Drug Therapy in the Pediatric Patient

Jan Bazner-Chandler

RN, MSN, CNS, CPNP

Safe Drug Administration

Administration of drugs during the first year of life can be a challenge due to rapid changes in body size, body composition, and organ function.

Historical Perspective

It was not until the 1970’s that the effects of drug on the neonate and young infant was studied.

Pharmacokinetics

Absorption Distribution Hepatic metabolism Renal excretion

The Neonate – birth to 4 weeks

Neonate - Absorption

Two major factors affect the absorption of drugspH dependent passive diffusionGastric emptying

Gastric pH

Gastric pH (6-8) is directly related to the presence of amniotic fluid in the stomach.

Postnatally, gastric acid secretory capacity appears after the first 24 to 48 hours and gastric acidity decreases during the first weeks of life.

Adult values are achieved at about 3 months of life.

Gastric pH in premature infant

In the premature infants, gastric pH may remain elevated due to immature acid secretion.

Delayed Absorption

Prolonged emptying is seen in premature infant.

In the neonatal period the emptying rate is variable and prolonged.

Delayed absorption

Delayed absorption may also be a result of diminished pancreatic enzyme function and bile acid secretion.

Absorption from skin

Percutaneous absorption may be drastically increased due to immature epidermis and increased skin hydration.

Absorption from muscle

Absorption from intramuscular site may be unpredictable and decreased due to insufficient blood flow, poor muscle tone, and compromised muscle oxygenation.

Distribution

Distribution of drugs within the body is influenced by the amount and character of plasma proteins, and relative size of fluid, fat and tissue compartments of the body.Total body water Plasma proteins

Total Body Water

85 % in pre-term infant 78% in neonate 60% at 1 year 64 % in childhood (10 to 15 year old) 60% in adults 54% in elderly

Metabolism

Hepatic enzyme activity and plasma / tissue esterase activity are both reduced during the neonatal period.

The enzyme activity increases as the infant ages but can be compromised in cases of severely malnourished infants and children.

Metabolism

Plasma half-life 2 to 3 times longer in neonates.

Neonate Renal Excretion

Renal ExcretionAt birth, glomerular function is more advanced

that tubular function this persists until about 6 months of age.

This effects the efficiency at which the kidneys eliminate drugs.

This is especially important in the administration of aminoglycosides.

Infant – 5 weeks to 1 year

Infant - Absorption

Low acidity in stomach until around 2 years of age.

Gastric emptying still delayed. Percutaneous absorption: continue to be

increased through childhood.

Absorption - IM

Injected drugs are often erratically absorbed because of variability in muscle mass amount children and illness.

IM generally avoided due to pain and possibility of tissue damage.

Absorption - transdermal

May be enhanced in young children because the stratum corneum is thin and the ratio of surface area to weight is much greater than for older children and young adults.

Skin disruptions (abrasions, burns, eczema) increase absorption.

Absorption – transrectal

Transrectal is dependent on placement of the drug within the rectal cavity.Good for drugs such as acetaminophen

(Tylenol).Diazepam in status Epilepticus

Absorption - lungs

Varies less by physiologic parameters and more by reliability of the delivery device.

Beta agonists may be used for asthma, pulmonary surfactant for hyaline membrane disease.

Meds via mask

Infant - Distribution

Protein-binding capacity reaches adult values within 10 to 12 months.

Higher doses (mg / kg) of water-soluble drugs are required in younger children due to higher percentage of their body weight in water.

Infant – Hepatic Metabolism

Complete maturation of the liver develops by one year.

Cytochrome P-450 enzyme system in the small bowel and liver are the most important factor in drug metabolism.

Infant – Renal Excretion

Renal elimination depends on plasma protein binding, renal blood flow, GFR and tubular secretion all are altered in the first two years of life.

Drug Dosing

Dosing in children less than 12 years is always of function of age, body weight or both.

When very accurate levels dosing in needed, dose adjustments should be based on plasma drug concentration.

