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Nurses Role in Drug Therapy
Nurses use core drug knowledge and core patient variables:
To maximize the therapeutic effects of a drug
To minimize the adverse effects of a drug
To provide patient and family education
Enteral: through mouth/goes through GI
Parenteral: IV, intramuscular, through the blood, intra-arterial, etc. (Injections)
Managing Drug Therapy Through the Nursing Process: Assessment
Assessment of core drug knowledge
Assessment of core patient variables: initial gatherings from assessing the patient (health history)
Why is heart disease important for drug therapy? It won’t circulate well enough throughout the body
Drugs
Any chemical that affects the process of a living organism can broadly be defined as a drug
Drugs are chemicals that are introduced into the body that cause some sort of change
When drugs are administered, the body begins a sequence of processes designed to handle the new chemicals; which involves breaking down and eliminating the drugs.
Components of core drug knowledge are:
Pharmacotherapeutics
Therapeutic effect
Pharmacokinetics: ADME (Absorption, Distribution, Metabolism and Excretion)
Changes occur to drug in body
Pharmacodynamics
Effects on body
Contraindications and precautions: exclusions to why the patient shouldn’t take the med.
Adverse effects: side effects
Drug interactions
Sources of Drugs
Plants, foods, salts
Animal products
Inorganic compounds (i.e. aluminum, fluoride, iron, gold)
Synthetic sources
Drug Evaluation
After drugs are developed and identified, they must evaluate their actual therapeutic and toxic effects. This process in the US is tightly controlled and regulated by the FDA
Several (4) “phases” of clinical trials are performed
Purpose of Drug Therapy
Treat diseases
Prevent diseases
Diagnose diseases
Approaches to drug classification
Clinical indications
Body systems approach
9 Categories of Drugs
Nervous System Agents Cardiovascular System Agents Renal System Agents Respiratory System Agents Musculoskeletal System Agents Endocrine System Agents GI System Agents Immune System Agents Chemotherapeutic Agents
Common Drug Grouping: Family Group
Penicillin
Beta Blockers
Common Drug Grouping: Therapeutic Group
Antihypertensive
Analgesics
Anti-anxiety
Medication Preparations:
Local and Systemic
Local: effects confined to one area of body
0.1% topical hydrocortisone for a rash pr 1% lidocaine injected to anesthetize a wound.
Some topical drugs are absorbed through skin and have a systemic effect.
Systemic: absorbed into vascular system and delivered into cells, tissues, and organs.
Pharmacology
Is the study or science of drugs and the biological effects of chemicals
Pharmacotherapeutics
A branch of pharmacology
Incorporates the principles of drug actions
The use of drugs and the clinical indications for drugs to prevent and/or treat diseases
The desired outcome
Addresses two key concerns: drug’s effects on the body and the body’s response to the drug
Pharmacodynamics
Relates to how the drug affects the body; drug action
Turn on, turn off, promote, or block a response.
Pharmacokinetics
Relates to how the body acts on the drug
Involves the study of absorption, distribution, metabolism (biotransformation), and excretion of drugs (A D M E principle)
In clinical practice, it includes: onset of drug action, drug half-life, timing of the peak effect, duration of action, metabolism of the drug, and the site of excretion
Critical Concentration
In order for a drug to have a therapeutic effect in the reactive tissues, it must maintain a sufficiently high concentration in the body
The amount of a drug that is needed to cause a therapeutic effect is called the critical concentration
Loading Dose
Some drugs take a long time to reach a critical concentration level, so if their effects are needed quickly, a loading dose is recommended
Therefore, in order to reach therapeutic effects, the INITIAL dose is usually a higher dose and the critical concentration is maintained by recommended dosing schedule
Absorption
Absorption refers to what happens to a drug from the time it is introduced to the body until it reaches the circulating fluids and tissues.
Factors Influencing Absorption
Rate of absorption depends on route of administration.
Greater rate of absorption w/ increased blood flow because more blood to carry drug molecules into circulation.
Lipid soluble drugs absorbed faster because they can readily cross lipid cell membrane.
food or other drugs in stomach; Acidity of the stomach
gastric/intestinal motility
injection site heat or cold (cold-vasoconstriction, decreases absorption; hot- vasodilation, increases absorption)
Bioavailability
A term used to quantify the extent of drug absorption
Administration Routes
Oral (PO): Oral route is the most common, not invasive and less expensive. It is also the safest way to deliver drugs.
Rectal (PR): Administered via the rectum, usually given this route when patient is unable to take PO (ex. Tylenol/ASA suppositories)
Intravenously (IV): These drugs are injected directly into the vein, they reach their full strength at the time of injection, avoiding initial breakdown (ex. Gtts)
Intramuscular (IM): Drugs injected IM route are absorbed directly into the capillaries in the muscle and sent into circulation (ex. Vitamin B-12)
Subcutaneous Injections (Sub Q): Deposits the drug just under the skin, where it is slowly absorbed into circulation. Timing of absorption varies, depending on the fat content of the injection site and the state of local circulation (ex. Insulin, heparin)
Administration Routes Cont.d
Mucous Membranes (Sublingual, buccal): Usually given for fast absorption, i.e. SubLingual NiTroGlycerin
Topical (skin): Long acting, absorbed slowly. Fevers may increase absorption (temperatures causes the membrane to disintegrate, releasing more drug), i.e. Narcotic patches, birth control
Inhalation: Inhaled through the mouth or nose. Usually to treat respiratory condition, i.e. Albuterol, Spiriva.
