Ophthalmic Antibacterial Agents & Their Uses

Three main types of topical ocular antibiotic

• Antibacterial Chemical Agents
• Broad Spectrum Antibiotics
• Narrow Spectrum Antibiotics

Guidelines for Use

• Recognition of infection as being bacterial as opposed to viral, fungal or protozoan. Bacterial often leave substantial encrustation on lashes. Bacterial inf of the conjunctiva is usually accompanied w/yellowy-white gummy muco-purulent discharge (as opposed to white and stringy in allergic reactions). Lids may stick together, especially overnight. Viral and fungal infections are more commonly accompanied by profuse tearing without discharge/encrustation. Involvement of conj may spread to cornea also.
• History tends to be acute - irritation/signs are sufficient to make px come in straight away. However px w/minor infections and who already have a bit of ocular irritation might not notice. Perhaps that case can be managed simply w/better ocular hygiene
• Selection of appropriate primary and secondary therapy: Product Selection, Treatment Regimen & Predicting Outcome. Often product selected w/regimen and that's it. Shotgun approach involves choosing drug, using on px, give px a small supply and regimen and get them to come back in a day or two. From there if improvement move on to a written order/refer for Rx. Using a broad spectrum antibiotic will usually work. Most things can be managed w/out cultures being taken.
• Product selection and use - allergies - more likely w/aminoglycoside antibiotics eg neomycin but chloramphenicol can cause sensitization if inappropriately used. Will there be a fridge to put the chloramphenicol in and will the px use it? Will overnight treatment be necessary? In which case - ointments!

Regimens & Px Education

• Initially around 5x a day at regular intervals NOT AS NEEDED TELL THEM THIS. If more severe broad spec stuff can be administered every couple of hours for the first day or two. Ophthalmic viscous solns 'morning and night'. If v severe use drops and ointment. w/round the clock drops. If it's really bad and they need to do that maybe refer. If there's any corneal involvement then initially should definitely be every two hours. Note all this stuff down obvs.
• Duration of therapy: Good regimen is 7 to 10 days but some products will suggest just 5. Treatment should be until 2 or 3 days after infection no longer apparent.
• Never assume px knows what they are doing. Take time to educate on instillation, application, hygiene, storage and disposal of the pharmaceuticals. Px needs to understand importance of compliance. If they aren't going to be able to comply w/drops dispense ointment.
• Ideally no px should be given anti-infective drugs w/out the opp. for a follow-up. Patient must be told to come back at a specific time if the condition doesn't improve? Could do quick phonecall if all seems ok and then sort something else out. If all seems ok can usually instruct px to continue w/therapy until 2-3 days after they think it has subsided. Such a follow-up visit doesn't need to include a full eye test.
• If eye appears worse on follow-up then appropriate changes in therapy need to be made and the px referred, at least for cultures. In rare cases it should always be considered that the infection is actually fungal or viral and that you got it wrong, doofus.

Bit on Management of Infections

• Styes or many other inflammatory infections of the eyelash follicles/glands/accessory lacrimal glands can be readily managed w/ocular hygiene and maybe some anti-infective ointment. If untreated they can sometimes develop into chronic conditions or something more serious (orbital cellulitis!) which would require urgent referral.
• Lids should be cleansed w/lid scrubs then the ointments worked into the lid margin and antibac drops used if the bulbar conj is also affected. Nightly and morning use of the ointments should sort it out. Although these drugs have little action on the bacteria inside the inflamed loci they should stop the infection spreading IE THEY ARE BACTERIOSTATIC not bacteriocidal.
• w/styes the same sort of treatment will work, w/eyelid margin cleansing w/warm compresses for 5 to 10 mins to promote expression of the infected foci before starting w/the antibacterial agents. Longer term/recurrent conditions maybe need broad spectrum antibiotics or combination products and the therapies should be alternated 2 weeks at a time. This greatly reduces the chance of resistance developing.

USING OPHTHALMIC ANTIBAC DRUGS IN CHILDREN

Kids often develop a sticky red eye that's caused by communally transmitted bacteria eg in school. These conditions will often resolve w/careful ocular hygiene - for example a twice daily wash w/an astringent along w/ a cotton bud to remove the discharge. If antibiotics are deemed necessary then caution is advised - don't overexpose the eye to the antibiotics and limit their repeated & chronic use.

