the medicine

Question 1

what is intrinsic the solution rate (IDR)

Answer 1

The rate of dissolution is dependent on mainly variables. For example, particle size, viscosity, pH, temperature.

However, the intrinsic dissolution rate is a measure of dissolution, which is independent to these variables

Question 2

What are the units for intrinsic dissolution rate?

Answer 2

cm/s

Question 3

What letter represents the intrinsic dissolution rate

Answer 3

k

Question 4

what does a larger value of k suggest

Answer 4

A faster dissolution rate

Question 5

what are the two equations for intrinsic dissolution rate

Answer 5

k = D/h and kCs = dm/dtA

Question 6

Why are salts important in pharmacy?

Answer 6

improvement in drug solubility may be achieved by forming a salt. It may improve dissolution rate

Question 7

is the dissolution rate high or low of a weakly acidic drug in a low pH

Answer 7

low

Question 8

Is the dissolution rate of a weekly acidic drug high or low in a high pH?

Answer 8

high

Question 9

is the dissolution rate of a weakly basic drug high or low in a high pH?

Answer 9

low

Question 10

is the dissolution rate of a weakly basic drug high or low at a low pH

Answer 10

high

Question 11

suggest why a weakly acidic drug is converted to basic salt, then the dissolution of a basic salt forms a weakly acidic drug again (HD)

Answer 11

HD to NaD to HD again

Sodium ions increase the pH of the diffusion layer, allowing the free drug to be more soluble in the diffusion Layer

D- complexes back with hydrogen ions (H+) to form HD again. It’s forms as a fine precipitate of the free acid this decreases particle size and increases surface area. This increases dissolution rate, and the absorption of HD

Question 12

describe dissolution of an acidic salt of a weakly basic drug in gastric fluids
example [chlopromazine hydrochloride]

Answer 12

hydro chloride ions lower the pH of the diffusion layer, and ensure it is lower than the gastric/intestinal fluids

this increase solubility/dissolution in the diffusion layer

Precipitation of the free base is avoided as absorption into the small intestine is rapid

Question 13

why is salt choice important in formulation?

Answer 13

can deliberately choose a salt to decrease apparent solubility

for example, formulations with sodium salt can have a bitter taste in solution

Formulations with magnesium salt decreases solubility, therefore less drug is in the solution, and the bitter taste is reduced

Question 14

What is the common ion effect?

Answer 14

Adding a common ion reduces the apparent solubility of a slightly soluble electrolyte

AB (solid) = B- + A+ (solutions)
increasing the apparent [] of A or B will push equilibrium towards the left, more solid AB will precipitate

Question 15

what does the Noyes-Whitney equation assume

Answer 15

it assumes a constant surface area of solid during dissolution

Question 16

we need a dissolution equation for changing surface area what law do we use

Answer 16

Hixson-Crowell cube root law

Question 17

what is the Hixson-Crowell cube root law

Answer 17

it assumes drug powder consists of un uniformly sized particles

radius of particles is not assumed, constant throughout the dissolution process

Rate of dissolution is based on the cube root of the weight of the particles

Question 18

what is the Hixson-Crowell cube root law

Answer 18

cube root Mt = cube root Mo -kt

where:
Mt= undissolved mass at time t
Mo= mass at the start
t= time
k= the cube root of the dissolution rate constant

can be y=mx+c

Question 19

what does -k suggest

Answer 19

that the gradient is negative. and the y intercept is cube root Mo ( mass at the start )

Question 20

what is salting in

Answer 20

when solubility has increased the effects is referred to as salting in. (hydro trophy)

commonly occurs when salts of organic acids are added

Increasing the amount of salt added, increases the effect

Question 21

What is hydrotrophy?

Answer 21

salting in

Question 22

what is more common salting in or salting out?

Answer 22

salting out

Question 23

what is salting out

Answer 23

when the apparent solubility has decreased

inorganic electrolytes, commonly decrease solubility. ions of electrolytes, interact with water molecules, reducing the amount of water available for dissolution of nonelectrolyte.

The effect is greater with highly saturated electrolytes.

eg: LiCl having a greater effect than CsCl

Question 24

what is complexation

Answer 24

it may be possible to interact a poorly soluble drug with a soluble material to form a soluble macromolecule complex.

this is a reversible process

eg: I2 + KI = KI3-

Question 25

what are cyclodextrins

Answer 25

A hollow cylindrical molecule made up to glucose units in a cyclic arrangement.

they have the ability to form inclusion complexes.

They can also be used to improve the rate of dissolution of a drug

Question 26

What is an inclusion complex?

Answer 26

part of the drug molecule that inserts into the hollow central cavity of the cyclodextrin molecule.

Question 27

Do exothermic reactions, increase or decrease solubility

Answer 27

Decrease solubility

Question 28

Do endothermic reactions, increase or decrease solubility

Answer 28

Increase solubility