NCLEX-RN: Pharmacology

Pharmacology: Drug Metabolism

Focus topic: Pharmacology

Pharmacology: Stages of Metabolism

Focus topic: Pharmacology

Definition: Drug metabolism in the human body is accomplished in four basic stages—absorption, transportation, biotransformation, and excretion. For a drug to be completely metabolized, it must first be given in sufficient concentration to produce the described effect on body tissues. When this critical drug concentration level is achieved, body tissues change.

A. Absorption.

  • The first stage of metabolism refers to the route a drug takes from the time it enters the body until it is absorbed in the circulating fluids.
  • Drugs are absorbed by the mucous membranes, the gastrointestinal tract, the respiratory tract, and the skin.
    a. The mucous membranes are one of the most rapid and effective routes of absorption because they are highly vascular.
    b. Drugs are absorbed through these membranes by diffusion, infiltration, and osmosis.
  • Drugs given by mouth are absorbed in the gastrointestinal (GI) tract.
    a. Portions of these drugs dissolve and absorb in the stomach.
    b. The rate of absorption depends on the pH of the stomach’s contents, the food contained in the stomach at the time of ingestion, and the presence of disease conditions. This is why some drugs must be given on an empty stomach, while others should be given with food.
    c. Most of the drug concentrate dissolves in the small intestine, where the large vascular surface and moderate pH level enhance the process of dissolution.
  • Methods of injection include intradermal, subcutaneous, intravenous, intramuscular, and intra-arterial injections.
    a. Parenteral methods are the most direct, reliable, and rapid route of absorption.
    b. The actual administration site will depend on the type of drug, its action, and the client.
  • Another route of administration is inhalation or nebulization through the respiratory system.
    a. This method is not as rapid as parenteral injections but is faster than the GI tract.
    b. Drugs administered through the respiratory tract must be made up of small particles that can pass through to the alveoli in the lungs.
  • The final mode of absorption is the skin.
    a. Most drugs, when applied to the skin, produce a local rather than a systemic effect. Exceptions are nitrates and pain medications.
    b. The degree of absorption will depend on the strength of the drug as well as location where it is applied on the body surface.

B. Distribution.

  • The second stage of metabolism refers to the way in which a drug is transported from the site of introduction to the site of action.
  • First a drug enters or is absorbed by the body.
    a. The drug binds to plasma protein in the blood.
    b. Then the drug is transported through circulation to all parts of the body.
  • As a drug moves from the circulatory system, it crosses cell membranes and enters the body tissues.
    a. Some of the drug is distributed to and stored in fat and muscle.
    b. Greater masses of tissue (such as fat and muscle) attract the drug.
  • The amount of drug that is distributed to body tissues depends on the permeability of the membranes and the blood supply to the absorption area.
  • A drug that first accumulates in the brain may move into fat and muscle tissue and then back to the brain because the drug is still chemically active.
    a. The drug is released in small quantities from the tissues and travels back to the brain.
    b. Equal drug and blood concentration levels in the body are maintained.

C. Metabolism or biotransformation.

  • The third stage of metabolism takes place as the drug—a foreign substance in the body—is converted by enzymes into a less active and harmless agent that can be easily excreted.
  • Most of this conversion occurs in the liver.
    a. Both synthetic and biochemical reactions take place.
    b. Some conversion does take place in the kidney, plasma, and intestinal mucosa.
  • Synthetic reactions: liver enzymes conjugate the drug with other substances to make it less harmful for the body.
  • Biochemical reactions: drugs are oxidized, reduced, hydrolyzed, and synthesized so they become less active and more easily eliminated from the body.

D. Excretion.

  • The final stage in metabolism takes place when the drug is changed into an inactive form or excreted from the body.
  • The kidneys are the most important route of excretion.
  • The kidneys eliminate both the pure drug and the metabolites of the parent drug.
    a. During excretion these two substances are filtered through the glomeruli.
    b. They are then secreted by the tubules.
    c. Finally, they are reabsorbed through the tubules or directly excreted.
  • Other routes of excretion include the lungs (which exhale gaseous drugs), feces, saliva, tears, and mother’s milk.

Pharmacology: Factors That Affect Drug Metabolism

Focus topic: Pharmacology

A. Personal attributes.

  • Body weight.
  • Age.
  • Sex.

B. Physiological factors.

  • State of health.
  • Disease processes.

C. Acid–base and fluid and electrolyte balance.
D. Permeability.
E. Diurnal rhythm.
F. Circulatory capability.
G. Genetic and immunologic factors.
H. Drug tolerance.
I. Cumulative effect of drugs.
J. Other factors.

