Anti-infective eye preparations

By | 2011-05-25

Care should be taken to distinguish superficial ocular disease caused by infections from other conditions that may result in a red or inflamed eye. Where possible the causative organism should be identified and any initial choice of a broad-spectrum antibacterial, or combination of antibacterials, modified according to bacterial sensitivity data. The severity of an infection may determine the choice of drug and frequency of application. When dispensing antibacterials, it is considered preferable to choose topical preparations of drugs that are not usually used to treat systemic infections. Primary bacterial conjunctivitis is usually acute and corticosteroids are unnecessary. The normal conjunctival flora of the dog consists of a number of species whereas the cat conjunctiva harbours relatively few micro-organisms. Hence, with the exception of conjunctivitis due to Chlamydophila (Chlamydia) infection, primary bacterial conjunctivitis is rare in cats; viral infections are the more frequent cause of conjunctivitis seen in this species. Where only one eye is involved but, for prophylactic reasons, the other eye is also being treated, medication should be applied first to the unaffected eye to minimise the possibility of cross-infection.

Antibacterial preparations

Antifungal preparations

Ocular fungal infections may be superficial, for example mycotic keratitis, or intra-ocular such as mycotic endophthalmitis; both conditions are rare in the UK. Intra-ocular manifestations of systemic mycotic infections in dogs and cats, such as blastomycosis, cryptococcosis, geotrichosis, and histoplasmosis, usually present as a focal granulomatous posterior uveitis, often involving the retina and other tissues of the eye.

Specialist antifungal preparations are available from Moor-fields Eye Hospital, after identification of specific fungi by appropriate laboratory procedures.

Most topical antifungal drugs have poor corneal penetration and systemic antifungals such as ketoconazole and amphotericin B are used for treatment.

Antiviral preparations

Feline herpesvirus (FHV) is a common cause of acute conjunctivitis and chronic keratitis and is also a potential respiratory pathogen. Trifluridine has been shown to be efficacious against feline herpesvirus-1 in vitro and appears to be clinically useful. Aciclovir has very limited in vitro effect thus its clinical use is limited in cats. Ganciclovir has been shown to be effective in human herpes simplex keratitis but its use in cats remains to be investigated. Oral lysine has been shown in vitro to inhibit virus replication and uncontrolled studies in both humans and cats seem to show a beneficial effect. Clinical trials in cats are currently in progress to test the efficacy of this amino acid in FHV-1 infections.

Some forms of equine superficial punctate keratitis may be due to equine herpesvirus infection; aciclovir may be effective in these cases.

ACICLOVIR

(Acyclovir)

Indications. See notes above

Dose: Horses, cats: eye ointment, apply 5-6 times daily

Prescription-only medicine:® Zovirax (GSK) UK Eye ointment, aciclovir 3%

GANCICLOVIR

Indications. See notes above

Side-effects. Local irritation, conjunctival hyperaemia

Dose:

Cats: apply 1 drop 4-6 times daily. Maximum period of treatment 21 days

Prescription-only medicine:® Virgan (Chauvin) UK

Eye drops, ganciclovir 0.15% in gel basis

LYSINE

(L-Lysine)

Indications. Feline herpesvirus infection, see notes above

Warnings. Formulations containing propylene glycol are toxic to cats and must not be used

Dose:

Cats: by mouth, 250 mg daily. May be given during clinical episode of FHV 1 infection and also long-term in carrier cats. Higher doses of 500 mg have also been used

Preparations containing lysine are available from health food shops

TRIFLURIDINE

(Trifluorothymidine)

Indications. See notes above

Dose:

Cats: eye drops, apply 4-6 times daily for 3-4 days until clinical improvement, then apply 3 times daily

Prescription-only medicine: ® Trifluridine Eye Drops 1%

Eye drops containing trifluridine are not generally available. Contact the local pharmacist or Moorfields Eye Hospital to obtain a supply in the UK