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How to calculate therapeutic index
LD50/ED50
Therapeutic window
The range of doses between the minimum dosage and maximum dosage that produces a therapeutic effect
What can affect a patient's response to a drug?
Gender, age, weight
Tolerance
When the body becomes less responsive to the effects of a drug, so larger doses are needed
Effect of high tolerance
Toxic effects are more likely
Why might tolerance occur?
1. Repeated use of a drug stimulates increased metabolism of that drugs, so the body gets better at breaking it down
2. The body may adapt to offset the effects of the drug by desensitising target receptors
What prescription drugs can people become addicted to?
Valium
Physical dependence
When the body cannot function without the drugs, the user must keep taking it to avoid withdrawal effects
Ways to administer a drug
1. Oral
2. Rectal
3. Pulmonary
4. Injection
5. Topical
Pros to rectal
Good when the patient cannot take oral, e.g. vomiting or unconscious
Suppositories
Solid, cone-shaped, medicated substances inserted into the rectum, vagina, or urethra
Pulmonary
Administered to the lungs in a form of gas
Topical
On the skin, used normally for local, but patches can be used also
Subcutaneous
Administers directly under the skin, absorption is slow giving a sustained effect
What can affect the bioavailability?
The formulation of the tablets, the solubility, how easily absorbed it is, susceptibility to being broken down by enzymes
What do prostaglandins do?
Cause pain, inflammation and fever
What happens when a tissue is injured?
Prostaglandins are synthesised and bind to receptors
What do these prostaglandins receptors do?
Stimulate sensory nerve fibres at the site of injury to send signals to the brain, which interprets it as pain
What makes a good synthesis?
It has very few steps, good yield and little waste, also should be cheap and readily available
Therapeutic effect
The desirable and beneficial effect - alleviates symptoms
Side effect
Unintended secondary effect of the drug on the body
Toxic effect
A side effect that is harmful to the body
What can cause a toxic effect?
Taking the drug in too high a quantity
Therapeutic index
The ratio of the toxic dose to the therapeutic dose
What does a high therapeutic index mean?
That there is a large difference between the toxic dose and the therapeutic dose
Psychological dependence
Needing a drug to feel good
How is oral taken in?
Absorbed by the stomach or small intestine into the blood
Pros to oral
Easy to administer, convenient for patient
Cons to oral
Slow effect
How is rectal taken in?
Into the bus, vagina or urethra
Pros to pulmonary
Very fast onset
Ways of injection
Intravenous, subcutaneous and intramuscular
Intravenous
Straight into the blood stream
Intramuscular
Into skeletal muscle
Bioavailability
The proportion of the administered dose that reaches the blood circulation
Prostaglandins on blood vessels
Causes dilation of blood vessels, causing inflammation and can send a signal to the hypothalamus to increase the body temperature
What is a drug?
A substance that when introduced to an organism, brings about a change in biological function
4 ways drugs can be made
1. Completely from extracting plants
2. Pure compounds isolated from natural resources
3. Semi-synthetic compounds
4. Synthetic compounds
What is a medicine?
A substance that treat, prevents or alleviates the symptoms of disease
What do non active substances in a drug do?
Improve taste, consistency or administration
How does a drug produce an effect on the body?
It interacts with a particular target molecule, such as a specific enzyme or receptor
What is the ultimate goal of drug researching?
To find a drug better than the current ones
First stage in drug development process
To identify lead compounds
How are lead compounds found?
Through biological testing of compounds obtained by:
1. Isolation from natural sources
2. Chemical synthesis
3. Searching through existing banks of compounds
What do lead compounds do?
They can be developed further
Stage one of trials
Animal testing
Stage two of trials
Human testing - for side effects
Stage three of trials
Human testing - for therapeutic effect
Stage four of trials
Human testing on a large group (placebo done here)
Stage five of trials
Human testing to the public
Placebo effect
When someone feels better but without taking the real drug
LD50
The dose that causes a lethal effect in 50% of the population - using in animal testing
TD50
The dose that causes a toxic effect in 50% of the population - using in human testing
Why does the solubility of the drug affect its bioavailability so much?
