We need to be very careful when giving any medicine to an infant or a child. Even over-the-counter (OTC) medicines are serious medicines. Children cannot be considered as miniature adults and adult medications should never be used in children as children’s responds to drugs differently than adults. Only paediatric medications should be used in children or infants as pediatric patients products have been appropriately evaluated and approved for them by regulators.
Read below information on how children’s responds to drugs differs from adults and how serious it can be if they were given with adult medication or if they accidentally take the medication.
There are many physiologic differences between children and adults which can effect pharmacokinetics and pharmacodynamics of drug. Pharmacokinetics refers to the effects suffered by the drug when in contact with the organism i.e, this means liberation, absorption, distribution, metabolism and excretion (LADME) of drug. Pharmacodynamics refers to the relationship between drug dosage and effect in a certain organ or system.
Factors such as gastric pH and emptying time, intestinal transit time, immaturity of secretion and activity of bile and pancreatic fluid plays main role in that.
At birth, Gastric pH is practically neutral (6-8), then falls to approximately 1-3 within the first 24 h following birth, and later on gradually returns to neutrality by day 10. It slowly declines again thereafter to reach adult values (2-3). This gastric acid differences may affect the dissolution and absorption of drugs.
In normal adults, gastric emptying is biphasic, a rapid (10-20 min) first phase is followed by an exponentially slower phase. In the preterm infant, gastric emptying is slow and linear. It approaches adult values within the first 6-8 months of life. Gastric emptying affect absorption of drugs.
Intestinal transit time is prolonged in neonates because of reduced motility and peristalsis, but appears to be reduced in older infants which affect distribution of drugs.
Immaturity of secretion and activity of bile and pancreatic fluid leads to impaired fat digestion in neonates and infants in the first few months.
The bioavailability of some drugs is influenced by the metabolism by the intestinal microflora, which is different in infants, children and adults. During fetal life, the gastrointestinal tract is sterile. From birth, microbial colonization occurs and bacteria are detected within 4-8 hours. The digestive tract colonization influences the bile salts metabolism and gastrointestinal motility. The types of bacteria that colonize the digestive tract of the full-term neonates are different depending on whether the neonate receives maternal or artificial milk.
Intramuscular administration of drugs is unreliable in neonates and the pharmacokinetics are unpredictable because of decrease of the blood flow to muscle, which varies quite considerably over the first 2-3 weeks of life, less muscular mass and a higher proportion of water.
At birth, the blood-brain barrier (BBB) is still not fully mature and medicinal products may gain access to the central nervous system with resultant toxicity.
In very young infants, the total body water is high (80-90% of the body weight (BW)) while fat content is low (10-15% BW). The amount of total body water decreases to 55-60% by adulthood. The extracellular water content is about 45% in neonates, and especially large in neonates with low birth weights, compared with 20% in adulthood. These changes will result in a relatively higher volume of distribution of water-soluble drugs in pediatric population than in adulthood.
The liver is quantitatively by far the most important organ for drug metabolism. It constitutes 5% of the BW at birth but only 2% in adults. Blood flow and drug-metabolising enzymes are reduced in children; the former reaches adult rates by around one year of age.
Drug metabolism mechanisms can be classified into phase I, involving structural alteration of the drug molecule, and phase II reactions, consisting of conjugation with another often more water-soluble moiety.
At birth, both phase I and II metabolic enzymes may be immature. The different capacity to metabolize drugs in children may result in higher or lower drug plasma levels than those reached in adults.
Excretion of drugs by the kidneys is dependent on three processes, glomerular filtration (GFR), tubular secretion and reabsorption. They are dependent on renal blood and renal plasma flow, which increase with age as a result of an increase in cardiac output and a reduction in peripheral vascular resistance.
At birth, renal blood flow is only 5 to 6% of cardiac output, 15 to 25% by one year of age and reaches adult values after two years of age.
Infant urinary pH values are generally lower than adult values.
In general, the absorption, plasma protein binding, metabolism and excretion levels of children are reduced whereas the volume of distribution is increased. However, this is not always certain, as these processes are also dependent on the drug characteristics.
References: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3857037/
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