Pharmacokinetic phases Flashcards
Pharmacokinetic phases overview definition
how medication travels through the body
Pharmacokinetic phases
-absorption, distribution, metabolism, excretion
Absorption defintion
refers to the transmission of medication from the location of administration to the blood stream
Absorption common routes of administration
enteral (GI tract) and parenteral (injection)
Absorption information
- the rate of medication absorption determines how soon the medication will take effect
- the amount of medication absorption determines its intensity
- the route of administration affects the rate and amount of absorption
Absorption Other routes of administration
Routes: oral, sublingual/buccal, mucous membranes (rectal, vaginal), subcutaneous/intramuscular, intravenous
-Po–>subcutaneous–>intramuscular–> intravenous (slow to fast absorption)
Oral route
- enteric coating: buffer to avoid GI upset
- medications that have “contin” “xl” “SR” “ER” “IR” means that they have a coating that is time sensitive. It is released over time, and if they are crushed/broken it is a lethal dose
Oral route: barriers to absorption
medications must pass through the layer of epithelial cells that line the GI tract
Oral route: absorption pattern
-varies greatly due to the following variables: stability and solubility of the medications, GI pH and emptying time, presence of food in stomach or intestines, other medications currently being administered, forms of medications (enteric-coated pills, liquids)
Sublingual/ Buccal route
-applied under the tongue
Sublingual/buccal barriers to absorption
if swallowed before being dissolved, gastric pH may inactivate medication
Sublingual/buccal absorption pattern
absorbed quickly systemically through highly vascular mucous membrane
Other mucous membranes route
rectal, vagina
Other mucous membranes barriers to absorption
presence of stool in rectum or infectious material in vagina limits tissue contact
Other mucous membranes absorption pattern
easily absorbed with both local and systemic effects
Inhalation route
via mouth or nose
Inhalation barriers to absorption
inspiratory effort
Inhalation absorption pattern
rapidly absorbed through alveolar capillary network
Intradermal/topical route
situated or applied within the layers of the skin
Intradermal/topical barriers to absorption
epidermal cells closely packed
Intradermal/topical absorption pattern
- absorption slow and gradual
- effects primarily local, but systemic as well, especially with lipid soluble medications passing through subcutaneous fatty tissue
Subcutaneous and intramuscular route
deltoid
subcutaneous and intramuscular barriers to absorption
capillary wall has large spaces between cells therefore there is no significant barrier
subcutaneous and intramuscular absorption pattern
Rate of absorption is determined by:
- solubility of the medication in water
- highly soluble medication will be absorbed in 10-30 mins
- poorly soluble medications will be absorbed more slowly
- Blood perfusion at the site of injection: sites with high blood perfusion (ex. mucous membranes) will have rapid absorption and sites with low blood perfusion (ex. skin) will have slow absorption
Intravenous route
IV
Intravenous barriers to absorption
no barrier
Intravenous absorption pattern
immediate: administration directly to blood
complete: all of it reaches the blood
Distribution
is the transportation of medications to sites of action by bodily fluids.
Distribution may be influenced by the ability to:
- travel to the site of action through the bloodstream (peripheral vascular or cardiac disease may delay medication distribution)
- leave the bloodstream by traveling between the capillaries’ cells
- plasma protein binding
- barriers
(distribution) Plasma protein binding:
medications compete for protein-binding sites within the bloodstream, primarily albumin. The ability of a medication to bind to a protein can affect how much of the medication will leave and travel to target tissues. Two medications can compete for the same binding sites, resulting in either toxicity or decreased bioavailability
(distribution) Barriers
medications that are lipid soluble or have a transport system can cross the blood-brain barrier or the placenta
Metabolism (biotransformation) definition
changes medications into less active or inactive forms by actions of enzymes
Metabolism (biotransformation) info
- primarily occurs in the liver, but it also takes place in the kidneys, lungs, bowel, and blood
- factors influencing the rate of medication metabolism
List of factors influencing the rate of medication metabolism
age, an increase in certain medication-metabolizing enzymes, first-pass effect, similar metabolic pathway, nutritional status
Factors influencing the rate of medication metabolism: age
-infants have limited medication-metabolizing capacity. The aging process can also influence medication metabolism, but it varies by individual. In general, hepatic medication metabolism tends to decline with age.
