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PHARMACOLOGY 2ND YEAR > PHARMACOKINETICS > Flashcards

PHARMACOKINETICS Flashcards

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1
Q

What is zero order elimination?

A

A process where a constant amount of drug is eliminated over time, regardless of concentration

Very few drugs exhibit zero order elimination at therapeutic doses; it often occurs in overdose situations.

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2
Q

Which drugs are commonly eliminated by zero order kinetics?

A
  • Aspirin
  • Ethanol
  • Phenytoin
  • Heparin

These drugs exhibit zero order elimination primarily in overdose scenarios.

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3
Q

What happens to the half-life in zero order elimination?

A

It becomes meaningless as it depends on the drug concentration.

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4
Q

What is pharmacokinetics?

A

The study of how the body affects a drug, including absorption, distribution, metabolism, and excretion.

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5
Q

What is pharmacodynamics?

A

The study of how drugs affect the body at the cellular, molecular, and physiological levels.

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6
Q

What physicochemical properties affect drug movement across cell membranes?

A
  • Molecular size and shape
  • Solubility at absorption site
  • Degree of ionisation
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7
Q

What is the molecular weight range for most drugs?

A

200 – 1000 Da

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8
Q

What are the mechanisms of crossing cell membranes?

A
  • Diffusion through aqueous pores
  • Passive lipid diffusion
  • Carrier-mediated transport
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9
Q

What type of transport do SLC transporters facilitate?

A

Passive movement of solutes down a concentration gradient.

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10
Q

What role do P-glycoproteins play in drug transport?

A

They are primary active transporters that move endogenous substances and foreign chemicals (drugs) across cell membranes.

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11
Q

What is the impact of pH on drug movement?

A

It affects the degree of ionisation of drugs, influencing their ability to cross cell membranes.

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12
Q

What is ‘ion trapping’?

A

The phenomenon where a drug becomes concentrated in a compartment due to pH differences affecting its ionisation.

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13
Q

What factors affect the absorption of orally administered drugs?

A
  • Physicochemical properties of the drug
  • pH within the gastrointestinal tract
  • Surface area available for absorption
  • Splanchnic blood flow
  • Presence of food
  • GIT motility
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14
Q

What is the first pass effect?

A

Pre-systemic metabolism of drugs, primarily in the liver, before they reach systemic circulation.

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15
Q

Which drugs undergo significant first pass metabolism?

A
  • Isoniazid
  • Morphine
  • Buprenorphine
  • Propranolol
  • Glyceryl trinitrate
  • Ethanol
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16
Q

What is bioavailability?

A

The fraction of an administered dose that reaches systemic circulation.

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17
Q

What can affect bioavailability?

A
  • Formulation
  • Enzyme activity
  • Activity of transporters
  • Gastric pH
  • Intestinal motility
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18
Q

How can drug interactions reduce bioavailability?

A

Through agents like tetracyclines with cations, cholestyramine, and antacids.

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19
Q

What are the different routes of drug administration?

A
  • Oral
  • Sublingual
  • Topical
  • Transdermal
  • Pulmonary (inhalation)
  • Rectal
  • Parenteral
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20
Q

What is the central compartment in drug distribution?

A

The vascular system and well-perfused organs (heart, brain, liver, lungs, kidneys).

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21
Q

What is the significance of plasma protein binding?

A

It can limit drug concentrations in tissues and at the site of action.

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22
Q

What clinical significance does tissue binding have?

A
  • Prolongs duration of action
  • May contribute to drug toxicity
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23
Q

What is Therapeutic Drug Monitoring (TDM)?

A

Measuring plasma concentration of drugs with a narrow therapeutic index.

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24
Q

What is the role of albumin in drug binding?

A

It binds acidic drugs and is a key carrier of drugs in plasma.

