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Pharmacology > Drug disposition & Fate of drugs > Flashcards

Drug disposition & Fate of drugs Flashcards

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1
Q

MUST have some ability to dissolve in WATER to move around (be
absorbed, reach sites of action.)

A

Drugs

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2
Q

must also have a
certain degree of lipid solubility to move around (leave and enter capillaries,
enter and leave cells.)

A

Drugs

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3
Q

Drug concentrations in the ____ (measured in either serum or plasma)
are USUALLY proportional (and usually linear) to drug concentrations at the
site of action.

A

blood stream

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4
Q

Drug concentration in the _______ is ALMOST ALWAYS an excellent
predictor of drug action (either efficacy or toxicity)

A

blood stream

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5
Q

are the consequence of physiologic process (that may or
may not be altered by disease.)

A

Pharmacokinetics

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6
Q

are the PRIMARY difference between basic and clinical
pharmacology.

A

Disease-included differences

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7
Q

are the PRIMARY difference between
Veterinary pharmacology and Human pharmacology”.

A

Species differences in pharmacokinetics

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8
Q

General Principles of Routes of Administration (Drug Absorption)

A

Drug dissolve in body fluid (water).
Drugs enter the circulatory system as fluid enters the circulatory system.
Drugs must enter the circulatory system before they can distributed to sites of
action.
(Drugs for enteric effects are an obvious exception.)
Therefore, drugs are not IN the body until they are IN the bloodstream.

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9
Q

Advantages of Oral administration

A

Convenient, cheap, no need for sterilization, variety of dose forms
(fast release tablets, capsules, enteric coated layered tablets, slow release,
suspensions, mixtures)
You can get the dose back of you move fast enough.

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10
Q

Disadvantages of Oral administration

A

Variability due to physiology, feeding, disease, etc.
Intractable patients
First-pass effect
Efficiently metabolized drugs eliminated by the liver before they reach the
systematic circulation.

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11
Q

Patient and Pharmaceutical Factors

A

Pill compression, coatings, suspending agents, etc.
GI transit time (too slow or too fast), inflammation, malabsorption, syndromes

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12
Q

Regional Differences of Oral administration

A

Stomach
mechanical preparation
“flat” absorptive surface
pH extreme
Rumenoreticulum
stratified squamous epithelium
pH varies with diet
metabolism by bacterial flora
significant volume of fluid compared to body water
Small Intestine
large absorptive functions
relatively neutral pH
Colon/Rectum
accessible
large absorptive surface

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13
Q

The bolus remains relatively spherical.

A

Liqid soluble vehicle

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14
Q

entry of drug into
circulatory system limited by rate of drug ______ (Movement from the
“bolus” to the tissue fluid).

A

“dissolution”

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15
Q

Advantages of Subcutaneous Administration

A

Can be given by the owner (small patients)
Vasoconstrictor can be added to prolong effect at site of interest

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16
Q

Disadvantages of Subcutaneous Administration

A

Variability

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17
Q

Much like intramuscular (though the architecture of the tissue is much different)

A

process of subcutaneous

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18
Q

Patient and Pharmaceutical Factors of Subcutaneous

A

More autonomic control over blood flow (than muscle)
dehydration, heat, cold, stress

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19
Q

Topical Advantages

A

IF systemic therapy – easy painless application (e.g. mass medication of cattle)
IF skin therapy – reduced systemic effects/enhanced skin effects

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20
Q

Topical Disadvantages

A

Patients groom themselves (topically applied, orally absorbed)
Toxic skin reactions
Variable blood flow to skin
COMPLEX relationship between drug, vehicle , skin physiology

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20
Q

process of topical

A

Diffusion through stratified epithelium
“Passage” through adnexal structures

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21
Q

Patient and Pharmaceutical Factors of Topical

A

Lipid solubility and molecule size
Skin hydration and abrasion
Area of application
Ambient an patient temperature

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22
Q

Vehicle Effects of Topical

A

“like” vehicles retain drug on skin surface
(e.g, aqueous drug in aqueous vehicle, lipid drug in lipid vehicle)
Drugs in “unlike” vehicles leave the vehicle to move on to skin
(e.g, aqueous drug in lipid suspension, lipid drug in aqueous suspension)

