SAS

• Three Phases of Drug Action

  1. Pharmaceutic Phase

  2. Pharmacokinetic Phase

  3. Pharmacodynamic Phase
• Pharmaceutic Phase


  • Disintegration – breakdown of tablet into smaller particles
  • Dissolution - dissolving of the smaller particles in the GI fluid before absorption
  • 1st phase of drug action
  • Rate limiting – time it takes for the drug to disintegrate and dissolve to become available for the body to absorb it
• Pharmacokinetic Phase


  • The process of drug movement to achieve drug action
  • 2nd phase of drug action
  • What the body does to the drug- refers to the study of how the body processes drugs
  • Includes absorption, distribution, metabolism (biotransformation), and excretion
• Absorption


  • Passive absorption - movement of a drug from the site of administration into the bloodstream
  • Active absorption - requires a carrier such as an enzyme or protein, energy is required
  • Pinocytosis - process by which cells carry drug across their membrane by engulfing the drug particles
• Factors Affecting Absorption


  • Surface area
  • Contact time with surface
  • Circulation
  • Solubility (water soluble vs lipid soluble)
  • Ionization (weak versus strong acid/base)
  • Drug form & drug concentration
  • Bioavailability (after first pass thru liver)
  • Route of administration (enteral & parenteral)
  • Additives: alter the location of disintegration of drugs as well as increase or decrease the rate of absorption
• Drug Absorption varies by form

  • Liquids, elixirs, syrups (fastest)
  • Suspension solutions
  • Powders
  • Capsules
  • Tablets
  • Coated tablets
  • Enteric-coated tablets (slowest)
• Distribution


  • The transport of drugs from the blood to the site of action
  • A drug must be distributed to its site of action to have an effect
• Factors Affecting Distribution


  • Perfusion Rate
  • Permeability of Membranes
  • Protein binding
  • Tissue Localization
  • Blood Brain Barrier
  • Placenta
• Metabolism (Biotransformation)


  • Process by which the body changes the chemical structure of a drug to another form called a metabolite
  • Metabolite: a more water soluble compound that can be easily excreted
  • Major organ is the liver
  • First Pass Phenomenon - drugs are first absorbed through the small intestine then arrive at the liver via the portal circulation, where they undergo considerable biotransformation before entering the systemic circulation
• Variations in Metabolism


  • Pharmacogenetics - hereditary influences on drug responses
  • Circadian Rhythms - the rate of drug absorption, hepatic clearance, half-life and duration of action, differ depending upon the time of day a drug is administered
  • Effects of Gender and Age
• Excretion


  • Process where drugs are removed from the body
  • Kidneys are the major organs of excretion
  • Lungs excrete gaseous drugs
  • Biliary excretion (bile & feces) is important for a few drugs
  • Intestines, sweat, saliva and breast milk constitute minor routes of drug excretion
  • Clearance of drugs - elimination of drugs from circulation by all routes, affects the time a drug remains in the body and the dosage required
• Plasma Half-Life


  • The time it takes for the concentration of the drug in the plasma or the total amount in the body to be reduced by 50%
  • Drugs with short half-lives are quickly eliminated from the body
  • Drugs with longer half-lives stay in the body longer
• Pharmacodynamic Phase


  • What a drug does to the body- refers to the study of the mechanism of drug action on living tissue
  • Drugs may increase, decrease or replace enzymes, hormones or body metabolic functions
  • Chemotherapeutic drugs alter an abnormal parasite or growth on the body such as bacteria, viruses or neoplastic tissue
• Effects of Drugs


  • Therapeutic / Desired effect: curative, supportive, substitutive, chemotherapeutic, restorative
  • Adverse drug reaction (ADR)
  • Adverse event
  • Side-effect
  • Drug toxicity
  • Drug abuse
  • Hypersensitivity / allergy
• Safety of a drug


  Determined by the degree between therapeutic and toxic doses
• The nurse is monitoring the therapeutic drug level for a client on vancomycin (Vancocin) and notes that the level is within the acceptable range
• Protein bound drug


  50% of the drug is bound to protein
• Interval of drug dosage

  Related to half-life
• Pharmacokinetic phase


  1. Absorption

  2. Distribution

  3. Metabolism

  4. Excretion
• Inhaled medications should not only be taken in the morning
• Hepatic impairment


  Increases the duration of action for most medications
• Beware of medications that sound alike, and read the labels carefully.
• Percocet


  • contains oxycodone and acetaminophen
• Percodan


  • contains oxycodone and aspirin
• Percodan should not be given to someone who has an adverse reaction to aspirin.
• Nursing implications


  • Check that medication order is complete and legible
  • Know why the client is receiving the medication
  • Check the drug label three times before administration
  • Know the start date that the drug was ordered and the ending date
• Categories of drug orders

  • Standing orders
  • One-time (single dose)
  • PRN
  • STAT (at once)
• Right dose


  The dose prescribed for a particular client
• The nurse is responsible for questioning any dose that looks too high or too low.
• Always consult a peer or pharmacist if the dosage appears incorrect.
• Beware of pediatric doses that are based on body weight. Weights can change daily so regular assessment of dosages is crucial.
• Nursing implications for right dose

  • Calculate the drug dose correctly
  • For some medications, two nurses are needed to sign off on a new order such as heparin and insulin
  • Check the PDR, American hospital formulary, drug package inserts, or other drug references for recommended range of specific drug doses
• Right time


  The time at which the prescribed dose should be administered
• Nursing implications for right time

  • Administer drugs at the specified times
  • Drugs may be given 0.5 hour before or after the time prescribed if the administration interval is > 2 hours
  • Administer drugs that are affected by foods, before meals (e.g. tetracycline)
  • Administer drugs that can irritate the stomach (gastric mucosa) with food such as aspirin or potassium
  • The drug administration schedule can sometimes be flexible in order to accommodate the client's activities for the day or preferences
  • It's the nurse's responsibility to be aware of test's or procedures that are taking place that may affect the medication administration (e.g, fasting blood tests, endoscopy)
  • Check the expiration date on medications and return to pharmacy if expired
  • Antibiotics need to be given evenly over 24 hours as opposed to T.I.D
• Right route


  Necessary for adequate or appropriate absorption
• Nursing implications for right route

  • Assess client's ability to swallow before administering p.o.
  • Do not crush or mix medications into other substances before consultation with the pharmacy. Do not mix meds into sweetened juices for kids or add to formula for babies. Follow all med administration guidelines for that specific drug.
  • Use aseptic technique when administering drugs. Use sterile technique when administering parenteral meds.
  • Administer drugs to appropriate sites.
  • Stay with client until p.o meds have been swallowed.
  • If it's necessary to combine a medication with another substance, explain this to the client.
• Avoid distractions during medication preparation and administration as they can cause errors.
• Putting the 10 rights of drug administration into practice can be challenging, especially for new nurses.
• It is standard practice to have another nurse recompute and double check calculations to avoid miscalculation.
• Medication Reconciliation involves creating a complete list of medications a patient is receiving and constantly updating the list.