Pharmacokinetics: How the body acts on the drug.
o Absorption: Movement of drug from site of administration to various tissues of
body. Occurs in the
... [Show More] gut and liver. Entry into bloodstream. Enteric coating vs.
liquid. Vulnerability to gastric secretions. Gastric emptying time. Ph of RX. pH of
gastric secretions. Presence of food in the gut.
o Distribution: Movement of drug by circulatory system to intended site of action.
The ability of a drug to move into body’s tissues. Bonding with key receptors.
Depends on circulation to the site of action. Inhibited by blood brain barrier. Lipid
barrier not developed in infants. Implications of pain Rx in labor.
o Metabolism: Change that occurs in a drug- to a more or less potent form; to a
more soluble form; to an inactive form. Takes place in the LIVER . Impaired if
liver is damaged. Is impaired if liver not yet developed (age is a factor).
Metabolites may or may not be toxic. Some meds increase the production of
metabolizing enzymes. Others compete for enzymes (metabolic pathways) in the
liver. Poor nutrition can alter the availability of needed enzymes in the liver.
o Elimination: Exit thru urine or bile. Happens in the kidney. If the kidney fails and
excretion fails metabolites may have toxic effects. Excretion can depend on the
pH of urine in the renal tubules.
Routes of absorption and factors affecting absorption:
o IV: direct entry into the venous system. Most complete and rapid route. Can’t be
retrieved. Risk of sepsis.
o IM: Perfusion or blood flow to the muscle. Fat content of the muscle. Temperature
of the muscle: cold causes vasoconstriction and decreases absorption; heat causes
vasodilation and increases absorption. Takes 20 mins for absorption. Water
soluble absorbed better. Lipid soluble best given in adipose.
o SC : Perfusion or blood flow to the tissue. Fat content of the tissue. Temperature of
the tissue: cold causes vasoconstriction and decreases absorption; heat causes
vasodilation and increases absorption. Takes 20 mins for absorption. Water
soluble absorbed better. Lipid soluble best given in adipose.
o PO : Acidity of stomach. Length of time in stomach.Blood flow to gastrointestinal
tract.Presence of interacting foods or drugs.
o PR (rectal) : Perfusion or blood flow to the rectum. Lesions in the rectum. Length
of time retained for absorption.
o SL/Buccal: Perfusion or blood flow to the area. Integrity of the mucous
Membranes. Presence of food or smoking.Length of time retained in area.Very
rapid.
o Topical : Perfusion or blood flow to the area.Integrity of skin.
o Inhalation : Perfusion or blood flow to the area. Integrity of lung lining. Ability to
administer drug properly.
Tolerance : Can result in 10-14 consecutive days of narcotic therapy. People can mount a
counter-reactive response to a medicine when the body tried to create stability. Over time
people need larger doses of tranquilizers or opiates to find relief because the body [Show Less]