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Ocular Pharmacology > Pharmacology > Flashcards

Pharmacology Flashcards

1
Q

Different types of drug barriers relating to eyes

A
  • Tear film
    • basal tear formation 0.5-2.2ul/min
    • Layers: lipid, aqueous, mucin
    • Thickness: 7 microns
    • 10-30uL max surface volume vs 35-56uL gtt
  • Cornea-
    • epithelium thick in diabetes/ thin in keratoconus
    • Window of access to the aqueous
  • Conjunctiva + sclera-
    • facilitate <20% of drug passage to iris and cilliary body
  • Iris
    • lypophayllic pigment is colour sensitive(darker eyes require stronger dugs
  • Anterior chamber aqueous humor-200ul recycled every 50min
  • Crystalline lens- anterior epithelium is most metabolically active part of the lens
  • Cilliary body- primary drug metabolism site
  • Vitreous
  • Blood rerina barrier
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2
Q

What is the difference between 1st and zero order kinetics

A
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3
Q

Definition of pharmacology

A

Biological science of the preparation, actions and properties of
drugs in living organisms

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4
Q

What is the lock and key model in pharmacology?

A

A drug has affinity for
only one unique receptor

Most drugs are not perfectly selective, resulting in various side effects

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5
Q

Definition of intrinsic activity

A

Capacity to produce (vs inhibit) a biological effect

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6
Q

Definition of Allostery

A

A stereospecific phenomenon whereby a bound ligand
influences specificity of a second site

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7
Q

Define EC50

A

‘effective’ concentration in 50% of subjects

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8
Q

Define ED50

A

‘effective’ dose in 50% of subjects

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9
Q

Define IC50

A

‘inhibitory’ concentration in 50% of subjects

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10
Q

Define hypersensitivity

A

Result of chronic antagonism

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11
Q

Define partial agonist

A
  • low intrinsic activity with potency and affinity within therapeutic range, reduced
    dependency and withdrawal effects
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12
Q

Define pharmacodynamics

A

Drugs effect on body

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13
Q

Define pharmacokinetics

A

Body’s effect of drug

Pharmacokinetics (ADME)

  • Absorption influenced by:
    • Fast pass metabolism
    • Barriers - decree of vascularity at the site of administration
    • Patient age, gender, weight, pregnancy, health
  • Distribution
    • Volume of distribution (Vd) = dose/[drug in plasma]
    • Influenced by route of administration
  • Metabolism
    • Reflected by drug half life
    • Influenced by health of metabolizing organs
  • Elimination
    • Routes include fecal, urinary, sweat, respiration and saliva
    • Drug clearance = [drug volume eliminated]/time
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14
Q

Define polypharmacy

A

Taking 5 or more medications daily

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15
Q

Define posology

A

Science of drug dosing

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16
Q

Define selectivity

A

ability to produce a desired effect versus adverse effect

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17
Q

Define specificity

A

ability to act at a specific receptor

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18
Q

Define tachyphylaxis

A

rapidly decreasing therapeutic response

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19
Q

Define bioavailability

A

amount of active drug reaching target tissue

20
Q

Lethal index

Therapeutic index

A

Lethal: LD50:ED50

Therapeutic: TD50:ED50

21
Q

Drug classification by use

A
  • Supplemental: e.g. insulin
  • Supportive: e.g. glucose
  • Prophylactic: e.g. low dose aspirin
  • Symptomatic: e.g. diphenhydramine(anti allergy)
  • Diagnostic: e.g. fluorescein
  • Therapeutic: e.g. methotrexate(chemo)
22
Q

Ligand gated ion channels

A

A group of transmembrane ion-channel proteins which open to allow ions such as Na⁺, K⁺, Ca²⁺, and/or Cl⁻ to pass through the membrane in response to the binding of a chemical messenger

e.g. GABAA, AChN, glutamate

23
Q

G-protein coupled receptors

A

Located in the cell membrane that binds extracellular substances and transmits signals from these substances to an intracellular molecule called a G protein

eg AChM and rhodopsin

Some examples of GPCRs include beta-adrenergic receptors, which bind epinephrine; prostaglandin E2 receptors, which bind inflammatory substances called prostaglandins; and rhodopsin, which contains a photoreactive chemical called retinal that responds to light signals received by rod cells in the eye

This is the MOST COMMON receptor type targeted by ophthalmic drugs

24
Q

Enzymatic receptors

A

An enzyme-linked receptor, also known as a catalytic receptor, is a transmembrane receptor, where the binding of an extracellular ligand causes enzymatic activity on the intracellular side

eg Insulin, epidermal growth factor

25
Q

Calcium release receptors

A

Calcium-induced calcium release (CICR) describes a biological process whereby calcium is able to activate calcium release from intracellular Ca²⁺ stores

e.g. calcineurin, nitric oxide synthase, cytokines

26
Q

Intracellular or nuclear receptors

A

Intracellular receptors are receptors located inside the cell rather than on its cell membrane. Classic hormones that use intracellular receptors include thyroid and steroid hormones.

