1. Chapter 4
How Drugs Work

2. Local and Systemic Effects
Drugs with local effects
Used to treat one specific area of body
Can have systemic side effects
Learning Objective 4-1

3. Examples of Drugs with Local Effects
Lidocaine injection: numbs patient’s jaw for dental work
Lidocaine patch: relieves pain of shingles
Bacillus Calmette-Guérin (BCG) solution: prevents and treats bladder cancer tumors
Corticosteroid creams: counteracts inflammation caused by eczema
Benzoyl peroxide: mild acne treatment
Learning Objective 4-1

4. Local and Systemic Effects (cont’d)
Drugs with systemic effects
Travel through bloodstream to reach specific body tissues
Target specific body systems; may have effects on other systems also
Learning Objective 4-1

5. Common Drugs and the Body’s Systems
[Insert untab4-1]
Learning Objective 4-1

6. How Drugs Work in the Body
Solid forms of drugs go through three phases
Pharmaceutic phase
Pharmacokinetic phase
Pharmacodynamic phase
Learning Objective 4-2

7. How Drugs Work in the Body (cont’d)
Liquid forms of drugs go through two phases
Pharmacokinetic phase
Pharmacodynamic phase
Learning Objective 4-2

8. The Pharmaceutic Phase—Entering the Body
Drug breaks into small particles in gastrointestinal tract
Drug dissolves and releases medication into body
Drugs in solid form turn into form body can take in and use
Learning Objective 4-2

9. The Pharmaceutic Phase—Entering the Body (cont’d)
Some tablets are made to dissolve in stomach acids
Time-release capsules and extended release capsules are made to dissolve very slowly in stomach
Enteric coated tablets do not break apart until in alkaline environment of intestines
Learning Objective 4-2

10. The Pharmacokinetic Phase—Entering the Bloodstream
Pharmacokinetics refers to activities involving drug within body after it has been administered
Happens after patient swallows pill or capsule and medication dissolves
Injected medications take effect so quickly because they are ready for use immediately as liquids
Learning Objective 4-2

11. The Pharmacokinetic Phase—Entering the Bloodstream (cont’d)
Drug goes through four activities inside body:
Absorption
Distribution
Metabolism
Excretion
Learning Objective 4-2

12. Absorption
Drug is taken into bloodstream through walls of stomach or intestines
Bloodstream carries drug to places in body that drug is meant to reach and affect
Speed of absorption depends on how drug is given, rate at which drug dissolves, and conditions inside body
Learning Objective 4-2

13. Absorption Rates by Administration
Fastest absorption: inhalation, IV, sublingual
Second-fastest absorption: IM injection
Third-fastest absorption: SubQ injection
Learning Objective 4-2

14. Distribution Bloodstream carries drug to target place
Bioavailability: sometimes only part of drug is available to do job once it reaches correct site
Portions of drug may have been bound to protein in blood
Some drugs are not fat soluble and cannot cross body tissues around brain, placenta, or testes
Learning Objective 4-2

15. Metabolism
Liver metabolizes drugs: takes out all important chemicals body needs (active ingredients)
Remaining ingredients are turned into substances body can get rid of
Liver cannot fully metabolize drug sometimes; if liver is diseased, lower dosages may be required
Learning Objective 4-2

16. Excretion Liver gets rid of inactive leftovers by sending to kidneys
Kidneys excrete leftovers in urine
Learning Objective 4-2

17. Excretion
Some medications bypass liver and go straight to kidneys; if kidneys are diseased, lower dosages may be required
Drugs that bypass liver and kidneys are eliminated through sweat, breast milk, breathing, and feces
Learning Objective 4-2

18. Half-Life Time it takes body to eliminate 50 percent of drug
Drugs with short half-life are administered more frequently
Longer half-life drugs are administered less often
Patients with liver or kidney disease may have problems eliminating a drug; half-life may be longer for them and toxic levels may build up
Learning Objective 4-2

19. The Pharmacodynamic Phase—Going into Action
Drugs actions and effects within body
Whole body is exposed to possible effects when traveling through bloodstream
Primary effect: intent of active ingredient
Secondary effects: all other effects of drug
Learning Objective 4-2

20. Drug Reactions Contraindications Adverse reactions Allergic reactions
Idiosyncratic reactions
Drug tolerance
Cumulative drug effect
Toxic reactions
Learning Objective 4-3

21. Contraindications Contra = “against”, indication = “sign”
Circumstances under which a drug or treatment should not be used
Learning Objective 4-3

22. Adverse Reactions
Harmful side effects, or adverse reactions, may occur when medications are taken
May:
Be mild, severe, or even life threatening
Happen after the first dose, after several doses, or after many doses
Happen in a predictable way or without warning
Learning Objective 4-3

