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VPTox > Topic 2 Part 3 > Flashcards

Topic 2 Part 3 Flashcards

1
Q

What is drug excretion?

A

Process by which a drug or metabolite is removed from the body

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2
Q

What are the routes of drug excretion?

A
  • Renal
  • Faecal
  • Lung
  • Milk
  • Sweat, saliva & tears
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3
Q

What is renal excretion of drugs?

A
  • Most common route of excretion
  • Removal of parent drug or metabolite in urine
  • Polar drugs or metabolites undergo direct renal excretion
  • 3 processes involved in kidneys to excrete a drug: filtration, secretion, reabsorption
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4
Q

What happens during the filtration process of renal excretion?

A
  • Glomerular filtration rate (GFR)
  • Only free drug can pass through the capillary in glomerulus
  • Normal GFR = ~ 125 ml/min
  • Bound drugs cannot pass through (too big)
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5
Q

What occurs during the secretion process of renal excretion?

A
  • Takes place in proximal convoluted tubule
  • By active tpt of drugs/metabolites from blood into the tubule
  • Acid pump: actively secretes weak acids
  • Basic pump: actively secretes weak bases
  • Potential site for drug-drug interaction: pumps have low specificity & can tpt many drugs; drugs compete for same transporter
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6
Q

What occurs during the reabsorption process of renal excretion?

A
  • Takes place in distal convoluted tubule
  • As drug moves towards DCT, its conc. increases & diffuses back to blood to blood circulation (passive reabsorption)
  • Most drugs are passively reabsorbed
  • Can also be active reabsorption by transporter
  • Only non-ionized drugs can be reabsorbed
  • Ionized/polar drugs are not reabsorbed
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7
Q

What are the factors affecting renal excretion?

A
  1. Urine pH
  2. Urine flow rate
  3. Plasma protein binding
  4. Competition for active tubular secretion
  5. State of renal function
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8
Q

How does urine pH affect drug excretion process?

A
  • affects the ionization of drugs
  • drugs are weakly basic/acidic
  • Therefore, ionized with varying degree depending on pH
  • Alkaline urine: promote excretion of acidic drug
  • Acidic urine: promote excretion of basic drug
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9
Q

How does urine flow rate affect the drug excretion process?

A
  • increased flow rate promotes excretion

- drugs/metabolites with low urine solubility (patients advised to drink more water to promote excretion)

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10
Q

How does plasma protein binding affect the drug excretion process?

A
  • drugs bound to albumin are excreted slower than free drug
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11
Q

How does the state of renal function affect the drug excretion process?

A
  • Renal failure results in low drug clearance –> prolonging drug effect
  • If not monitored well, will lead to toxicity
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12
Q

What are pharmacokinetic parameters?

A
  • Bioavailability (F)
  • Volume of distribution (V.d)
  • Clearance (Cl)
  • Half-life (t₁/₂)
  • Loading dose (D.l)
  • Steady-state plasma conc. (C.ss)
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13
Q

What is bioavailability?

A
  • Fraction of chemically unchanged drug (%) that reaches the systemic circulation by any route
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14
Q

What is volume of distribution?

A
  • Hypothetical volume of body fluid into which the absorbed drug is disseminated (if it were uniformly distributed)
  • It is a dilution factor –> about distribution
  • The greater the value –> the more drug is diluted (in blood plasma) –> means more of drug is distributed in tissue
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15
Q

How to calculate volume of distribution?

A

total amount of drug in the body/drug blood plasma concentration [C(mg/ml)]
= F x drug dose (mg) / plasma drug conc. (mg/ml)

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16
Q

What is the volume of distribution?

A
  • The dose required to give a certain plasma concentration can be determined if the V.d for that drug is known
  • The V.d is not a physiologic value –> more of a reflection of drug distribution throughout the body
  • depends on several physicochemical properties (e.g. solubility, charge, size)
17
Q

What is clearance (Cl)?

A
  • A measure of the capacity of the body to remove a drug

- expressed as ml/min

18
Q

How to calculate Cl?

A

Rate of elimination (mg/min) / plasma drug concentration (mg/ml)

19
Q

What is half-life (t.1/2)?

A

Time required for concentration of drug to be reduced by half

20
Q

What is the steady state plasma concentration (C.ss)?

A
  • Repeated dosing of a drug at regular intervals –> plasma conc. increases until a steady state is reached
  • The rate of drug availability = the rate of drug elimination
  • Steady-state occurs after a drug has been given for approx 4-5 half-lives
  • Can relate drug conc. to clinical response
21
Q

What is loading dose (D.L)?

A
  • One single dose required to achieve desired plasma drug concentration
22
Q

How to calculate laoding dose?

A

bioavailability x loading dose = volume of distribution x desired plasma drug conc.

23
Q

What is the unit for loading dose?

A
  • mg

VPTox (4 decks)

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