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23
Q

Intraperitoneal Advantages

A

Larger absorptive surface are than IM / Subcutaneous

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24
Intraperitoneal Disadvantages
Drugs or vehicles may cause peritonitis Damage to organs by needles Injection into organs
25
Patient and Pharmaceutical Factors of Intraperitoneal
Generally restricted to laboratory animals.
26
Intrathecal Advantages
Direct delivery to site of action
27
Disadvantages Intrathecal
Difficult dose calculation Intrathecal CSF volume is not proportional to body weight Toxicity likely, and toxicity may be unusual Introduce infection into a VERY bad location
28
Process Intrathecal
Absorption is usually by diffusion and very slow
29
Intra-actular Advantages
Direct delivery to site of action. High concentrations can be produces in the joint.
30
Disadvantages Intra-actular
It may be difficult to hit the joint space depending on the species (size of joint space). Difficult dose calculation Joint space volume depends on disease Introduce infection. (PSGAG - Adequan® - interjections now generally get “antimicrobial chaser”) Joint “flushes: don’t count.
31
Process Intra-actular
Absorption from the site to systemic is variable but often quite fast. Systemic concentrations of the drug may be produced. Effects in joint may not persist. (Drug and dose form dependent)
32
Used primarily for anti-tumor therapy and infectious disease therapy when blood supply is questionable.
Intra-arterial
33
Produce extremely high concentrations “pointed at” (this is not really targeting) the tissue of interest.
Intra-arterial (advantage)
34
Disadvantages Intra-arterial
Dose calculation is best guess. Intra-arterial lines difficult to insert/maintain. Dosing is still really systemic. Limited number of efficacy studies (especially in animals)
35
Process of Intra-arterial
Produce AND SUSTAIN high blood-to-tissue gradient to increase tissue concentrations of drug. Requires sustained infusion or application of tourniquet following bolus dosing.
36
Per rectum advantages
Access to GI absorption in unconscious or vomiting patients Drug can be recovered before absorption is complete
37
Per rectum disadvantages
Animals may not willingly retain the drug
38
Process Per rectum
As for oral without mechanical preparation by stomach
39
Drug Distribution Physiologic “spaces”
Vascular space (plasma / plasma water + RBC’s) There is also “tissue space” Size -7% of body weight Equilibria between water and various plasma / serum proteins between ionized and unionized drug between ionized and unionized drug between plasma and cells Distribution in 10 to 30 minutes (mixing)
40
Extracellular Space (exist in both vascular and tissue spaces)
Size 15 – 20% of body weight includes extracellular fluid in bloodstream (plasma) Equilibria between water and proteins between ionized and unionized drug Distribution in 30 minutes to 1.5 hours
41
Intracellular space (exist in both vascular and tissue spaces)
Size 35 – 45% of body weight Equilibria between ionized and unionized drug intracellular pH different (lower) than extracellular Distribution in 30 minutes to 12+hours
42
Reserved spaces
Special barriers between plasma and tissue fluid CSF aqueous humor prostatic fluid Distribution in minutes to never
43
Movement between spaces
Vascular space (extracellular) to tissue (extracellular) space Transcytotic Endothelial junctions wit inflammation Diffusion through endothelial cell membranes Carried in cells or on proteins in very special circumstances Extracellular space (of tissue) to intracellular space (of tissue) Diffusion through lipid bilayer of cells Vascular extracellular space to vascular intracellular space (drugs can mocve into RBC’s and WBC’s) Diffusion through lipid bilayer of cells WBC may actively acquire certain drugs
44
Diffusion Limited Distribution
Diffusion is usually slow (relative to mixing and distribution within vascular system) Tissue distribution of the drug controlled by the ability of the drug to diffuse into the tissue
45
Blood flow limited distribution
Diffusion can be VERY rapid Tissue distribution of the drug controlled by the rate of drug delivery to the tissue (total mg/minute) which is controlled by blood flow / gram of tissue Brain and liver concentration rise faster than muscle or fat
46
_____________ concentration rise faster than muscle or fat
Brain and liver
47
How does Enterohepatic Circulation work?
Drug or it’s Phase II conjugate excreted in bile Drug reabsorbed or Conjugate cleaved by bacteria and drug reabsorbed
48
Why do you care? (Enterohepatic Circulation)
interrupt to improve drug elimination Insecticide poisonings, Phenobarbital overdoses, et
49
How does Mammary Excretion work?
Non – ionic Diffusion (lipid solubility and size dependence) Inflammation reduces barriers to penetration (masititis) Ion trapping normal milk pH = 6.6 (slightly acidic versus blood) Mastitic milk pH is slightly higher
50
Why do you care? (Mammary Excretion)
May affect treatment of some bacterial infections of the mammary gland Nursing animals may be exposed to toxic concentrations of drug in the milk
51
The volume of fluid that “appears” to contain the amount of drug in the body
Volume of Distribution
52
Partially determines the relationship between dose and plasma concentration
Volume of Distribution
53
Roughly describes “tissue penetration”
