Drug Absorption Flashcards
What are four processes of drug therapy and what do they mean?
Pharmaceutical process is getting the drug into the patient.
Pharmacokinetic process is getting the drug to the site of action.
Pharmacodynamic process is producing the correct pharmocological effect.
Therapeutic process is producing the correct therapeutic effect.
What are nine ways of administering drugs?
Oral Intravenous Subcutaneous Intramuscular Sublingual Rectal Inhalation Nasal Transdermal
What is ADME?
Absorption
Distribution
Metabolism
Elimination
What is absorption?
The process of movement of unchanged drug from the site of administration to the systemic circulation.
What is Tmax?
The time to peak concentration.
The more rapid the rate of absorption the earlier the drug concentration peak.
What Cmax?
The peak concentration of drug.
Increasing the dose doesn’t affect the time at which the peak concentration is reached but does increase the peak concentration.
What is AUC?
Area under the drug concentration curve. This represents the amount of drug that reaches the systemic circulation.
What are therapeutic range and therapeutic index?
A drug is active over a range of concentrations which is therapeutic range. Below this range there will be little pharmacological activity and above it means toxicity.
Therapeutic index is a measure of the range at which the drug is safe and active.
What is bioavailability?
Amount of drug which reaches the circulation and which is available for action.
A drug given intravenously has 100% bioavailability.
What factors affect bioavailability?
Formulation
Ability of drug to pass physiological barriers.
GI effects
First pass metabolism.
How do ionised drugs work?
Both ionised and un-ionised forms of the drug will be present but the ionised drug doesn’t cross the membrane so the un ionised form will distribute evenly across the membrane so an equilibrium is established.
Eg proton pump inhibitors and antacids.
What does the Henderson Hasselbach equation show?
The relationship between the local pH and the degree of ionisation.
What is the ability of a drug to diffuse across a lipid barrier expressed as?
Lipid water partition coefficient. This is the ratio of the amount of drug that dissolves in the lipid and water phase when they’re in contact.
What is filtration?
Normally occurs through channels in the cell membrane and the drug needs to have a low molecular weight and size. Pushed by hydrostatic or osmotic pressure.
What gastrointestinal aspects affect drug absorption?
Motility is the speed of gastric absorption. This can be affected by other drugs, food and drink and illness (diarrhoea and pain).
Eg migraine reduces the rate of stomach emptying and therefore the rate of absorption of analgesic drugs.
What is first pass metabolism?
Drugs taken orally go to the liver and are metabolised so fast that they don’t get into the blood. The gut lumen and wall also speed this up.
It is increased in pregnancy.
So need to increase drug to lead to an effect.
What is an advantage of subcutaneous and intramuscular routes and what drugs are best administered this way?
Avoids first pass metabolism.
Water soluble drugs are best used as some other drugs are not well absorbed by this route.
What is sublingual absorption and why is it useful?
Sublingual absorption from the buccal mucosa Bypass first pass metabolism which would inactivate the drug so it enters the circulation directly.
Eg GTN for angina.
Why is rectal absorption useful and what is a disadvantage?
Bypass first pass metabolism and useful if there is irritation of the stomach.
Absorption tends to be slow.
What are five considerations when thinking about administering drugs?
Purpose and site of drug action Disease effects Patients ability to take medicine Speed of action Reliability of absorption