  • Psychological.
  • Emotional.
  • Environmental.

K. Responses to drugs vary.

  • Responses depend on the speed with which the drug is absorbed into the blood or tissues.
  • Responses depend on the effectiveness of the body’s circulatory system.

Pharmacology: Factors That Affect Drug Absorption

Focus topic: Pharmacology

A. Absorption factors.

  • Solubility of the drug.
  • Route of administration: oral, subcutaneous, topical, sublingual, or intramuscular.
  • Client’s sex, age, and health status.
    a. Females absorb IM injections slower than males because they have increased adipose tissue and a smaller blood supply.
    b. Older clients respond slower to oral medications, and this is often related to lower gastric acid in the stomach.
    c. Certain diseases decrease tissue perfusion.

B. Distribution factors.

  • Cardiac output and circulation influence how the drug reaches the target tissues.
  • If a drug is attached to serum proteins and the protein level is low, there would be more free drug in the bloodstream; this condition indicates that dosage should be decreased with certain drugs (warfarin, phenytoin, and barbiturates).
  • Drug half-life is the time it takes for the half of the amount of the drug taken to be eliminated or metabolized. The shorter the half-life of a drug, the quicker it is eliminated.
    a. If the client takes 20 mg of a drug with a half-life of 2 hours, only 10 mg of the drug will be in the body 2 hours after administration.
    b. Two hours later, there will only be 5 mg of the drug left.
    c. The half-life of a drug can be influenced by many factors such as metabolism and genetics.
    d. It is important to note that the half-life for any drug is the half-life for a healthy person.
    e. The half-life of drugs for individuals with liver or kidney dysfunction would be different.

C. Clients with impaired liver function or liver disease may lose much of the therapeutic value of a drug.

  • Drugs that pass through the liver (called first-pass effect) before being absorbed into the bloodstream may be affected by the liver status.
  • Certain drugs that go from the GI tract to the portal vein to the liver may need to have their oral dosages adjusted upward to compensate for partial deactivation (lidocaine, morphine, propranolol, verapamil).

D. Kidneys also play a role in drug absorption––depends on tissue perfusion, disease, and urinary pH.

  • Renal disease interferes with renal clearance, and drugs (potassium chloride or digoxin) can reach toxic levels in the bloodstream.
  • The more alkaline the urine, the faster certain drugs are excreted (salicylates, barbiturates, and sulfonamides). Sodium bicarbonate will make urine more alkaline.
  • Some drugs are excreted faster when urine is acidic (amphetamines and ephedrine). Vitamin C will make urine more acidic.

Pharmacology: Origin and Nomenclature of Drugs

Focus topic: Pharmacology

Pharmacology: Common Sources

Focus topic: Pharmacology

A. Plant sources.

  • Roots, bark, sap, leaves, flowers, and seeds from medicinal plants can be used as drug components.
  • Component substances.
    a. Alkaloid.
    (1) Alkaline (base) in reaction.
    (2) Bitter in taste.
    (3) Physiologically powerful in activity.
    b. Glycoside: a compound containing a carbohydrate molecule.
    c. Resin: soluble in alcohol; insoluble in water.
    d. Gum.
    (1) Mucilaginous (gelatinlike) excretion.
    (2) Used in bulk laxatives; may absorb water.
    (3) Used in skin preparations as a soothing effect (e.g., Karaya gum).
    e. Oil.
    (1) Fixed oil: Does not evaporate on warming; occurs as a solid, semisolid, or liquid (e.g., castor oil).
    (2) Volatile oil: Evaporates readily; occurs in aromatic plants (e.g., peppermint).

B. Animal sources.

  • Processed from an organ, from organ secretion, or from organ cells.
  • Insulin, as an example, is a derivative from the pancreas of sheep, cattle, or hogs.

C. Mineral sources.

  • Inorganic elements occurring in nature, but not of plant or animal origin; may be metallic or nonmetallic.
  • Usually form a base or acid salt in food.
  • Dilute hydrochloric acid (HCl), as an example, is diluted in water and then taken through a straw to prevent damage to teeth by acid.

D. Synthetic sources.

  • A pure drug made in a laboratory from chemical, not natural, substances.
  • Many drugs—sulfonamides, for example—are synthetics.

Pharmacology: Methods of Naming Drugs

Focus topic: Pharmacology

A. Chemical name.

  • Precise description of chemical constituents with the exact placement of atom groupings.
  • “N-methyl-4-carbethoxypiperidine hydrochloride” is an example of a chemical name.

