ADME Two Flashcards
What does drug absorption refer to?
The passage of drug from the site of administration into the circulation
What administration technique results in immediate absorption?
Intravenous injection (100% absorbed)
What sort of administration is difficult for absorption?
Orally taken drugs have to overcome several barriers so are often are delayed and incompletely absorbed
What are two key factors of absorption?
Rate and Extent?
What is meant by rate with regards to absorption?
How rapidly does the drug get from the site of administration to the general circulation?
What is meant by extent in regards to absorption?
How much of the drug administered enters general circulation (% bioavailibility)
What are the types of drug adminstration?
Enteral
- Oral (po)
- Sublingual
- Rectal
Parenteral
- IV
- IM
- Subcutaneous
- Intradermal
- Lungs
What are the two most common routes of adminstration
IV (Rate = immediate, extent=100%)
Oral (Rate=gradual, extent=incomplete)
What are the advantages of IV administration?
- Very rapid
- Precise control (100% Bioava)
- Avoids problems with absorption, drug breakdown before entering circulation
- Good for drugs that are too irritating to be taken by mouth or given by tissue injection
What are the disadvantages of IV administration?
Skill required (dont want air embolism) Careful preparations of injected material (sterile etc) Most hazardous
What are the advantages of oral administration?
80% drugs do this
Safest, most convenient and economic
What are the disadvantages of oral administration?
Slow (0.5 to 3 hrs for effect)
Unpredictable with regards to Rate, Extent, Reproducibility
What are the three steps of drug tablet consumption?
Disintegration
Dissolution
Absorption
What are the drug factors influencing the oral bioavailibility of drugs?
Decomposition in acid gastric juices
Decomposition by gut enzymes
Degradation by gut microorganisms
Food may alter absorption rate and amount
Metabolism by gut wall enzymes
Metabolism by liver enzymes before entering systemic circulation
What is the rate limiting step of drug passing through the gi tract?
The stomach, as does not get absorbed here but depends on gastric emptying rate
What are the patient factors influencing absorption?
Stomach emptying rate
Intestinal motility
Interactions with food
how does stomach emptying rate influence absorption?
Major factor!
Rate increased with hunger
Rate decreases with vigorous exercise, food, pain
How does intestinal motility influence absorption?
Increased motility due to gastroenteritis and diarrhoea
-This decreases transit time (important for drugs with low water solubility)
Decreased motility with various drugs (Narcotics)
How does interactions with food change absorption?
e.g Chelation of tetracycline with metal ions (ca)
How do capillaries influence drug movement?
Most capillaries are relatively porous- thus drugs leave the blood regardless of whether they are poorly lipid soluble, charged or polar
What is the exception to the capillary factor?
The bbb has no pores, and glia cells for protection, thus only lipid soluble drugs diffuse across the BBB, unless a drug undergoes active transport.
How does blood flow influence drug distribution?
The tissues that receive more blood receive more drug.
Rate of distribution to tissues depends on blood flow rate. ie liver, lungs, heart receive drugs rapidly, muscles do not.
