.gov.sg). Always verify before recommending or referring for any specific product, as registration status and product availability may change.^[5]

Why use topical agents over oral/systemic antibiotics?

For the vast majority of anterior segment bacterial infections, topical ophthalmic antibiotics are strongly preferred over systemic oral or intravenous antibiotics. Topical delivery achieves vastly higher local drug concentrations at the site of infection while minimising systemic drug burden and preserving the systemic antibiotic armamentarium against resistance pressure.

High local drug concentrations

Topical drops achieve conjunctival and corneal drug levels 100–1,000× higher than those achievable with equivalent oral doses — reliably exceeding MICs for the most common ocular pathogens at the site of infection.

Minimal systemic absorption

Nasolacrimal drainage is the primary systemic absorption route; applying nasolacrimal occlusion (finger pressure at the inner canthus for 1–2 min) after instillation markedly reduces systemic entry. Oral antibiotics achieve consistently poor penetration into the avascular cornea via the systemic route.

Antimicrobial stewardship

Reserving systemic antibiotics for true systemic indications (orbital cellulitis, gonococcal conjunctivitis, chlamydia, dacryocystitis, endophthalmitis) preserves the effectiveness of the oral antibiotic armamentarium and reduces community resistance pressure — a key priority in Singapore.

Reduced systemic side effects

Topical therapy avoids oral antibiotic-associated adverse effects: gastrointestinal upset, antibiotic-associated diarrhoea, Clostridioides difficile, systemic drug allergy, and drug interactions — particularly relevant for elderly and polypharmacy patients.

Systemic antibiotics are mandated for: gonococcal conjunctivitis (IM/IV ceftriaxone), chlamydial conjunctivitis (oral azithromycin 1 g stat or doxycycline 100 mg BD × 7 days, combined with topical azithromycin), orbital cellulitis, dacryocystitis, endophthalmitis, and all neonatal ophthalmia neonatorum — where systemic therapy is required in addition to topical drops. These cases require urgent medical referral and are beyond the scope of optometric community management.^[3,4]

How to use ophthalmic antibiotics — patient instructions

Instillation technique

Wash hands thoroughly with soap and water before handling any eye drop bottle or ointment tube.
Tilt the head back slightly and gently pull down the lower eyelid to form a small pocket (lower fornix) with one finger.
Hold the bottle or tube inverted and squeeze one drop (or a small ribbon of ointment approximately 1 cm) into the lower fornix — do not allow the tip to contact the eye, eyelid, or any surface; contamination of the tip can introduce organisms into the bottle.
Gently close the eye and apply nasolacrimal occlusion by pressing a clean fingertip firmly against the inner corner of the closed eye (over the lacrimal sac) for 1–2 minutes — this markedly reduces systemic drainage and maximises drug contact time with the ocular surface.
If more than one drop preparation is prescribed, wait at least 5 minutes between instillations — apply the least viscous preparation first (drops before gels or ointments).
Recap the bottle or tube immediately after use; discard single-use vials after use; observe the stated expiry and discard multi-dose bottles within the period stated on the label (typically 4 weeks after opening for preserved formulations).

Contact lens guidance

Remove all contact lenses before instilling antibiotic drops or ointment. Do not reinsert lenses until the full antibiotic course is completed and the infection has fully resolved, as confirmed by the treating clinician.
If the patient was wearing lenses when the infection was identified, discard the current lens pair, the lens case, and any opened lens solution — all may be contaminated with the causative organism and serve as a reinfection reservoir.
BAK-preserved formulations must not be used with soft contact lenses in situ. If a preservative-free formulation is used, lenses should still be removed for at least 15 minutes before reinsertion — although total lens cessation throughout the treatment period is strongly recommended.

Monitoring & red-flag referral

Review at 48–72 hours: If symptoms are not clearly improving — worsening discharge, increasing conjunctival injection, or new symptoms — reassess urgently and refer to a doctor or ophthalmologist. The diagnosis may be incorrect (viral, allergic, or non-infectious) or the causative organism may be resistant to the chosen agent.
Immediate red-flag referral — same day: Refer urgently to ophthalmology if any of the following are present or develop: reduced visual acuity, corneal haze or infiltrate, significant pain or photophobia, hypopyon, ciliary flush, periorbital swelling, or contact lens association with any corneal sign whatsoever.
Complete the full course: Patients must complete the prescribed antibiotic course even if symptoms resolve early — premature cessation leads to clinical relapse, selection of resistant organisms, and potential for treatment failure in subsequent episodes.
Children and neonates: All neonatal conjunctivitis must be referred urgently to paediatric ophthalmology; confirm correct instillation technique with parents or carers for young children; erythromycin ointment is approved from birth; chloramphenicol and tobramycin from ≥2 years.

Common ophthalmic antibiotics in Singapore

All agents listed are, or have been, registered with HSA Singapore or are available through registered importers. Verify current product registration at hsa.gov.sg before prescribing. Apply antimicrobial stewardship principles: reserve fluoroquinolones for severe infections, corneal disease, and Pseudomonas cover.