Factors influencing the rate of medication metabolism: an increase in certain medication-metabolizing enzymes
-this can cause a particular medication to be metabolized sooner, requiring an increase in dosage of that medication to maintain a therapeutic level. It can also cause an increase in metabolism of other medications that are being used concurrently
Factors influencing the rate of medication metabolism: first-pass effect
- some oral medications are inactivated on their first pass through the liver and may be required a higher dose to achieve a therapeutic effect, or must be given by a nonenteral route because of their high first- pass effect. These medications are usually given by alternate routes such as sublingual or IV
- loses bioavailability of the drug (part of drug is lost)
Factors influencing the rate of medication metabolism: similar metabolic pathway
-when two medications are metabolized by the same pathway, they can interfere with the metabolism of one or both of the medications. In this way, the rate of metabolism can be decreased for one or both of the medications, leading to medication accumulation
Factors influencing the rate of medication metabolism: nutritional status
-a malnourished client may be deficient in the factors that are necessary to produce specific medication metabolizing enzymes. Consequently, medication metabolism may be impaired
Outcomes of metabolism
- increased renal excretion of medication
- inactivation of medications
- increased therapeutic effect
- activation of pro-medications (pro-drugs) into active forms
- decreased toxicity when active forms of medications are converted to inactive forms
- increased toxicity when inactive forms of medications are converted to active forms
Excretion: definition
the elimination of medications from he body primarily through the kidneys. Elimination also takes place through the liver, lungs, bowel, and exocrine glands
-renal dysfunction may lead to an increase in duration and intensity of medication response, so BUN and creatinine levels should be monitored
Lab values: low and high for ALT and AST
ALT: 0-35 and AST: 0-40
Lab values: low and high for BUN and creatinine
BUN: 10-20 and Creatinine: 0.5-1.2
Primary site of metabolism
liver=ALT and AST
Primary site of excretion
kidneys= BUN and Creatine
High Therapeutic Index
- Medications with high TI have a wide safety margin
- there is no need for routine serum medication level monitoring
- ex: tylenol, tums, over the counter drugs
Low Therapeutic Index
- medications with low TI have a low safety margin
- have serum medication levels monitored closely, require prescriptions
- measured by: Peak and trough
TI Peak
Peak: highest concentrated effect in body
- monitor peak levels based on the route of administration
- ex: oral medications may have a peak of 1-3 hours after administration
- ex: IV medications may have a peak time within 10 minutes
TI Trough
Trough: blood is drawn immediately before the next medication dose regardless of the route of administration
Half life (t 1/2) definition
-refers to the period of time needed for the medication to be reduced by 50% in the body
Half life information
- may be affected by liver and kidney function
- usually takes four half-lives to achieve a steady state of serum concentration (medication intake=medication metabolism and excretion); after 4 half lives, medication is excreted from the body
- short half life=short dosing intervals, tylenol
- long half life=greater risk for toxicity, longer intervals (ex. once a day, every other day)
Short Half-Life
- medications leave the body quickly (4 to 8 hours)
- short dosing interval or minimum effective concentration (MEC) will drop between doses
Long Half-Life
- medications leave the body more slowly (24+ hour) there is a greater risk for medication accumulation and toxicity
- medications are given at longer intervals without loss of therapeutic effects
- medications take a longer time to reach a steady state
Medication Prescription: Types
- routine order/standard prescription (1hour window)
- single/one time prescription
- STAT prescription (15 mins to execute order)
- PRN prescription (as needed)
- Standing prescription
- components of prescription order
- communicating medication prescriptions
Routine order/standard prescription (1hour window)
- medications that are given on a regular schedule
- may or may not have a termination date
- without a specified termination date, the prescription will be in effect until the provider discontinues it or the client is discharged
- certain medications such as opioids and antibiotics must be reordered within a specified amount of time or will automatically be discontinued
Single/one time prescription
- gives once at a specified time or as soon as possible
- ex. a one-time prescription instructs the nurse to administer warfarin (coumadin) 5 mg PO at 1700
