Podcast
Questions and Answers
Which model proposed that a drug and receptor interaction is a flexible and dynamic process?
Which model proposed that a drug and receptor interaction is a flexible and dynamic process?
- Lock-and-key model
- Static binding model
- Induced-fit model (correct)
- Rigid docking model
In the context of biological systems, what is the behavior of water in acid-base reactions?
In the context of biological systems, what is the behavior of water in acid-base reactions?
- It acts as a neutral molecule and does not get involved in acid-base reactions.
- It acts exclusively as a strong base.
- It acts exclusively as a strong acid.
- It acts as both a weak acid and a weak base. (correct)
What is the definition of a base in the context of acid-base chemistry?
What is the definition of a base in the context of acid-base chemistry?
- A substance that forms hydronium ions.
- A substance that remains neutral in an aqueous solution.
- A substance that accepts protons. (correct)
- A substance that donates protons.
What best describes an ionized acid?
What best describes an ionized acid?
According to the context of drug-receptor interactions, what can occur due to the drug-receptor association?
According to the context of drug-receptor interactions, what can occur due to the drug-receptor association?
What does a low pKa value indicate about an acid?
What does a low pKa value indicate about an acid?
What is the relationship between the pKa of a base and its conjugate acid?
What is the relationship between the pKa of a base and its conjugate acid?
What characterizes a weak acid in terms of pKa and its interaction with water?
What characterizes a weak acid in terms of pKa and its interaction with water?
A chemical with a pKa of 14 would be described as:
A chemical with a pKa of 14 would be described as:
Why is understanding a drug's acid-base chemistry important?
Why is understanding a drug's acid-base chemistry important?
Flashcards
Lock and Key Model
Lock and Key Model
The initial model of drug-receptor interaction, where the drug fits perfectly into a receptor like a key into a lock.
Induced Fit Model
Induced Fit Model
The understanding that both drugs and receptors are flexible and can adjust their shape during interaction.
Structural Features and Pharmacological Action
Structural Features and Pharmacological Action
Predicable pharmacological effects from changes in a drug's structure, explained by the lock-and-key model's assumption of a rigid fit.
Acid-Base Properties of Drugs
Acid-Base Properties of Drugs
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Water as an Amphoteric Molecule
Water as an Amphoteric Molecule
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What is pKa?
What is pKa?
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What does a low pKa indicate?
What does a low pKa indicate?
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What does a high pKa indicate?
What does a high pKa indicate?
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What is the pKa of a base?
What is the pKa of a base?
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How is pKa useful in drug development?
How is pKa useful in drug development?
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Study Notes
Acid-Base Properties of Drugs
- Drugs are classified as acids or bases.
- Acid-base properties influence drug biodistribution and partitioning.
- An acid is a proton donor.
- A base is a proton acceptor.
- Un-ionized acids (e.g., carboxylic acids) donate protons to form ionized conjugate bases (e.g., carboxylate).
- Ionized acids (e.g., ammonium compounds) donate protons, yielding un-ionized conjugate bases (e.g., amine derivatives).
- Un-ionized bases accept protons and form ionized conjugate acids.
- Ionized bases accept protons and form un-ionized conjugate acids.
Acid/Conjugated Base and Base/Conjugated Acid Pairs
- Water is amphoteric; it can act as both an acid and a base in biological systems.
- Water can accept protons from acidic drugs (forming hydronium ions) or donate protons to basic drugs (forming hydroxide ions).
Acid Strength
- pKa is a measure of acid strength.
- pKa is the negative logarithm of the modified equilibrium constant (Ka).
- A lower pKa indicates a stronger acid.
- Strong acids (low pKa) have equilibria that favor the formation of products (conjugate acid and base).
- Weak acids (high pKa) have equilibria that favor the reactants (un-ionized acid).
- A pKa for a base is the pKa of its conjugate acid.
- A pKa for an acid is the pKa of its conjugate base.
Examples of Acid-Base Reactions
- Specific examples of acid-base reactions involving various compounds (hydrochloric acid, sodium hydroxide, dihydrogen phosphate, ammonium chloride, acetic acid and its conjugate base, indomethacin, saccharin, ephedrine HCl).
Percent Ionization
- Percent ionization is calculated using equations.
- The equations for percent ionization vary depending on whether it's an HA acid (e.g., carboxylic acids) or a BH⁺ acid (e.g., amines).
- The % ionization of a drug can be influenced by the pH of the surrounding environment.
- pH = pKa indicates 50% ionization. Increasing pH one unit from pKa will cause increased ionization for HA acids (up to 90.9% ionized) but decreases for BH⁺ acids (down to 9.1% ionized).
Drug Ionization and pKa
- Understanding the pKa is important for drug solubility and biodistribution.
- Ionized (polar) drugs tend to dissolve in water, while un-ionized (nonpolar) drugs tend to dissolve in lipids.
- The pKa of a drug determines which form (ionized or un-ionized) predominates at a given pH.
- Adjusting pH can influence the ionization state of a drug, thus its solubility.
Drug Distribution and pKa
- Drug distribution (e.g., in the blood, tissues, across biological membranes, including gastric mucosa and intestinal tract ) is influenced by ionization.
- Unionized forms of drugs cross membranes more readily than ionized forms.
- Ionized forms are more water soluble.
- Factors like pH, pKa, protein binding can influence these effects.
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