Drug dosage

1. Drug dosage

2. Depends on multiple factors A drug usually has one desired effect that causes a change in a target organ or structure It will also have secondary effects because it will be absorbed by other areas of the body Dose-response relationship

3. Main effect – the effect you want the drug to have Side effects – secondary effects that may or may not be desirable or helpful Goal is to use a dose of a drug that is effective, but has minimal side effects Main effects and side effects

4. Making dosage decision Compare dosage to the percentage of people showing different effects ED10- effective dose where 10% of people show response of interest Example – dosages of a drug used to increase attention (main effect) but also has 2 side effects Heart palpitations death Dosage-response curve

5. A measure of drug safety The ratio of the dosage at which 50% of patients would be expected to die (LD50) to the dosage where 50% would show the desired effect (ED50) The larger the ratio the safer the drug The safest drug is one that has the most specific action. Few side effects when it is given at therapeutic dosages Therapeutic Index

6. Infants take longer to metabolize most drugs because of an immature liver Older adults also do not metabolize drugs quickly because their system less efficient Age as a factor that influences the drug response curve

7. Gender specific drug response – males and females physiologically different Psychological factors – expectations most notably Other factors influencing drug-response curve

8. Metabolic tolerance – long term use of a drug can result in chronic elevation of enzymes that metabolizes the drug Neuronal tolerance – prolonged use of a drug causes physical and chemical changes in neurons effected by the drug If the drug is an antagonist to a neurotransmitter (NT), the neurons may produce more of the NT If an agonist, facilitates the action of the NT, the neuron could decrease the number of post-synaptic receptors or increase the release of enzymes History of Usage - Tolerance

9. Behavioral tolerance – the subject learns to overcome the effects of the drug – drug levels remain high, but you learn to function normally “acting sober” Learned tolerance – the body becomes classically conditioned a drug is given repeatedly in the same environment The body reacts to the drug by producing enzymes to metabolize it Now the environment signals the drug is coming and body reacts before drug is taken Behavioral and learned tolerance

10. Drug interaction – the effects of taking 2 drugs are not just additive; the response to 1 drug is greatly increased or decreased by the administration of a second Can be useful or it can be a problem Example of a useful interaction: Drug A not effective at low dosages High dosages aren’t safe – the LD is low making the LD/ED small If drug B increases the effect of drug A so it will be effective at lower dosages, that is good Drug Interactions on dose response curve

11. Interaction increases undesirable side effects Mixing alcohol with anti-depressants such as prozac increases the risk of liver damage – a possible side effect of both Undesirable Interactions