What is the best initial treatment for acute conjunctivitis (pink eye) in an adult, considering viral, bacterial, and allergic causes?

Initial Treatment for Acute Conjunctivitis in Adults

For most adults with acute conjunctivitis, treatment should be guided by clinical presentation: supportive care alone for viral conjunctivitis (most common), topical antibiotics for bacterial conjunctivitis with mucopurulent discharge, and topical antihistamines with mast-cell stabilizers for allergic conjunctivitis with itching. 1

Distinguishing the Etiology

Viral Conjunctivitis (Most Common)

• Watery discharge, follicular reaction on inferior tarsal conjunctiva, preauricular lymphadenopathy, and concurrent upper respiratory symptoms strongly suggest viral etiology 1, 2
• Often starts unilaterally but becomes sequentially bilateral within days 2
• May present with subconjunctival hemorrhages, chemosis, and marked eyelid swelling 2

Bacterial Conjunctivitis

• Mucopurulent or purulent discharge with matted eyelids on waking, papillary (not follicular) reaction, and absence of itching favor bacterial cause 1, 2
• Can be unilateral or bilateral 2
• Preauricular lymphadenopathy less common unless hypervirulent organisms involved 2

Allergic Conjunctivitis

• Itching is the hallmark symptom, bilateral presentation, watery discharge with mild mucous component 1, 2
• Often concurrent allergic rhinitis or asthma 2
• No preauricular lymphadenopathy or matted eyelids 2

Treatment by Etiology

Viral Conjunctivitis

Supportive care only—antibiotics provide no benefit and should be avoided. 1, 3

• Refrigerated preservative-free artificial tears four times daily to dilute viral particles and inflammatory mediators 1
• Cold compresses for symptomatic relief and to reduce inflammation 1, 3
• Topical antihistamines (second-generation) may be used for itching and discomfort 1
• Strict hand hygiene with soap and water is critical to prevent transmission 1, 3
• Avoid close contact for 10-14 days from symptom onset 1
• Self-limited, typically resolves in 5-14 days 2

Critical caveat: Topical corticosteroids should never be used without ophthalmology supervision, as they prolong adenoviral infections and can worsen HSV infections 4, 1

Bacterial Conjunctivitis

For mild disease: Supportive care alone is appropriate, as 64% resolve spontaneously by days 6-10 without treatment 1, 5

For moderate-to-severe disease: Prescribe a 5-7 day course of broad-spectrum topical antibiotic 1

• Topical fluoroquinolones (moxifloxacin 0.5% three times daily) are preferred first-line agents with superior gram-positive coverage including some MRSA strains 1
• Alternative options if fluoroquinolones unavailable: polymyxin B-trimethoprim, erythromycin ointment, or ofloxacin 0.3% four times daily 1
• No single antibiotic has proven superiority—choice can be based on dosing convenience and cost 1, 6
• Topical antibiotics provide earlier clinical remission (68% cure vs 55% placebo by days 4-9) and allow faster return to work 1, 7

Special situations requiring systemic antibiotics:

• Gonococcal conjunctivitis (marked eyelid edema, profuse purulent discharge): Requires ceftriaxone 250 mg IM single dose plus azithromycin 1 g oral single dose, with daily monitoring until resolution 1, 8
• Chlamydial conjunctivitis: Requires azithromycin 1 g oral single dose or doxycycline 100 mg oral twice daily for 7 days, as >50% have concurrent infection at other sites 1, 8
• Both require treatment of sexual partners and consideration of sexual abuse in children 1

Allergic Conjunctivitis

First-line treatment: Topical antihistamines with mast-cell stabilizing properties (e.g., olopatadine, ketotifen) 4, 1, 3

Adjunctive measures:

• Wear sunglasses as allergen barrier 4, 8
• Cold compresses and refrigerated preservative-free artificial tears 4, 8
• Avoid eye rubbing and known allergens 4

Second-line for persistent symptoms: Brief 1-2 week course of low side-effect profile topical corticosteroids (fluorometholone, loteprednol) with monitoring of intraocular pressure 4, 1

Avoid: Chronic use of topical vasoconstrictors causes rebound vasodilation 4, 1

Red Flags Requiring Immediate Ophthalmology Referral

Do not treat empirically if any of the following are present—refer urgently: 1, 8

• Visual loss or decreased vision
• Moderate-to-severe pain (beyond mild irritation)
• Corneal involvement (opacity, infiltrate, ulcer on examination)
• Severe purulent discharge suggesting gonococcal infection
• Conjunctival scarring or pseudomembrane formation
• History of herpes simplex virus eye disease
• Immunocompromised state
• Recent ocular surgery or trauma
• Lack of improvement after 3-4 days of appropriate therapy

Common Pitfalls to Avoid

• Never prescribe antibiotics for viral conjunctivitis—they cause unnecessary toxicity and promote resistance 1, 3
• Never use topical corticosteroids without definitively excluding HSV—they potentiate viral replication and can cause corneal perforation 1
• Never use topical antibiotics alone for gonococcal or chlamydial conjunctivitis—systemic therapy is mandatory 1, 8
• Never miss gonococcal conjunctivitis—delayed treatment can lead to corneal perforation within 24 hours 1
• Instruct patients to return if no improvement in 3-4 days 1, 8