Neonatal and Premature Infant Care
Age definitions that change doses
Gestational age at birth plus postnatal age equals postmenstrual age (PMA). Nearly every neonatal dose and interval is anchored to PMA and current weight, not chronologic age alone; a 3-week-old born at 26 weeks is functionally far more immature than a term 3-week-old. Renally cleared drugs (aminoglycosides, vancomycin) are the classic example - extended intervals (e.g., gentamicin every 36–48 h) until PMA and renal function mature, with levels guiding adjustment.
Disease-specific therapy
Apnea of prematurity: caffeine citrate load 20 mg/kg then 5–10 mg/kg/day (citrate salt is twice the base; 10 mg citrate = 5 mg base). Patent ductus arteriosus: indomethacin or ibuprofen - avoid with necrotizing enterocolitis, renal impairment, or significant thrombocytopenia. Early-onset sepsis: ampicillin plus gentamicin covers group B Streptococcus and E. coli; add acyclovir for suspected HSV. Extremely low birth weight infants may receive fluconazole prophylaxis. Vitamin K 0.5–1 mg IM at birth prevents hemorrhagic disease of the newborn. Surfactant for respiratory distress syndrome; inhaled nitric oxide for persistent pulmonary hypertension.
Displacement and immature-barrier traps
Sulfonamides displace bilirubin (kernicterus risk); ceftriaxone does the same and precipitates with calcium. Chloramphenicol causes gray baby syndrome from immature glucuronidation. Thin skin and an immature blood–brain barrier increase absorption and CNS penetration of topical and sedating agents.
Worked example
Order: caffeine citrate 20 mg/kg load for a 1.2 kg infant. Dose = 24 mg of caffeine citrate, which equals 12 mg caffeine base. If the order is written in base but the vial is labeled as citrate, converting incorrectly delivers a twofold underdose or overdose.