Pharmacology Basics (Chapter 2)
Define Pharmacology
The broadest term for the study or science of drugs
Any chemical that affects the physiological processes of a living organism can be defined as a drug
Pharmacology encompasses a variety of topics including absorption, biochemical effects, distribution, drug
history/origin, Excretion, metabolism, etc.
5 Rights in Medication
1. Right Patient
2. Right Drug
3. Right Route
4. Right Time
5. Right Dose
Four processes involved in pharmacokinetics
Pharmacokinetics is the study of what happens to a drug from the time is put in the body until the parent drug and all
metabolites have left the body. Specifically, the combined processes of pharmacokinetics include drug absorption into,
distribution and metabolism within, and excretion from the body represent
Absorption
The movement of a drug from its site of administration into the bloodstream for distribution to the tissues
o Bioavailability is the extent of drug absorption
o A drug that is absorbed from the intestine must first pass through the liver before it reaches the systemic
circulation.
If a large proportion of the drug is chemically changed into inactive metabolites in the liver, then a
much smaller amount of the drug will pass into the circulation (e.g., will be bioavailable)
This is First-Pass Effect
First Pass Effect reduces the bioavailability of the drug to less than 100%
Many drugs administered by mouth (PO) have a bioavailability less than 100%
Note: Drugs administered by the intravenous route are 100% bioavailable
If two drug products have the same bioavailability and same concentration of active ingredient,
they are said to be bioequivalent (e.g., a brand-name drug and the same generic drug)
Three routes of administration:
o Enteral Route: the drug is absorbed into the systemic circulation through the mucosa of the stomach and/or
small intestine
Orally admin drugs are absorbed from the lumen in the blood system and transported to the liver
Metabolism takes place within the liver via the hepatic system.
Hepatic enzymes metabolize the drug and the remaining active ingredients are passed
into the general circulation
Enteric coating is designed to protect the stomach by having drug dissolution and absorption occur
in the intestines.
Drug absorption may be altered by patients who’ve had parts of their small intestine removed.
This is called Small Intestine Syndrome
Sublingual and Buccal Routes:
Sublingual: drugs administered under the tongue (oral mucosa). Absorption is quick due
to large blood supply under the tongue
The drugs bypass the liver and yet are systemically bioavailable.
Buccal: drugs administered between the cheek and the gums
Similar effects that Sublingual has
o Parenteral Route
Parenteral is a general term meaning any route of administration other than the GI tract
Most commonly refers to injection
Intravenous delivers the drug directly into the system circulation where it is
distributed with the blood throughout the body
Intramuscular and Subcutaneous are absorbed more slowly than Intravenous
These drug formulations are usually absorbed over a period of several hours
Some are specially formulated to be released over days, weeks or months
, The fastest route by which a drug can be absorbed
Parenteral – Fastest
Enteral – 2ND Faster
Topical – 3rd Fastest
Drugs can be injected several ways
Parenteral routes have the advantage of bypassing the first-pass effect of the liver
Route Guide
Higher cost Aseptic Technique
Intravenous (IV) More rapid onset Can’t be self- More freq. monitoring
More control of drug administered including correct
level in blood Irreversibility of drug administering and IV
Option of larger fluid action/inability to site
volume, therefore retrieve medication Flushing of line before
diluting irritating drugs Fluid overload risk and after if intermittent
Avoids first-pass Higher risk of infection IV infusions are used
metabolism Embolism risk (sudden Protocol education
blocking of artery) regarding same site
usage
Injection discomfort Aseptic Technique
Intramuscular (IM); IM and subQ routes Risk of damage Use of anatomical
Subcutaneous (subQ) result in more rapid Slower onset of action landmarks to identify
absorption compared to compared to IV correct IM/subQ site
oral Only small amounts Use of correct gauge
Several drugs may be (3mL IM and 1mL subQ) SubQ routes are limited
administered to a few drugs (insulin,
simultaneously if heparin)
compatible in Selection of correct
syringe/without syringe size
contraindication
Slow onset of action and Enteral routes include
Oral (PO) Easier and more variable absorption oral admin and various
convenient First-Pass effect dosage forms (liquids,
Less expensive Risk of GI irritation solutions, tablets, etc.)
Safer than injection Some are
Reversible recommended with
food vs others are not
If oral forms are given
via nasogastric tube or
gastrotomy tube, pre-
assessment is required
(and patient’s head is to
remain elevated) along
with pre and post
flushing of tube (30-
60mL)
Patients may swallow Must be placed under
Sublingual, buccal Absorbed more rapidly pill instead of keeping tongue
(subtypes of oral, but more from oral mucosa. Leads under tongue Once dissolved, drug
to more rapid onset of Pills are often smaller to may be swallowed
parenteral than enteral)
action handle Drug is usually without
Avoids breakdown of
, drug by stomach water and water soluble
Avoids first-pass because
gastric absorption is
bypassed
Risk of discomfort or Absorption is erratic and
Rectal Relatively rapid embarrassment unpredictable but safe
absorption Higher cost than oral route when nausea or
Good alternative when route vomiting prevents oral
PO is not available dosing of drugs
Useful for local or Patient must be placed
systemic drug delivery on his/her left side for
Usually leads to mixed safe and effective
first-pass and non-first- insertion
pass metabolism Gloves required
Can be awkward to self- Maximal absorption of
Topical Delivers meds directly to administer topical drugs is
affected area Risk of irritating skin enhanced with skin that
Decreased likelihood of Messy is clean and free of
systemic drug effects Higher cost than oral debris
Gloves help minimize
cross-contamination
If patient’s skin is not
intact, sterile technique
must be used.
Excessive perspiration Transdermal drugs are
Transdermal (subtype of Provides relatively can affect rate of to be placed on
topical constant rate of absorption alternating sites and on
absorption Patch may peel off clean, non-irritated,
1 patch can last 1-7 days Cost is higher non-hairy surface and
Avoids first-pass Irritation risk only after previously
metabolism Drug absorption may be applied patch has been
impacted if skin is removed
inflamed, damaged, etc.,
leaning to systemic side
effects
Rate of Absorption can Inhaled meds are to be
Inhalational Rapid absorption be too rapid increasing used exactly as
Directly delivered to lung risk for exaggerated prescribed
tissues drug effects Instructions need to be
Requires additional given to patient and/or
patient education family
Risk of difficulty with
administration
technique
Distribution
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