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Flashcards in Introduction to Healthcare Science Deck (229)
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What is the difference between a drug and a medicine?

- A drug is a substance that alters normal physiological function
- A medicine is the means by which drugs are delivered to the sire of action in the body


Difference between pharmacology and therapeutics?

- Pharmacology is the study of drugs and their affects
- Therapeutics is the treatment of diseases


What is pharmacodynamics?

How the drug acts


What is pharmacokinetics?

How the body acts on the drug


What are the main routes of administration?

- Enteral (oral)
- Nasogastric
- Sublingual
- Controlled release
- Rectal
- Parenteral (IV)
- Skin
- Eye
- Lungs
- Nose


What is the therapeutic index?

- Ratio between lethal dose and therapeutic dose
- The higher the index, the safer the drug (How close is the safe dose to the toxic dose)


What are the main stages to consider in pharmacokinetics?



How is the duration of action of a drug measured?

Half life


What is a drugs half life?

Time taken for the concentration of the drug in the blood to decrease by half


How can we influence a drugs duration of action?

Modified release, controlled release, slow release


Advantages of controlled release drugs?

- Less dosage frequency and more patient adherence
- Reduce incidence of adverse effects


Disadvantages of controlled release drugs?

- Expensive
- Lack of standardisation


What is a drugs bioavailability?

The percentage or fraction of the administered dose which reaches the systemic circulation of the patient


What are the factors affecting bioavailability?

- Dose form
- Chemical form
- First pass metabolism effect


How is drug distribution measured?

Two compartment model (blood and tissues)
Volume of distribution is a theoretical concept that measures the extent to which a drug moves into the tissues
- Large volume of distribution most in the tissue
- Small volume most in blood


How is drug elicitation measured?

Described by clearance
- Clearance is the volume of plasma completely cleared of drug per unit time


Where does drug elimination occur?

Major site is the liver but also happens in the GI tract, kidneys and lungs


Where does drug excretion occur?

- Major site is the kidney but also GI tract, saliva, sear, breast milk
- If GI tract, sometimes reabsorbed


How long does it take to reach a steady state of drug concentration in blood?

Usually around 5 half lives and the same to go back down


Why are modified release drugs better?

Modified release would hopefully show less harsh peaks so less likely to go into the toxic dose or dipping into the sub-therapeutic level


What needs to be considered when choosing the right route of administration?

- System or local
- Speed of action
- Duration of action
- Bioavailability
- Accuracy of dose
- Adverse effects: some routes will have more than others
- Patient status: do they need to be able to swallow, does it need injection


What is drug clearance?

- Clearance is the volume of plasma completely cleated of drug per unit time
- Cp – concentration of drug in plasma


What is drug metabolism?

- Changes one chemical compound into another
- Usually makes molecules more water soluble to enable excretion by the kidney or biliary system
- Usually changes drugs into less active agents


What are the two phases of liver metabolism?

Phase 1
- Catalysed by cytochrome p450 enzymes by oxidation, hydrolysis reduction etc – enhancing the solubility
- Often still chemically active
Phase 2
- Conjugation by adding a glutathione, methyl or acetyl group
- More water soluble and easier to excrete
- Less active or inactive


Do drugs always undergo both stages od liver metabolism?

Drugs may undergo only one of these phases or both- not a particular order
- E.g. Aspirin: Phase 1 – hydrolysis to salicylic acid and Phase 2- conjugation with glycine or glucuronic acid
Pro drugs such as Enalapril
- Hydrolysis of its ethyl ester (phase 1_
- Metabolite is active drug but poorly absorbed when giving orally


Give an example of a drug with a toxic metabolite?



How is paracetamol metabolised?

Phase 1 to toxic metabolite
- The OH on the benzine ring is metabolites (loses H) to form NAPQI which directly attacks cells causing liver injury
Phase 2 to non-toxic metabolites
- Conjugation with glutathione
- Stops build-up of toxic metabolites


What happens when take too much paracetamol?

If take too much, there is not enough glutathione to prevent toxicity for phase 2


What is the treatment for parceatamol overdose?

Treatment gives acetylcysteine within 8 hours (donor for glutathione)


What is first pass metabolism?

If a drug is extensively metabolised in the liver, we say it undergoes first pass metabolism so very little drug is actually absorbed into the blood – affects the bioavailability