Exam 1 Study Guide
Chap. 2
Two drug phases
1.Pharmacokinetic phase
2.Pharmacodynamic Phase Pharmacokinetic Phase: is the process of drug movement through the body necessary to achieve drug action. Includes Absorption, Distribuion, Metabolism, and Excretion.
Pharmacodynamic Phase: is the study of the effects of drug on the body. ( Receptor binding, post receptor effects, and chemical reactions). Digestion starts in the mouth-Salvia starts the breakdown!!!! Pharmacokinetic Phase:
Absorption is the movement of the drug through the blood stream after its administration. Disintegrations is the breakdown of the oral drug into smaller particles. Dissolution is the time it takes the drug to disintegrate and dissolve to become available for absorption. Acidic is faster than alkaline environment. Absorption methods
Passive transport
Diffusion: is across the semipermeable membrane high to low concentration. Requires no energy. It stops when the concentration is equation on both sides of the membrane. In oral drugs GI (higher concentration) moves to the blood stream (lower concentration). Facilitated diffusion: is the same principal but requires a carrier protein to move the drug. Active Transport
Requires carrier and energy to move the drug against the concentration gradient. Pinocytosis
Taking a bit out of the particles and bringing them into the cell. Lipid soluble drugs and nonionized drugs are absorbed faster than water soluble and ionized drugs Factors affecting absorption
Blood circulation (poor circulation, vasoconstrictors, shock or disease), Pain, stress, solid, hot foods, high fat foods slow gastric emptying, Exercise decreases Blood flow, pH, Route of administration (IV, Oral, IM)
Drug movement from GI tract to liver
From mouth to the gut to portal vein and the liver drugs may be metabolized to an inactive form and excreted reducing the amount of the active drug available to achieve desired effect. This is first pass effect (first pass metabolism)
Bioavailability is the percentage of the drug left for activity. May be affected by absorption and first pass metabolism for oral drugs. Bioavailability is always less than 100%.
Factors affecting Bioavailability
Drug form Route of administration
Gastric mucosa and motility Administration w/food and other drugs
Changes in liver metabolism Drug distribution: is the movement of the drug form the circulation to tissues. Protein binding ( highly and weakly protein bound drugs)
Drugs drugs( unbound)
Volume of drug distribution
Competition over protein binding sites leads to more free drug Low plasma protein levels causes more free drugs floating around
Low albumin same thing (elderly considerations)
BBB (blood brain barrier)
Water soluble drugs do not cross the BBB You want to be careful with those who are pregnant some drugs cross the placenta and cause damage
Drug metabolism (biotransformation: changing the drug chemically to form that is ready for excretion)
Half life: from administration to reduction of the drug in the body to a half. Affected by.-
previous dose, metabolism, and elimination. Ex. Ibuprofen= 2hr 6am 200mg in two hrs= 100mg 8am
100mg in 2 hrs= 50mg 10am
50mg in 2hrs= 25mg 12pm
25mg in two hrs=12.5mg 2pm
12.5mg in 2 hrs= 6.25mg 4pm
Steady state=plateau=amount administered= amount eliminated usually achieved by 4- 5th half life if given consistently Loading dose= large initial dose of medication (seizure medications) smaller doses to follow consistent time intervals. Drug excretion (elimination) Kidneys
Creatinine clearance
BUN
Glomerular filtration rate lower in older and female due to decreased muscle mass
Urine pH 4.6-8
Liver (bile)
Feces
Lungs
Saliva, sweat, breast milk
Pharmacodynamics Phase: Primary effect-desirable response
Secondary effect- desirable or undesirable response Ex. Benadryl (primary effect= treatment of allergies, Secondary effect= CNS depression (sedation)) Drug response relationship
Potency: the amount of drug needed to elicit specific physiological response
Physiological response at very low concentration=low potency
Therapeutic index Onset: time it takes for drug to reach minimum effective concentration Peak: highest concentration in blood Duration: length of time taken for drug to exert a therapeutic effect Below therapeutic response= under dose making it ineffective Above therapeutic response= overdosed maybe toxic Therapeutic drug monitoring Peak drug level: highest plasma concentration of drug Trough drug level: lowest plasma concentration of the drug. Receptor theory
Drugs bind to receptors To activate receptors To produce a response
To inactivate a receptor Drugs can compete for the same receptor site. If one is bound the other one is going to be free. Four receptor families
Cell membrane-imbedded enzymes
Ligand-gated ion channels
g-protein-coupled receptor systems
transcription factors Agonists
Activate receptors Produce desired response Pushers/stimulators Antagonists Prevent receptor activation Block response Preventors/ stimulators Nonspecific: multiple receptor sites Nonselective: works on multiple receptors Cholinergic receptors: eye, heart, blood vessels, stomach, bronchus, and bladder Mechanisms of drug action
Stimulation
Depression
Irritation
Replacement
Cytotoxic action
Antimicrobial action
Modification of immune status Side effects Secondary effects
Common, chronic conditions, gener, ethnicity, age, may influence secondary effects of the drug. Adverse reactions More severe than side effects Undesirable effects
Rare unexpected, undesirable effects with normal dose
Drug Toxicity
Drug level exceeds therapeutic range Overdose or drug accumulation
Underlying condition, age, genetics Pharmacogenetics
Biologic variations Study of genetic factors influencing individual response Tolerance Decreased drug responsiveness over time Tachyphylaxis
Acute, rapid decrease in drug responsiveness regardless of time
Placebo effect
Drug response not attributed to chemical drug properties Pharmacodynamics
Drug interactions Altered drug effect due to interaction with another drug. Pharmacokinetic interactions Changes occurring in absorption, distribution, metabolism, and excretion Drugs can block, decrease, increase the adsorption of other drugs
Increasing or decreasing gastric emptying time
Changing gastric pH Forming drug complexes Metabolism-inducers or inhibitors drugs may require higher or lower dose of one medication Don’t forget herbal products!!! Additive Sum of effects of two drugs Synergistic Effect is much great than effects of either drug alone Antagonistic One drug reduces or blocks effect of other drug. Drug-nutrient interactions
Food may increase, decrease, or delay drug response Drug-laboratory interactions Drug may cause misinterpretation of test results Drug-induced photosensitivity Skin reaction caused by sunlight