23. Adverse Reactions
[Insert figure 4-13]
Learning Objective 4-3

24. Allergic Reactions
Happen when patient’s immune system responds to drug as if it were an antigen
Immune system produces antibodies to combat invader
Usually take time to build up; most occur after patient has received more than one dose of drug
Be aware of how allergies or reactions are flagged in patients’ charts
Learning Objective 4-3

25. Signs and Symptoms of Drug Allergies
Itching and skin rash
Urticaria (hives)
Dyspnea
Wheezing
Cyanosis
Swelling of eyes, lips, or tongue
Sudden loss of consciousness
Learning Objective 4-3

26. Idiosyncratic Reactions
Response to drug is unusual and different from what is normally expected
It is unclear why some patients have idiosyncratic responses to some medications
Learning Objective 4-3

27. Drug Tolerance
Decreased response to drug; same dosage no longer has same effect
Patients may need larger dosage of medication to get desired results
Learning Objective 4-3

28. Cumulative Drug Effect
Part of medication dose remains active in body due to body being unable to fully metabolize and excrete the full dose before another one is taken
Too much medication can build up in body and cause harmful reactions
Liver and kidneys are organs that metabolize and excrete medications from body
Learning Objective 4-3

29. Toxic Reactions
Certain circumstances can produce toxic reactions of most drugs
Dosages too large
Unsafe amount of drug remaining in bloodstream, or above therapeutic level
Kidneys are not working properly and cannot excrete drug in patient’s urine
Learning Objective 4-3

30. Angioedema Type of allergic reaction to medication
Edema is abnormal build-up of fluid
Angioedema appears as welts, or ridges, below skin
Usually appear around eyes, lips, mouth, throat, and sometimes other parts of body
Learning Objective 4-4

31. Anaphylactic Shock Most serious allergic reaction to medication
Requires immediate medical attention
Usually occurs soon after patient is given drug to which he is extremely sensitive
Learning Objective 4-4

32. Signs and Symptoms of Anaphylactic Shock
[Insert untab4-2]
Learning Objective 4-4

33. Drug Interactions
Drug-drug interactions occur when one drug interacts with or interferes with action of another drug
Synergism: two drugs work together
Antagonism: one drug reduces effects of another drug
Potentiation: one drug increases or prolongs effects of another drug
Learning Objective 4-5

34. Synergistic Drug Reactions
Two or more drugs work together to produce an effect greater than what each drug would have produced alone
Combination medications take advantage of positive aspects of synergism
Negative effects can occur also
Learning Objective 4-5

35. Antagonistic Drug Reactions
One drug interferes with action of another drug either canceling each other out or making one drug less powerful
Patients should be warned about antagonistic reactions
Learning Objective 4-5

36. Obtaining a Patient’s Medical History
Physician needs to be aware of all medications patient is currently taking
Patients should be encouraged to be forthcoming and complete
Ask patient if he has adjusted drug dosages on his own
Explain need to know alcohol or drug use for potential drug interactions; remind patient of confidentiality
Learning Objective 4-5

37. Obtaining a Patient’s Medical History (cont’d)
If patient is unable to remember all medications:
Ask for names of physicians, dentists, and other health care professionals patient is seeing; this may help with recall of prescriptions
Have patient or family member collect patient’s prescriptions and OTC medications and bring them to next appointment
Learning Objective 4-5

38. Drug Interactions (cont’d)
Food-drug interactions occur when foods eaten interact with or interfere with action of a drug
Foods contain chemicals that affect body
Patients need to know about any possible food-drug interactions and adjust their diets accordingly
Learning Objective 4-6

39. Drug Interactions (cont’d)
Some medications should be taken on an empty stomach
Food may interfere with absorption
Some medications irritate stomach and cause nausea, vomiting, or epigastric irritation
Taking them with food is helpful
Some drugs, when taken with certain foods, produce enhanced effects in the body
Learning Objective 4-6

40. Food-Drug Interactions
[Insert untab4-3]
Learning Objective 4-6

41. Factors Influencing Drug Responses
Age
Weight
Gender
Pre-existing disease or condition
Learning Objective 4-7

42. Age Can affect dosage size
Organs are more immature in children, so drug metabolism is different
Learning Objective 4-7

43. Weight Dosages calculated for average 150 pound patient
Adjustments in dosage can be made for higher or lower weight
Learning Objective 4-7

44. Gender
Females may require smaller dose than males due to makeup of bodies
Men and women differ in amount of body fat
Males and females also differ in ratio of body mass to body water
Learning Objective 4-7

45. Pre-existing Disease or Condition
Liver or kidney disease affects drug metabolism
Pregnancy affects choice of medications due to ability to cross placenta
Learning Objective 4-7