pediatrics pharmacology
Post on 18-Dec-2014
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Pharmacology and Pediatrics
Age Groups of Pediatrics Population
Group Age
Preterm or premature Less than 36 weeks gestational age
Neonate Less than 30 days of age
Infant 1 month until 1 year of age
Child 1 year until 12 years of age
Adolescent 12 years of age until 18 years of age
Oral Drug Absorption in the Neonate vs Older Children and Adults
Drug Oral Absorption
Acetaminophen Decreased
Ampicillin Increased
Diazepam Normal
Digoxin Normal
Penicillin G Increased
Phenobarbital Decreased
Phenytoin Decreased
Sulfonamides Normal
AGE-RELATED PHARMACOKINETIC DIFFERENCES IN CHILDREN COMPARED WITH ADULTS
Premature Neonate Neonate Infant Child Adolescent
Absorption
Gastric acidity Decreased Decreased Decreased Equal Equal
Gastric emptying time Decreased Decreased Equal Equal Equal
GI motility Decreased Decreased Decreased Equal Equal
Pancreatic enzyme activity
Significantly decreased
Decreased Decreased Equal Equal
GI surface area Increased Increased Increased Increased Equal
Skin permeability Significantly increased
Increased Equal Equal Equal
Distribution
Body composition Equal
Blood-brain barrier Decreased Decreased Equal Equal Equal
Plasma proteins Significantly decreased
Decreased Equal Equal Equal
Metabolism
Liver Decreased Decreased Decreased Equal/Increased Equal
Elimination
Renal blood flow Decreased Decreased Decreased Equal Equal
Glomerular filtration Decreased Decreased Decreased Equal Equal
Tubular function Decreased Decreased Decreased Equal Equal
Drug Distribution
• Drug distribution in the neonate depends on– Amount of body water, body fat and drug binding
• Body water (BW)– Neonates have more BW than adults (70% vs 50%)– Full-term: 70% body weight is water– Pre-term: 85% body weight is water
• Body fat– Pre-term infants have much less fat than full-term– Lipid soluble drugs may not be accumulated
• Drug binding to plasma proteins– Binding of drugs to albumin is reduced– Drug competition for binding albumin may occur
Drug Excretion• GFR is much lower in newborns than in older infants,
children or adults
• This limitation persists during the first days of life and improves thereafter
• Neonatal GFR based on body surface area – Birth: Only 30-40% of the adult value– 3 weeks: 50-60% of the adult value– 6-12 months: Reaches adult values – Thus, renal elimination occurs is very slow initially
• Toddlers– Have shorter drug elimination (t½) than older children and
adults probably due to ↑ renal elimination and metabolism
Pediatric Dosage Forms
• Elixir– Alcoholic solutions in which the drug molecules are
dissolved and evenly distributed– No shaking is required– Generally, all doses contain equivalent amounts
• Suspension– Contains undissolved drug particles that must be
distributed throughout the vehicle by shaking– Caution: Risk of administering unequivalent doses may
lead to toxicity or lack of efficacy
• Prescriber awareness and care giver education on these differences is important
Compliance
• Compliance may be difficult to achieve since it involves many factors– Parent’s ability to follow directions– Measuring errors– Spilling and spitting out
• Recommendations to improve compliance– Pill boxes– Calibrated medicine spoon– Ask if parent gives another dose after spitting out– Stress importance of duration of treatment– Instruct whether to wake the child during q6h dosing– Give some responsibility to the child for his/her care
Pediatric Drug Dosage
• Most drugs approved for use in children have pediatric doses, stated in mg/kg
• If recommendations are not available, an approximation can be made by any of several methods
• Methods include : Age, weight, or surface area– Age: Young’s rule– Weight: Clark’s rule– Doses based on age or weight are conservative– Doses based on surface area are more adequate
• The calculated pediatric dose should never exceed the adult dose!
Clark’s Rule
• Formula for Clark's Rule is:
Weight of the child in pounds/150 ("normal" adult weight) X the usual adult dose
• The adult dose of a medication is 30 mg. The child's weight is 30 lbs. What is the correct dose?
30/150 = 1/5
1/5 x 30 mg = 6 mg • Preferred method
Young’s Rule
• Pediatric doses for children over the age of 2 based on the adult dose. Not as precise as Clark’s rule.
Take the age of the child in years and divide that by their age plus 12.
• Multiply this number times the adult dose.
Pediatric dose = [age/(age + 12)] x adult dose
• 2/14 X 250mg = 35 mg for a child age 2 yrs
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