B. Generic name.

  • Reflects chemical name of the drug, but is simpler.
  • It is never changed and used commonly in medical terminology.
  • The synthetic narcotic “meperidine” is an example of a generic name.

C. Trademark name (brand name, proprietary name).

  • Appears in literature with the sign ® (e.g., Demerol®).
  • The sign indicates the name is registered; use of the name is restricted to the manufacturer that is its legal owner.
  • Trademark name is capitalized or shown in parentheses if generic name stated.

Pharmacology: Drug Classification

Focus topic: Pharmacology

Pharmacology: Classification by Action

Focus topic: Pharmacology

✦A. Anti-infectives.

  • Antiseptics.
    a. Action—inhibit growth of microorganisms (bacteriostatic).
    b. Purpose—application to wounds and skin infections, sterilization of equipment, and hygienic purposes.
  • Disinfectants.
    a. Action—destroy microorganisms (bactericidal).
    b. Purpose—destroy bacteria on inanimate objects (not appropriate for living tissue).

✦B. Antimicrobials.

  • Sulfonamides.
    a. Action—inhibit the growth of microorganisms.
    b. Usage—reduce or prevent infectious process, especially for urinary tract infections.
  • Antibiotics (e.g., penicillin).
    a. Action—interfere with microorganism metabolism.
    b. Usage—reduce or prevent infectious process.
    c. Specific drug and dosage based on culture and sensitivity of organism.

✦C. Metabolic drugs.

  • Hormones obtained from animal sources, found naturally in foods and plants.
  • Synthetic hormones.

D. Diagnostic materials.

  • Action—dyes and opaque materials ingested or injected to allow visualization of internal organs.
  • Purpose—to analyze organ status, disease state, and function.

E. Vitamins and minerals.

  • Action—necessary to obtain healthy body function.
  • Found naturally in food or through synthetic food supplements.

✦F. Vaccines and serums.

  • Action—prevent disease or detect presence of
    disease.
  • Types.
    a. Antigenics produce active immunity.
    (1) Vaccines—attenuated suspensions of microorganisms.
    (2) Toxoids—products of microorganisms.
    b. Antibodies—stimulated by microorganisms or their products.
    (1) Antitoxins.
    (2) Immune serum globulin.
    c. Allergens—agents for skin immunity tests.
    (1) Extracts of materials known to be allergenic.
    (2) Can be used to relieve allergies.
    d. Antivenins—substances that neutralize venom of certain snakes and spiders.

✦G. Antifungals—check growth of fungi.
✦H . Antihistamines.

  • Action—prevent histamine action.
  • Purpose—relieve symptoms of allergic reaction.

✦I. Antineoplastics—prevent growth and spread of malignant cells.

Pharmacology: Classification by Body System

Focus topic: Pharmacology

Pharmacology: Central Nervous System

Focus topic: Pharmacology

A. Drugs affect central nervous system (CNS) by either inhibiting or promoting the actions of neural pathways and centers.

  • Action-promoting drug groups (stimulants).
    a. Antidepressants—psychic energizers used to treat depression.
    b. Caffeine—increases mental activity and lessens drowsiness.
    c. Ammonia—used for revival for fainting spell (client smells cap, not contents of bottle).
  • Action-inhibiting drug groups (depressants).
    ✦a. Analgesics—reduce pain by interfering with conduction of nerve impulses.
    (1) Narcotic analgesics—opium derivatives may depress respiratory centers; must be used with caution when the respiratory rate is less than 12.
    (a) Adverse reactions can differ from drug to drug and can include: constipation, respiratory depression, blurred vision, nausea, vomiting, drowsiness, dizziness, weakness, dry mouth, confusion, difficulty urinating, itching.
    (b) Clients must be assessed for adverse reactions.
    (c) A narcotic antagonist drug counteracts depressant drugs.
    (d) The most common antagonist drug is Narcan (naloxone).
    (2) Nonnarcotic antipyretics—reduce fever and relieve pain.
    (3) Antirheumatics—analgesics given to relieve arthritis pain; may reduce joint inflammation.
    ✦b. Alcohol—stimulates appetite when given in small doses but is classified as a depressant.
    ✦c. Hypnotics—sedatives that induce sleep; common form is the barbiturates.
    ✦d. Antispasmodics—relieve skeletal muscle spasms; anticonvulsants prevent muscle spasms or convulsions.
    ✦e. Tranquilizers.
    (1) Relieve tension and anxiety, preoperative and postoperative apprehension, headaches, menstrual tension, chronic alcoholism, skeletal muscle spasticity, and other neuromuscular disorders.
    (2) Tranquilizers and analgesics frequently given together (in reduced dosage); the one drug enhances the action of the other (synergy).
    f. Anesthetics—produce the state of unconsciousness or conscious sedation painlessly.