27
Q

Agonists mode of action

A
  • Direct: e.g. Isoproterenol(Beta blocker)
  • Indirect: e.g. Cocaine
    • a substance that enhances the release or action of an endogenous neurotransmitter but has no specific agonist activity at the neurotransmitter receptor itself
  • Mixed: e.g. Tamoxifen
    • a drug which under some conditions behaves as an agonist while under other conditions, behaves as an antagonist.
  • Inverse: e.g. Emedastine
    • a drug that binds to the same receptor as an agonist but induces a pharmacological response opposite to that of the agonist.
  • Partial: e.g. Buspirone
    • drugs that bind to and activate a given receptor, but have only partial efficacy at the receptor relative to a full agonist

Inverse agonist can produce a lower response than antagonist

28
Q

Antagonists

A
  • Binds reversibly and ireversibly
  • Binding site selectivity:
    • Competitive (compete for the same binding site used by an endogenous agonist)
    • Non-competitive (allosteric)- implies that the antagonist, while still opposing the action of the agonist, does so without competing with it for the binding site. The agonist may bind there all it wants; it will still do no good. Unaffected by agonist dose. Binds to site distinct from agonist binding site, causes changes in agonist binding site
    • Uncompetitive (allosteric binding in presence of substrate slows ligand dissociation and response rate) require agonist. Locks receptor with agonist attached so agonist cannot disassociate and restimulate
29
Q

Drug classification by use

A
30
Q

Define efficacy

A

[affinity] X [intrinsic activity]

31
Q

Physiologic receptor motif superfamily

A
  • Ligand gated ion channels
    • Receptors interact with substrate In ways that allow channel opening for a specific ion to create a flow of ions in a specific direction
    • Eg GABAA, AChN, glutamate
  • G-protein coupled
    • 7 transmembrane domains
    • Most common receptor type targeted by ophthalmic drugs
    • Eg AChM, rhodopsin
    • Phosphorylation of G protein to GTP
  • Enzymatic
    • Single transmembrane spanning domain
    • Eg insulin, epidermal growth factor
  • Calcium release
    • Interacts with a receptor in the cell that releases Ca from sarcoplasmic reticulum
    • Eg calcineurin, nitric oxide synthase, cytokines
  • Intracellular or nuclear
    • Substrates must be able to readily pass through the lipid bilayer
    • Eg steroids and hormones
32
Q

Define teratogenesis

A

congential malformation

33
Q

Pharmacokinetic model of the eye

A

Cornea is a thick barrier - important as an immune barrier
Stroma has little resistance to the passage of drugs, esp water soluble
AC has little resistance for water soluble drugs
Iris is quite porise, can absorb drugs readily to enter systemic circulation
Anterior lens is a good means of protection
Vitreous has low profusion resistance
ILM of retina is not much of a barrier, retinal BVs have tightly knit walls to prevent absorption of
drugs here
- Blood retinal barrier
Choroidal vessels are fenestrated and absorb and release drugs readily

34
Q

Henderson-hasselbach equation

A

The large majority of drugs are weak acids or bases
Their ionization constant pKa defines the pH at which ionized and unionized forms are equal in
concentration
Only uncharged drugs are lipid soluble; charged drugs are water soluble
In increasingly acidic environments, the above rxn will move to the left as excessive levels of protons
flood the environment
Log[protonated/unprotonated] = pKa -pH

35
Q

Drug pKa vs pH

A

Normal test pH is aroung 7.1-7.6, ie slightly basic
Strongly buffered drugs can alter teat pH
Weak bases are most stable at low pH since protonated charged state reduces metabolism
Inflammation creates an acidic environment
Charged drugs accumulate in aqueous media
Uncharged drugs readily leave aqueous environments to cross lipid barriers
pH = pKa + log ([A-]/[HA])
[H+] = Ka + ([HA]/[A-])