STAT prescription
- (15 mins to execute order)
- given only once, given immediately
- ex. digoxin 0.125 mg IV bolus stat
PRN prescription
- (as needed)
- the nurse uses clinical judgement to determine the client’s need for medication
- ex: pain meds
Standing prescription
- written for specific circumstances/specific units
- ex: the critical care unit has a standing prescription to treat a client who has systole
- being able to administer drug w/o physicians order
Components of prescription order
- client’s name
- date and time of script
- name of medication
- dosage of medication (cannot change)
- route administration (cannot change)
- time and frequency of medication administration: exact times or number of times per day
- signature of prescribing provider
Communicating medication prescriptions
- origination of medication prescriptions
- taking a telephone prescription
- medication reconciliation
Communicating medication prescriptions: Origination of medication prescriptions
- provider needs to sign the prescription usually within 24 hours
- medication prescriptions are transcribed or entered electronically in to the medication administration record (MAR) by a nurse or other provider
Communicating medication prescriptions: taking a telephone prescription
- have a second nurse to listen
- read back the prescription to the provider: client’s name, name of medication, dosage, time of administration, frequency, route
- remind the provider that the prescription must be signed within the specified amount of time
Communicating medication prescriptions: medication reconciliation
- required by the joint commission
- the nurse should compile a list of current medications ensuring that all medications are included, with correct dosages and frequency. This list should be compared with new prescriptions and reconciled to resolve any discrepancies. This list becomes the current list. This process should take place on admission, when transferring between units, and at discharge.
Safe medication administration: six rights of safe medication administration
- right client
- right medication
- right dose
- right time
- right route
- right documentation
- order to the MAR, MAR to the Med, Med and MAR at the bed, so your patient won’t be dead***
Six rights of safe medication administration: Right client
-verify patient identification (need 2 IDs: name and DOB) ask and check ID band (MRN), check for allergies
Six rights of safe medication administration: right medication
-read the label three times: when the container is selected, when removing the dose from he container, and when the container is replaced
Six rights of safe medication administration: Right dose
-check drug reference t ensure dose is within usual range
Six rights of safe medication administration: right time
-generally acceptable to administer medication 30 minutes before or after the scheduled time
Six rights of safe medication administration: right route
-oral, topical, subcutaneous, IM and IV
Six rights of safe medication administration: right documentation
-reassess the patient: record medication, dose, route, time, clients response to the medication
Safe medication administration: additional considerations
- assessment
- education
- evaluation
- medication refusal
Safe medication administration: assessment
- collect appropriate data before administrating medication (for example, checking apical heart rate before giving digitalis preparations)
- assess the client for physical and psychosocial factors that may affect medication response
Safe medication administration: education
-provide accurate information about the medication therapy and its implications (therapeutic response, side/adverse effects)
Safe medication administration: evaluation
-determine the effectiveness of the medication based on the client’s response as well as the occurrence of side/adverse effects
Safe medication administration: medication refusal
- client’s have the right to refuse
- determine the reason for refusal, provide information regarding the risk of refusal and actions taken
Error Reduction
- LISTEN to your patient
- have the PROVIDER enter the order–minimize usage of verbal/telephone orders-use only in emergency/facility protocol
- use all the rights
- use generic names
- never administer a medication prepared by someone other than yourself!***
- complete medication reconciliation on admission, transfer, and discharge
- avoid distractions
- use verbal prescriptions only for emergencies
- evaluate client response to a medication
- report all errors
- use the nursing process to prevent medication errors
Error Reduction: what if you make a medication error?
1st- as a nurse, you are entering into the most trusted profession, we consistently rank #1
2nd–you have an ethical responsibility to report medication errors
3rd–don’t panic… but you should do one thing first…..
