Sunday 11 January 2009

Other Anti-Infectives & Their Uses

There are a variety of ocular and peri-ocular infections that require use of antibacterials other than the ones outlined in the last post. For example chlamydia and viral, fungal or protozoan infections. Some of these are monitored by GPs but if the cornea is involved the ophthalmologist will probably be responsible for treating it.

DISINFECTANTS FOR OCULAR USE

Iodine is a general purpose disinfectant which was widely used before the introduction of other topical anti-infective drugs. It is still used today in a specially prepared form - povidone iodine PoM HP Betadine - to routinely cleanse the eyelid and periocular skin prior to surgery. It damages the phospholipid membranes of organisms inc. all microbes and thus exerts a disinfectant effect. As the product is bacteriocidal further spread of infection should be prevented.

CHLAMYDIAL EYE INFECTIONS AND THEIR TREATMENT

Chlamydia is usually an STD but can be assoc w/some forms of respiratory tract disease and the causative agent of trachoma, a major cause of blindness. The infection of the conj causes inclusion conjunctivitis characterised by a florid follicular reaction. Management is best done at an STD clinic. Treatment options include
  • PoM Aureomycin was once available as a topical chlortetracycline ointment but could still be available from a hospital pharmacy. This is a protein synthesis inhibitor that is effective on chlamydia. Treatment should be QDS over a period of 2 to 4 weeks usually along w/systemic tetracycline. Not recommended for use in children and eyelid photosensitivity reactions may occur.
  • Topical erythromycin ointment. This is another protein synthesis inhibitor that's active on chlamydia, classified as a macrolide antibiotic. It's not marketed in the UK but a pharmacy prepared or imported ointment can be used. Treatment is again QDS for 2-4 weeks w/oral erythromycin or tetracyclines.
  • Oral tetracyclines or macrolides. Standard treatment for chlamydial infections requires the use of systemic antibiotics. Tetracyclines include doxycycline (PoM Vibramycin) or minocycline (PoM Minocin) while macrolides include erythromycin (PoM Ilosone) or azithromycin (PoM Zithromax). Treatment is BD for 2-4 weeks or a single mega dose of azithromycin. There are many drug-drug interactions to be considered simply because the macrolide antibiotics can interfere with the biotransformation of many other drugs.
ACNE, ROSACEA AND THE EYE

Patients w/acne or rosacea are more likely to present with blepharitis or blepharoconjunctivitis. The causative agent of acne is propionobacterium acnes and is susceptible to a range of antibiotics.
  • Topical (skin) benzoyl peroxide. This chemical decomposes slowly to give active oxygen radicals that have general antibacterial/antiseptic actions. In addition the chemical acts as a drying agent and a keratolytic action to promote keratin removal. Used as topical lotions or gels from once daily to QDS. Eg GSL Acnecide, GSL Nericur, GSL panoxyl. Contact with eyes and mucous membranes should be avoided.
  • Topical (skin) salicyclic acid. Has both antibacterial and keratolytic properties. Used as a topical lotion - GSL Acnisal.
  • Topical (skin) metronidazole. Binds to protein and is bacteriostatic. General use for acne/rosacea as a topical gel - PoM Rozex.
  • Topical or oral erythromycin - a macrolide antibiotic that blocks protein synthesis and is bacteriostatic. Used on its own as a topical lotion or gel (eg PoM Eryacne) or in combination with benzoyl peroxide (eg PoM Benzamycin gel) or zinc acetate (PoM Deteclo). Also used orally for chronic cases - PoM Erymax or PoM Tiloryth.
  • Topical or oral tetracyclines - several different drugs are available, all being bacteriostatic protein synthesase inhibitors.
  • Topical tretinoin - essentially an irritant that stimulates vitamin A dependent division of sub-epidermal cells and in doing so acts as a keratolytic - promoting removal of superficial/overlying keratin plugs. Used as a topical skin product at 0.025% concentration in lotions, gels or creams. Avoid eyes, mouth, mucous membranes.
  • Topical isotretinoin/topical skin adapalene - similar to tretinoin above
PSORIASIS

A chronic skin condition often assoc w/acne-like conditions and for which similar treatment options are available eg antiseptics such as povidone-iodine, salicyclic acid or coal tar lotions. Can also be treated w/topical retinoids like tazaratolene (PoM Zorac gel) or oral retinoids such as acitretinin (PoM Neotigason). An alternative to retinoids is to use topical vitamin D analogues eg tacalcitol (PoM Curatoderm gel) or calcipotril (PoM Dovonex cream).

