Dosage Calculations:
Chapters 1, 2

Chapter 1: Drugs/Agents and Factors Affecting Their Action

Drug Uses

Given a drug, you should be able to classify that drug into one of the following categories:

• Symptomatic treatment (ex. Tums to relieve heartburn )
• Preventative drugs (ex. varicella vaccine to prevent chickenpox )
• Diagnostic drugs (ex. radiopaque dyes used during endoscopic procedures to visualize structures )
• Curative drugs (ex. amoxicillin to cure strep throat infection )
• Health maintenance drugs (ex. iron sulfate to treat iron-deficiency anemia )
• Contraceptive drugs (ex. birth control patch to prevent pregnancy )

Dosage Forms

You should be able to differentiate dosage forms, identify correct route of administration, and determine which form is best for a given client.

• Tablets
  • Timed
  • Sustained-release (SR)
• Capsules
• Troches (lozenges)
• Suppositories
• Solutions
• Suspensions
• Emulsions
• Topical preparations
  • Semisolids (ex. creams & gels )
  • Topical patches
• Implants
• Parenteral products
  • Ampules
  • Vials

~~NOTE: The prescriber's DEA number is required on prescriptions written for controlled substances.

Review Box: 1-1, p. 13

• "Controlled Substances Schedules"

The Product Insert: p. 17

Detailed description of the drug - federal requirement that all of the following are included:

• Brand name
• Generic name
• Description
• Clinical pharmacology
• Indications & usage
• Contraindications
• Warnings
• Precautions
• Overdosage
• Dosage and administration
• How supplied

Principles of Drug Action

You must understand these principles in order to later understand pharmacokinetics

• Drugs do not create new cellular functions
  • Instead they alter existing ones
    • Antibiotics slows down the growth or reproduction of bacteria
• Drugs may alter the chemical composition of body fluid
  • Antacids neutralize stomach acids
• Drugs may accumulate in tissues
  • Anesthesia accumulate in tissue to depress nerve function
• Drugs may form a chemical bond with receptors
  • Drugs can only fit into specialized receptors within the body
  • As in a key entering a lock to illicit a pharmacological response
  • The better fit, the stronger response
  • See figure 1-8
  • Agonist versus antagonist

Review Safe Nursing Practice: 1-2, p. 20

"Adverse Drug Effects"

Understand these terms: p. 20, 21

• Side effect
• Allergic reaction
• Toxicity
• Therapeutic dose
• Therapeutic index
• Adverse effect
• Teratogenic drug
• Drug tolerance
• Dependence
• Physical dependence
• Psychological dependence

Pharmacokinetic Factors in Drug Therapy

This semester we will study these concepts for each of the drug classifications discussed. This is a process that occurs in the following specific order.

• Liberation
  • Release of the drug from the form of administration to make it available for absorption
• Absorption
  • Drug passes from site of administration into blood stream for delivery to site(s) of action
• Distribution
  • Drug carried by blood flow to site of action / tissue delivery
• Biotransformation / Metabolism
  • Process that converts the active form of drug into one that can be excreted from the body
  • Usually occurs in the liver
• Elimination
  • Removal of metabolized drug from the body
    • Usually occurs in the kidneys
    • But may occur in the feces, respiratory tract, breast milk, saliva or sweat

Review Figure 1-11, 1-12, 1-13, p. 24, 25

• Gives a visual depiction of:
  • Plasma concentration of a drug versus time
  • After bolus
    • Also known as loading dose
  • After multiple oral doses
• These concepts are important to understanding why a patient may need a "loading dose", why patients need to take their medications on time, and why some medications must be monitored using blood levels.
  • Drug half-life is the time it takes for a drug to be eliminated by ½ of its original concentration.
  • Steady state is the level at which the drug concentration is fairly constant.

Monitoring Drug Therapy

Any client undergoing pharmacologic treatment should be monitored to insure efficacy, therapeutic effects, and for toxicity.

