Opb654- Antiinfectives

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5 Antibacterial Drug Mechanisms

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-Affect Cell Wall Structure
-Affect Cell Membrane
-Affect DNA Synthesis
-Affect Protein Synthesis
-Affect Intermediate Metabolism

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Penicillin (Beta-lactam)

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-antibacterial drug-> Inhibit cell wall synthesis
-Effective against gram +ve
-Acquired resistance (drug deactivating enzymes produced by bacteria)
-Allergic reaction problem
-Alter normal microflora of body
-25+ types (pneumonia, STDs, meningitis, tissue infections, UTIs, Bronchitis, Pharyngitis

-CAUTION OF HYPERSENSITIVITY REACTIONS-> CROSS SENSITIVITY

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Cephalosporins (Beta-lactam)

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-antibacterial drug-> Inhibit cell wall synthesis
-Similar structure to penicillins (action and resistance)
-Good against gram +ve bacteria, modest against gram –ve
-Broad spectrum, bactericidal, poor oral activity-> IV
-First, second, third generation compounds
-Septicaemia, pneumonia, meningitis, UTI, Sinusitis

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Beta-Lactam (penicillin and cephalosporin) Action

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Interferes with cross-linking of peptide chain (final step in bacterial cell wall formation)
Peptide chains give cells wall strength

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Polymixin B

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-Antibacterial drug-> affects cell membrane
-Cationic surfactant that interacts with cell membranes, increases permeability and causes cell leakage
-Effective against some gram –ve bacteria, some pseudomonas strains
-Popular for Tx of infections of the conjunctiva and lids
Risks: Neurotoxicity, nephrotoxicity

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Gramicidin

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-Antibacterial drug-> affects cell membrane
-Ineffective against gram –ve bacteria

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Propamidine (Brolene)

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-Action: Divalent cationic surfactant, affects cell membranes
-Activity: Active against Stap aureus, Streptococcus pyogenes, not active against Pseudomonas, some antifungal properties, action not inhibited by pus
-Use: Minor conjunctivitis blepharitis, acanthamoeba
-Adverse: Sensitization
-Pack: Eye drops 0.1%, 10mL bottle, ointment
-Dose: 2-3 times daily for ~1 week
-Available over the counter without Rx, S2

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Drugs Affecting Intermediate Metabolism Action

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Synthesis of folic acid in bacterial cells only (not human)
-Folate required for DNA synthesis -> humans obtain from diet
-Sulfonamides inhibit folic acid synthesis-> contains sulfanilamide -> competes with p- aminobenzoic acid (PABA) for the enzyme involved in folate synthesis
(diagram in notes)

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Sulfacetamide (Bleph-10 Allergan)

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-Action: Sulfonamide, bacteriostatic
-Use: Conjunctivitis, trachoma, generally replaced by other agents, superseded
-Adverse: Allergic reactions common
-Pack: eye drops 10%, 15mL bottle
-Dose: every 2-3 hours during the day for ~1 week
-Available OTC
-S3, ask about sulphur allergies
-Irritant, avoid

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Drugs Affecting Bacterial Protein Synthesis Action

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-Takes place in ribosomes, differ eukaryotes and prokaryotes, sub-units in bacterial cells are 30S and 50S, human cells are 40S and 60S
-Some can interact with human mitochondrial ribosomes causing group toxic effects

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Chloramphenical (Chloromycetin, Clorsig)

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-Antibacterial drug-> affects bacterial protein synthesis
-Bind to 50S
-Action: Broad Spectrum (corynebacterium, E.coli, Haemophilus, streptoccoi), not effective against Pseudomonas, low toxicity (limits use), binds to bacterial ribosomes, inhibits protein synthesis
-Use: Prescribed for topical therapy, effective against gram +ve and –ve bacteria, chlamydia, mycoplasma, rickettsia and spirochetes, rarely used systemically (< resistance)
-Adverse: Toxicity, Anaemia, Optic neuropathy, bone marrow depression, fear of possible aplastic anaemia (may be fatal) limits use in some countries (USA), low systemic absorption, gray baby syndrome (child inability to excrete drug⇒ only in inappropriate dosing)
-Pack: eye drops 0.5%, 10mL bottle, fridge
minims, 20 per box
ointment 1%, 4g
-Dose: eye dorps 1-2 drops every 2-6 hrs for 2-3 days then reduce frequency
-S3, PBS

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Tetracyclines (Optycin, Latycin)

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-Antibacterial drug-> affects bacterial protein synthesis
-Bind to 30S
-Action: Broadest spectrum (gram +ve and –ve), bacteriostatic, resistance develops slowly, not effective against pseudomonas, poor corneal penetration
-Use: Ocular infections, chlamydial infection
-Adverse: Few side-effects topically, local reactions in isolated cases, oral tetracyclines can permanently yellow teeth and slow bone growth in children
-Pack: ointment 1%, 5g now compound pharmacy product (largely superseded by oral azithromycin for trachoma)
-Dose: Apply into lower conjunctival sac every 2 hrs, treatment duration depends on severity of condition