Distribution
Process by which the drug is delivered to tissues
Distribution of an absorbed drug depends on: Blood flow Protein binding Free, unbound drug = active drug Solubility
Protein-Bound Drugs
When the drug is bound to protein, it is unable to pass through the capillary walls.
The bonds will dissolve in time, and the drug molecules will become free and active.
When the patient has a lower-than-expected protein level, the distribution of the drug is altered.
Factors that affect distribution of drugs:
Perfusion of the reactive tissue Scar tissue- avascular Adipose tissue – poor blood supply Abscesses Solid tumors Protein binding Drug’s lipid solubility
Metabolism (Biotransformation)
Chemical reactions the body uses to convert drugs and other chemicals into non toxic substances. It is the process by which drugs are changed into new, less active chemicals
The liver is the single most important site of drug metabolism
Products of drug metabolism:
Metabolites
Inactive or active
Active metabolites
Therapeutic or adverse
First Pass Effect
This phenomenon occurs when an orally administered drug, after being absorbed, travels through the circulatory system into the liver where the drug is metabolized and loses much of its effectiveness.
For this reason, oral doses are usually much higher, taking into consideration the first pass effect.
First Pass Route
Oral Route
Everything else is non-first route
Cytochrome P-450 System
Primary oxidative enzyme responsible for biotransformation of many drugs.
Some drugs can induce or inhibit this system, altering metabolism of other drugs.
Some drugs can compete with each other for the enzyme
Underdeveloped in children, & decreased in elderly and patients with liver disease.
Excretion
Excretion is the removal of a drug from the body.
Sources of Excretion: Kidneys: play the most important role Skin Saliva Lungs Bile Feces
Processes Involved in Renal Excretion
Glomerular filtration.
Most drug particles pass easily through the spaces of the capillary walls into the urine in the proximal tubule.
Passive tubular reabsorption.
The drug particles will try to move from the area of greater concentration to that of lesser concentration.
Active tubular secretion.
Active transport systems in the renal tubule work to move some drugs from the blood and into the urine.
Factors That Affect
Renal Excretion
Drug excretion can be increased if the pH of the urine encourages the drug to become an ion.
Overuse of the active transport system also affects excretion.
As the transport system becomes overloaded, some of the drug particles will remain in the blood until they can be moved by the transport system.
Two drugs can be given together to deliberately slow the rate of excretion of one or both of the drugs.
Half-Life
The time it takes for the amount of drug in the body to decrease to one-half of the peak level it previously achieved.
Example: If a patient takes 20mg of a drug with a half-life of 2 hours, 10mg of the drug will remain 2 hours after administration; 2 hours later, 5mg will be left and in 2 more hours 2.5mg will remain.
It helps the nurse determine the appropriate timing for a drug dose or determining the duration of a drug’s effect on the body
Clearance
The rate at which drug molecules disappear from the circulatory system is effected by several factors.
This rate is called clearance or clearance rate of a drug.
Renal excretion and hepatic metabolism are the major modes of clearance.
The gender of the patient can also alter the clearance of some drugs.
Pharmacodynamics
The biologic, chemical, and physiologic actions of a particular drug within the body.
The pharmacodynamics of a drug are responsible for its therapeutic effects and sometimes its adverse effects.
Drugs cannot create new responses in the body; they can only turn on, turn off, promote, or block a response that the body is inherently capable of producing.
Drug–Receptor Interactions
Most drugs create their effects in the body by attaching to special sites, called receptors.
At the receptor site, the drug is able to stimulate the cell to act in a way that the cell is designed to act.
An agonist causes the cell to act.
An antagonist or blocker prevents something else from attaching to the cell blocking and action.
Variables That Influence the Dose of a Drug
Potency (amount needed) and efficacy (how well did response occur)
The level of the drug needed in the body to produce an effect
Maintenance and loading doses
Maintenance dose—daily dose
Loading dose—larger than usual dose to reach an therapeutic effect quicker
Therapeutic index
The difference between an effective dose and a toxic dose
Peaks & Troughs
Onset: time it takes for the drug to elicit a therapeutic response
Peak: time it takes for a drug to reach its maximum effect
Duration: time that drugs concentration is sufficient to elicit a response
Peak & Trough levels may be ordered by a physician to determine the levels of a drug and adjust the dose and time as needed. Peak level is drawn 1 hour AFTER administration and trough is drawn 30 minutes PRIOR to next dose
Peak = adjust dose (Vancomycin 500mg or 1 gram) Trough = adjust time or frequency (Q12 hours, Q24 hours)
Adverse Effects
An adverse effect of drug therapy is a usually undesirable effect other than the intended therapeutic effect.
Too much of a therapeutic effect.
Other pharmacodynamic effects of the drug.
