Pediatric Dosage Calculation

Posology

• Posology involves the dose or quantity of a drug administered to achieve a therapeutic effect.
• Drug dose refers to the amount of medicinal preparation or radiation given at one time.
• Dosage involves determining the amount, frequency, and number of medicine doses for a specific patient.

Dosage Calculation for Children

• Various rules are employed to calculate dosages for infants and children.
• These methods provide approximate dosages.
• Children may exhibit greater susceptibility to certain drugs compared to adults.

Young's Rule (for Children Aged 1 to 12)

• Formula: Child dose = (age in years / age(years) + 12) multiplied by adult dose
• Example: If an adult dose is 100mg for a child weighing 40kg, the child’s dose using Young's Rule is 37mg.

Clark's Rule (for Children Under 2 Years)

• Formula: Child dose = (Weight in pounds / 150) multiplied by adult dose
• Example: If an adult dose of medication is 30mg for a child who weighs 30lbs, the child’s dose is 6mg.

Fried's Rule (for Infants Up to 1 Year)

• Formula: Infant dose = (Age in months/150) multiplied by the adult dose
• Example: If a physician orders 50mg of diphenhydramine orally every six hours PRN for a four-year-old child, the dose using Fried’s Rule is 16mg of diphenhydramine.

Dilling's Formula

• Formula: Child dose = (Age in years/20) multiplied by adult dose.
• If an adult dose is 100mg for a child weighing 40kg, the child’s dose using Dilling's Formula is 35mg.

Square Meter Surface Area Method

• The square meter surface area method provides a more reliable dosage calculation.
• The average body surface area for adults is 1.73 m².
• Child's dose calculation: Body surface area of child (m²) / 1.73 multiplied by adult dose.
• BSA (m²) can be derived from the square root of: Height (cm) multiplied by Weight (kg) / 3,600

Calculation of Doses for Adults

• Physiological functions, including metabolic rate and kidney functions, often correlate with body surface area.
• Drug doses can use the amount of drug/m² multiplied by body surface area.
• Individual dose can be calculated using the formula: Amount of drug/m² multiplied by Body surface area in m².
• Individual's dose is often given in mg/kg multiplied by body weight in kg.

Dosage Form Necessity

• Many drugs are administered in small (milligram) quantities, necessitating precise weighing.
• Low dosage of potent drugs requires solid forms such as tablets and capsules, prepared with fillers or diluents to increase size for easy handling.
• Dosage forms ensure safe and convenient administration of accurate drug doses
• Dosage forms protect the drug from destructive elements like atmospheric oxygen, moisture, oxidation, hydrolysis, and reduction, often with coatings
• Enteric coatings protect drugs from degradation by gastric acid after oral administration, dissolving in alkaline pH instead
• Dosage forms can mask bitter, salty or offensive taste or odors through capsules or flavored syrups.
• Dosage forms allow for insoluble or unstable drugs to be administered as liquid suspensions
• Dosage forms enable drugs to be administered in clear liquid solutions
• Dosage forms permit rate-controlled and sustained drug release, such as controlled-release tablets
• Dosage forms enable drug action through topical application, e.g., creams and transdermal patches
• Dosage forms facilitate drug action via insertion into body cavities, like suppositories
• Dosage forms achieve drug action by direct delivery into the bloodstream or body tissues via injections.
• Dosage forms enable drug action through inhalation therapy using inhalation aerosols

Additives in Dosage Forms

• Dosage form action and form depends on the additives included
• Additives refer to non-drug components with specific functions within the formulation

Classifications of Additives included in Formulations

• Vehicles refer to solid, semisolid, or liquid materials that assist in drug formulation.
• Solvents, aqueous or non-aqueous, are used to dissolve drugs.
• Bases are semi-solid vehicles that incorporate drug substances in formulations like ointments, pastes, and suppositories..
• Diluents increase bulk or reduce drug concentration.
• Disintegrating agents facilitate disintegration of ingested dosage forms into smaller particles.
• Colouring agents enhance the dosage form's appearance with appropriate color.
• Flavouring agents give a pleasant flavour, especially important in liquid dosage forms.
• Sweetening agents impart a sweet taste to preparations.
• Manufacturing additives improve the manufacturing process

Dosage Form Packaging

• Proper packaging, labeling, and storage maintain pharmaceutical product stability and effectiveness.
• Specifications vary for parenteral, non-parenteral, pressurized, and bulk containers made of glass, plastic, and metal.
• A container serves as a device that holds the pharmaceutical preparation.

Container Features

• Containers should be rigid to withstand normal handling and prevent damage.
• Container material must not react unfavorably with the contents.
• Containers should protect contents from environmental deterioration caused by oxygen and moisture.
• Containers should prevent moisture loss
• Containers must prevent leakage of contents.
• Containers must impede the entry of dirt, chemicals, or microbial contamination.
• Containers should be sterilizable without altering its integrity.
• Containers should provide protection from light when necessary.
• Ideally, the container should not absorb medicaments or additives from the contents.
• The container should not impart anything to the contents.
• The container must be easy to label.
• The container must be pharmaceutically elegant

Container Types classified by Protection Ability

• Well-closed containers protect contents from external solids and loss, functioning under normal handling, storage, and shipping conditions.
• Tight containers protect contents from external liquid, solid, and vapor contamination, preventing changes due to efflorescence, deliquescence, or evaporation.
• Hermetically sealed containers prevent air and gases from passing through, maintaining sterility for sterile preparations.
• Light-resistant containers protect contents from photochemical deterioration, using amber glass or opaque plastic.
• Temper-evident containers feature a mechanism that reveals irreversible opening.
• Child-resistant containers are designed to be difficult for children to open.

Container Types classified by Number of Doses

• Single-dose containers provide a single dose of medication, are not resealable to maintain sterility, e.g., ampoules.
• Multi-dose containers allow successive dose withdrawals without compromising the strength or purity of the remaining contents and are hermetically sealed, e.g., vials.

Explore pediatric dosage calculations using Young's, Clark's, and Fried's Rules. Learn about body surface area methods for accurate medication dosing in children. Examples included.