MEDICINES AND DRUGS

Option D

Part 1

What is a drug?

What is the difference between a drug and a medicine?

List different types of medicines.

How are new drugs developed?

Pharmaceutical products

A medicine or drug is any chemical that does one or more of the following to the human body:

alters its physiological state (=how it functions), including consciousness, activity level or coordination

alters incoming sensory sensationsalters mood or emotions

Stages in development of a drug

Identify disease, could be new disease. Identify target e.g. gene or enzyme which is

necessary for disease to progress. Identify ‘lead’ molecule which can act on

gene/enzyme in the disease organism or host and isolate or manufacture it.

Preclinical trials: testing of ‘lead molecule’ in laboratory, ‘in vitro’: the lead molecule is tested on

animal/human cells and tissues which have been removed from the body and are kept in an artificial environment

‘in vivo’: testing in live animals (usually 3 different species) to establish LD50 which is the amount which kills 50 % of animal population.

Stages in development of drug Clinical trials: on humans!!

Testing of its effectiveness and dose range on humans

using the placebo effect. This is a ‘blind trial’ in which half of the people/patients involved are given the drug whilst the other half are given a similar substance which is not the drug but none of the patients know which half they are in. All patients should/could experience placebo.

Structural modifications likely to be made to, for instance, improve effectiveness or reduce side-effects.

Submission of reports on drug and its trials to regulatory bodies.

Monitoring of the drug after it has been launched; molecule might need further structural changes.

How are drugs administered?

Administering drugs (1) Oral: taken in by the mouth e.g. tablets,

syrups, capsules. Parenteral - by injection:

intravenous: into a vein of the blood stream – used for immediate impacts as its fastest method; drug is immediately pumped around the body by the blood.

intramuscular i.e. into the muscles, e.g. many vaccines, local anaesthetics, usually used when a large dose needs to be administered.

subcutaneous: in the layer of the skin directly below the cutis (dermis and epidermis) e.g. dental injections, morphine, insulin. Slow.

Administering drugs (2)

Inhalation: e.g. medication for respiratory conditions such as asthma.

Rectal: inserted into the rectum e.g. treatment for digestive illnesses, drug absorbed into the blood stream.

Skin patches: e.g. hormone treatments.

Discuss the following terms

Dosing regime Tolerance Side-effects Therapeutic window

Terms Dosing regime = the amount of drug used

for each dose i.e. how much drug should be taken in to obtain desired therapeutic effect.

Tolerance Tolerance refers to the body’s reduced

response to a drug i.e. its therapeutic effect is less than what it is intended, usually as a result of taking the drug over a long period of time. As a result more of the drug needs to be taken to achieve the same initial physiological effect with the danger of exceeding the lethal dose.

Therapeutic window (1) The therapeutic window is the range of dosage

over which a drug can be safely administered to a typical population. It is the range in concentration in the blood within which an administered drug must remain. The therapeutic window has a lowest and highest level.

The lowest level of concentration is called the effective level or ED50; below this level the drug loses its therapeutic effect.

The highest level is the toxic or LD50 level (= the dose needed to kill 50 % of (animal) population) above which adverse side-effects can occur.

Therapeutic window (2)

wide therapeutic window small effective dose (ED50) and larger lethal

dose (LD50) as a result there is a big difference between effective and lethal dose.

narrow therapeutic window small difference between effective and lethal

dose usually because lethal dose is small.

Terms (2) Side-effects = physiological effects

which are not intended and therefore undesired (intended = therapeutic effects); these could be: beneficial e.g. protect against heart disease. benign e.g. causing drowsiness, nausea constipation. adverse i.e. causing damage to other organs.

 

Placebo effect The placebo effect occurs when a person experiences

a positive therapeutic effect although a substance which is not a drug has been administered; the human body is fooled into healing itself naturally.