✦B. Precautions to be taken with CNS drugs.

  • Drugs that act on CNS may potentiate other CNS drugs.
  • Client may be receiving other medications; find out drug name and dosage.
  • Dependence on CNS drugs may occur.

Pharmacology: Autonomic Nervous System

Focus topic: Pharmacology

A. The autonomic nervous system (ANS) governs several body functions so that drugs that affect it will at the same time affect other system functions.
B. The ANS is made up of two nerve systems—the sympathetic and parasympathetic.

  • Sympathetic—the protective emergency system.
  • arasympathetic—the stabilizing system.

C. Each system has a separate basic drug group acting
on it.

  • Adrenergics—mimic the actions of sympathetic system.
    a. Vasoconstrictors—stimulants such as adrenalin.
    (1) Action is to constrict peripheral blood vessels, thereby increasing blood pressure.
    (2) Dilate bronchial passages.
    (3) Relax gastrointestinal tract.
    b. Vasodilators—depressants such as nicotinic acid.
    (1) Antagonists of epinephrine and similar drugs.
    (2) Vasodilate blood vessels.
    (3) Increase tone of GI tract.
    (4) Reduce blood pressure.
    (5) Relax smooth muscles.
    (6) Caution: If drug is to be stopped, reduce dosage gradually over a period of a week; do not stop it suddenly.
  • Cholinergics—mimic actions of parasympathetic system.
    a. Cholinergic stimulants (e.g., Prostigmin or neostigmine).
    (1) Decrease heart rate.
    (2) Contract smooth muscles.
    (3) Contract pupil in eye.
    (4) Increase peristalsis.
    (5) Increase gland secretions.
    b. Cholinergic inhibitors (anticholinergics).
    (1) Decrease gland secretion.
    (2) Relax smooth muscle.
    (3) Dilate pupil in eye.
    (4) Increase heart action.

Pharmacology: Eye

Focus topic: Pharmacology

A. Anesthetics.

  • Use: brief local anesthesia used for measurement of intraocular pressure, removal of foreign bodies, or other superficial procedures.
  • Caution: If used repeatedly, may result in increased risk of CNS and cardiovascular toxicity.

B. Anti-infectives/antifungals/antivirals.

  • Use: superficial ophthalmic infections like bacterial conjunctivitis.
  • Caution: Hypersensitivity may occur when small amounts absorbed.

C. Beta blockers.

  • Use: management of chronic open-angle glaucoma.
  • Caution: Systemic absorption minimal but may occur and may result in bradycardia, hypotension, bronchospasm, or delirium in elderly.

D. Cholinergics (direct-acting).

  • Use: treatment of open-angle glaucoma.
  • Caution: Avoid conditions in which pupillary constriction occurs. If significant systemic absorption occurs, bronchospasm, sweating, and salivation may occur.

E. Cholinergics (cholinesterase inhibitors).

  • Use: treatment of glaucoma not controlled with short-acting miotics or other agents.
  • Caution: May intensifiy the actions of cocaine and some other local anesthetics; additive toxicity with antimyasthenics, anticholinergics. Use cautiously in clients with history or risk of retinal detachment.

F. Corticosteroids.

  • Use: management of inflammatory eye conditions.
  • Caution: Used to treat infectious ocular processes (avoid use in herpes simplex keratitis, fungal, and viral ocular infections as it may mask symptoms; diabetes, glaucoma, or epithelial compromise).

G. Cycloplegic mydriatics.

  • Use: management of uveitis.
  • Caution: Use cautiously in clients with a history of glaucoma; systemic absorption may cause anticholinergic effects such as confusion, unusual behavior, flushing, hallucinations, slurred speech, drowsiness, tachycardia, dry mouth.

Pharmacology

Pharmacology: Gastrointestinal System

Focus topic: Pharmacology

A. Drugs affecting GI system act on muscular and glandular tissues.
B. Antacids—counteract excess acidity.

  • Have alkaline base.
  • Used in the treatment of ulcers.
  • Neutralize hydrochloric acid in the stomach.
  • Given frequently (2-hour intervals or more often).
  • May be given with water.
  • May cause constipation, depending on type of medication.
  • Baking soda is a systemic antacid which changes the pH balance in the body. Most other antacids coat the mucous membrane and neutralize hydrochloric acid.

C. Emetics—produce vomiting (emesis).
D. Antiemetics-blocks the body’s response that produces nonbeneficial nausea and vomiting.

