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Pharmaceutics II Quiz 1
Terms in this set (37)
A cluster of many trillions, quadrillions, or more molecules.
Consists of a unique assembly of specific atoms connected through chemical bonds.
in a liquid medium to release molecules.
in a liquid to form a suspension
Aspirin: when the aspirin crystal is placed in water, the crystal arrangement breaks down and the aspirin molecules are randomly dissolved in the bulky solution.
Physicochemical properties of drug molecules
in water or particular organic solvent
- partitioning between different phases: aqueous solution to liquid membrane and vise versa.
Binding to surfaces: containers,
What determines physiochemical properties of drug molecules?
1. Structure and size
2. The ability to become
3. Polar functional groups (polarity)
4. Hydrophobic residues
Ionized organic molecules
Are much more soluble in water than those which are "neutral"
Non ionized drugs
Are more soluble in body lipids than those which are charged size (molecular weight)
1. Relative size of drug molecules
A drug whose molecular weight is less than 900Da is considered to be a "small drug molecule"
1. Size of drug molecule
- big molecules are more difficult to
from their crystalline state
- big molecules are more difficult to "move around" when dissolved in a solution
- this may result in a slow mixing of the drug and its surrounding environment (solvent)
2. Tendency to ionize
- Acids losing a proton (to water) to ionize: AH → H+ + A-
- Bases gaining a proton (from water) to ionize: B + H+ → BH+
- Tendency to ionize, or remain ionized is unique for each drug (unique pKa values)
an ionized drug is a water soluble drug
Acids losing a proton (to water) to ionize
AH → H+ + A-
Bases gaining a proton (from water) to ionize
B + H+ → BH+
What is an ionized drug?
A water soluble drug
2. Ionization state of
- drug molecules which contain
at least one nitrogen atom
which can accept a proton
- drug molecules which can accept a proton become ionized with a positive charge (-NH+)
The pH value at which the ionized and unionized form of the drug exist in equal concentrations.
- drug molecules which contain a carboxyl (-COOH)
- drug molecules which can release a proton and become ionized with a negative charge (-COO-)
Neutral drug molecules
A requirement for optimal drug absorption across cell membranes.
Log P >> 0
Characterize lipophilic miscible with lipids environment
Log P << 0
Typifies polar compounds soluble in the water phase
3. Functional groups
- Typically portions of organic molecules containing atoms other than carbon
- Are portions of drug molecules which might be able to ionize ("Acid dissociation - base protonation" lecture)
- Are portions of drug molecules which may be chemically reactive ("Chemical properties of drugs" lecture)
Drugs containing "neutral" functional groups
- cannot ionize
- generally contain polar functional groups which allow them to interact with water molecules (interaction with water molecules confers some limited aqueous solubility).
4. Hydrophobicity of drugs
- significant portion of the structure of
almost all drug molecules
consists of alkyl and/or aryl residues.
- very low water solubility if they are "neutral"
- the more "alkyl/aryl" functionality in a molecule the lower the aqueous solubility
How can hydrophobicity of drugs be painful for patients
Precipitation of hydrophobic drug molecules can occur in certain physiological environment e.g. muscles and this can be painful for the patient!
alkyl/aryl characteristics and their relation to hydrophobicity
The more alky/aryl characteristics the drug has, the more hydrophobic the drug becomes and the more insoluble it becomes
What types of interactions can occur between individual molecules, or more secifically a drug molecule and the surrounding environment?
Molecular Interactions in Solution
- Involve both repulsive and
- Are unique for each different drug molecule (e.g. characteristic boiling points, or solubility)
- Occur between drug molecules and their environment: Other drug molecules, Solvent molecules surrounding the drug molecule.
Drug and solvent molecules
- Van der Waals Forces (the attractive forces)
- hydrogen bonding (attractive)
- hydrophobic ("drug avoiding solvent molecules")
van der Waals forces
Fluctuating dipole (London)
Which molecule interactions would enhance drug solubility?
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