36
Q

Barriers to intraocular delivery

A

Corneal tear drainage, episcleral blood flow and intraocular
convection limit influx of locally administered drugs into the
posterior segment
Size of drug plays a role in which can penetrate ILM

37
Q

Drug Half-Lives and Metabolism

A

Drug metabolism rates: each drug has an absorption (and elimination) half-life describing the time it
takes for 50% of the drug to be processed
Absorption, clearance and elimination kinetics are unique to a given drug and assume two distinct
profiles; Zero order and 1st order
-

In some cases, drugs follow both zero order and 1st order kinetics depending on their concentration; in
this case they are classified as mixed order
For drugs with 1st order kinetics, their concentration exponentially impacts their rate of
processing by a given receptor (aka carrier)
-

During the metabolic phase, when the levels of a carrier far exceed its substrate drug concentration, the
kinetics are said to be non-saturable
For drugs with zero-order kinetics (like ethanol and salicylates) their rate of processing is
independent of their concentration, so doubling a dose means it will take twice as long to
metabolize
-

With Zero-order kinetic drugs, there is a greater demand for dose modification: loading VS
maintenance

38
Q

First ordervs zero order

A

Dosing schedule
First order Kinetics:
- Steady state is achieved when rate of intake = rate of elimination
Zero order kinetics:
- Greater demand for dose modification (loading vs maintenance)
- Doubling a dose calls for twice the time to be metabolized

39
Q

Dosing interval

A

To best avoid undesired fluctuation of plasma drug levels, dosing intervals are recommended at less or
equal to a drug’s half-life; in this way drug concentration never drops lower then 50%
- Dosing according to a drug’s half-life is readily accomplished with sustained release drugs
Dosing intervals less than 1/3 of a drugs half-life results in plasma drug levels that are similar to
those seen with continuous infusion
-
Because most antibiotics have a high therapeutic index (very safe), dosing schedules for severe infection
is often don’t in a loading dose fashion since large peaks in plasma levels are not toxic

40
Q

Drug-plasma equilibrium

A

1st order kinetics

  • Steady state is reached in this case in 3-5 drug half lives with first order kinetics
  • Conversely a 3-5 half-lives following the last dose, 90% of a systemic drug is eliminated
41
Q

Dose modulation

A

One way to achieve the designated therapeutic drug level is to modulate the dose concentration
Another way is to modulate dose frequency OR do both
- Greater frequency –> less potential for toxicity

42
Q

Common therapeutic malpractice

A
  • Steroids: long term topical or oral
  • Cataracts and glaucoma risks
  • Beta-blockers
  • Cardiovascular & respiratory risks
  • Mitotic
  • Retinal detachment risk
  • Oral carbonic anhydrase inhibitors
  • Electrolyte imbalance risk
43
Q

Malpractice legalities

A

4 components of a malpractice case

  • Standard of care: what standard of care is expected?
    • . Present once a relationship is established with patient, regardless of fees or setting
    • Informed consent in a language the patient comprehends involves a discussion of alternative therapies, drug or procedure risks and warnings, abnormal findings
  • Breach of care: did the level of care not meet the standard?
  • Evidence of injury: how was the patient affected?
  • Proximate cause: did the injury occur around the same time as the breach of care took place?
44
Q

Common therapeutic negligence

A

In order of most to least common

  • Failure to diagnose
    • Glaucoma, tumors of the visual system, retinal detachment
  • Delayed diagnosis
  • Misdiagnosis
    • . Herpes keratitis, fungal disease, pseudomonas ulcers
  • Improper management
  • Failed/delayed referral or consultation
    • Schedule follow-up before patient leaves office
45
Q

DEA drug schedules

A

The DEA has established 5 distinct categories or schedules for drugs which relate to the drug’s
acceptable medical use as well as its abuse or dependency potential
I: no currently accepted medical use and a high potential for abuse (eg heroin)
II: a high potential for abuse, with use potential leading to severe psychological or physical
dependence (eg hydrocodone, Adderall)
III: A moderate to low potential for physical and psychological dependance (eg testosterone)
IV: A low potential for abuse and low risk of dependence (eg Valium)
V: Lower potential for abuse than schedule IV drugs (eg penicillin)

46
Q

FDA Safety/Monitoring rgarding pregnancy

A

Category Warning
A No evidence of risk in women
B No evidence of risk in animals
C Animal toxicity evidence
D Risks may be about equal to benefits

X Risks outweigh benefits

47
Q
A

Ocular Pharmacology (10 decks)

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