ABSORPTION & INTERACTION OF MEDICATIONS

2012 /2013

Pharmacokinetics

Student Learning Outcomes

See outline for SLO's

Overview

This week we will start by tracing the path a medication takes to enter the body, how it travels to the site of action, is broken down and excreted

Then how the medication produces its effects at the site of action

How to safely administer medications following the 8 (10 rights)

Conclude with Surgical Asepsis ( safe delivery of parental medications)

Introduction

Over 11,000 brand name and generic medications available

Each medication requires distinct Application Indications Observation for adverse effects Mechanism of actions Some are prescribed for more then one illness

The RN must have an understanding of each medication prior to its administration

Introduction

Pharmacology – is the study of medicationPharmacotherapy - / Pharmacothetreputics

-application of a drug for the purpose of diagnosis, prevention or treatment of suffering (Adams & Urban)

Pharmacokinetics – absorption, distribution, metabolism, (biotransformation), excretion

What Are the Benefits of This Info?

Assists us to:1.2.3.4.5.6.

Introduction

Passage of drugs across membranesMedications must get into the bodyDiffusion

Takes into account Membrane structure

Drugs must pass thru cells vs. between

Drugs Cross Membranes By:

Traveling via channels and pores Must have small ions Sodium & potassium are examples

Transport systems – carriers that move drugs from one side of the cell membrane to the other Transportation depends on the structure of the drug

molecule

Diffusion

Drugs Cross Membranes By:

Direct penetration of the membrane Most drug use this route These drugs must be lipid soluble

Remember cell membrane walls consist of lipidsOther

Polar molecules – uneven distribution of electrical charges therefore do not penetrate cells Kanamycin (antibiotic)

Ions

Molecules that have a net electrical charge pH dependent ionization Many drugs weak acids or weak bases Acid may give up (H+) ions Bases may take up (H+) ion

Note

Acids tend to ionize in basic solutionsBases tend to ionize in acidic mediaIonization – any process by which a neutral

atom gains or loses electrons thus developing a net charge

ASA (acidic) is absorbed better in stomach acid then in base lower GI environment Remaining non ionized and therefore absorption is

increased

Ion Trapping

Drugs will be trapped on the side that favors their ionization Acidic drugs will accumulate on the alkaline side Alkaline drugs will accumulate on the acidic side Treatment for poisoning an example we can change

the pH of urine thus enhancing excretion

Factors That Affect Absorption

Absorption – “movement of medication from its site of administration into the blood stream ”

Rate of dissolution Drug must first dissolve before it can be absorbed

Drugs that dissolve faster are absorbed faster Repository

Factors That Affect Absorption

Absorption dependent on the properties of the drug and on the physiological & anatomical attributes of the surface

Surface area The larger the surface area the faster the absorption Anesthesia delivered via the lungs

Factors That Affect Absorption

Blood flow Drugs absorbed most rapidly from sites with the most

blood flow IV – directly into the blood stream IM – muscles have a good blood supply

Any thing that impedes or enhances blood supply can impact absorption

Heating pad vs. ice pack

Factors That Affect Absorption

Drug Solubility Lipid soluble drugs can readily cross the cell

membranes

pH Partitioning Just addressed

Routes

IV- no barriers to absorption- Immediate & complete absorption - Disadvantages

- Incontinent, costly, medication irretrievable- Fluid overload- Infection- Emboli

Routes

IM Only barrier – capillary wall Drug can easily pass thru tissue Absorption depends on

Water soluble will be absorbed more rapidly Blood flow

Disadvantages Discomfort Nerve damage

Routes

Subcutaneous Nearly identical to IM

Oral

Barriers1. Lining of GI tract2. Capillary wall

3. Absorption pattern solubility

stabilitygastric & intestinal ph.gastric emptyingfood in GIOther medsspecial medication coatings

Oral

Absorption takes place along the GI mucosa either in the stomach or lower GI tract

Absorbed meds enter blood stream and go directly to the liver Hepatic first pass effect

Hepatic microsomal enzymes Advantages

Easy & inexpensive (relatively) Safer – potentially reversible Good choice for senior citizens

Oral

Disadvantages Variable absorption rate Inactivation of certain medications Requires a conscious & cooperative client Age

Change in gastric pH can affect medication absorption

Pharmaceutical Preparation

TabletsEnteric coating (do not crush) Sustained release preparations

Additional Routes

Topical Skin, eyes, ears, nose, mouth, & vagina

InhalationRectal suppositories – cut in half length wise

Distribution “Movement of drugs throughout the

body’’

Affected by Blood flow to the tissues

- Exiting the vascular tissue- to site of action

Drug Solubility Lipid soluble drugs are not limited by the barriers that

normally limit water soluble drugs (Adams & Urban)

Distribution

Tissue storage Some tissues have a greater ability to accumulate and

store drugs Bone marrow Teeth Eyes Adipose tissue

Distribution

Determined: Protein binding

Bonds reversible Albumin – large molecule that remains in the blood

stream & therefore amount of med available to the site of action may be limited

Only a few molecules will bind at any one time Multiple Meds may compete at binding sites – resulting

in Over doseSpecial Barriers

Blood brain & placental barriers

Distribution

Distribution

Entering the cells. Ph., lipid solubility etc. Drugs may produce effects by.