Such childhood infections are often caused by Staphlococcus SP which is a gram +ve bacterium. Other causes include streptococcus (+) and haemophilus (-). Gram negative bacteria are also the cause of upper respiratory tract and ear infections. All of these could be rapidly responsive to broad spectrum antibiotic therapy by less so to narrow spectrum. In newborns it's important to distinguish infections from the above bacteria and more serious infections from more virulent gram positive organisms like gonococcus and chlamydia which would require more careful treatment (ophthalmia neonatorum)

CURRENTLY AVAILABLE UK ANTIBACTERIAL DRUGS
***revised laws in 2005 (SI 764-766) mean that all optometrists may sell and supply P medicines containing anti-infectives***

Three main types - broad spectrum antibiotics, narrow spectrum antibiotics and general purpose antibacterial drugs

General Purpose Diamidine Ophthalmic Antibacterials

• For mild infections of the conj and eyelids where there isn't subtantial mucopurulent discharge. These drugs belong to a class called 'amidines' which indirectly block production of DNA, mRNA and protein synthesis by interfering w/the cell's purine uptake. So the infection can't spread. These are usually bacterostatic then aren't they - slowly down the growth of bacterium as opposed to wiping it out.
• There is no evidence to support the prophylactic use of these drugs for corneal or conjunctival abrasions or other foreign body injuries. They are all P Medicines
• Propamidine 0.15% P Golden Eye drops/Brolene eye drops 10ml bottle
• Dibromopropamidine 0.15% P Golden Eye ointment/Brolene eye ointment 3.5g tubes w/lanolin (possible allergies)
• Recommended doseage = 4x a day. Medical attention should be sought if the eyelid condition doesn't show improvement within two days.

BROAD SPECTRUM OPHTHALMIC ANTIBIOTICS

These are suitable for the management of acute onset, mild and mod-severe infections of the external eye. Important that these products are applied regularly eg at least 4 times a day for drops. All the broad spectrum antibiotics are expected to show similar efficacy.


1. Chloramphenicol

• Inhibits protein synthesis in bacteria - bacteriostatic. Interferes w/assembly of amino acids into peptide chains so that the synthesis of key peptides and proteins is slowed down and the overall rate of bacterial cell division is too.
• Indicated for use to manage bacterial infections of eyelids, conjunctiva and cornea. It can be expected to be effective against the majority of bacteria causing infections of the external eye but isn't expected to show useful efficacy against gram negative pathogens like pseudomonas sp.
• Chloramphenicol 0.5% eyedrops in multidose bottles are now readily available as P Medicines in 10ml bottles eg P Optrex Infected Eyes Eye Drops, P Golden Eye Antibiotic Eyedrops. Also PoM chloramphenicol minims 0.5%. Chloramphenicol eyedrops are preserved w/phenylmercuric nitrate and P Meds include a note saying a band keratopathy could develop w/use of the preservative. It would disappear once the drops were discontinued.
• Ointments w/1% chloramphenicol are also available eg P Optrex Infected Eyes Eye Ointment, PoM Chloromycetin, PoM Chloramphenicol eye ointment. All 4g tubes.
• Recommended doseage is 5x/day initially and continued treatment should be 4x a day for 7 days. PoMs containing Chloramphenicol can be used on infants but the P Medicine eyedrops are not currently licensed for infant use.
• WARNINGS: Not intended for repeat use, some would advise caution when doing 7 days worth. Warning indicating possibility of aplastic anaemia but evidence for this is weak

2. Gentamycin PoM used in hospital eye clinics
3. Neomycin PoM indicated for styes, bleph,
4. Tetracyclines - interfere w/protein chain in different way to chloramphenicol

NARROW SPECTRUM ANTIBIOTICS

• Suitable for amangement of some acute onset, mild-moderate severity bacterial infections of the external eye ie conjunctivitis and blepharoconjunctivitis. Current UK example is Fusidic Acid. Only active against some of the more common causes of infection
• Again fusidic acid inhibits protein synthesis but at a slightly different place to chloramphenicol. In order for a protein to be assembled the mRNA needs to be repeatedly bound and unbound to specific sites on the ribosomes. An enzyme called translocase is responsible for this step and fusidic acid acts by indirectly interfering with the translocase.
• Fusidic acid is usually bacteriostatic but can become bacteriocidal w/high doses. The problem is some common causes of infection eg streptococcus pneumonia or haemophilus influenzae are less likely to show significant sensitivity to fusidic acid. Both of the above are often also assoc w/throat or ear infections.
• Available as viscous eyedrops PoM Fucithalmic contains 1% fusidic acid in a viscous solution of a 0.5% carbomer gel. Indicated for BD usage but can be applied four times a day in the first couple of days if the infection is serious enough. The twice daily regimen is especially useful for children providing that they don't have naso-pharyngeal or ear infections too. It's applied into the lower cul-de-sac like an ointment.
• Fusidic acid can be used as a chloramphenicol alternative in cases of corneal/conjunctival abrasion. Also in chronic recurrent blepharitis a patient may respond well to it along w/the appropriate hygiene measures. The drops should in that case be applied to the lid margin with a cotton bud. It can be used as an alternative to chloramphenicol or framycetin eye ointments, being switched every two weeks or so to increase the chance of an effect and reduce the chance of resistance developing.

BROAD SPECTRUM COMBINATIONS PoM
Bacitracin Zinc, Polymyxin B, Gramicidin