MANAGEMENT OF VIRAL INFECTIONS OF THE EYE

Certain viral infections of the eye can be managed easily and with a favourable outcome providing a prompt and correct diagnosis is made and the appropriate referral is arranged so that therapy is instigated and adhered to. In considering viral infections the differential diagnosis is very important. Things to consider
  • HSV - acute onset, initial symptoms include foreign body sensation, itching, tingling or moderate jabbing pain. Objective early signs for HSV corneal positive staining w/flu or rose b may be punctate initially (especially in infant cases) but these small foci soon coalesce to form either linear or branched patterns. At a later stage if significant epithelial erosion has occurred (ie there were substantial dendrites) then infiltrating stromal keratitis can develop.
  • EKC - acute onset, initial symptoms include slight irritation and itching accompanied by profuse lacrimation. Objectively there could be superficial punctate keratitis or the appearance of subepithelial discrete opacities that are non-staining. At a later stage the condition should resolve to a quiet eye despite residual epithelial or subepithelial deposits.
  • HZ - subacute onset, initial symptoms include itching maybe assoc w/periocular skin + eyelid tenderness as well as involuntary twitching. Objectively: early onset pseudo-dendritic (feathery) corneal patterns may be evident that may stain positively although not very well w/flu or rose bengal. Such pseudodendrites may be mucous plaques that change position/size/shape on the cornea on a daily basis. The removal of these plaques will be painful and then the area will stain well w/rose bengal. Such signs are usually preceded by pain especially for the eyelid skin or peri-ocular facial skin and eruptions/blisters may develop on the skin. In later stages HZ may resemble HSV.
MANAGEMENT OF EKC
  • EKC is not generally indicated for treatment with antiviral drugs. Management includes use of eye baths and decongestants like naphazoline 0.01% as needed to reduce lacrimation and promote ocular comfort. Also possibly a mild to moderate corticosteroid eg betamethasone to reduce the further development of corneal epithelial infiltrates. Such therapy should be q6hrs and should be tapered after 7 days. General hygiene to stop cross-infection is important. The total treatment period is not more than two weeks.
MEASUREMENT OF HERPES SIMPLEX INFECTIONS (HSV)
  • Prompt management w/antiviral drugs and care should be taken to prevent infection of the other eye if the condition is unilateral (it often is). Ophthalmic antivirals work by stopping the virus replicating DNA. They are generally pro-drugs that need to be biotransformed into their active form by infected epithelial cells.
  • Regardless of the severity of presenting signs treatment can be commenced with aciclovir 3% ophthlamic ointment PoM Zovirax 4.5g tube at q2hr or q3hr especially for the first 24hrs at which time the regimen reduced to q4hr. Such a treatment should be maintained for seven days only w/examinations at days 1, 3 & 7. Again it's important that therapy be continued for a few days after resolution is clearly underway so if everything looks good after seven days another 3-5 would be good.
  • Stuff like zovirax cold sore cream obvs isnt for the eyes but could be used if the eye infections are assoc w/mouth ulcers.
  • If the HSV infection is severe at presentation systemic administration of antiviral drugs such as aciclovir PoM Zovirax tablets is needed. In addition the recovery from the HSV infection can be acheived by removing the virus-infected corneal epithelial cells before beginning antiviral therapy ie debridement under intense topical anaethesia w/lots of tetracaine 0.5% or cocaine 4% eye drops. Epithelial cell resurfacing then needs to be carefully reassessed on follow-up visits.
  • If the infection is severe and the corneal stroma is involved w/deep lesions careful use of strong ocular corticosteroids eg PoM Maxidex or Pred Forte providing the patient can be seen on a daily basis to ensure that there's no further progression of the dendritic/infiltrating ulcers. Mydriatic cycloplegic use is also recommended to offset the iritis and flare.
MANAGEMENT OF HZ INFECTIONS

Two options. Often hard to differentiate between a HZ and a HSV so treatment may be a bit wrong initially!

  • For milder cases of HZ affecting the cornea where it's fairly certain that HSV isn't present it should be treated as an inflammatory condition w/PoM Maxidex, PoM Pred Forte or PoM Betnesol eyedrops qds perhaps w/antibiotic eyedrops after removal of the epithelial plaques by rubbing. Follow-up should be every 24hr to ensure that further infection does not develop. This topical treatment should best be accompanied by oral antivirals as zoster (aka shingles) is usually a systemic infection. PoM Zovirax 3-5x200mg/day for 5-10 days. Topical antivirals a la HSV are needed if further dendrites appear.
  • In more severe cases w/eyelid vesicles/pustules/general mucopurulent discharge and general encrustation or if dendrites keep on developing, treat as if there were HSV present with topical acyclovir. Careful steroid therapy is appropriate as long as the px can been seen every 24 to 48 hours until the condition is clearly resolving. The corticosteroid needs to control the stromal involvement but without worsening the condition by delaying re-epithelialisation or facilitating a secondary infection. Mydriatic cycloplegic treatment is also essential to offset the iritis and flare. Systemic corticosteroids PoM Prednisolone may be needed. Cold compresses and adjunct use of ocular lubricants may provide much needed symptomatic relief.
I'm going to start a new post now cos this is fucking huge

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