ocular pharmacology i,dr.kuricnchi,16.03.17
TRANSCRIPT
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OCULAR PHARMACOLOGY I
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Pharmacologic Principles• Pharmacokinetics deals with the cycle of a drug
through the body, including the absorption, distribution, metabolism, and excretion of that drug.
• To achieve a therapeutic effect, a drug must reach its site of action in sufficient concentration.
• Pharmacokinetics and dose together determine• bioavailability or concentration of the active drug at
the therapeutic site
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• Pharmacodynamics refers to the biological activity and clinical effect of drugs
• Included within the area of pharmacodynamics are the tissue receptor for the drug and the intracellular changes initiated by the binding of the active drug with the receptor.
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• Pharmacotherapeutics is the application of a drug in order to reach a given clinical endpoint,
• such as the prevention or treatment of disease
• The therapeutic dose may vary for any• patient, based on the patient's age, gender,
race, other currently prescribed medications,• and preexisting medical conditions
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• Toxicity refers to the adverse effects of either medication or environmental chemicals
• influenced by pharmacokinetics and/or pharmacodynamics
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Pharmacokinetics
• Amount administered• Drug concentration and solubility• Viscosity• Lipid solubility• pH and ionic charge• Surfactants• Reflex tearing• Tissue binding of medication
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• Topical Administration – Eyedrops• maximizes the anterior segment concentrations while
minimizing systemic toxicity.• Very little of an administered drop is retained by the eye• The amount of time that a drug remains in the tear
reservoir and tear film is• called the "residence time" of a medication. It is affected
not only by drug formulation but• also by the timing of subsequent medication, tear
production, and drainage
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• simple measures to improve ocular absorption of materials
• Patients using more than one topical ocular medication should be instructed to allow 5 minutes between drops
• Blinking also diminishes a drug's effect by activating the nasal lacrimal pump mechanism
• compressing the nasolacrimal duct with digital pressure at the medial canthus or closing the eyelids for 5 minutes after instillation of each drop.
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• a drug with poor solubility may need to be provided in a suspension.• A suspension requires agitation so that the active medication is
redistributed prior• to administrat ion. Suspensions may be more irritating to the
ocular surface than solutions
• Ointments• Another strategy for increasing the contact time of ocular
medications is the use of ointments.• Commercial oil-based ointments usually consist" of petrolatum and
mineral oil.• The mineral oil allows the ointment to melt at body temperature
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Local AdministrationPeriocular injections• Injection of medication beneath the conjunctiva or
the Tenon capsule• allows drugs to bypass the conjunctival and corneal
epithelial barriers and absorb passively down a concentrat ion gradient into the sclera and intraocular tissues
• allow medications to reach therapeutic levels behind the lens-iris diaphragm-especially useful for drugs with low lipid solubility
• helpful in delivering medication closer to the local site of action
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Periocular injections
In anterior segment inflammation or infection
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Intraocular medications• instantly delivers effective concentrations at the
target site. 2 types of intraocular injections:• intracameral injections into the anterior chamber • intravitreal injections into the vitreous cavity• Intraocular implants allow the slow release of
medication over months to years
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Systemic Administration• Drugs with higher lipid solubilities more readily
penetrate the blood- ocular barrierThe ability of systemically administered drugs to gain access to the eye is also influenced • by the degree to which they are bound to plasma
proteins. Only the unbound form can cross the blood-ocular barrier.
• bolus administration of a drug exceeds the binding capacity of plasma proteins and leads to higher intraocular drug levels than can be achieved by a slow intravenous drip
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Sustained-release oral preparations
• offer a more steady blood level of the drug,
• avoid marked peaks and valleys, and
• reduce the frequency of administration.
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Intravenous injections
• diagnostic or therapeutic• sodium fluorescein and indocyanine green, are
used for retinal angiography to diagnose retinal and choroidal disease.
• Edrophonium chloride is used intravenously in the diagnosis of myasthenia gravis.
• intravenous administration of an antibiotic is an effective way of maintaining intraocular levels in endogenous infections
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Methods of Ocular Drug Design and Delivery
Prodrugs• inert compounds that are activated by one of the
enzymatic systems within the eyeSustained-release devices and gels:• Delivery devices Devices have been developed that deliver
an adequate supply of medication at a steady-state level, thus achieving beneficial effects with fewer adverse effects.
• The gel form - thickens on contact with the tear film, maintaining therapeutic levels while decreasing the dosing to once daily.
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Collagen cornea shields – • Porcine scleral tissue is extracted and molded into
contact lens-like shields that are useful as a delivery system to prolong the contact between a drug and the cornea.
• Drugs can be incorporated into the collagen matrix during the manufacturing process, or absorbed into the shield during rehydration, or applied topically while the shield is in the eye.
• the drug is released gradually into the tear film, and high concentrations are maintained on the corneal surface and in the conjunctival cul-de-sac.
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• Liposomes are synthetic lipid microspheres that serve as multipurpose vehicles for the topical delivery of drugs, genetic material, and cosmetics
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Antibiotics
Penicillins – bactericidal, gram positive cocci, poor ocular penetration on systemic administration, freshly prepared topical penicillin in ophthalmia neonatorum
Cephalosporins – intravitreal cephazolin & ceftriaxone
Aminoglycosides – intravitreal amicacin, topical tobrmycin, gentamycin
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Tetracyclines – broad spectrum, doxycycline good occular penetration
Macrolides – trachoma, toxoplasmosis, lyme disease
Vancomycin – bactericidal, gram positive, intravitreal
Fluroquinolones – topical drops
Chloramphenicol – lid infections
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Antibiotics• Principal Antibiotic Agents
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Combination Ocular Anti-Inflammatory and Antibiotic Agents
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AntifungalPolyene antibiotics – Amphotericin B: Fungal corneal ulcer Fungal endophthalmitis (intravitreal)Nystatin – Candida albicansNatamycin (5%)– filamentous fungi, Candida albicans
Imidazoles – also acanthamoeba, miconazole, ketoconazole
Triazoles – fluconazole, itraconazole
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Antifungal Agents
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Antiviral
Treat herpes infections
Pyrimidine derivatives – IDU topical
Purine derivatives – Acyclovir: 3% oint, Oral (400mg), EB virus, CMV.Gancyclovir: intravitreal implants
Foscarnet – herpes, CMV
Zidovudine - CMV
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Antiviral Agents
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• What are the different modes of ophthalmic drug delivery?
• What are the advantages of eye drops/ eye ointments?
• What are the indications and advantages of periocular injections?
• Enumerate the commonly used anti-biotics/anti fungals/anti virals in ophthalmology?
• How will you avoid systemic absorption of topically applied medications?
• What advice would you give to a patient regarding administration of any eye drops?