IB CHEMISTRY: OPTION D (MEDICINAL CHEMISTRY)

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236 Terms

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How to calculate therapeutic index

LD50/ED50

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Therapeutic window

The range of doses between the minimum dosage and maximum dosage that produces a therapeutic effect

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What can affect a patient's response to a drug?

Gender, age, weight

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Tolerance

When the body becomes less responsive to the effects of a drug, so larger doses are needed

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Effect of high tolerance

Toxic effects are more likely

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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

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What prescription drugs can people become addicted to?

Valium

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Physical dependence

When the body cannot function without the drugs, the user must keep taking it to avoid withdrawal effects

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Ways to administer a drug

1. Oral
2. Rectal
3. Pulmonary
4. Injection
5. Topical

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Pros to rectal

Good when the patient cannot take oral, e.g. vomiting or unconscious

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Suppositories

Solid, cone-shaped, medicated substances inserted into the rectum, vagina, or urethra

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Pulmonary

Administered to the lungs in a form of gas

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Topical

On the skin, used normally for local, but patches can be used also

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Subcutaneous

Administers directly under the skin, absorption is slow giving a sustained effect

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What can affect the bioavailability?

The formulation of the tablets, the solubility, how easily absorbed it is, susceptibility to being broken down by enzymes

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What do prostaglandins do?

Cause pain, inflammation and fever

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What happens when a tissue is injured?

Prostaglandins are synthesised and bind to receptors

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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

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What makes a good synthesis?

It has very few steps, good yield and little waste, also should be cheap and readily available

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Therapeutic effect

The desirable and beneficial effect - alleviates symptoms

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Side effect

Unintended secondary effect of the drug on the body

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Toxic effect

A side effect that is harmful to the body

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What can cause a toxic effect?

Taking the drug in too high a quantity

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Therapeutic index

The ratio of the toxic dose to the therapeutic dose

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What does a high therapeutic index mean?

That there is a large difference between the toxic dose and the therapeutic dose

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Psychological dependence

Needing a drug to feel good

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How is oral taken in?

Absorbed by the stomach or small intestine into the blood

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Pros to oral

Easy to administer, convenient for patient

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Cons to oral

Slow effect

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How is rectal taken in?

Into the bus, vagina or urethra

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Pros to pulmonary

Very fast onset

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Ways of injection

Intravenous, subcutaneous and intramuscular

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Intravenous

Straight into the blood stream

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Intramuscular

Into skeletal muscle

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Bioavailability

The proportion of the administered dose that reaches the blood circulation

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Prostaglandins on blood vessels

Causes dilation of blood vessels, causing inflammation and can send a signal to the hypothalamus to increase the body temperature

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What is a drug?

A substance that when introduced to an organism, brings about a change in biological function

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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

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What is a medicine?

A substance that treat, prevents or alleviates the symptoms of disease

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What do non active substances in a drug do?

Improve taste, consistency or administration

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How does a drug produce an effect on the body?

It interacts with a particular target molecule, such as a specific enzyme or receptor

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What is the ultimate goal of drug researching?

To find a drug better than the current ones

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First stage in drug development process

To identify lead compounds

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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

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What do lead compounds do?

They can be developed further

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Stage one of trials

Animal testing

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Stage two of trials

Human testing - for side effects

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Stage three of trials

Human testing - for therapeutic effect

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Stage four of trials

Human testing on a large group (placebo done here)

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Stage five of trials

Human testing to the public

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Placebo effect

When someone feels better but without taking the real drug

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LD50

The dose that causes a lethal effect in 50% of the population - using in animal testing

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TD50

The dose that causes a toxic effect in 50% of the population - using in human testing

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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

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Why are fat soluble drugs good?

Because they will be able to pass through the cell membranes quicker

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What do receptor agonists do?

Bind to a cell membrane protein receptor, mimicking the effect of the normal molecule that binds, triggering the reaction

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What do receptor antagonists do?

Bind to the receptor so the normal molecule cannot, preventing a response from the cell

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What do analgesics do?

Reduce pain

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Mild analgesics

Prevent the production of prostaglandins

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How is the production of prostaglandins prevented?

The enzyme cyclooxygenase is inhibited

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What does cyclooxygenase do?

Helps synthesise prostaglandins

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How do mild analgesics work?

Inhibit the production of chemical messengers that cause pain swelling and fever - at the site of the pain

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Why is salicylic acid not good?

It causes severe irritation of the stomach lining and vomiting and gastric bleeding

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Salicylic acid

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What is the difference between salicylic acid and acetyl salicylic

The OH group is replace with an ester

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Why is acetyl salicylic acid better than salicylic acid?

Because it doesn't cause stomach bleeding

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What is acetylsalicylic acid also know as?

Aspirin

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What is aspirin used as?

An analgesic and anti inflammatory agent

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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

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Prophylactic

Something that prevents a disease

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Synergism

Combination of two drugs causes an effect that is greater than the sum of the individual effects of each drug alone

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Example of synergism

Ethanol and aspirin

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How can you make aspirin?

Warming excess ethanoic anhydride with 2-hydroxybenzoic acid

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Reactants in aspirin synthesis

2-hydroxybenzoic acid and excess ethanoic anhydride

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What type of reaction is the synthesis of aspirin?

Addition elimination

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What happens when you added water to the reaction mixture?

A white precipitate forms

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What can you do with this white precipitate?

Filter it out, wash with pure water and leave to dry

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Percentage yield

Actual yield/theoretical yield x 100

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Anhydride

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How can we purify aspirin?

Recrystallisation

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Main impurities in aspirin

Unreacted salicylic acid

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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

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Determination of purity of an aspirin sample

Chromatography or melting point

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How can we tell if a particular compound has been made?

IR

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How can you increase the solubility of a drug?

Make the ionic salt of the drug

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Making the ionic salt of aspirin

Reacting the carboxyl group with a strong alkali to for a COO-

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Most common salt of acidic drugs

Sodium salts

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How to convert aspirin to aspirin sodium?

React it with NaOH

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How can you convert an anime to its salt?

Reacting the amine with a strong acid

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Most common salt of basic drugs

Chloride salt

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Beta lactam ring

A four carbon rim that helps penicillin to work

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What happens to penicillin if the ring is broken?

The penicillin is no longer active

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Bacteria cell wall formation?

Contains a polymer made up of sugar chains cross linked with peptides

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How does penicillin work?

Irreversibly inhibiting transpeptidase

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What does transpeptidase do?

Cause the cross links in the cell wall

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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

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What was the first penicillin to be found?

Penicillin G

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Cons to penicillin G

Easily broken down by stomach acid, must be given by injections

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How was penicillin modified?

The side chains were modified so it can resist stomach acid

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How are some bacteria now resistant to penicillin?

They produce an enzyme called penicillinase