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Macrolides

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-Antibacterial drug-> affects bacterial protein synthesis
-Alternative to penicillins, similar effect
-Treat pneumonia, genital infections, legionnaires disease, chlamydial infections
-Resistant organisms
-Ear damage, GI disturbance
-Azithromycin, Erythromycin

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Azithromycin

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-Antibacterial drug-> affects bacterial protein synthesis
-Bind to 50S
-Action: Broad spectrum macrolid antibiotic with anti-inflammatory properties, inhibits protein synthesis, inhibits macrophage activity
-Use: Ocular infections, chlamydial infections, toxoplasma, STDs, malaria, respiratory infections
-Adverse: GI, HA, bitter taste, hypersensitivity
-Pack: 1.5% drops, compound pharmacy product (superseded by azithromycin)
-Dose: apply daily, treatment duration depends on severity of infection, long half life (68hrs)⇒ one high oral dose Tx, Oral 1g for adults, 20mg/kg for children

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Erythromycin

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-Antibacterial drug-> affects bacterial protein synthesis
-Bind to 50S

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Aminoglycosides Action and Examples

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-Antibacterial drug-> affects bacterial protein synthesis
-Bind to 30S unit of bacterial ribosome preventing protein synthesis
-Active against aerobic gram –ve and some gram +ve bacteria
-Rapid action, bacrtericidal
-If oral can cause nephrotoxicity (kidney damage) and otoxicity (ear damage)
-Not for systemic use
-Streptomycin, Framycetin, Gentamicin, Neomycin, Tobramycin

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Framycetin

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-Antibacterial drug-> affects bacterial protein synthesis
-Aminoglycoside

-Action: Isomer of neomycin, broad spectrum effective against gram-positive and –negative bacteria
-Use: Conjunctivitis, blepharitis, abrasions, styes, topical application, poor ocular penetrance
-Adverse: Kidney, ears affected, contact allergies
-Pack: eye drops 0.5%, 8mL bottle
-Dose: eye drops 2 drops every 1-2 hours decreasing to 3/times per day

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Gentamicin

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-Antibacterial drug-> affects bacterial protein synthesis
-Aminoglycoside

-Action: Broad Spectrum antibiotic, some resistant gram-positive organisms, bactericidal, poor ocular penetration when applied topically
-Use: Treatment of external eye and adnexal infection (bacterial conjunctivitis), prophylaxis following surgery or trauma (abrasions), suspected pseudomonas
-Adverse: Transient irritation, damage ears, kidneys, sensitisation reduced
-Pack: 0.3% 5mL bottle & minums
-Dose: 1-2 drops q4h, if severe 2 drops hourly
-1.3% fortified for bacterial keratitis

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Neomycin

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-Antibacterial drug-> affects bacterial protein synthesis
-Aminoglycoside

-Action: Broad spectrum antibiotic, some resistance from gram-positive organisms, bactericidal, not effective against pseudomonas
-Use: Bacterial infection, rarely used systemically, used prophylactically with steroid after surgery or for inflammation cover
-Adverse: ears, kidneys affected, hypersensitivity
-Pack: 0.5% minims, Neosporin drops, ointment, compound product

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Tobramycin

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-Antibacterial drug-> affects bacterial protein synthesis
-Aminoglycoside

-Action: Broad Spectrum, some resitance from gram +ve organisms, bactericidal
-Use: Treatment of external eye and adnexal infection (bacterial conjunctivitis), prophylaxis following ocular surgery or surface trauma, suspected pseudomonas
-Adverse: Ocular and systemic toxicity, superinfection ⇒ retarded corneal wound healing
-Pack: eye drops 0.3%, 5mL bottle
ointment 0.3%, 3.5g
-Dose: eye drops 1-2 drops every 4 hours
-Severe infection: 2 drops hourly until improvement
-1.3% fortified for bacterial keratitis

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Drugs Affecting Bacterial DNA Synthesis

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-New generation quinolones and fluorinated quinolones (fluoroquinolones)
-Broad Spectrum, little resistance
-Use only for microbial keratitis, extremely severe conjunctivitis
-Active against Pseudomonas & Staphylococcus
-Cause: Kidney stones, headache, nausea
-Not for use in children under 8yrs (cartilage damage)

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Fluoroquinolones

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-Antibacterial drug-> affects bacterial DNA synthesis
-Newest group, major area for new drugs
-Inhibit DNA synthesis during bacterial replication, unique mechanism means cross-resistance with other antibiotics less likely
-Well absorbed orally
-Inhibit DNA-gyrase, preventing supercoiling of DNA molecule
-Ciprofloxacin, Ofloxacin

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Ciprofloxacin (Ciloxan, Ciloquin)

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-Antibacterial drug-> affects bacterial DNA synthesis
-Action: Active against broad spectrum of gram+ve and –ve ocular pathogens
-Use: Bacterial keratitis, severe bacterial conjunctivitis, effective, safe, limit use to prevent resistance
-Adverse: Super infection, discomfort, burning, itching, hyperaemia, precipitates on corneal ulcers
-Pack: 0.3% 5mL bottle
-Dose:
-Corneal Ulcers= day 1: 2 drops every 15min for 6 hours then every 30min, Day 2: 2 drops every hour, Days 3-14: 2 drops every 4 hours
-Bacterial Conjunctivitis = Days 1-2: 1 drop every 2 hrs while awake, days 3-7: 1 drop every 4hrs while awake