This can be done by a couple of means:

• Observe for desired effect: lower BP, decreased pain, ect
• Blood test for desired effect: monitor level of medication in blood for therapeutic activity or toxicity
  • Peak and trough

Below is a list of information which may affect labs:

• Medication history
  • Significant information to determine an contraindications in drug therapy (birth control pills and history of blood clots), past allergic reactions, or current drug therapy that may interfere with needed drug therapy
• Blood sampling for drug levels
  • Many drugs cause significant adverse effects when given outside dosing range
  • Many drugs have to be at a certain level to be effective
• Client's age, weight, & concurrent medications
  • Many drugs are calculated based on patient weight in kilograms
  • Age may signal a decrease in kidney function and could be important
  • Concurrent drugs may decrease or increase the potency of other drugs
• Knowledge of client's renal, hepatic, and cardiac function
  • Decreased health in either of these areas may require a higher or lower (usually) dosing of the medication

Individual Variation of Pharmacological Response

The following factors influence individual client's responses to drugs:

• Age
• Gender
• Body weight
• Body surface area (BSA)
• Basal metabolic rate (BMR)
• Disease state
• Genetic factors
• Placebo effect
• Time of administration
• Tolerance
• Environmental factors
• Idiosyncratic responses

Herbals / Botanical Medicine

Healthcare professionals need to be increasingly aware of herbal / botanical products as clients are using these over-the-counter substances in greater proportion. Many patients do not consider these to be drugs and forget to tell us about them.

Do not be mistaken: These types of medications can cause severe reactions!

Common OTC medications:

Chapter 2: Principles and Methods of Drug Administration

~~NOTE: YOU ARE NOT RESPONSIBLE FOR those sections covering "The Nursing Process and Medication Administration" p. 38-40

~~NOTE: YOU ARE RESPONSIBLE FOR the section titled "Implementation: Preparing to Administer Medications" on p. 41

Review Safe Nursing Practice 2-3, p. 41

• "Preparing Drugs for Administration"

Review Safe Nursing Practice 2-4, p. 41- 51

• "Seven Rights of Medication Administration"

These concepts are vital to safe medication administration and should be adhered to any time drugs are given to a client.

• Right drug
• Right dose
• Right client
• Right time
• Right route
• Right documentation
• Right to refuse

Review Table 2-1, p. 42, 43

• "Abbreviations Commonly Found in Drug Orders"

Healthcare professionals use abbreviations whenever possible. However, as all written communications / documentation within the medical setting are legal documents, only legally recognized abbreviations may be used.

Review Table 2-5, p. 49

• "Common Routes of Drug Administration"

Review Safe Nursing Practice 2-12, p. 52

• "Oral Administration of Medications"

Safely Administering Parenteral Medications

Healthcare professionals must observe the following universal precautions in order to prevent the spread of infection.

• Thoroughly wash hands before and immediately following any procedure in which you are exposed to blood or body fluids.
• Wear gloves whenever coming into contact with blood or body fluids.
• Properly dispose of used sharps in a puncture-proof container appropriately labeled with the biohazard symbol.
• If accidentally stuck with a used sharp - immediately seek treatment from the local Emergency Department and follow facility protocol for documenting the incident.
• Follow facility policies when assisting in treatment of clients with known communicable diseases - always insure patient confidentiality is maintained.

Intramuscular Administration

• 90 degree angle
• Insert needle to a depth of 1 inch to reach the muscle, otherwise it will be subcutaneous
• Z-tract reserved for iron because it stains the skin (see chapter 22)
• Most commonly used muscles are the deltoid, gluteus medius, minimis, and maximus
• The deltoid site is reserved for clear, nonirritating solution quantities of 1 mL or less
• The site should have sufficient muscle mass, adequate circulation, free of infection, ulcers, and scars
• Avoid frequent use of the same area which over time could decrease drug absorption and compromise tissue integrity
• Gluteal muscles are the preferred site in adults and older children
  • Dorsogluteal
  • Ventrogluteal
• Gluteal muscles are not used in children who are not walking or at least 1 year of age since these muscles are not well developed
  • Vastus lateralis site is the best choice for children under 3 years of age
  • May also be used for adults

Subcutaneous Administration

• 45 degree angle with a 5/8 inch needle, 90 degree angle with a ½ or 5/8 inch needle
• You should be able to pinch at least 1 inch of subcutaneous tissue
• See Figure 2-14, p. 59 commonly used sites
• 90 degree angle should be used for heparin and insulin injections

Intradermal Injections

• 15 degree angle
• 1 mL tuberculin syringe with a 26 g, 5.8 inch needle
• Most commonly used for diagnostic tests such at allergy tests
• The preferred site is the inner aspect of the central forearm
  • Other hairless areas such as the upper chest and shoulder blades can be used

Administration of eye drops

• See Figure 2-17, p. 61

Administration of ear drops

• In young children pull the pinna down and back
• In adults pull the pinna up and back
• The patient should wait 5 minutes before getting up