Binding with receptors.

Metabolism

Also known as “Biotransformation”“Enzymatic alteration of the drug structure Most often takes place in the liverMultiple enzymes

Hepatic microsomal enzymes – Latest research is focusing on identifying individual

characteristics and specific function of these enzymes

Consequences of Metabolism

Accelerated renal excretionDrug inactivationIncreased therapeutic actionActivation of “prodrugs” (inactive substance

changed to active substance)Increased toxicityDecreased toxicity

Factors Impacting Drug Metabolism

Age Induction of drug metabolizing enzymes

Stimulates liver to breakdown itself faster or this change may affect other medications

Hepatic First pass effectNutritional statusCompetition between drugs

Question?

List three problems you would see for a client with decreased liver function when it comes to metabolizing drugs ?

1. 2. 3.

Excretion

“Removal of drugs from the body.” Options

- glomerular filtration- Drugs removed from

blood & discarded into the urine

- Passive tubular reabsorption - Frequently occurs

with lipid soluble drugs

- Active tubular secretion – active pumping of drug into tubular urine

Modifiers of Renal Excretion

pH – dependent ionization > excretion rate

Competition for active tubular transport Competition between drugs for active transport

Age 1.2. 3. Lab test

Nonrenal Routes of Drug Excretion

Breast milkBileLungsSweatSaliva

Plasma Drug Levels

Minimum effective concentration Below MEC therapeutic effects of med will not occur

Toxic concentrationTherapeutic Range Drug half life (t5)

Loading & maintenance doses Peak & Trough

Time Response

Pharmacodynamics

Drug receptor interactions Functional macromolecule in a cell to which a drug

binds to produce its effects

Pharmacodynamics

1. Receptors are normal points of control 2. Receptor function regulated by body3. Meds only Mimic, block, normal functions4. Can not confer new functions

Pharmacodynamics

5. Meds Therapeutic effects due to body’s preexisting capabilities.

6. Research – ongoing

2 Agonists

Medication Interactions

Agonist - medication that produces the same response as the endogenous substance – (actual molecule in the body that produces the desired effect) (some times these substances produce a great erect then the endogenous substance)

partial agonist - medication that produces a weaker effect

Antagonist - drug that prevents the agonist from producing the desired effect

Medication Interactions

Drug may enhance or inhibit drug action Additive - 1+1 + 2

Two drugs from a similar therapeutic class produce a combined summative effect

Synergistic effect - medications acting together produce a greater effect them each of them alone 1+1 += 3 Medication manufactured as a combination drug

• Synercid – comb antibiotic – effective against “Staph infections ”

Remember

Medication interactions :Meds

Enhance absorption Decrease absorption Reverse the effects

Foods All of the above OJ + Iron

Determinants that Affect Drug Therapy

Clinical Factors Age, weight Present health

disorder Other disease entities Client drug

compliancePharmacokinetics

Absorption Distribution Metabolism (t1/2) Excretion

Administration Drug form Route of

administration Multiple drug therapy. Drug interactions

Pharmacodynamics Onset, peak , &

duration Therapeutic range Side effects and

adverse effectsPharmacogenitics

Practice Question

Mr. T has liver and kidney disease he is administered a medication that is manufactured to have a 30 hour half life. You expect the duration of this mediation for him to:

A. B. C. D.

Answer

Example

Digoxin Effects OD Nursing assessments Nursing interventions

Nursing Process

AssessmentsNursing Interventions Cultural considerationsEvaluation

Nursing Process Transcultural Considerations

Assessment Cultural & ethnic background Time away from country of origin Travel history & language ability Nonverbal communication patterns Food preferences and health practices Traditional health practices

Nursing Diagnosis

Knowledge deficit: food and drug interactions related to new prescription as evidenced by “I do not understand this why I can not eat a lot of bananas”

Nursing Diagnosis

Planning Assist clients to develop a dietary plan that optimizes

health focused on decreasing or eliminating interactions with medications

Interventions Client teaching Teaching the family Optimizing dietary intake and decreasing chance for food

and drug interactions Provide information in client’s preferred language

Evaluation

Conclusion

Remember the nurse is the client’s last line of defense when it comes to administration of medication

References

Adams, M.P., & Urban, C.Q., (2013) Pharmacology: connections to nursing practice (2nd ed.) Boston: Pearson

Potter, P.A., Perry, A. G., Stockert, P. A., Hall, A.M. (2013) Fundamentals of nursing (8th ed.) St. Louis: Elsevier