- For severe, ulcerating infections of the cornea. Certain antibiotics can be prepared as special concentrated solutions to manage the bacterial infection with an antibiotic w/proven efficacy against the bacterial strain responsible for the infection. This can only be done providing laboratory culture tests have been performed w/isolates from the infected eye. It's important that the therapy be very intensive and be administered to a hospitalised patient eg q15 to q30 minutes for 24h, at q1h q2h for the next day or so...
- These are only made in a hospital pharmacy as and when needed. Short shelf lifes and unpreserved.
- Some of the more commonly used fortified antibiotics are the aminoglycosides as fortified 1% gentamycin or neomycin. Fortified polymyxin B solutions may be used for indentified gram -ve infections. Fortified cephalosporin eyedrops can be used for gram positive ulcers.
Any bacterial or viral infection that fails to respond to therapy may be the result of an opportunistic infection w/fungi or even protozoa and required the use of a different type of fortified antibiotic. Few specific anti-fungal drugs exist and even fewer are specifically indicated for use in ocular infections caused by fungi and protozoa let alone for topical ocular use.
Fungal infections are normally already severe by the time a diagnosis is made so they are managed by a specialist. Many are initially diagnosed as viral infections because the acute/sub acute red eye, lacrimation, little or no discharge and marked foreign body sensation and photophobia suggest HSV. Even punctate staining and dendrites have been reported. Buuuut if linear railway-track like infiltrates are present that may be a clue that the infection is fungal/protozoan.
Suspect a fungal/protozoan infection if there's a failure of the red eye to show a positive response to antibacterial or antiviral therapy over 3 to 4 weeks. As a general rule anything like this should be assumed to be a fungal or protozoan infection unless proven otherwise - appropriate measures should be taken. Unusually high levels of pain (more than the level of 'red eye' would suggest) are another indicator. The reason for this is mayhaps the way the infective organism associates with the corneal nerves. The diagnosis will be made in part on the detection of fungal hyphae in scrapings from the ocular surface or maybe the patient's contact lens case that they have let rot into ming. NB Treatment of fungal infections can only be done via a major hospital centre as the drugs used need to be prepared by a specialist pharmacy. The therapies include:
- Topical Antifungal Drugs eg Natamycin 3% or 5% ophthalmic suspension. This suspension can be prepared in a hospital pharmacy w/a power and a suitable vehicle for the powder. There's a US commercial product that they may be able to use too, NATACYN. If prepared it needs to be stored in a refrigerator at 4 degrees C. Treatment for fungal keratitis should be q1hr for 3 to 4 days, day and night. Thereafter the dosing can be reduced to q2hr or q3hr. A less intensive regimen could be used if it's only fungal keratitis or fungal blepharitis. If there isn't any improvement within 7 to 10 days then the causative organism is not likely to be a susceptible fungus. The treatment period is normally 14 to 28 days if responsive but more established cases may require weeks.
- Imidazole Antifungal Drugs eg econazole and ketoconazole can be prepared in a hospital pharmacy also. They have a broad spectrum of activity against various fungi. They work generally by altering protein synthesis and so are fungistatic. The regimen is the same as Natamycin, again w/established cases taking several weeks. They can also be used orally.
- Polyene Antibiotics eg amphotericin B. This is primarily marketed as an antifungal for i.v. use (PoM Fungizone or PoMHP Amphocil) but the powder can be reconstituted in sterile water and made into eyedrops that have to be protected from light and kept in the fridge. The drug binds to sterols in cell membranes and can exert a fungistatic or fungicidal action depending on intensity of use. It's reserved for case where the initial condition is already severe or a condition which hasn't responded well to Imidazole or Natamycin. 0.1% concentration is used because the drug is very toxic. Regimen is every 30 mins or every hour for 2-3 days then reducing the frequency over the course of 7-10 days
The example here is the mighty Acanthameoba. There isn't really a fixed treatment for these infections. All represent last stage measures to try and save a cornea and even the entire eye and may need to be continuted for even 6 to 9 months. Following diagnosis w/history, scrapings etc. Hospital-based therapies have included
- First a topical disinfectant like 0.2% chlorhexidine q1hr for a few days then down to q2hr or q4hr if the infection is under control
- then add concurrent intensive therapy w/a broad spec antibiotic like gentamycin 1% eye drops q2hr. The fortified gentamycin will be HP. The antibacterial therapy is to aid the sterilization of the ocular surface and this should reduce any possible replication of the ameobae (they feed on bacteria). In later stages a broad spectrum combo antibac therapy like Neosporin eyedrops may be used instead on a similar intensive regimen
- Use an oral anti-infective like ketaconazole 200-400mg (PoM Nizoral). This can be used concurrently with the disinfectant eyedrops since this antifungal has some effect on protozoan plasma membranes as well and can be protozoocial. Again this is HP. These sorts of drugs are far less effective against acanthameoba cysts.
- An adjunct corticosteroid therapy is essential if scarring of the corneal tissue is to be kept to a minimum. At some point after initial therapy the decision to start using corticosteroids has to be made. Generally they haven't been started until at least 4 days after commencement of the intial treatment. When used it's PoM Maxidex or PoM Pred Forte @ q6hrs.
- Adjunct therapies should also include cycloplegics and narcotic analgesics AND oral antifungal drugs if the ocular infection is associated w/skin or mucous membrane infections.
When certain inflammatory diseases of the eye there are special uses of cycloplegic-mydriatic drugs. These uses are para-therapeutic and a substantial extension of the use of these drugs for diagnostic purposes. Homatropine and Atropine are the standard cycloplegics for this use but cyclopentolate can still be used. In such uses the instillation of the cycloplegic is repeated at an interval and duration appropriate for the severity of the inflammation and associated complications eg posterior synaechiae. A single use might be advocated to reduce the risk of development of iris adhesions, BDS use might be routine for recurrent iritis, while more frequent and prolonged use might be appropriate for substantial intraocular inflammation when administered concurrently w/anti-inflammatory drugs.
- Used as PROPHYLACTIC MEASURE to reduce chance of posterior synechiae
- Used as SUPPORTIVE MEASURE - to promote px comfort
- as a MANAGEMENT OPTION to break pos. synechiae - you can just keep piling the drops in until they break!
No comments:
Post a Comment