Common medication errors:
- wrong medication or IV fluid
- incorrect dose or IV rate
- wrong client, route, time
- administration of known allergic medication
- omission of dose
- incorrect discontinuation of medication or IV fluid
Error Reduction: use the nursing process to prevent medication errors
- ensure knowledge of the medication to be administered. Use appropriate resources: provers, nurses, physicians, pharmacists, poison control centers, sales reps from drug companies, nursing pharmacology textbooks, Physicians desk reference, newsletters, professional journals, professional websites
- obtain information about the client’s medical diagnoses and conditions: ability to swallow; allergies; and heart, liver, and/or kidney disorders
- determine whether the medication prescription is complete
- interpret the medication prescription accurately
Error Reduction: interpret the medication prescription accurately: common abbreviations list
- PO: per os (by mouth)
- NPO: NOTHING per os
- mL: milliliter
- BID: twice daily
- TID: three times daily
- QID: four times daily
- IM: intramuscular
- NG: nasogastric
- PRN: pro re nata (as needed)
- q: every
Error reduction: NEVER EVERS
- cc or cc’s never use- use mL (commonly looks like two o’s in handwriting)
- trailing zeros (6.0, 100.0)- missed decimal results in med errors. instead, write 6 mg or 100 mg
- naked decimals (.6, .1)-missed decimal results in med errors. Instead, write 0.6mg or 0.1 mg
- q.d./qd/QD-write daily instead
- SC/SQ, sub-q: write out subcutaneously
- HS: write hour of sleep or betime
- @&+/– write “at” “and” or “per”
- DC, dc, d/c, D/C: write discharge or discontinue
- u, U, or IU– write units
- Question the provider if the prescription is unclear, refuse to administer a medication if it is thought to be unsafe****
SALAD Meds (sound alike/look alike drugs)
- dobutamine- DOBUTamine
- Dopamine-DOPAmine
Adverse effects
- are undesired, inadvertent, and unexpected dangerous effects of the medication
- can occur at both therapeutic and higher than therapeutic doses
Adverse medication effects: hepatotoxicity
- may occur with many medications. Because most medication are metabolized in the liver, the liver is particularly vulnerable to drug-induced injury.
- ****Damage to the liver cells can impair metabolism of many medications causing medication accumulation in the body and producing adverse effects.
- Many medication can alter normal values of liver function tests with no obvious clinical signs of liver dysfunction
Nursing intervention/client education: hepatotoxicity
- when two or more medications that are hepatotoxic are combined, the risk for liver damage is increased
- liver function tests are indicated when clients start a medication known to be hepatotoxic and periodically thereafter
- monitor clients for manifestations of hepatotoxicity, such as nausea, vomiting, jaundice, and anorexia
Adverse Medication Effects: Nephrotoxicity
-may occur with a number of medications, but it is primarily the result of certain antimicrobial agents and NSAIDs. Damage to the kidneys may interfere with medication excretion, leading to medication accumulation and adverse effects
Nursing intervention/client education: nephrotoxicity
-aminoglycosides injure cells in the renal tubules of the kidney. Monitor serum creatinine, and BUN, as well as peak and trough medication levels for clients taking medication that is nephrotoxic
Adverse Medication Effects: Toxicity
-is an adverse medication effect that is considered severe and may be life-threatening. it may be caused by an excessive dose, but it also can occur at therapeutic dose levels
Nursing intervention/client education: toxicity
-liver damage will occur with an acetaminophen (tylenol) overdose. there is a greater risk of liver damage with chronic alcohol use. The antidote acetylcysteine may be used to minimize liver damage
Adverse Medication Effects: anaphylactic reaction
-is a life-threatening, immediate allergic reaction that causes respiratory distress, sever bronchospasm, and cardiovascular collapse
Nursing intervention/client education: anaphylactic reaction
-treat with epinephrine, bronchodilators, and antihistamines. provide respiratory support and inform the provider
