#2 Drug action

The potency of a drug is determined by

the dose needed to produce the desired therapeutic effect

Efficacy

The maximum effect a drug may produce

Potency

a function of the amount of the drug required to produce an effect

More of a less potent drug is required to produce a desired effect equivalent to that of a more potent drug (T/F)

True

Potency

a function of the amount of the drug required to produce an effect

Administering more drug will not increase the efficacy but can often increase the probability of an ________

adverse reaction

Efficacy and potency of drug are

Unrelated

*Drugs with a high TI are generally "safer" (T/F)

True

Therapeutic Index (TI)

the ratio of the mean lethal dose (LD 50) to the median effective dose (ED 50)

TI = LD50/ED 50

Pharmacologic effect

• Produce same action as endogenous agent

• Block action of endogenous agent

Therapeutic effect

• predictable, dose-related effect

Adverse effect

exaggerated effects on target and non-target tissues/organs

therapeutic effect

• In order for a drug to exert its therapeutic effect, it must bind with the receptor site on the cell membrane. Because different drugs compete for the same receptor sites, the drug with the stronger affinity for the receptor will bind to more receptors than the drug with the weaker affinity.

• Agonists or Antagonists

Agonist

• Has affinity for a receptor

• Combines with the receptor

• Produces an effect

• Ex: morphine, which binds to opioid receptors and reduces pain

Antagonist

Counteracts the action of the agonist

Three types of antagonist

Competitive

Noncompetitive

Physiologic

Competitive antagonist

Ex: Naloxone, binds to the same opioid receptors as opioid agonists (like heroin, morphine, fentanyl, etc.) but does not activate them and effectively reversing the overdose effects

Noncompetitive antagonist

Ex: Ketamine, binding alters the receptor's shape, preventing the agonist from activating the receptor, even if the agonist is still present

Physiologic

Ex: insulin lowers blood glucose levels, glucagon, which acts on different receptors, can increase blood glucose levels and counteract the effects of insulin, making glucagon a physiological antagonist to insulin

Adverse reactions

exaggerated effects on target and non-target tissues/organs

1. Side effects

2. Toxic reaction

3. Idiosyncratic reaction

4. Allergic reaction (hypersensitivity reaction)

5. Teratogenic effect

   
   

Side effect

occurs when a drug acts on non-target organs to produce "undesirable" effects

EX: -Nausea with: codeine, antibiotics, ibuprofen

-Sedation with: antihistamines

Toxic reaction

• predictable, dose related rn that acts on target organs

• More common than allergic rns

• Excessive levels of drug

• Damage to tissues/organs can be reversible or irreversible

Ex: tinnitus with aspirin

Idiosyncratic reaction

• Genetically-related abnormal response to a drug

• A drug having an opposite reaction than the therapeutic rn

Ex: sedatives causing hyperactivity

Allergic reaction (hypersensitivity reaction)

• Non-predictable, immunologic response of the body toward the drug

• Signs/symptoms: Rash, swelling, itching (hives or urticaria), wheezing, coughing, difficulty breathing, angioedema, anaphylaxis

Aspirin reactions

Side effect: upset stomach

Toxic reaction: tinnitus

Allergic reaction: hives

Teratogenic effect

• Drugs affect the fetus

• FDA pregnancy categories:

A,B,C,D and X

(least to most risky to fetus)

FOODS WITH POTENTIAL FOR CROSS-HYPERSENSITIVITY WITH LATEX HYPERSENSITIVITY

apples

papayas

avocados

peaches

bananas

pears

carrots

pineapples

celery

potatoes

cherries

rye

chestnuts

strawberries

hazelnuts

tomatoes

kiwis

wheat

melons

DENTAL OBJECTS COMPOSED

OF LATEX:

Gloves

Rubber dam

Local anesthetic cartridges (stopper)

Syringes (black rubber inside)

Bite block

Strings that hold gown on

Glasses bridges

Pharmacokinetics

What happens to a drug once it's administered.

Four major steps:

• Absorption

• Distribution

• Metabolism

• Excretion

Absorption

acidic drugs more readily absorbed in an acidic environment.

Distribution

highest amount of blood flow, higher concentration of drug

*Half-life:

the amount of time that passes for the concentration of a drug to fall to one half of its blood level at any time

Metabolism

Primary site: liver

Excretion

Main route: kidneys

Other routes: Sweat, saliva, respiratory tract, G.l. tract, breast milk

Oral (Enteral route)

Ex.: Almost all Rx and OTC meds (ORAL MEDICATIONS, TABLETS, CAPSULES, STAX, LIQUIDS → SOLUTIONS or SUSPENSIONS)

* COMMONLY for PATIENTS who are able to SWALLOW

Advantages: simple, safe, conv., overdose=retrievable

Disadvantages: slower onset, irritating, certain drugs inactivated by stomach acid

Enteral route:

-directly into G.l. Tract

1. Oral (PO)

2. Rectal (R)

Rectal (Enteral route)

Ex.: suppositories (Dulcolax, GLYCERIN)

Advantages: can be used if patient can't take meds PO

Disadvantages: irregular absorption patient acceptance poor

Parenteral Routes

bypasses the gastrointestinal tract

a. Intravenous (IV)

b. Intramuscular (IM)

C. Subcutaneous (SC)

D. Intradermal

E. Intrathecal

Intravenous (parenteral route)

Ad: most rapid, predictable drug response, emergency route

Disad: Drug irretrievability, local irritation, (phlebitis), Allergy

Intramuscular (parenteral route)

Ex: Vaccines, B12 injection

Ad: rapid absorption, irritating drugs well tolerated; give larger amounts of solution, useful for drugs destroyed in G.l. Tract

Disad: repetitive admin.

Subcutaneous (Parenteral route)

Ex: insulin, injectable LA

Ad: slow, controlled absorption; readily can determine if allergy

Disad: irritating drugs can be painful

Intradermal Route (Parenteral)

TB skin test

contraceptive inserts (Norplant®)

Intrathecal Route (parenteral)

inj. in spinal subarachnoid space (spinal anesth.) Epidural

Inhalation Route

General anesthesia, nitrous oxide analgesia, asthma meds, some vaccines, some osteoporosis meds, insulin

Topical Route

Topical anesthesia, creams, lotions, ointments, gels, sprays, powders, and transdermal patches

Sublingual/Buccal Route

nitroglycerin (Nitrostat)

Factors that Affect Drug Absorption

1.Patient Compliance

2. Age

3. Gender

4. Pathologic state

5. Genetic variations

6. Placebo effect

7. Time of administration

8. Other medications

Who are more susceptible to drug effects?

Kids, elderly, and female