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Ofloxacin (Ocuflox)

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-Antibacterial drug-> affects bacterial DNA synthesis
-Action: Active against broad spectrum of gram+ve and –ve ocular pathogens
-Use: Bacterial keratitis, severe bacterial conjunctivitis
-Adverse: Super infection, transient eye pain, hyperaemia,  risk of corneal perforation
-Pack: 0.3% 5mL bottle
-Dose:
-Bacterial conjunctivitis= Days 1-2: 1 drop every 4hrs while awake, Days 3-10: 1 drop every 6hrs
-Corneal Ulcers= Day 1: 2 drops every 15min for 6hrs then every 30min, Day 2: 2 drops every hour, Days 3-14: 2 drops every 4hrs

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Antibacterial use for:
BACTERIAL CONJUNCTIVITIS

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-Resolves in 10-14 days
-Staphylococcus aureus, staph. Epidermidis, Streptococcus pneumonia, hemophilus influenza
-Microbiological investigations (swabs) rarely needed
-Hygiene
-Topical antibiotics shorten course
-Broad spectrum antibiotic (gram+ive and –ve)
-4 times/day for 1 week

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Antibacterial use for:
BACTERIAL KERATITIS

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-Sight threatening
-CL wear and pseudomonas
-Microbial work up
-Broad spectrum antibiotic (immediately)
-Monotherapy with fluoroquinolone or dual therapy with fortified cephalosporin and aminoglycoside
-Drops hourly
-Ineffective corneal ulcers: Day1: 2 drops every 15min for 6hrs, then 30min, Day 2: 2 drops every hr, Days 3-14: 2 drops every 4hrs

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Antibacterial use for:
CORNEAL ABRASION

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-Heals spontaneously within few days
-Ice packs and oral analgesics for pain
-Subepithelial lesions referred immediately
-Broad-spectrum topical antibiotic used 4 times per day until epithelial healing

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Antibacterial use for:
ANTERIOR BLEPHARITIS

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-Anterior eye lid margin
-Chronic recurrent nature
-Lid hygiene, tear supplements
-Weak corticosteroids and antibiotics (chloramphenicol, erythromycin, gentamicin) ⇒ short term

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Antibacterial use for:
POSTERIOR BLEPHARITIS

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-Meibomian gland dysfunction
-Chronic recurrent nature
-As above treatment
-Systemic tetracyclines (doxycycline 100mg per day for 1 mth, then 50mg for 2 mths)
-Mild topical steroid (FML) and topical antibiotic 1-2 weeks to reduce inflammation and bacterial load
-Optimel antibacterial honey

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Antibacterial use for:
CHLAMYDIAL CONJUNCTIVITIS

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-Refer
-Oral doxycycline 100mg per day for 10-14 days
-one or two 1gm doses of azithromycin
-topical treatment ineffective

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Antibacterial use for:
DACRYOCYSTITIS

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-Bacterial or fungal infection of lacrimal sac and tear drainage system
-Oral broad-spectrum antibiotics
-Refer for aspiration if painful, surgical reconstruction

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Antibacterial use for:
GONOCOCCAL KERATOCONJUNCTIVITIS

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-Acute bilateral sight threatening disease caused by gram-ve diplococcus infection, Neisseria gonorrhoea ⇒ corneal perforation
-Lytic Enzymes in mucopurulent discharge must be washed away
-Systemic infection requiring systemic antibiotics
-Penecillin, 1gm ceftriaxone intramuscularly daily for 5 days, oral doxycycline, topical gentamycin 1.3% hourly

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Antibacterial use for:
HORDEOLUM INTERNAL/ EXTERNAL

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-Abscess of sebaceous gland
-Internal (acute staph infection of meibomian gland)
-External (acute staph infection of lash follicle and zeiss or moll gland)
-Resolve spontaneously
-Warm compresses, lid hygiene
-Broad-spectrum antibiotic 1 week course (external)
-1 week course of oral antibiotic if sig. cellulitis
-Epilation or curettage may assist drainage

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Antibacterial use for:
PRESEPTAL CELLULITIS

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-Infection of subcutaneous eyelid tissue anterior to orbital septum
-Requires urgent systemic treatment
-Haemophilus influenza, streptococcus pneumonia cause?
-Oral antibiotics for ~10days ⇒ penicillin, cephalosporin
-IV application may be required in children or if oral response does not occur

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Antibacterial use for:
ROSACEA KERATITIS

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-Inflammatory skin condition
-Butterfly rash of cheeks and nose
-Posterior blepharitis, corneal involvement
-Oral tetracycline(doxycycline 100mg/day for 1mth, 50mg/day for 2mths), erythromycin, or azithromycin
-Tear supplements and weak topical steroids helpful