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PVS > Pharmacology: Pharmacokinetics > Flashcards

Pharmacology: Pharmacokinetics Flashcards

1
Q

What are the enteral methods of drug administration?

A

Sublingual, swallowing and rectal (which bypasses the liver)

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2
Q

How are enteral drugs designed to be absorbed along the acidic part (stomach) of the GI tract or neutral part (intestine)?

A

Drugs are designed to dissolve at high or low pH

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3
Q

How does age effect enteral drug absorption?

A

Elderly: Less proteins & water in the body
Infant (human): >77% of water (human adult average ~70%)
pH of the GI-tract may change with age

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4
Q

In general, compounds that are rapidly absorbed by the enteral route have…

A

a. Low degree of ionization
b. High lipid/water partition in the non ionized form
c. Relatively low MW < 1000
d. A biological affinity with transporters/facilitated diffusion (e.g. cephalporins are absorbed by a transporter for dipeptides).

(NB. a/b/c = Lipinski’s rules)

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5
Q

In general compounds that are not rapidly absorbed by the enteral route have…

A

a. High degree of ionization (ions need specific channels/transporters: Na vs. Mg): Must be neutral to cross the membrane
b. Low lipid/water partition in the non ionized form (flows with the peristaltic mvt & eliminated or needs transporter e.g. glucose)
c. Too large (e.g. chemicals forming precipitate flows with the peristaltic mvt & eliminated).
d. Degraded by specific enzymes (e.g. insulin, epinephrine, histamine,…)

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6
Q

Weak acids ……………. a proton (H+) to form …………….

A 
Weak acids (HA) donate (H+) to form anions: 
HA↔H++A-
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7
Q

Weak bases ……………. a proton (H+) to form …………….

A 
Weak bases (B) accept a proton (H+) to form cations: 
BH+ ↔B+ H+
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8
Q

What is first pass metabolism?

A

If a drug is metabolised BEFORE it reaches the systemic circulation
Oxidation & Conjugation to make compounds water soluble. Many drugs are “inactivated” and excreted this way by the liver

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9
Q

What happens to lipophilic drugs that undergo first pass metabolism?

A 
Phase 1 (catabolic): Oxidation, reduction and/or hydrolysis 
Phase 2 (anabolic): synthetic conjugation

The drug is then water soluble and usually inactive

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10
Q

What happens to lipophilic drugs that undergo first pass metabolism?

A 
Phase 1 (catabolic): Oxidation, reduction and/or hydrolysis 
Phase 2 (anabolic): synthetic conjugation

The drug is then water soluble and usually inactive

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11
Q

Where do the enzymes for first pass metabolism live?

A

In the smooth endoplasmic reticulum of the hepatocytes

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12
Q

What is enterohepatic circulation?

A

Drugs metabolized may recycle several times before entering the systemic circulation (the drug follows bile salts)

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13
Q

When a drug is metabolised what can happen to the metabolite?

A

Detoxified (inactivated) eg Phenol
Similar activity to the drug eg. Diazepam
Have a different activity eg Ipronazid (anti-depressant) to Isoniazid (anti-tuberculosis)
Form toxic metabolites eg. Phenacetin

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14
Q

How does CYP P450 work?

A

Drug-R + O2 —–(NADPH to NADP by CYP)—-> Drug-OR +H2O

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15
Q

Where are CYP enzymes found?

A

The majority are in the liver but some are found in the walls of the intestine
In mammals CYP is bound to the endoplasmic reticulum

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16
Q

What is the most important CYP enzyme?

A

CYP 2D6 only represents 2% of enzymes in the liver but carries out 1/3 of metabolism of drugs in the liver

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17
Q

What are the topical drug administration methods?

A

Skin: Local slow & sustained effects (hours to weeks, e.g. patches).
Eye drops: local effect to renew frequently (washed away rapidly).
Nasal instillation local systemic effect.

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18
Q

What is the benefit/drawback of intradermal administration?

A

Slow absorption

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19
Q

What are the advantages and disadvantages of subcutaneous administration?

A

Faster absorption but fat layer may trap lipid soluble compounds
Massage increases blood flow and absorption.

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20
Q

What are the advantages and disadvantages of IM administration?

A

Very fast absorption
Physical activity/massage increases absorption.
Absorption: liquid>suspension>emulsion

21
Q

When is intravascular administration used?

