Pharmacokinetics Absorption and Distribution 2

an important consequence of administering drugs by different routes is that there can be a?

• Different Bioavailbility

The standard of comparison in determining bioavailability, against which all other routes are compared, is the?

• IV Dose

Factors that can affect bioavailability include?

• Metabolism

• Lipid Solubility

• Chemical Stability

• Drug Formation

drug plasma levels decline over time, This decline is the result of?

• The Drug being Metabolized and Excreted.

The plasma level reflects the concentration of drug at the target site more?

• Closely than the dose and may indicate tissue exposure

Drug will produce a pharmacological effect when the plasma level…?

• Falls within Therapeutic Range

IV plasma Concentration Diagram

Oral Plasma Concentration Diagram

The plasma half-life (t_½) is time interval during?

• During which the Drug Concentration is Reduced by 50% / 1/2

Plasma Half life provides an important indicator for the?

• Duration of Drug Action

Therefore drugs with a short plasma half-life will have a?

• Short Duration of Action.

• and require more frequent administration than drugs with a long plasma half-life.

Drugs are distributed throughout the body through the various?

• Fluid Compartments of the Body

• Body Water is between 50-70% of Weight.

• Lower range being women.

Highly fat-soluble drugs may accumulate?

• In fat.

Body water is distributed in the following main compartments?

• Blood Plasma = 5% TBW

• Interstitial and Lymph = 17% TBW

• Intracellular Fluid = 30-40 % TBW

• Transcellular Fluid = 5 % TBW

• Fat = 20 % TBW

Drugs exist in what 2 Forms within Compartments?

• Free and Bound Forms

What is the only Drug Form that can move between Compartments?

• Free Drug

The equilibrium of distribution between the various compartments depends on?

• Permeability between Tissue

• Binding within Compartments

• pH partition

• Fat: Water Partition

Lipid-soluble drugs reach?

• All Compartments

• and may accumulate in Fat

lipid-insoluble drugs are mainly confined to?

• Plasma and Interstitial Fluid.

• Most do not  enter the brain.

The blood brain barrier is caused by a continuous?

• Layer of Epithelial Cells

• joined by tight junctions and surrounded by pericytes.

making the brain inaccessible to drugs with?

• Insufficient Lipid Solubility

Volume of Distribution Diagram Calculator

The two main reasons why a drug may be confined to blood plasma are?

• V_d less than 5L

• Molecular Size

• Plasma Protein Binding

• for example heparin.

Drugs distributed in the Extracellular Compartment have a V_d between?

• V_d between 5L and 15 L

• for example gentamicin and carbenicillin 

Drugs distributed throughout all compartments and water have a vD of ?

• V_d greater than 15L

• Aka Lipid Soluble Drugs.

• Morphine E.G

Pharmacokinetic interaction occurs when?

• drug A alters the concentration of drug B that reaches the site of action.

Certain drugs can alter the rate of gastric?

• Gastric Emptying

• Results in Slower GI Absorption

• Mainly in Small Intestine

atropine inhibits?

• Gastric Emptying

metoclopramide hastens?

• Gastric Emptying