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25
What is amiodarone?
A medication used to treat certain types of serious irregular heartbeat.
26
What can contribute to drug toxicity?
Zoledronic acid and aminoglycosides (e.g., gentamicin).
27
What are the effects of aminoglycosides like gentamicin?
They can accumulate in the vestibular system (causing ototoxicity) and kidney (causing nephrotoxicity).
28
What is Therapeutic Drug Monitoring (TDM)?
Measurement of plasma concentration of some drugs with a narrow therapeutic index.
29
List some drugs that require Therapeutic Drug Monitoring.
* Phenytoin * Carbamazepine * Phenobarbitone * Sodium valproate
30
What is the formula for Total Drug Concentration (TD)?
TD = B + UB, where B is bound drug and UB is unbound drug.
31
What happens if less drug is bound due to hypoalbuminemia?
There will be more free/unbound drug to cause effect and to be excreted.
32
What is the blood-brain barrier?
A selective barrier formed by brain capillary endothelial cells with continuous tight junctions.
33
How do drugs penetrate the blood-brain barrier?
Drug penetration is transcellular.
34
What influences drug penetration into the brain?
Lipid solubility of the drug (lipid/water partition coefficient).
35
True or False: The more lipophilic a drug is, the greater the uptake into the brain.
True.
36
What can increase drug access into the brain?
Altered capillary permeability due to inflammation (e.g., meningitis).
37
What is adipose tissue's role in drug distribution?
It acts as a reservoir for lipid-soluble drugs.
38
What factors determine placental transfer of drugs during pregnancy?
* Drug's lipid solubility * Extent of protein binding * Degree of ionisation
39
What is a teratogen?
A drug that causes physical or functional abnormalities in a developing fetus.
40
Define Volume of Distribution (Vd).
A hypothetical volume that relates drug serum concentrations to the amount of drug in the body.
41
What does a high Volume of Distribution (Vd) indicate?
The drug is extensively distributed in the body.
42
What is the unit of measurement for Volume of Distribution?
L/kg.
43
What is the formula for calculating Volume of Distribution?
Vd = D / Cp, where D is the total amount (dose) of drug and Cp is plasma concentration.
44
What can alter a drug's Volume of Distribution?
* Obesity * Age * Abnormal fluid retention * Hypoalbuminemia
45
What is metabolism in pharmacology?
The enzymatic conversion of chemical structures, producing active or inactive metabolites.
46
What is the aim of drug metabolism?
To produce metabolites that are usually inactive, more polar, and readily excreted.
47
Name the primary site of drug metabolism.
Liver.
48
What are Phase One reactions in drug metabolism?
Reactions that introduce or expose a functional group on the parent compound, usually resulting in loss of pharmacological activity.
49
What are common Phase One reactions?
* Oxidation * Reduction * Hydrolysis
50
What is the role of Cytochrome P-450 enzymes?
They are responsible for the metabolism of most medications.
51
What occurs during Phase Two metabolism?
Conjugation reactions form covalent linkages with polar substances, usually resulting in inactive metabolites.
52
What is a pro-drug?
A compound that undergoes biotransformation before exhibiting pharmacological effects.
53
What factors can alter drug metabolism?
* Interindividual variation in CYP450 enzymes * Pharmacogenomics * Enzyme induction * Enzyme inhibition
54
What is enzyme induction?
The process of stimulating transcription of genes encoding CYP enzymes, increasing enzyme synthesis and activity.
55
What is enzyme inhibition?
The suppression of transcription of genes encoding CYP enzymes, decreasing enzyme synthesis and activity.
56
How does grapefruit juice affect drug metabolism?
It inhibits intestinal enzymes (specifically CYP3A4), increasing oral bioavailability of drugs.
57
What is the metabolic pathway of ethanol?
* Alcohol dehydrogenase (ADH) * Microsomal Ethanol Oxidizing System (MEOS)
58
What happens to drug metabolism in the elderly?
Metabolic capacity may be reduced due to decreased liver function and body composition changes.
59
What is 'grey baby syndrome'?