Fostering patient cooperation and compliance

• Patient must be ready to learn or take on the responsibility
• Teach to level of patient ability to understand
  • Language
  • Cultural values
  • Religious beliefs
  • Physical ability (hearing impaired, arthritis, ect)
  • Older adults learn best when return demonstration is available
  • Several brief sessions is more effective than one long period
  • Recognize why patients are not compliant
    • Inadequate understanding of the illness
    • Dissatisfaction of prescriber
    • Dissatisfaction with diagnosis
    • Cost of medication
    • Inconvenience (drug must be taken multiple times during the day)
    • Number of medications
    • Adverse effects of medications
    • Forgetfulness
    • Stigma of illness
  • Provide information about disease and positive effect treatment has
  • Use devices such as medication calendars or pill boxes to help patients remember
  • Make attempt to reduce number of medications or doses to be taken

Chapter 5 - Drug Therapy for Pediatric Clients

Review Box 5-1, p. 114

• "Pharmacokinetic Differences in the Pediatric Client"

Review Safe Nursing Practice 5-1, p. 115

• "Administration of Medication to Children"

Keep in mind pediatric calculations based on age is not accurate since children come in various sizes . . . . . . Kids are not just little adults! An adult dose of a medication can kill a child! If you don't leave this course with anything else - remember that! ALWAYS calculate a child's weight prior to drug administration. I would even check the physician's calculations. You can never be too cautious!

Pediatric Drug Sensitivity

• Neonates & infants are especially sensitive to drugs due to immature organ systems
• Be alert for body temperature regulation issues while child is under pharmacologic treatment
• Cardiovascular agents may produce exaggerated effects due to immaturity of system

Review Box 5-2, p. 117

• "Guidelines for the Administration of Medication to Children"

Site selection depends on the child's age and muscular development

• Under 3 years
  • Preferred site for IM injections is the vastus lateralis
• Over 3 years
  • Preferred site for IM injections is the ventrogluteal and dorsogluteal

The nurse should evaluate the parent's ability to stay and help with the child if support or restraint is needed. Not all parents can watch their child being "hurt". Try not to be judgmental if a parent does not wish to stay in a treatment room during treatment or injections. In fact, in my experience, most children do much better if the parent is not present. But, still, the parent must be given the choice.

Review Box 5-3, p. 120

• "Teaching Children About Drug Therapy"

Disregard "Intravenous Therapy" section pp. 102 - 104

Review Safe Nursing Practice 5-4, p. 126

• "Accidental Poisonings"

Review "Home Care / Client Teaching", p. 126

Chapter 6 - Drug Therapy for Geriatric Clients

The elderly (> 65 yrs.) make up 12% of U.S. population

• Consume 30% of all prescription drugs
• 70% regularly consume OTC drugs
• Polypharmacy: consumption of more than one medication
  • Increased risk for drug interactions

Review Box 6-1, p. 132:

• "Pharmacokinetic Differences in the Geriatric Client"

Absorption

• Reduced gastric acidity may decrease absorption
• Slower gastric emptying may decrease absorption
• Decreased gastrointestinal muscle tone and motor activity may decrease absorption
• Increased incidence of constipation = laxatives which may increase the movement of drugs through the GI system and decrease absorption
• Reduction of blood flow results in decreased absorption
• Thinner skin results in faster topical absorption

Distribution

• Decreased total body water results in diminished distribution of water-soluble medications
• Increased body fat results in drugs that are distributed in fat remaining in the system longer
• Loss of muscle tone results in decreased distribution of IM medications

Metabolism

• Decreased liver enzymes results in the body's ability to transform active drugs into inactive metabolites

Elimination

• Decreased glomerular function decreases elimination and may result in increased risk for toxicity

Review Safe Nursing Practice 6-1, p. 134

• "Factors Related to Drug Problems in the Elderly"
  • Sensory changes
  • Impaired memory
  • Increased number of medications
  • OTC drugs, expense, diet
  • Communication

Review Safe Nursing Practice 6-3, p. 137

• "Administration of Drugs to the Elderly"

Review Box 6-2, p. 138

• "Teaching Older People"

Review Safe Nursing Practice 6-5, p. 139

• "Promoting Health"

Review "Home Care / Client Teaching", p. 140

Math Section:

Dosage Calculations (8th ed) by Pickar

Chapters 1, 2

This first math lesson is simply review. Please use your Dosage Calculations text to review fractions and decimals in chapter 1 and ratios, percents, simple equations, and ratio-proportion in chapter 2.

There are plenty of practice problems in the text. The answers are in the back of the book.