A

Mostly used when need to accurately control the body concentration of drugs. Typically used when compounds have narrow margins of safety between therapeutic and toxic index

22
Q

What is the drawback with IV administration?

A

Drug injected cannot be recalled (whereas stomach pump or emetics can be used for enteral routes & other means exist to delay dermal/muscular injections).
A slow administration is needed to avoid side effects

23
Q

What are the advantages and disadvantages of inhalation administration?

A

Gas and aerosols have a rapid systemic effect but dependent on:
1- the tidal volume
2- the size of the aerosol particle (not true for gas). The smaller the more likely to reach alveolar ducts and sacs. Otherwise get stacked in bronchi

24
Q

What are the advantages and disadvantages of inhalation administration?

A

Gas and aerosols have a rapid systemic effect but dependent on:
1- the tidal volume
2- the size of the aerosol particle (not true for gas). The smaller the more likely to reach alveolar ducts and sacs. Otherwise get stacked in bronchi

25
Q

What are the main and secondary routes of drug excretion?

A

GA)

Secondary routes: Milk, sweat

26
Q

When the pH of the urine < pH of blood what happens to drug excretion?

A

a) Trapping of basic drug in urine therefore increased renal excretion
(b) Greater reabsorption of acid drug therefore reduced renal excretion

27
Q

When the pH of the urine > pH of blood what happens to drug excretion?

A

(a) Trapping of acid drug in urine therefore increased renal excretion
(b) Greater reabsorption of basic drug therefore reduced renal excretion

28
Q

Define Quantitative Pharmacokinetics (PK)

A

Changes in plasma/tissue drug concentration with time

29
Q

Define Quantitative Pharmacodynamics (PD)

A

Changes in biological response with time

30
Q

Define drug absorption rate

A

The Amount of Drug Absorbed from Administration Site to Measurement Site per Unit Time
Units: Mass or Moles per time

31
Q

Absorption rate from bolus intravenous administration can be considered…

A

instant

32
Q

Absorption rate from infusion administrations eg intravenous infusion, transdermal patch etc follows….

A

zero order kinetics

33
Q

Absorption rate from diffusion type administrations eg oral, intramuscular etc tend to follow….

A

first order kinetics

34
Q

What is the infusion rate (IR)?

A

Absorption rate from infusion administration = Infusion Rate (IR) and rate is independent of the Amount of drug (zero order)

35
Q

Absorption rate from oral administration tends to be proportional to….

A

….amount of drug (first order)

Amount of drug at administration site decreases with time therefore, rate of absorption decreases

36
Q

Define drug elimination rate

A

The Amount of Parent Drug Eliminated from the Body per Unit Time

Units: Mass or Moles per time

Elimination rate is defined with respect to irreversible removal of parent drug and does not include metabolites

37
Q

Define volume distribution

A

The volume into which a drug appears to be distributed with a concentration equal to that of plasma OR A proportionality constant relating the Blood/plasma concentration to the amount of drug in the body

38
Q

If Vd is in the order of 0.1-0.3L/Kg then the drug is most likely…

A

water soluble and distributes to the ECF

39
Q

If Vd is in the order of 0.6L/Kg then the drug most likely ……

A

distributes to the ECF and ICF

40
Q

If Vd is high (in the order of 2L/Kg) then the drug is probably….

A

accumulating in a particular site

41
Q

What is total body (blood) clearance?

A

The volume of blood/plasma cleared of parent drug per unit time OR A constant relating the rate of elimination to the blood/plasma concentration

42
Q

Rate of elimination =

A

Blood/plasma clearance x Blood/plasma conc

43
Q

Cl total =

A

Cl(hepatic) +Cl(renal) + Cl(Pulmonary)

44
Q

Rate of elimination cannot exceed the….

A

Rate of flow to the organ

45
Q

How do we determine Total body clearance (CL)?

A

Blood/Plasma clearance is determined from the area under the blood/plasma concentration versus time curve (AUC) from an IV administration

CL = Dose/AUC for IV or = FDose/AUC
where oral availability = F

46
Q

What is bioavailability (F)?

A

the fraction or percentage of administered dose that reaches the plasma

47
Q

How do we determine bioavailability (F)?

A

F = ( Dose IV/ Dose oral) x (AUC IV/AUC oral)

48
Q

What is the elimination rate constant (k)?

A

A constant relating the rate of elimination to the amount of drug in the body
k = clearance/ vd

PVS (43 decks)

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