PSYCH 460--Psychopharmacology

drug - an exogenous chemical not necessary for normal cellular functioning that significantly alters the functions of certain cells in the body (the nervous system is of particular interest in psychopharmacology) when taken in relatively low doses (Carlson, chap. 4)

• according to that definition, which of the following are NOT drugs? Prozac, Valium, grain alcohol (ethanol), nicotine, caffeine, saccharine, LSD, vitamin E, androstenedione
• there is no universally accepted definition for the term "drug"

drug action - refers to how the drug alters the functioning of cells in the body (esp. the nervous system) physiologically or molecularly; e.g., reuptake inhibition, facilitation of neurotransmitter release, receptor blockade, direct receptor stimulation (any alteration of one of the steps involved in synaptic transmission would be considered a drug action)

site of action - refers to where the cells are (or the type of cells) that are altered; e.g., the site of action of cocaine is at dopamine synapses

drug effect - refers to the behavioral, mental, or outwardly observable physiological changes produced by the drug; e.g., analgesia, lowered body temperature, activation of the EEG, arousal, euphoria, hallucinations, sleep, change in blood pressure

pharmacokinetics - i.e., distribution within the body; drugs must get from the site of administration to the site of action

1. the drug must be taken up by and transported in the blood
2. if the drug is to act in the brain, it must also cross the blood-brain barrier
3. if depot binding occurs in the blood or in fat tissue, this may prevent or inhibit the drug from being distributed to other tissues; it may also drastically alter the time course of distribution

routes of drug administration

1. intravenous injection (IV) - injection directly into a vein; results in very fast uptake of drug; most accurate dosing
2. intraperitoneal injection (IP) - into the gut or peritoneal cavity; fairly fast uptake and reliable dosing; most often used with small experimental animals such as rats and mice
3. intramuscular injection (IM) - into a large muscle, e.g., in the upper arm or buttocks; rapidity of uptake and reliability of dosing is variable
4. subcutaneous injection (SC) - under the skin; useful only for small injections; rapidity of uptake and reliability of dosing are variable
5. oral administration - by mouth; most common way to give drugs to humans (but rarely used with experimental animals, which just spit them out); least reliable way to get accurate dosing; will not work with drugs that are destroyed by stomach acid or digested by enzymes in the stomach (e.g., peptides such as insulin)
6. sublingual administration - under the tongue
7. intrarectal administration - by rectal suppository
8. inhalation - by inhalation of a gas directly into the lungs; very rapid uptake and rapid delivery to the brain
9. topical application - applied to the skin or mucus membranes (e.g., in the nose)
10. intracerebral administration - directly into brain tissue (used most often experimentally, but some drugs--such as antibiotics--that do not cross the blood-brain barrier must be administered this way
11. intracerebroventricular administration - into the lateral ventricles of the brain

dose-response curve - a graph showing the relationship between dose of the drug (plotted on the horizontal axis) and measureable response to it (plotted on the vertical axis); see text for an illustration

therapeutic index - the ratio of the dose of a drug that causes toxic side effects 50% of the time and the dose that causes the desired therapeutic benefit 50% of the time

TI = LD₅₀ / ED₅₀

• drugs that have a low TI are considered more dangerous because it is relatively easy to overdose (the toxic dose is not much more than the therapeutic dose) - e.g., barbariturates
  
• drugs that have a high TI are considered safer because it is relatively difficult to overdose (the toxic dose is several times the therapeutic dose - e.g., benzodiazepines
  

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