Week 4 - topic 1 Flashcards
Psychopharmacology
Psychopharmacology is the study of the effects of drugs on the nervous system, and consequently, behaviour
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Drugs
An exogenous chemical not necessary for normal cellular functioning that significantly alters the functions of certain cells of the body when taken in relatively low doses
Drug effects
Observable changes in an individual’s physiology and/or behaviour
Sites of action
The locations where drug molecules interact with molecules on or in cells to affect biochemical processes
- Drugs that produce the same behavioural effects can have different sites of action
Pharmacokinetics
Pharmacokinetics: The process by which drugs are absorbed, distributed within the body, metabolised and excreted
- the life cycle of a drug molecule
- > absorption
- > distribution
- > metabolism
- > excretion
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Drug absorption - injections
Many routes of drug administration
1) Injection
Intravenous = inject into the vein. Fastest route
Intraperitoneal = inject into the peritoneal cavity - abdominal wall
Intramuscular = inject directly into a large muscle
Subcutaneous = inject into the space beneath the skin
Drug absorption - others
2) Oral
Most common form
Sublingual Administration = placing it beneath the tongue.
3) Inhalation
E.g. smoking, general anesthetic
This is distinct from insufflation (sniffing/snorting a drug)
4) Topical administration
Directly onto the skin (e.g. steroid cream)
Drug distribution
How Drugs Enter into the CNS
- Drugs exert effects at their sites of action
- Mostly on or in cells of the CNS
- Most important factor in determining the rate is lipid solubility (ability of fat based molecules to get through cell membranes)
Drug metabolism and excretion
- Drugs do not stay in the brain forever
- Many drugs are metabolised and deactivated by enzymes that are in the brain, liver, and blood
- All drugs are eventually excreted
- Enzymes can sometime transform molecules of a drug into other forms that are also active
- This can cause the drug to have a long lasting effect
Drug effectiveness
The effects of a small dose of a relatively effective drug can equal or exceed the effects of larger amounts of a relatively ineffective drug
Dose response curve
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Most drugs have multiple effects
for example codeine while being an analgesic - reducing pain, also changes heart rates and respiration
- margin of safety
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Therapeutic index
The Therapeutic index measures drug’s margin of safety
- Administer the drug to a sample of participants
- Calculate the dose that produces therapeutic effects in 50% of the sample
- Calculate the dose that produces adverse (toxic) effects in 50% of the sample
- > Therapeutic Index = toxic dose/therapeutic dose
Why do drugs vary in their effectiveness?
Sites of Action
Drug Affinity
Drug affinity
Affinity is the readiness with which two molecules join together.
- > Drugs with high affinity = effects with low concentration administered
- > Drugs with low affinity = effects with high concentration administered
- Most desirable drug has high affinity for sites of action producing therapeutic effects and low affinity for sites of action producing toxic side effects
Effects of repeated drug administration
If a drug is taken repeatedly, the effect of the drug on brain and behaviour can change
- some effects of drugs show tolerance or sensitisation and others do not
Tolerance
- a decrease in the effectiveness of a drug if that drug is administered repeatedly
- Tolerance is your body compensating for how the drug impacts on your nervous system
-> coffee becomes less and less effective
Sensitisation
an increase in the effectiveness of a drug that is administered repeatedly
-> repeated use of cocaine makes people become more sensitive to movement disorders and seizures
Compensatory mechanisms
- Decrease in effectiveness of binding with receptors
2. The coupling process becomes less effective
Withdrawal symptoms and physical dependence
- if someone takes a drug regularly enough to develop a tolerance to it, they are likely to experience withdrawal symptoms if they immediately stop taking the drug.
- physical dependence can be seen as the compensatory changes following repeated use of a drug that result in withdrawal symptoms when the drug is no longer taken.
Placebo effect
- If a person expects that a placebo can have a physiological or psychological effect, then administration of the placebo could produce the expected effect. This is the placebo effect.
Placebo effects in research
- Placebos are often used in experimental research. For example, when testing a new drug, an experimenter might administer the new drug to half of the participants in a sample, and then administer a placebo to the other half.
- The idea is that the placebo controls for the effects of mere administration of a drug.
- Thus, a researcher is able to determine if a drug has significant behavioural effects, above and beyond the effects of administering and receiving any inactive substance.