Brand (Generic)	Mechanism / Class	Dosing	Min. Age	Side Effects & Precautions	Clinical Notes
Fucithalmic Fusidic acid 1% viscous eye drops POM	Fusidic acid — gram-positive protein synthesis inhibitor; bacteriostatic/cidal	1 drop BD	≥2 years	Transient blurring, stinging, local hypersensitivity	First-line for staphylococcal blepharoconjunctivitis; not effective against Pseudomonas — do not use for CL-associated keratitis
Xepanicol Chloramphenicol 0.5% eye drops POM	Chloramphenicol — broad-spectrum bacteriostatic; 50S ribosomal inhibitor	1–2 drops every 2–4 h; reduce to QID as resolves; complete full course	≥2 years	Stinging, local hypersensitivity; avoid if personal or family history of aplastic anaemia	Broad-spectrum including H. influenzae; historically first-line for bacterial conjunctivitis in Singapore
Tobrex Tobramycin 0.3% eye drops & ointment POM	Aminoglycoside — bactericidal; broad-spectrum including Pseudomonas aeruginosa	Mild–moderate: 1–2 drops every 4 h. Severe/keratitis: every 30–60 min then taper. Ointment: 2–3× daily or nocte.	≥1 year	Ocular irritation, lid oedema, hypersensitivity; keratopathy with prolonged intensive use	Key agent for CL-related Pseudomonas keratitis; refer urgently for any corneal involvement
Ciloxan Ciprofloxacin 0.3% eye drops & ointment POM	Fluoroquinolone (2nd-gen) — bactericidal; broad-spectrum including Pseudomonas	Keratitis: 2 drops every 15 min (6 h) then every 30 min Day 1; taper Days 2–14. Conjunctivitis: every 2 h Days 1–2, then QID Days 3–7.	≥1 year	White corneal crystalline precipitate during loading dose (benign, self-resolving); stinging, bitter taste	First-choice for bacterial keratitis and Pseudomonas cover; loading-dose crystalline deposits are benign
Vigamox Moxifloxacin 0.5% eye drops POM	Fluoroquinolone (4th-gen) — bactericidal; enhanced gram-positive spectrum; preservative-free	1 drop TID for 7 days; keratitis: as directed by ophthalmologist	≥1 year	Ocular irritation, transient blurred vision, dry eye	Preferred for enhanced gram-positive cover (MRSA some strains); preservative-free; suitable for CL-related mixed infections
Gentamicin 0.3%Gentamicin sulfate 0.3% eye drops & ointment POM	Aminoglycoside — bactericidal; strong gram-negative coverage including Pseudomonas	1–2 drops every 4 h; severe/keratitis: every 1–2 h then taper. Ointment: 2–3× daily or nocte.	≥2 years (supervised)	Ocular irritation, conjunctival injection, punctate keratopathy with prolonged use	Long-established broad-spectrum agent; widely available in SNEC, NUH, and TTSH formularies
Erythromycin 0.5%Erythromycin 0.5% eye ointment POM	Macrolide — bacteriostatic; gram-positive and Chlamydia trachomatis cover	Apply ribbon 1–6× daily; nocte for blepharitis; QID for acute infection; neonatal prophylaxis: single application at birth	Neonates and above	Transient blurring (ointment), stinging; limited gram-negative coverage	Standard neonatal ophthalmia neonatorum prophylaxis; for chlamydia, combine with systemic therapy and STI referral

Legend

POMPrescription Only Medicine — Sold or supplied to the public on prescription only.

PPharmacy Medicine — Sold or supplied from any licensed retail pharmacy under pharmacist supervision.

OTCGeneral Sales List (GSL) — Sold or supplied to the public without restriction.

Dosing reflects standard adult doses unless noted. Always refer to the approved product insert for full prescribing information. BD = twice daily, TID = three times daily, QID = four times daily, OD = once daily, nocte = at night.

References

[1] Tan SZ, Walkden A, Au L, et al. Twelve-year analysis of microbial keratitis trends at a UK tertiary hospital. Eye. 2017;31(8):1229–1236. PMID: 28524876.
[2] Lim CHL, Carnt NA, Farook M, et al. Risk factors for contact lens-related microbial keratitis in Singapore. Eye. 2016;30(3):447–455. PMID: 26742862.
[3] Saw SM, Ooi PL, Tan DT, et al. Risk factors for contact lens-related Fusarium keratitis: a case-control study in Singapore. Arch Ophthalmol. 2007;125(5):611–617. PMID: 17502500.
[4] Sheikh A, Hurwitz B. Antibiotics versus placebo for acute bacterial conjunctivitis. Cochrane Database Syst Rev. 2006;(2):CD001211. PMID: 16625540.
[5] Republic of Singapore. Optometrists and Opticians Act 2007 (No. 16 of 2007). Singapore Statutes Online. Available at: sso.agc.gov.sg/Act/OOA2007 (accessed March 2026).
[6] George PP, Chng OSY, Siow K, et al. Is there scope for expanding the optometrist's scope of practice in Singapore? A survey of optometrists and opticians. Cont Lens Anterior Eye. 2019;42(3):258–264. PMID: 30819628.
[7] Wilhelmus KR. Bacterial keratitis. Cochrane Database Syst Rev. 2003;(4):CD001647. PMID: 14583934.
[8] Dart JK, Stapleton F, Minassian D. Contact lenses and other risk factors in microbial keratitis. Lancet. 1991;338(8768):650–653. PMID: 1679463.
[9] Bourcier T, Thomas F, Borderie V, Chaumeil C, Laroche L. Bacterial keratitis: predisposing factors, clinical and microbiological review of 300 cases. Br J Ophthalmol. 2003;87(7):834–838. PMID: 12812878.
[10] Health Sciences Authority Singapore. Medicines — product registration. Available at: hsa.gov.sg (accessed March 2026).

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