Principles of Paediatric Prescribing

Paediatric prescribing differs from adult practice because body size, body composition and organ maturity change rapidly from birth to adolescence, so dose, formulation, route and monitoring all depend on age and weight. Most serious errors come from weight, unit, decimal point and concentration mistakes rather than from poor drug choice.

Age groups. Preterm neonate (under 37 weeks), term neonate (first 28 days), infant (to 1 year), child (1 to 12 years), adolescent (12 to 18 years). Record age in days for the first month and in corrected age for preterm infants.

Absorption. Gastric pH is high and emptying is slow in the first weeks, which raises absorption of acid-labile drugs such as benzylpenicillin and lowers absorption of weak acids such as phenobarbital and phenytoin. Intramuscular absorption is erratic in neonates and skin absorption is increased.

Distribution. Total body water is about 75 to 80% of weight in neonates, so water-soluble drugs such as gentamicin need higher mg/kg doses. Low albumin and bilirubin competition raise the free fraction of highly bound drugs.

Metabolism and excretion. Glucuronidation is immature at birth, which slows clearance of morphine, paracetamol and chloramphenicol. Many drugs are cleared faster than in adults (mg/kg basis) between 1 and 6 years. Glomerular filtration is low at birth and reaches adult values, corrected for surface area, at about 1 year.

Choose a medicine with paediatric safety and dosing data, a suitable paediatric formulation and the simplest effective route. Use the oral route when the child can swallow and absorb, and the intravenous route when perfusion, vomiting or severity demand it.

Prescription content. Write the generic name, dose in mg or mcg with the mg/kg basis, route, frequency, indication, duration, current weight with date, age and allergies. Write “micrograms” and “units” in full, use a leading zero (0.5 mg) and never a trailing zero (5 mg, not 5.0 mg).

Dose logic. Calculate each dose and the daily total, compare with the adult maximum, and round to a measurable volume within about 10%. Use an independent second check for opioids, insulin, potassium, digoxin, anticonvulsants, aminoglycosides and chemotherapy.

Medicines to avoid or restrict. - Aspirin under 16 years: avoid because of Reye syndrome, except Kawasaki disease and specialist antiplatelet use. - Codeine: avoid under 12 years, and under 18 years after tonsillectomy or adenoidectomy, because of ultra-rapid metabolism.

Tramadol is avoided under 12 years in most labels.

• Tetracyclines under 8 years: avoid, except short courses of doxycycline for severe indications such as rickettsial infection and cholera.
• Chloramphenicol and sulphonamide-containing drugs in neonates: avoid (grey baby syndrome, kernicterus).
• Ceftriaxone in neonates with jaundice, or receiving calcium-containing infusions: avoid.
• Fluoroquinolones: restricted to specialist indications.
• Sedating antihistamines, promethazine and cough and cold preparations under 6 years: avoid.
• Loperamide in acute gastroenteritis: avoid.
• Preparations containing benzyl alcohol in neonates: avoid (gasping syndrome).

Weight extremes. Use actual weight in children of usual weight. In obesity, dose water-soluble drugs on ideal or adjusted weight and cap at the adult maximum. In malnutrition use current weight, start low with drugs of narrow margin, and avoid large fluid boluses unless the child is in shock.

Kidney and liver impairment. Estimate glomerular filtration with a bedside creatinine-based formula and reduce dose or extend interval for aminoglycosides, vancomycin, penicillins at high dose and renally cleared anticonvulsants. In hepatic impairment lower paracetamol, opioid and benzodiazepine doses.

Off-label use. Common and often unavoidable. Use the best available evidence, document the reasoning and inform the carer.

Administration. Use oral syringes marked in mL, never household spoons. Prefer dispersible or liquid forms, check palatability, and do not hide medicine in a full feed.

Special groups. Adolescents need confidentiality, contraception and pregnancy checks before teratogenic drugs. Breastfed infants of mothers taking sedatives or opioids need observation. In East Africa, weight-band dosing and dispersible tablets for malaria, pneumonia and diarrhoea are usual, and weighing scales may be unavailable, so a length-based estimate is used.

Monitoring. Re-weigh at every change in therapy and recalculate when weight changes by more than 10%. Children on long-term treatment outgrow doses, so anticonvulsant and antiretroviral doses need review each visit. Measure drug levels for gentamicin, vancomycin, phenytoin, phenobarbital and digoxin.

Referral and escalation. Seek senior or pharmacist review for any neonatal prescription, any dose outside the usual range, unlicensed formulations, and more than three concurrent medicines.

Stopping. Write a stop or review date on every antimicrobial and short-course drug. Switch intravenous to oral within 48 to 72 hours when the child is improving and absorbing. Report suspected adverse reactions.