E. H2-receptor antagonists—block gastric acid secretion (e.g., cimetidine [may inhibit the absorption of warfarin], ranitidine).
F. Antiulcer drugs—sucralfate; give 1 hour ac and at hs; nonsystemic.
G. Digestants—relieve enzyme deficiency by replacing secretions in digestive tract.
H. Antidiarrheals prevent diarrhea by thickening the stool or by slowing intestinal spasms.

I. Cathartics—affect intestine and produce defecation.

  • Provide temporary relief for constipation.
  • Rid bowel of contents before surgery, and prepare viscera for diagnostic studies.
  • Counteract edema.
  • Treat diseases of GI tract.
  • Are contraindicated when abdominal pain is present.
  • Classifications.
    a. By degree of action.
    (1) Laxative—mild action.
    (2) Cathartic—moderate action.
    (3) Purgative—severe action.
    b. By method of action.

Pharmacology: Respiratory System

Focus topic: Pharmacology

A. Drugs that act on respiratory tract, tissues, and cough center.
B. Action is to suppress, relax, liquefy, and stimulate depth and rate of respiration.
C. Bronchodilators—relax smooth muscle of trachea and bronchi.

  • Sympathomimetics.
    a. Taken PO or inhaled (fewer side effects).
    b. Beta2 agonists preferred (e.g., albuterol, metaproterenol).
  • Anticholinergics (e.g., atropine sulfate by
    nebulizer or metered dose inhaler).
  • Theophyllines.
    a. Monitor serum levels.
    b. Examples: theophylline PO, aminophylline IV.
  • Anti-inflammatory agents—reduce bronchospasm.
    a. Mast cell inhibitor (e.g., cromolyn sodium).
    b. Corticosteroids (PO, IV, or inhaled).

Pharmacology: Urinary System

Focus topic: Pharmacology

A. Drugs that act on kidneys and urinary tract.
B. Action is to increase urine flow, destroy bacteria, and perform other important body functions.

  • Diuretics.
    a. Rid body of excess fluid and relieve edema associated with heart failure, pulmonary edema, certain renal diseases, cirrohosis, and liver failure.
    b. Increase sodium excretion resulting in water excretion from the kidneys.
    c. Some can result in significant loss of potassium, which can cause fatal cardiac arrhythmias. Some drugs that act on the GI tract and circulatory system also are diuretic in action.
  • Urinary antiseptics choice based on susceptible bacteria found in urine culture. Some drugs are more active with alkaline urine.
  • Acidifiers and alkalinizers—certain foods will also increase body acidity and alkalinity.
  • Urinary tract stimulant.
    a. Increase contraction of the urinary bladder.
    b. Used in postoperative nonobstructive urinary retention caused by neurogenic bladder.

Pharmacology: Circulatory System

Focus topic: Pharmacology

A. Drugs that act on heart, blood, and blood vessels.
B. Action is to change heart rhythm, rate, and force and to dilate or constrict vessels.

  • Cardiotonics—used for heart-strengthening.
    a. Direct heart stimulants that speed heart rate (e.g., caffeine, adrenalin).
    b. Indirect heart stimulants (e.g., digoxin).
    (1) Stimulate vagus nerve.
    (2) Slow heart rate and strengthen it.
    (3) Improve cardiac output, thereby improving circulation.
    (4) Do not administer if apical pulse below 60.
  • Cardioprotective drugs.
    a. Beta-adrenergic blockers.
    b. Calcium-entry blockers.
  • Antiarrhythmic drugs—used clinically to convert irregularities to a normal sinus rhythm.
  • Drugs that alter blood flow.
    a. Anticoagulants—inhibit blood-clotting action (e.g., heparin, warfarin).
    b. Thrombolytic agents (streptokinase, urokinase)—clot busters used to lyse already formed blood clots where ischemia may be fatal (myocardial infarction, pulmonary embolism, ischemic stroke, or arterial thrombosis). Very precise indications rule the use of these drugs, which are not free from serious side effects (bleeding).

c. Platelet-inhibiting agents (aspirin, dipyridamole)—agents that decrease platelet aggregation and inhibit thrombus formation. Antiplatelet drugs are most effective for arterial clots that are composed largely of platelets.
d. Vasodilators (nitroglycerine)—increase blood flow; can decrease ischemic episodes associated with activity if given prior to activity.
e. Hemorrhagic agents (e.g., Trental [pentoxifylline])—help blood flow more easily through narrowed arteries, increasing the amount of oxygen delivered by the blood when the muscles need more (such as during exercise) thereby increasing walking distance/duration and decreasing pain.

  • Blood replacement.
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