Allergic and Idiosyncratic Response
The most serious allergic response is called anaphylaxis.
Bronchospasms, vasodilation, increased vascular permeability (edema of the airways, angioedema: difficulty breathing, swallowing, etc.)
Idiosyncratic responses- unusual; the opposite of what is anticipated (aka.. paradoxical effect)
Toxicities
Neurotoxicity (central nervous system)
Signs and symptoms: drowsiness, auditory and visual disturbances, and seizures.
Hepatotoxicity (liver)
If liver damage occurs, the drug will not be metabolized as efficiently. Hepatitis, jaundice, elevated liver enzymes, fatty liver.
Nephrotoxicity (kidneys)
Signs and symptoms: decreased urinary output, elevated blood urea nitrogen, increased serum creatinine, altered acid-base balance, and electrolyte imbalances.
Ototoxicity (eighth cranial nerve)
Signs and symptoms: tinnitus, hearing loss, light-headedness, vertigo, and nausea.
Cardiotoxicity (heart)
Signs and symptoms: irregularities in conduction, heart failure, and damage to the myocardium.
Immunotoxicity (immune system)
Signs and symptoms: immunosuppression.
Drug Interactions
A drug interaction occurs when two drugs or a drug and another element have an effect on each other.
This interaction may:
Increase or decrease the therapeutic effect of the drugs.
Create a new effect.
Increase the incidence of an adverse effect.
Negative effects from drug interactions are those that decrease the therapeutic effect &/or increase the adverse effects.
Drug interactions may take place in any phase of pharmacokinetics.
Drug interactions can also change the pharmacodynamics of a drug.
They may be beneficial!
Drug Interactions Affecting Absorption
Drug absorption is often decreased because of drug interactions.
If a drug binds with another substance in the GI tract, less of the drug is available to be absorbed.
This binding of a drug is termed chelation.
Drug absorption may also be increased as a result of a drug interaction or the presence of food in the GI tract.
Two Types of Distribution
Competitive protein binding.
i.e. NSAIDS can displace protein-bound warfarin from its binding sites.
Drug alteration of the extracellular pH.
Drugs move into the higher pH EC environment to be ionized. Once ionized, trapped on that side of the membrane.
Drug Interactions Affecting Metabolism
Probably the most important and common drug interaction is one that alters the metabolism of a drug.
If two drugs that affect the cytochrome P-450 system must be administered to a patient together, the dose of one of the drugs may have to be adjusted.
Consider: grapefruit juice, certain herbs (i.e. St. John’s wort), alcohol, age.
Drug Interactions Affecting Excretion
Glomerular filtration is dependent on blood flow to the kidney.
Drugs that decrease cardiac output decrease the amount of circulating blood that is sent to the kidneys.
Renal reabsorption of a drug is dependent on whether a drug is ionized.
Drug Interactions Affecting Pharmacodynamics
The drug that has the weaker affinity for the receptor will not be able to exert its therapeutic effect.
Additive Effect
An additive effect occurs when two or more “like” drugs are combined.
An additive effect may be intentional or may unintentionally cause harm.
1+1=2
Synergistic Effect
When two or more “unlike” drugs are used together to produce a combined effect
1+1 = 3
Potentiated Effect
When one drug enhances another.
In other words, a drug that has a mild effect enhances the effect of a second drug.
Antagonistic Effect
The opposite of a synergistic effect.
Results in a therapeutic effect that is less than the effect of either drug alone because the second drug either diminishes or cancels the effects of the first drug.
Two drugs bind and “cancel” each other out
1+1 = 0
Chemical incompatibilities
Chemical incompatibilities between drugs change both the drug’s structure and its pharmacologic properties… beneficial or harmful.
Physical incompatibilities
Physical incompatibilities occur when two drugs are mixed together.
The mixture results in the formation of a precipitate.
Assessment of Core Patient Variables: Health Status
Concurrent medical conditions may increase the risk of adverse effects from drug therapy.
A patient’s chronic health condition may also necessitate drug therapy that may interact with other drugs.
Assessment of Core Patient Variables: Life Span and Gender
A patient’s age can greatly increase the risk of adverse effects from drug therapy.
Consider the old and the very young.
In addition, older adults are more likely to be receiving polypharmacy for multiple chronic illnesses.
Assessment of Core Patient Variables: Lifestyle, diet, and habits
The patient’s lifestyle, diet and other health habits can have an impact on drug interactions.
Assessment of Core Patient Variables: Environment
The patient’s environment may increase the likelihood that a certain adverse effect will occur.
For instance, some antibiotics can cause the adverse effect of photosensitivity.
The environment in which drug therapy is administered can also play a role in the early detection of adverse effects.
Assessment of Core Patient Variables: Culture and Inherited Traits
Researchers are beginning to study responses to drug therapy that are genetically determined in various ethnic and racial populations.
These responses may place the patient at greater risk than the rest of the global population for adverse effects or drug interactions.
Pharmacology and
the Nursing Process
Assess the problem Assess the options Select the therapy Nursing actions Re-assessment
6 Rights of Medication Administration
Right Drug Right Route Right Time Right Dose Right Client Right Documentation
