We only use aqueous solutions in the pump and try to avoid medications known to be epitheliotioxic such as Gentamicin, especially where we have an intact epithelium.

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It is also important to remember that most aqueous eye drops contain preservatives notably BAK. BAK is toxic to epithelial cells at concentrations at c 0.005% and above. BAK concentration is usually 0.02% in most preparations. The toxic effects of BAK can be mitigated by reducing concentration and the addition of serum/plasma and preservative free hyaluronate.

The use of preservative free aqueous solutions is thus to be preferred however this can become cost prohibitive. Where BAK containing medications are used it is important to mitigate the effects of BAK by the addition of serum/plasma and or a preservative free hyaluronate (e.g. Clinitas Soothe, Altacor pharma.)

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Combinations of drugs should always be considered carefully and the potential for adverse effects on efficacy and safety appraised. Mixing bacteriostatic with bactericidal antibiotics may lead to reduce efficacy and increase risk of antibiotic resistance. It should be noted that when antiobiotics are used by continuous ocular lavage we expect much higher tissue concentrations then when given by bolus and the pharmacokinetics of the same drug may be different in this situation.

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Below are medications we have used with no observable complications or reduction of efficacy.

Caveat: It must be noted that it remains the clinician’s responsibility for the mixing of any medication and that they must be aware of the dangers of polypharmacy and assess the pros and cons on a case by case basis. The following medications have been used on hundreds of equine patients over many years and whilst each case was assessed by a Veterinary Ophthalmologist and the medication regime closely monitored for efficacy and side-effects this is not based on peer reviewed literature to support either safety or efficacy.

 

Corneal support:

50:50 Clinitas soothe and plasma 3ml syringe, 30mm/day, changed very two days in cooler weather, daily in the warm summer months.

 

Corneal antibiotic prophylaxis:

e.g. non-infected superficial ulcer pending culture results

33:33:33 Clinitas soothe + Chloramphenicol + Plasma

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Corneal ulcer antibiotic treatment:

e.g. where corneal infection is suspected (corneal infiltrate, uveitis etc.) pending culture and cytology results.

33:33:33 plasma + chloramphenicol + ofloxacin 30-60 mm/day, 3 mls syringe

This is reassessed in the light of response to treatment, cytology and culture results and adjusted as needed. Combination antibiotics are continued where multiple bacteria with resistance profiles are found however the aim is usually to reduce to one antibiotic where possible.

Combinations of the following aqueous drops have been mixed and used via pump and lavage by our team. Note were possible plasma is added to the combination at a minimum of 33% of the total mix volume:

• Ofloxacin

• Levofloxacin

• Ciprofloxacin

• Chloramphenicol

• Gentacin (Tiacil in preference due to the EDTA and base)

• Voraconazole (Vfend , the intravenous injection)

• Cefuroxime

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Corneal melting:

Plasma is used by preference as it is less prone to clot in the tube.

Plasma and Ofloxacin and or gentacin (dependent on history , appearance, cytology and culture) as either:

50:50 plasma + gent or  oflox (or ciproflox)

33:33:33 plasma + gent + oflox (or ciproflox)

 

Fungal keratitis:

Voraconazole and either chloramphenicol or, if indicated, a fluroquinilone plus plasma and or hyaluraonte.

NB Terbinafine ointment may be added  where indicated.

 

Corneal stromal abscess:

Identification of bacteria or fungi responsible is challenging in these cases and therefore presumptive treatment with combinations of chloramphenicol and fluroquiinilone and or voriconazole are usually used, with the addition of 25-33% plasma depending on whether 2 or 3 anti-infective drugs are used.