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Flashcards in peds Deck (35):

What are key concepts in peds PK and PD

there is little info on PK&PD 2/2
variations in absorption of meds from GI, IM injection sites and skin, and premature and other newborn infants
they are NOT just little adults!
ADME varies between kids and adults, and kids and kids
Concomitant diseases can influence dosage and requirements to achieve a targeted effect
Weight based dosing for obese kids can lead to subtherapeutic doses


What are the peds age ranges

Premature: infant born <37 weeks
Neonate: birth-1 month
Infant: 1 month- 1 year
Children: 1-11 years
Adolescents: 12--16
Peds: <18
*Can start dosing kids as adults at 16


Are a lot of drugs used in peds

yes, most marketed drugs can be used for peds pts
but 1/4 have indications for specific use in peds
ADME is different between neonates, premature, children, and adolescents


What affects absorption from GI tract

pH dependent passive diffusion
gastric emptying time


What is gastric pH at birth

ranges from 6-8!
within 24 hours it decreases to 1-3
-in premature kids, pH stays high because of immature acid secretion


What happens in GI of premature infants

higher gastric pH= higher concentration of acid labile drugs (penicillins) and lower of weak acids (phenobarbital)
Passive and active transport may be fully developed by 4 months old
*Gastric emptying is slow


What factors affect IM absorption in premature infants

relative muscle mass
poor perfusion to various muscles
peripheral vasomotor instability
insufficient muscular contractions
-can't predict the net effect of these factors on drug absorption


What happens to skin absorption in peds

percutaneous absorption increased (underdeveloped epidermal barrier, increased skin hydration)
increased absorption of steroids
total body surface area:total body weight is highest in younger


What is drug distribution determined by in peds

Physicochemical properties of the drug (molecular weight, PKa)
Physiologic factors specific to the pt (total body water, protein binding, pathologic conditions)


What happens to total body water with age

fetus: 94%
premie: 85%
full term: 78%
adults: 60%
-gentamicin distribution volumes of 0.48 l/kg in neonates, and 0.2 l/kg in adults


EC fluid volume accounts for

50% body weight in premies
35% body weight in 4-6 mo. old
25% in kids 1 yr
19% in adults


What happens to distribution in newborns

decreased! 2/2
decreased plasma protein concentration, lower binding capacity of protein, decreased affinity of proteins for drug binding, competition for certain binding sites by endogenous compounds (like bili)


What about premies and distribution

May require larger loading dose than older kids to get to therapeutic concentration (ex. phenobarbital, phenytoin)


What happens to free drug in peds bodies

increased concentration of free drug (unbound)
Drugs bound to plasma proteins can not be eliminated by kidney
increase in free drug may also increase clearance


What happens to distribution based on body fat

body fat is lower, so highly lipid soluble drugs are distributed less widely in infants


What happens to metabolism in peds

It is much lower in infants than older kids bc while sulfation path is well developed, Glucuronidation pathway is underdeveloped!
ex: APAP is metabolized through the glucuronidation path, so they compensate by trying to metablize thru sulfation pathway


What is grey baby syndrome

decreased metabolism of chloramphenicol by Glucu pathway causes build up of chlormaphenicol


Morphine and infants

May need higher serum concentration of morphine to achieve efficacy
infants can NOT metabolize morphine to it's active 6-Glucuronide metabolite


What other drug oxidation is impaired in peds

theophylline, phenobarbital, phenytoin


What happens to GFR in peds

may be as low as 0.6-0.8 in premies, and is appx 2-4 in term infants
Processes may not fully dvelopuntil weeks-1 yr after birth


What are concerns about common cold remedies in beds

serious toxicities associated with antihistamines, decongestants, antitussives, and expectorants
FDA says do NOT use in <2 y/o, companies label not for use <4!


What is the concern with benzyl alcohol use in peds

Causes syndrome of:
metabolic acidosis, seizures, neurologic deterioration, gasping respirations, hepatic and renal abn, CV collapse, death
-it is a preservative used in IV flush solutions, IV DXM, methylprednisone, enoxaparin, midazolam, and multivitamins


What is the concern with tetracyclines

contraindicated in pregnant women, nursing mothers, and kids <8 because:
cause dental staining and defects in enamelization of deciduous and permanent teeth
Decrease in bone growth


What are concerns with fluoroquinolones

Not recommended for peds or pregnant women, may cause cartilage leisons and arthropathy; *tendonitis and rupture in all ages
<18 w/ inhalation anthrax
Tx complicated UTI and pyelo caused by E Coli
peds w/ CF


What are concerns with antidepressants

May increase risk of suicide in younger pts
Approved: Sluoxetine, Sertraline, Fluvoxamine
Always assess risk vs benefit; they have a BLACK BOX WARNING!


How do you determine dose in peds

MC and reliable method: Body weight!
Least reliable: Age!
most accurate: body surface area
(formulas rely on weight, age, body surface area, and mg per weight per day)


What is Clark's rule (weight)

(kids weight in lb / 150) x adult dose = child's dose


What is Fried's rule (age; for very young)

(age in mo./150) x adult dose = child's dose


What is Young's rule (age)

(age in yr/age +12 yrs) x adult dose = child's dose
*ONLY for kids 1-12


What is a nomogram

a chart that takes into account height and weight to calculate BSA
Dosage for BSA is un units per M2*


What is the MC way in which doses are expressed

units per Kg
But this means you have to know patient' weight! include on every Rx you write so the pharmacist can verify the dose
MUST specify per DAY or per DOSE
*always include indication on the label! (ex: for ear infection)


Know these conversions

1 teaspoon: 5 ML
1 tablespoon: 15 ML
1ounce: 30 ML
1 cup (8oz): 240 ML


What are ways to prevent calculation errors

Bracketing: write out "pt weights 20kg. 20kg x 8mg/kg/day = 160mg"
Ask colleague or staff
phone a pharmacist
*NEVER memorize peds doses... look them up!


Are organ systems normal in kids

no, they are not fully developed!
absorption may take longer, fat soluble drugs may take longer to distribute, may have slower or more rapid metabolism
Kids have slower excretion rates= more likely toxicities


How do you admin dropper meds to kids

on the cheek, not the back of the tongue