Pharmacokinetics Flashcards
What is the primary mechanism for drug transport across biological membranes?
Passive diffusion
This mechanism involves the drug diffusing across the membrane in the direction of its concentration gradient without active participation from the membrane.
How do lipid-soluble drugs diffuse through biological membranes?
By dissolving in the lipoidal matrix of the membrane
The rate of transport is proportional to the lipid:water partition coefficient of the drug.
What factors influence the rate of passive diffusion of drugs?
- Lipid solubility of the drug
- Concentration gradient across the membrane
A more lipid-soluble drug achieves higher concentrations in the membrane and diffuses more quickly.
What is the significance of pH in drug ionization?
Most drugs are weak electrolytes, and their ionization is pH dependent
This contrasts with strong electrolytes that are nearly completely ionized.
Define pKa in the context of drug ionization.
The negative logarithm of the acidic dissociation constant of a weak electrolyte
pKa is the pH at which the drug is 50% ionized.
What equation represents the ionization of a weak acid HA?
pH = pKa + log([A]/[HA])
Where [A] is the concentration of the ionized drug and [HA] is the concentration of the unionized drug.
What happens to the ionization of a weak acid if the pH is increased by 1 scale?
[A]/[HA] = 10
This means the concentration of the ionized drug is ten times greater than that of the unionized drug.
What is the result of decreasing pH by 1 scale on drug ionization?
[A]/[HA] = 1/10
This indicates that the concentration of the unionized drug is ten times greater than that of the ionized drug.
What types of drugs ionize more at alkaline pH?
Weakly acidic drugs that form salts with cations
Examples include sodium phenobarbitone and potassium penicillin-V.
What role do specialized proteins play in biological membranes?
- Enzymatic functions
- Carrier functions
- Receptor functions
- Signal transduction
These proteins contribute to the dynamic nature of biological membranes.
What is the term for substances that are foreign to the body?
Xenobiotics
Drugs are considered xenobiotics as they are not normally produced by the body.
What kind of molecules can exhibit lateral movement in biological membranes?
Lipid molecules
This characteristic contributes to the dynamic structure of biological membranes.
Fill in the blank: The concentration gradient across a membrane affects the rate of _______.
Diffusion
A greater difference in concentration enhances the speed of diffusion.
