2B Adsoption, distribution, & binding

Routes of administration effect what

Adsorption, drug concentration, solubility and ionization

Lipid-soluble drugs

Can pass through the cell membrane by passive diffusion

Ex: alcohol movement high to low

The larger the concentration gradient the faster the diffusion

Ionized drug

Are not lipid-soluble they have an electric charge keeping them from passing readily through membranes via diffusion

• extent of ionization determines the pH & intrinsic property called pKa

Do drugs that are weak acids ionize more readily in basic or acidic solutions

In a basic/alkaline solution and less in an acidic environment

*this is the opposite for weak bases

What pH is pKa

pKa is the pH at which a drug is 50% ionized & 50% non-ionized

• helps determine dosage & routes

Where does the highest concentration of a drug occur?

Where blood flow is the greatest, brain, heart, kidneys

How do drugs leave capillaries

Drugs can leave capillaries through pores, even if drugs are not lipid-soluble

Do lipid-soluble drugs enter the brain

Lipid-soluble drugs can easily enter brain tissue, but the BBB limits movement

Where is the chemical trigger zone (CTZ) and what is it

Area postrema, in the brain stem medulla, causes vomiting when toxic substances enter the blood

What is special about brain capillaries

They don’t have pores meaning less movement, maintaining a more stable environment

Drug depots

Binding at inactive sites where no biological effect is initiated

Depot binding

Affects magnitude & duration of drug action (why drugs has different impacts on different people) non-selective can result of drugs staying in body for a while

Ex: marijuana in hair