Only soluble molecules can pass through the intestinal wall, and only soluble can be transported n the blood
Why are fat soluble drugs good?
Because they will be able to pass through the cell membranes quicker
What do receptor agonists do?
Bind to a cell membrane protein receptor, mimicking the effect of the normal molecule that binds, triggering the reaction
What do receptor antagonists do?
Bind to the receptor so the normal molecule cannot, preventing a response from the cell
What do analgesics do?
Reduce pain
Mild analgesics
Prevent the production of prostaglandins
How is the production of prostaglandins prevented?
The enzyme cyclooxygenase is inhibited
What does cyclooxygenase do?
Helps synthesise prostaglandins
How do mild analgesics work?
Inhibit the production of chemical messengers that cause pain swelling and fever - at the site of the pain
Why is salicylic acid not good?
It causes severe irritation of the stomach lining and vomiting and gastric bleeding
Salicylic acid
What is the difference between salicylic acid and acetyl salicylic
The OH group is replace with an ester
Why is acetyl salicylic acid better than salicylic acid?
Because it doesn't cause stomach bleeding
What is acetylsalicylic acid also know as?
Aspirin
What is aspirin used as?
An analgesic and anti inflammatory agent
How has aspirin be used to prevent heart attacks?
If taken in low doses daily, it has an anti blood clotting effect, acting as an anticoagulant
Prophylactic
Something that prevents a disease
Synergism
Combination of two drugs causes an effect that is greater than the sum of the individual effects of each drug alone
Example of synergism
Ethanol and aspirin
How can you make aspirin?
Warming excess ethanoic anhydride with 2-hydroxybenzoic acid
Reactants in aspirin synthesis
2-hydroxybenzoic acid and excess ethanoic anhydride
What type of reaction is the synthesis of aspirin?
Addition elimination
What happens when you added water to the reaction mixture?
A white precipitate forms
What can you do with this white precipitate?
Filter it out, wash with pure water and leave to dry
Percentage yield
Actual yield/theoretical yield x 100
Anhydride
How can we purify aspirin?
Recrystallisation
Main impurities in aspirin
Unreacted salicylic acid
Recrystallisation
1. Dissolve the aspirin in hot solvent to form an almost saturated solution
2. Filtered while hot to remove any insoluble impurities
3. The solution cools and the aspirin forms solid crystals
4. Filter out the crystals
Determination of purity of an aspirin sample
Chromatography or melting point
How can we tell if a particular compound has been made?
IR
How can you increase the solubility of a drug?
Make the ionic salt of the drug
Making the ionic salt of aspirin
Reacting the carboxyl group with a strong alkali to for a COO-
Most common salt of acidic drugs
Sodium salts
How to convert aspirin to aspirin sodium?
React it with NaOH
How can you convert an anime to its salt?
Reacting the amine with a strong acid
Most common salt of basic drugs
Chloride salt
Beta lactam ring
A four carbon rim that helps penicillin to work
What happens to penicillin if the ring is broken?
The penicillin is no longer active
Bacteria cell wall formation?
Contains a polymer made up of sugar chains cross linked with peptides
How does penicillin work?
Irreversibly inhibiting transpeptidase
What does transpeptidase do?
Cause the cross links in the cell wall
How does the beta lactam ring react with the transpeptidase?
The OH on the side chain of transpeptidase reacts with the ring, breaking it open and reacting with the penicillin instead of its normal substrate
What was the first penicillin to be found?
Penicillin G
Cons to penicillin G
Easily broken down by stomach acid, must be given by injections
How was penicillin modified?
The side chains were modified so it can resist stomach acid
How are some bacteria now resistant to penicillin?
They produce an enzyme called penicillinase