Volume of Distribution
54
Units
Liters or milliliters describing the whole animal Liters/kg or milliliters/kg
55
Defines the volume of fluid that must be processed by organs of elimination
Volume of Distribution
56
is usually slow (relative to mixing and distribution within vascular system)
Diffusion
57
How does Salivary Excretion work?
Non – ionic diffusion into salivary secretions Drug in saliva passes into GI tract
58
They can recycle certain drugs like enteroheptic circulation (prolonged elimination) Can also trap certain drugs in the rumen pH dependent (enhanced elimination)
Ruminants
59
Conversion of a drug entity to a metabolite
Biotransformation
60
Chemical Mechanisms of Biotransformation
Oxidation, hydroxylation, hydrolysis, reduction, conjugation, (acetylation, glucuronidation, sulfation, etc.)
61
Efficiency (rate) of Biotransformation
Metabolic activity for a specific drug Blood flow to the organ Health of the organ and health of the circulatory system
62
organs involved in biotransformation
Liver (most important for most drugs) Lungs (especially for autocoids) Kidneys
63
Types of Biliary Excretion
Active secretion Passive secretion
64
Drugs with molecular weights > 300 mostly conjugates of original drug
Active secretion
65
Drugs with molecular weights < 300 biliary concentrations similar to plasma water
Passive secretion
66
Process of Renal Elimination
(Glomerular filtration + tubular secretion) – passive reabsorption = renal elimination
67
passive elimination of drug dissolved in plasma water ionized and unionized NOT protein bound drug
Glomerular filtration
68
energy dependent excretion by proximal kidney tubule organic acid and organic base pumps includes protein bound drugs
Tubular secretion
69
Passive reabsorption can be reduced by_____ or by ______
disease (accidental) therapy (intentional)
70
The volume of plasma water cleared of the drug during a specified time period.
Clearance
71
Organ clearance is calculated by determining the ___
flow (Q) and the efficiency of extraction C𝑙𝑒𝑎𝑟𝑎𝑛𝑐𝑒 = 𝑄 𝑥 𝐸
72
is the sum of all organ clearances
Total body clearance (Clt)
73
Units of Clearance
Volume / unit time (1/hr, 1/min, ml/hr etc) describing whole animal Volume / kilogram / unit time (1/kg/hr, ml/kg/min etc.)
74
The time for elimination of one half of the total amount in the body.
Elimination Half – Life or Half life
75
longest half – life
gentamicin example
76
is an initial dose of drug given to shorten the time to reach the steady-state concentrations.
loading dose
77
describes the rate of drug movement (oral, IM, SC, etc.) from the dose to the circulatory system.
Absorption Rate Constant
78
is a common measure used to compare two different drug formulations (tablets vs. elixir) or to compare products sold by two different manufacturers (trade name drugs vs. generics).
Bioavailability
79
The fraction of the dose absorbed determines a drug’s ____
bioavailability
80
Attempt to describe the actual events which control drug absorption, distribution, and elimination
Physiologic models
81
Attempt to accurately predict the time course of drug concentrations in one (usually blood or plasma) or two (urine as well) body fluids. Predictions area generally made for tissues which can be sampled from intact patients.
Mathematic Models
82
Enumerate Body Compartments
Central Compartment Blood volume Organs of elimination Peripheral compartment Muscle Subcutis Lung Tissue Deep compartments Fat (poor blood supply, lipid soluble drugs) Kidneys (amino glycosides)
83
If the pharmacokinetics of ABSORPTION change when we increase the dose , the drug is said to exhibit -_____
dose – dependent absorption
84
If the pharmacokinetics of ELIMINATION change when we increase the dose ), the drug is said to exhibit____
dose – dependent elimination.
85
The sum of all individual organ clearances. Usually determined by plasma sampling
Clearance, Total ( Clt )
86
The clearance “performed” by the kidney.
Clearance, Renal (Clr)
87
The clearance “performed’ by the liver.
Clearance, Hepatic (Clh)
88
Highest plasma concentration achieved following a single non- intravenous dose of a drug.
Peak plasma concentration ( Cmax )
89
Plasma concentration , may be followed by a subscript for time (Cpt – see Cp0 below)
Plasma concentration ( Cp )
90
The plasma concentration at zero time. Determine by extrapolating the plasma concentration versus time “curve” back to the Y (concentration) axis.
Plasma concentration at time zero ( Cp0 )
91
Portion of a non-intravenous dose of drug that reaches the systemic circulation.
Fraction of dose absorbed ( F )
92
Time required to eliminate 50% of any amount of drug from the body.
Half-life of elimination ( T1/2 )
93
The time that the Cmax (above) is achieved following a single non intravenous dose of drug.
Time of the peak plasma concentration (Tmax)
94
The volume calculated using the intercept of the “z” portion of a curve and the Y axis
Volume of distribution ( Vz )
95
Unit for Clearance, Total (Clt)
1/hr/kg
96
Unit for Clearance, Renal (Clr)
1/hr/kg
97
unit for Peak plasma concentration (Cmax), Plasma concentration ( Cp), and Cp0
mg/ml (or) mg/liter
98
Unit for Fraction of dose absorbed (F)
None or %
99
unit for Half-life of elimination (T1/2) and Tmax
hrs (or) minutes
100
unit for Volume of distribution ( Vz)
L/kg

Pharmacology (4 decks)

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