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PHC 532- Exam 3 > Phenytoin ADME > Flashcards

Phenytoin ADME Flashcards

1
Q

Phenytoin is assumed to have what bioavailability?

A

100% (F=1)

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2
Q

After PO administration of phenytoin, what happens to the absorption and peak concentrations?

A

Peak concentrations are delayed and there’s slow absorption

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3
Q

The time to achieve peak concentration is dependent on what?

A

The product and dose

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4
Q

What formulation of phenytoin isn’t recommended due to patient discomfort?

A

IM injection

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5
Q

What formulations absorb faster than phenytoin capsules

A

Suspension and chewable tablets

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6
Q

Obese patients have a ? Vd while taking phenytoin.

A

Larger

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7
Q

When bound concentrations of phenytoin decrease, what happens to the unbound concentration?

A

Remains relatively unchanged

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8
Q

Is there a change in loading dose needed with altered plasma binding?

A

Nope

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9
Q

What is phenytoin primarily bound to?

A

Albumin in the plasma

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10
Q

Disease states that are commonly associated with altered phenytoin plasma protein binding

A

Hypoalbuminemia, ESRD

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11
Q

Phenytoin is primarily cleared by what form of metabolism?

A

Hepatic metabolism

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12
Q

Enzyme that metabolizes ~90% of phenytoin

A

CYP2C9

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13
Q

Enzyme that metabolizes ~10% of phenytoin

A

CYP2C19

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14
Q

Phenytoin follows what form of PK?

A

Michaelis-Menten/saturable PK

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15
Q

Steady state serum concentrations of phenytoin do what after a dosage increase?

A

Increase in a disproportionate manner

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16
Q

Is Cssav of phenytoin proportional to the maintenance dose?

A

No

17
Q

Is the time to Css 3-5 half-lives for phenytoin?

A

No

18
Q

Elimination of phenytoin is limited to what?

A

Capacity limited

19
Q

Phenytoin CL decreases with what?

A

Increasing concentrations

20
Q

When the Css of phenytoin becomes greater than Km, what happens?

A

MD approaches Vmax and a small change in either the maintenance dose or Vmax can result in disproportionate changes in the new steady state concentration

21
Q

Phenytoin in pregnancy

A

Concentrations tend to fall

22
Q

Reduced GI motility in pregnancy does what to phenytoin absorption?

A

Enhance it

23
Q

Phenytoin in liver and renal disease

A

Binding of phenytoin to serum proteins is reduced

24
Q

What happens to the time to steady-state with an increase in the dose?

A

The time to Css increases

25
Q

True or false: Css increases more than proportionally with an increase in phenytoin dose

A

True

26
Q

True or false: different Vmax and Km values can provide the same steady state concentrations of phenytoin

A

True

PHC 532- Exam 3 (5 decks)

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