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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5320_Библиотеки_им_академика_М_И_Перельмана
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176
Pharmaceutical Dosage Forms and Drug Delivery
4. pHKa
-
imum at the isoelectric point.
Nature of adsorbent/ solid substrate
8.4.3 Wettability and Wetting Agents
wettability of a material can be
contact angle is the angle
the contact angle (θ-
hydrophobic
hydrophilic.
A wetting agent
1. Surfactants
2. Hydrophilic colloids: Acacia, bentonite, tragacanth, alginates, and cellulose derivatives act as
3. Solvents
FIGURE 8.5
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Interfacial Phenomena
8.5 Biological and Pharmaceutical Applications
177
• Physical stability of biphasic dosage forms
• Gas exchange in the lung
• Preventing absorption after oral overdose and poisoning
• Hemoperfusion
• Adsorption in drug formulation
• Adsorption to packaging components: Adsorption of medicaments onto the container and closure
• Improving drug dissolution
adsorption of a small amount of surfactant on the surface of drug particles.
• Protein adsorption: Adsorption of proteins onto surfaces is a fast process and depends on concen-
Review Questions
8.1
A Chemical adsorption is reversible
B
C
D
E All of the above
8.2
adsorption.
8.3
8.4
-
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178
Pharmaceutical Dosage Forms and Drug Delivery
8.6
g/ cm3
8.7 2
cm22
REFERENCES
-
J Pharm Pharmacol 64
Further Readings
Reminton’s The Science and Practice of
Pharmacy
Pharmaceutics: The Science of
Dosage Form Design
Physicohemical Principles of Pharmacy
Applied Physical Pharmacy
Surfactants and Interfacial Phenomena
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9
Colloidal Dispersions
On completion of this chapter, the students should be able to
1.
dispersions.
2.
3.
4.
6.
9.1 Introduction
dispersed phase, distributed throughout a con-
tinuous phase or dispersion medium
1. Molecular dispersions
clear or colored.
2. Colloidal dispersions
substitutes to maintain osmotic pressure.
3. Coarse dispersions
dispersions.
LEARNING OBJECTIVES
DOI: 10.1201/9781003389378-11
179
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180
Pharmaceutical Dosage Forms and Drug Delivery
•
•
• ®) is used as an
antifungal agent.
•
• Colloidal copper has been used in the treatment of cancer.
•
• ®
9.2 Types of Colloidal Systems
9.2.1 Lyophilic Colloids
A lyophilic colloid (solvent loving)-
lipophilic colloids
organic solvent. Hydrophilic colloids
in organic solvents and are thus referred to as lipophilic colloids.
9.2.2 Lyophobic Colloids
solvent- hating
molecules, particles, or material in an aqueous medium results in hydrophobic colloids. Special methods
.
9.2.3 Association Colloids
Association, or amphiphilic colloids
several monomers, or individual molecules, occurs, leading to micelle
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Colloidal Dispersions
TABLE 9.1
181
Property Hydrophilic Colloids Hydrophobic Colloids
Ease of dispersion of materials
in dispersion medium
Irreversible
Capable of acting as protective colloids Incapable of acting as protective colloids
precipitation
Stable
dispersion medium
Similar to that of the dispersion medium
critical micelle concentration (CMC
monomers that aggregate to form a micelle is called the aggregation number
the formation of association colloids is spontaneous, provided that the concentration of the amphiphile
9.3 Preparation of Colloidal Solutions
dispersion method
condensation methods).
• Dispersion methods
• Condensation methods
colloidal sulfur
9.4 Properties of Colloidal Solutions
9.4.1 Kinetic Properties
osmosis.
d
d
d
d
M
t
C
x
DfkT=
D
kT
f
R
f r= 6
πη
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182
9.4.1.1 Brownian Movement
Pharmaceutical Dosage Forms and Drug Delivery
dispersed- phase particles.
9.4.1.2 Diffusion
movement, called diffusion, of the dispersed- phase particles from a region of high concentration to a
Fick’s
rst- law equation:
DS
=− (9.1)
M is the mass of substance diffusing in time dt across a cross- sectional area S; dC/ dx is a con-
centration gradient; dC over the diffusion distance dx; D
D f, of the
Df
dependent on temperature, TEinstein’s law of diffusion:
(9.2)
or
=
kT is the absolute temperature; and f
R
number, N
=
(9.3)
6πr
RT
rN
6
πη
r
−
()
0
ρρ
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Colloidal Dispersions
183
ηr the radius of the particle.
DkT=
(9.4)
Stokes– Einstein equation:
D
=
9.4.1.3 Sedimentation
medium, the dispersed phase accumulates at the bottom, or sediments, and this process is called sedimen-
that of the dispersion medium, such as in the case of aqueous emulsions, the dispersed phase accumulates
vStokes’ law equation:
2
ρ
ρ
0
2
=
g
0
(9.6)
η
9
η
0
dispersion medium; and g
gω2xω is the angular velx is the distance of the particle from the center.
9.4.2 Electrical Properties
Electrical properties of the dispersed phase refer to the electrostatic charge on the surface of the particles
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184
9.4.2.1 Surface Charge
Pharmaceutical Dosage Forms and Drug Delivery
•
electrostatic charge on the particles is sought that promotes the formation of uniform dispersion
•
•
9.4.2.1.1 Ionization
the pKa
+
3
Ka of
positive charges equals the total number of negative charges in the protein, resulting in the net charge
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Colloidal Dispersions
9.4.2.1.2 Ion Adsorption
ions) on
+ ions in the
charged surface are called an electrical double layer. Figure 9.1
-
face charge.
FIGURE 9.1
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