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Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

Cmax

A

Maximum concentration of drug following administration

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2
Q

Tmax

A

Time at which maximum concentration of drug occurs

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3
Q

AUC

A

Area under the curve (of a concentration vs time curve)

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4
Q

What measures total systemic exposure to a drug?

A

AUC

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5
Q

Are the large majority of drugs eliminated by zero order or first order processes?

A

First order (concentration dependent)

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6
Q

Semi-log plot

A

Plotting log(concentration) against time

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7
Q

Relationship between half life and k

A

T1/2 = 0.693/k

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8
Q

Formula to calculate the concentration at any given time for first order drug

A

Ln C = -kt + ln C0

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9
Q

What percentage of a first order drug is eliminated by 4 half lives?

A

93.75%

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10
Q

How do you calculate half life for a zero order drug?

A

T1/2 = 0.5 A0/k0 (A0 is initial drug in system, k0 is the zero order rate constant (mass/time))

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11
Q

What effect does eating before taking an oral medication have on the pharmacokinetics of that drug?

A

Cmax is reduced and Tmax is delayed (because food inhibits gut housekeeper waves and thus slows absorption)

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12
Q

Why is it recommended that penicillin be taken on an empty stomach?

A

Because penicillin is degraded in acidic environments, and food presence slows absorption (increasing amount of drug degraded while in stomach)

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13
Q

Calculation for bioavailability

A

(Div * AUCoral) / (Doral * AUCiv)

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14
Q

Factors affecting oral availability of a drug

A

Solubility, polarity, size, lumen alterations of drug, first pass metabolism, drug transporters, pH

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15
Q

What type of drug best avoids being altered in the gut lumen when given orally?

A

Small, non-peptide molecules

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16
Q

Two examples of multi-drug transporters in the gut

A

P-glycoprotein and ABC cassette binding proteins

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17
Q

How do basic conditions in the stomach affect absorption of aspirin?

A

None will be absorbed in the stomach (requires acidic environment), but the small intestine will almost entirely make it for it

18
Q

What types of medications can be taken sublingually?

A

Lipid soluble molecules (nitroglycerin, buprenorphine)

19
Q

Why do rectally administered drugs have less first pass metabolism?

A

Venous drainage here is partially portal and partially systemic

20
Q

When drugs are administered IM or SubQ, how are they absorbed?

A

Large molecular weight drugs (100,000 and up) are drained by lymphatics, smaller are taken up by capillaries

21
Q

Is penicillin a good choice for treating meningitis? Why or why not?

A

No. Large and polar, does not cross BBB well

22
Q

Calculation for volume of distribution

A

(Amount of drug in body at equilibrium) / (Plasma drug concentration)

23
Q

Give the effects of tissue protein binding and plasma protein binding respectively on volume of distribution

A

Tissue protein binding - increases volume of distribution, plasma protein binding - decreases volume of distribution

24
Q

What are the two main plasma binding proteins and what type of molecule does each bind?

A

Albumin - binds acidic drugs, a1-acid glycoprotein - binds basic drugs

25
Q

Calculation for clearance

A

Elimination rate / (Plasma Concentration)

26
Q

Calculation for a loading dose

A

D = Vd*C (volume of distribution times desired concentration)

27
Q

The classic example of a drug that is freely filtered and not secreted

A

Inulin

28
Q

Which form of acids and bases tend to be reabsorbed from the kidney tubule, ionized or non-ionized?

A

Non-ionized (remember, lipophilic (i.e. non-polar non-ionized) substances can cross membranes easily

29
Q

When dosing drugs, what measurement do we use as a proxy for kidney function?

A

Creatinine clearance

30
Q

In two compartment models, what do the alpha and beta half lives represent respectively?

A

Alpha half life - distribution phase, beta half life - terminal elimination phase

31
Q

What effect does grapefruit juice have on the activity of p-glycoprotein?

A

Inhibits it (leading to an increase in drug levels)

32
Q

Give two examples of drugs with huge volumes of distribution and state whether this indicates greater distribution of drug in plasma or tissue

A

Greater in tissue. Nortriptyline (1300 L), Digoxin (440 L)

33
Q

Give two examples of drugs with small volumes of distribution and state whether this indicates greater distribution of drug in plasma or tissue

A

Greater in plasma (possibly only in plasma). Theophylline (35 L), Gentamicin (18 L)

34
Q

In two compartment models, what determines the elimination rate and biologic half-life

A

The beta (elimination) phase

35
Q

What two factors primarily determine elimination rate?

A

Blood flow to the eliminating organ and efficiency of the organ in eliminating the drug

36
Q

Relationship of clearance to volume of distribution

A

Cl = Vd*Ke (volume of distribution times elimination constant)

37
Q

Formula for estimating creatinine clearance

A

(140-age) * (Body weight in Kg) / (72 * Serum Creatinine) (applies to males, multiple by 0.85 for females)

38
Q

What system is used to classify patients with hepatic impairment?

A

Child-Pugh Score for Cirrhosis (takes into account serum bilirubin, albumin, ascites, INR)

39
Q

What effect does CHF have on drug pharmacokinetics

A

Decreases elimination (due to decreased blood flow to eliminating organs)

40
Q

What effects can pregnancy have on drug pharmacokinetics?

A

Decrease protein binding, increase renal excretion, variable effects on metabolism

41
Q

Approximately how many half lives are required to achieve steady state

A

4-5 half lives

Pharmacology (16 decks)

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