Flashcards in Drug Disposition III Deck (12):

1

## First Rate Drug Elimination (K>E)

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There is a constant fraction of drug elimination per unit time, creating a exponential curve

It is a fractional rate of drug elimination

2

## Biological Half Life (T>1/2)

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The time required to reduce the plasma drug concentration by 50%

t>1/2 = 0.693/K>E, which is to say that half life is inversely proportional to the first order rate constant

3

## Importance of Half Life

### Determines duration of action. Takes 5-6 half lives for a dose to be effectively eliminated. Can help determine dosage intervals.

4

## Rate of obsorption

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Affected by:

Route of administration

Blood flow

Slow-release preparations

Slow absorption means low peak concentrations and longer duration of action

5

## Plateau Principle

### Steady state plasma concentrations reached under zero order drug administration and first order drug elimination.

6

## Multiple Drug Dosing

### Given multiple dosings at fixed intervals, the rate of elimination will increase as the concentration of drug increases in the plasma. The rate of elimination will eventually reach the rate equal to the amount of a single dose between doses. (steady state)

7

## Plasma Clearence

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Defined as the volume of plasma from which a drug is fully removed per unit time (ml/min)

Plasma clearance is equal to the sum of all organs

Rate of elimination = Plasma Clearance x Plasma Conc.

8

## Steady State (Css)

### Rate of elimination = Rate of administration

9

## Rate of Administration

### = steady state x plasma clearance

10

## Choice of interval depends on

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Drug Half Life

Size of therapeutic window

Frequency/severity of adverse effects

Convenience and patient compliance

11

## Calculating Loading Dose

### Loading dose is roughly equal to twice the maintenance dose.

12