Child – 1 to 12 years

Pharmacokinetics

After one year similar to adults. They metabolize drugs faster than adults

until around age 2 years. Metabolism declines again at puberty. Increase in dosage or reduction in dosing

interval may be needed for drugs that are eliminated by hepatic metabolism.

Adolescent- 12 to 16 years

Dosage Determination

Body surface area calculations are the most accurate.

Mg / kg dosing is most common calculation.

Dosing – amoxicillin

Infants < 3 months or neonates 20 – 30 mg / kg / day in divided doses q

12 hours

Dosing – amoxicillin

po children > 3 months 25 – 50 mg / kg per day in divided doses q

8 hours 24 – 50 mg / kg per day in divided doses q

12 hour

Dosing – amoxicillin

Adults 250 to 500 mg q 8 hours or 500 to 875 q 12 hours (not to exceed 2-3

grams per day)

Weight

Remember 1 pound = 2.2 kg If you are converting a 6 pound 5 ounce

infant you will need to convert 5 ounces to a fraction. (hint 16 ounces in a pound)

Tylenol and Motrin

Acetaminophen can be given for infants 3 months of age and older

Dosing per Davis Drug Guide

Dosing: 10 to 15 mg / kg / dose every 4 hours

OTC Dosing

0-3 months 40 mg q 4 hours 4 to 11 months 80 mg q 4 hours 1-2 years 120 mg q 4 hours 2-3 years 160 mg q 4 hours 4-5 years 240 mg q 4 hours 6-8 years 320 mg q 4 hours 9-10 years 400 mg q 4 hours 11 years 480 mg q 4 hours 12-14 years 640 mg q 4 hours Greater than 14 years 650 mg q 4 hours

How provided?

Elixir 80 mg / 2.5 mL 80 mg / 5 mL 120 mg / 5 mL 160 mg / 5 mL

Drops: 80 mg / 0.8 mL Chewable tabs: 80 mg, 160 mg Tablets: 160 mg, 325 mg, 500 mg, 650 mg

Ibuprofen (Advil or Motrin)

Similar to acetaminophen in its ability to lower fever. FDA has approved it for infants over 6 months of age. One advantage is a longer lasting effect 6 to 8 hours).

Dosing

Children 6 mo – 12 years Antipyretic: 5 – 10 mg / kg every 6 hours Anti-inflammatory: 20 to 40 mg / kg / day

in 3 to 4 divided doses (not to exceed 50 mg / kg / day)

How provided?

Liquid: 100 mg / 5 mL Oral suspension: 100 mg / 5 mL Pediatric drops: 50 mg / 1.25 mL Chewable tablets: 50 mg, 100 mg Capsules: 200 mg Tablets: 100 mg, 200 mg, 300 mg, 400

mg, 600 mg, 800 mg

Clinical Pearl

Never alternate Tylenol / Motrin due to dosing times.

FDA Alert

Cough and cold medications that contain decongestants, antihistamines, cough suppressants, and expectorants are commonly used in children to provide temporary relief of symptoms of upper respiratory tract infection in children less than 2 years of age.

FDA Alert

During 2004 – 2005 1,519 children were treated in ERs for adverse eventsOverdosing3 deaths in infant younger than 12 months

Cause of death

All three infants had what appeared to be high levels of pseudoephedrine in postmortem blood samplesOne infant had a prescription and an OTC

cough and cold medication at one time.Two infant had OTC cough and cold

medications.

Conclusion

In children less than 2 years of age systematic reviews of controlled trials of OTC cold and could medications have concluded they are not more effective than placebo in reducing acute cough and other symptoms of upper respiratory tract infection.

Recommendations

In 2006 clinical practice guidelines for management of cough advised health care providers to refrain from recommending cough suppressants and other OTC cough mediations for young children.

FDA

On June 8, 2006 the FDA took enforcement action to stop the manufacture of carbinoxamine-containing medications in children aged less than 2 years.