Basic Principles Flashcards
What meds increases risk of kernicterus?
Sulfonamides and Ceftriaxone
Grey baby sydrrome was caused by?
Chlorimphenicol
Gasping syndrome is caused by?
Benxyl Alcohol (in some IV solutions)
Pharmocokinetics is what?
What the BODY does with the DRUG
ADME stands for what?
Absorption, Distribution, Metabolism and Elimination
Absorption =
bioavailability
Distribution =
Volume of Distribution
Elimination =
Clearance, half-life and rate constant
What are some routes of ABSORPTION?
IV, PO, PT, PR, IM, PERCUTANEOUS, IO, INHALED
Drug absorption = Bioavailability = (F)
Bioavailability is how much drug enters the systemic circulation
For IV meds (F) = 100%
consider F for other routes (PO, PR, SC, etc)
Rate of absorption is not the same as F
oral liquids, not tabs, compounded meds
What factors will affect drug absorption?
formulation of the medication, pH of stomach, lipid solubility
Patient factors that affect drug absorption;
1st pass, co-administration with food, gastric contents/emptying time, pH, surface area, size of bile salt pool (biliary atresia), bacterial colonization, and underlying diseases (short gut, etc)
1st pass mechanism
gut metabolism + liver metabolism; absorbed thru the gut then the portal vein then the liver; decreased in infants (hepatic immaturity)
Frequent feedings interfere with absorption because:
always something in the stomach; frequent Q 3 hour feeds; there is a constant buffer
Gastric emptying:
erratic in infants, slower vs adults (adult values at 6-8 months), contributes to reflux, affects time the drug reaches the Small intestine, caloric density of feeds
Gastric pH
less acid prduction (increased pH vs adults), term is 6-8 but drops to 1-3 within 24 hrs, but takes longer to normalize in preemies (~3wks), acid production does not correlate with PCA, but instead PNA
Why does pH matter?
affects stability ad ionization of a drug
PO phenobarb and phenytoin are weak acids, so absorption is:
decreased
PO PCN G, AMP, NAFF are acid-labile, so absorption is:
increased
GIT Surface area
more surface=more absorption; tight junctions are not as tight (higher molecular weighted meds sneak thru) which causes an increased permeability in infants vs children/adults
pancreatic function
if decreased (CF), decreased rate of synthesis, pool size and intestinal transport
immature gut flora in infants
affected by: age, delivery method, feeding type (EBM), drug therapy (acid suppression)
What medication is dependent upon gut bacteria?
Digoxin (10% is dependent on gut bacteria)
Decreased GI Absoption:
Reflux, short bowel syndrome, cardiac defects (shunting), hypo/hyperthyroidism (increases or decreases gut transit time)
RECTAL absorption ADVANTAGES:
less 1st pass, absorbed into the hemorrhoidal veins and if in the lower rectum, absorbed directly into system, upper rectum undergoes 1st pass
RECTAL absorption DISadvantages
Erratic PR absorption, infant forms not commercially available, dutting is not accurate, PO/IV suspensions and is often expelled before absorbed
IM absorption determined by:
blood flow at the site of injection, muscle mass, muscle activity
IM absorption is altered in preemies because:
less muscle mass, poor perfusion, peripheral vasomotor instability, insufficient muscle contractions
Which route is preferred in neonates?
IV
PERCUTANEOUS Absorption:
Enhanced in NN and infants due to thinner statum corneum, increased blood flow to the skin, increased total body surface area, can see systemic exposure to topically applied meds, WHAT ELSE IN IN THE CREAM
Aquaphor has been shown to
increase skin integrity and decrease losses
IO absorption
alternative; transport setting; marrow very vascular, up until 5 yrs
INTRApulmonary absorption
Goal is for local effects, but systemic absorption can occur, (tobi, dex), developmental changes and altered capacity of lungs alters the pattern of drug absorption
DISTRIBUTION
determined by: binding affinity of drugs for proteins, hydrophilic vs lipophilic, body composition (% of ECF and TBW), molecular weight, degree of ionization at body pH, hemodynamic factors (cardiac output)
Distribution and classical examples of difficult to treat infections in NICU include:
osteomyelitis, meningitis, endocarditis and MUST CONSIER DISTRIBUTION OF PARTICULAR MEDICATION WHILE CHOOSING DRUG THERAPY AND TARGET CONCENTRATIONS
VOLUME of distribution
The volume in which the amount of drug would need to be uniformly distributed to produce the observed blood concentrations
What explains the measured concentration to total amount of drug in the body?
Volume of Distribution
Protein Binding
binding of drugs to protein is decreased in infants: decreased amounts of plasma proteins, lower binding capacity, decreased affinity of proteins, competition for binding sites (bilirubin and kernicterus)
NICU patients have lowered albumins?
True
There is less Protein binding = more “free” drug
unbound drug is free to distribute out of plasma into the tissues and increases the volume of the distribution for total drug (Total = BOUND + UNBOUND; the BOUND is what IS NOT WORKING); you will have more than you want