A condition in neonates caused by immature hepatic conjugative systems leading to toxicity from chloramphenicol.
60
What is the metabolic pathway that accounts for less than 20% in neonates?
Glucuronidation ## Footnote This pathway is less mature in neonates compared to adults.
61
What is 'grey baby syndrome' associated with?
Chloramphenicol in neonates/premature babies ## Footnote Due to immature hepatic conjugative systems.
62
What percentage of chloramphenicol's metabolism is via glucuronidation in adults?
90% ## Footnote This highlights the difference in metabolic capacity between neonates and adults.
63
What is the age threshold for geriatric medicine?
≥ 65 years ## Footnote Focuses on the diagnosis, treatment, and prevention of disease in older people.
64
What happens to hepatic blood flow in the elderly?
May be reduced by 40% ## Footnote This affects drug metabolism and delivery to the liver.
65
Which drugs are most affected by reduced hepatic blood flow in the elderly?
Drugs with high extraction ratio like verapamil, morphine, propranolol ## Footnote These drugs are heavily dependent on hepatic clearance.
66
How much can the metabolic capacity of liver enzymes be reduced in the elderly?
Up to 60% ## Footnote This can lead to longer drug action and higher plasma concentrations.
67
Which phase of metabolic enzymes is more affected in the elderly?
Phase 1 metabolic enzymes (e.g., oxidation) ## Footnote Phase 2 processes are less affected.
68
True or False: Old age shows a linear decline in metabolic function.
False ## Footnote The decline is not linear and varies between individuals.
69
What is a key factor that alters drug metabolism related to gender?
Differences in alcohol dehydrogenase levels ## Footnote Females have less than males, affecting alcohol metabolism.
70
What are auto-inducers in drug metabolism?
An inducer that enhances its own metabolism ## Footnote This leads to pharmacokinetic tolerance.
71
What is the definition of excretion in pharmacokinetics?
Irreversible removal of drug (and metabolites) from the body ## Footnote Commonly occurs via the kidney or biliary tract.
72
What is the primary route for renal excretion?
Kidney ## Footnote Most drugs or metabolites are non-volatile, water soluble, low molecular weight.
73
What is the Glomerular Filtration Rate (GFR) in a healthy adult?
~ 125 mL/min ## Footnote About 180 L of fluid is filtered through the kidneys daily.
74
What is the average urine volume produced per day?
1 to 1.5 L ## Footnote This indicates that 99% or more of the filtrate is normally reabsorbed.
75
What is active tubular secretion?
Active transport process of drug from renal capillaries into renal tubules ## Footnote Requires energy and is extremely effective.
76
What determines the degree of tubular reabsorption of drugs?
pH of the fluid in the renal tubule and pKa of the drug ## Footnote The unionised drug is more easily reabsorbed.
77
What is biliary excretion?
Excretion of drugs into bile by the liver ## Footnote Drugs with a molecular weight > 300 daltons can be excreted.
78
What is enterohepatic circulation?
Recycling of hydrophilic drug conjugates through bile and intestine ## Footnote Active drug is released and reabsorbed back into circulation.
79
What is clearance in pharmacokinetics?
Volume of plasma cleared of drug per unit time ## Footnote Measured in mL/min or L/hr.
80
What is first-order elimination?
Rate of elimination is directly proportional to drug concentration ## Footnote Most drugs follow first-order kinetics.
81
What does the half-life (t1/2) of a drug represent?
Time taken to reduce the amount of drug in the body by 50% ## Footnote Units of time, usually in hours.
82
How is t1/2 determined?
By measuring incremental changes in plasma concentration (Cp) vs time ## Footnote Can also be determined using a semi-log plot.
83
What happens after 4 half-lives in first-order elimination?
Elimination is approximately 94% complete ## Footnote This illustrates the efficiency of drug clearance over time.
84
What is zero-order elimination?
Rate of elimination does not increase with increasing drug concentrations ## Footnote Occurs when the elimination systems become saturated.

PHARMACOLOGY 2ND YEAR (18 decks)

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