Pediatric Drug Dosing Calculator

#!/usr/bin/env python3
"""
Pediatric Drug Dosing Calculator
==================================
Weight-based and BSA-based drug dosing calculator for pediatric patients
with built-in safety checks, maximum dose limits, and age-appropriate
dosing validation.

Clinical Purpose:
    Medication errors are 3x more common in pediatric patients compared
    to adults (Kaushal et al., Pediatrics 2001). This tool calculates
    weight-based and BSA-based doses for common pediatric medications,
    enforces maximum dose limits, and flags potential dosing errors.

References:
    - Taketomo CK, Hodding JH, Kraus DM. Pediatric & Neonatal Dosage
      Handbook. Lexicomp. Latest Edition.
    - Kaushal R, et al. "Medication Errors and Adverse Drug Events in
      Pediatric Inpatients." JAMA. 2001;285(16):2114-2120.
    - Mosteller RD. "Simplified Calculation of Body-Surface Area."
      N Engl J Med. 1987;317:1098.

DISCLAIMER: This calculator is a clinical decision support tool only.
All doses MUST be independently verified by a licensed pharmacist or
physician before administration. Drug information may not reflect the
most current product labeling.
"""

import json
import math
from dataclasses import dataclass, field
from typing import Optional
from enum import Enum


class AgeCategory(Enum):
    PRETERM = "preterm_neonate"
    NEONATE = "neonate_0_28_days"
    INFANT = "infant_1_12_months"
    CHILD = "child_1_12_years"
    ADOLESCENT = "adolescent_12_18_years"


class RouteOfAdmin(Enum):
    ORAL = "PO"
    INTRAVENOUS = "IV"
    INTRAMUSCULAR = "IM"
    SUBCUTANEOUS = "SubQ"
    RECTAL = "PR"
    TOPICAL = "topical"
    INHALED = "inhaled"


@dataclass
class DrugDosing:
    """Pediatric drug dosing parameters."""
    name: str
    generic_name: str
    dose_per_kg: float  # mg/kg per dose
    dose_per_kg_max: float = 0.0  # mg/kg per dose upper range
    frequency: str = ""  # e.g., "Q6H", "Q8H", "once daily"
    max_single_dose_mg: float = 0.0  # Absolute max single dose
    max_daily_dose_mg: float = 0.0  # Absolute max daily dose
    route: list = field(default_factory=list)
    indication: str = ""
    age_restrictions: str = ""
    dose_per_bsa: float = 0.0  # mg/m2 (for BSA-based dosing)
    concentration: str = ""  # Available concentrations
    notes: list = field(default_factory=list)
    contraindications: list = field(default_factory=list)
    dose_adjustment_renal: str = ""
    dose_adjustment_hepatic: str = ""


# Common pediatric medications database
DRUG_DATABASE = {
    "amoxicillin": DrugDosing(
        name="Amoxicillin",
        generic_name="amoxicillin",
        dose_per_kg=25,
        dose_per_kg_max=45,
        frequency="Q8H (standard) or Q12H (high dose)",
        max_single_dose_mg=500,
        max_daily_dose_mg=3000,
        route=[RouteOfAdmin.ORAL],
        indication="Acute otitis media, sinusitis, streptococcal pharyngitis, UTI",
        concentration="250 mg/5 mL or 400 mg/5 mL suspension",
        notes=[
            "High-dose (80-90 mg/kg/day divided BID) for AOM with risk factors",
            "Standard dose (25-45 mg/kg/day divided TID) for uncomplicated infections",
            "Duration: AOM 10 days (< 2 years) or 5-7 days (>= 2 years)",
            "Strep pharyngitis: 50 mg/kg/day (max 1000 mg/day) x 10 days",
        ],
    ),
    "ibuprofen": DrugDosing(
        name="Ibuprofen",
        generic_name="ibuprofen",
        dose_per_kg=10,
        frequency="Q6-8H PRN",
        max_single_dose_mg=400,
        max_daily_dose_mg=1200,
        route=[RouteOfAdmin.ORAL],
        indication="Fever, mild-moderate pain, inflammation",
        age_restrictions="Not recommended under 6 months of age",
        concentration="100 mg/5 mL suspension",
        notes=[
            "Can alternate with acetaminophen Q3H (each given Q6H)",
            "Give with food to reduce GI irritation",
            "Avoid in dehydrated patients (nephrotoxicity risk)",
            "Avoid in varicella (risk of necrotizing fasciitis - debated)",
        ],
        contraindications=["Renal impairment", "Active GI bleeding", "Age < 6 months"],
    ),
    "acetaminophen": DrugDosing(
        name="Acetaminophen (Tylenol)",
        generic_name="acetaminophen",
        dose_per_kg=15,
        frequency="Q4-6H PRN",
        max_single_dose_mg=1000,
        max_daily_dose_mg=75,  # mg/kg/day
        route=[RouteOfAdmin.ORAL, RouteOfAdmin.RECTAL],
        indication="Fever, mild-moderate pain",
        concentration="160 mg/5 mL suspension (infant drops 80 mg/0.8 mL)",
        notes=[
            "Max daily dose: 75 mg/kg/day (not to exceed 4000 mg/day)",
            "Rectal dose same as oral",
            "Safe in neonates (10-15 mg/kg Q6-8H)",
            "Hepatotoxicity risk with overdose (>150 mg/kg acute ingestion)",
            "No anti-inflammatory effect",
        ],
    ),
    "amoxicillin_clavulanate": DrugDosing(
        name="Amoxicillin-Clavulanate (Augmentin)",
        generic_name="amoxicillin-clavulanate",
        dose_per_kg=25,
        dose_per_kg_max=45,
        frequency="Q12H (high dose) or Q8H (standard)",
        max_single_dose_mg=875,
        max_daily_dose_mg=3000,
        route=[RouteOfAdmin.ORAL],
        indication="AOM (2nd line), sinusitis, bite wounds, resistant UTI",
        concentration="400 mg/57 mg per 5 mL (ES formulation) or 250/125 per 5 mL",
        notes=[
            "High-dose: 90 mg/kg/day of amoxicillin component divided Q12H",
            "Use ES (600 mg/42.9 mg per 5 mL) for high-dose regimens",
            "Max clavulanate: 10 mg/kg/day (higher doses cause diarrhea)",
            "Common side effect: diarrhea, diaper rash",
        ],
    ),
    "ceftriaxone": DrugDosing(
        name="Ceftriaxone (Rocephin)",
        generic_name="ceftriaxone",
        dose_per_kg=50,
        dose_per_kg_max=100,
        frequency="Q24H (most indications) or Q12H (meningitis)",
        max_single_dose_mg=2000,
        max_daily_dose_mg=4000,
        route=[RouteOfAdmin.INTRAVENOUS, RouteOfAdmin.INTRAMUSCULAR],
        indication="Meningitis, serious bacterial infections, complicated UTI",
        age_restrictions="Avoid in neonates < 28 days (bilirubin displacement risk)",
        notes=[
            "Meningitis dose: 100 mg/kg/day divided Q12H (max 4 g/day)",
            "Standard infections: 50-75 mg/kg/day Q24H",
            "IM: mix with 1% lidocaine to reduce injection pain",
            "NEVER co-administer with calcium-containing solutions in neonates",
        ],
        contraindications=[
            "Neonates < 28 days receiving calcium-containing IV solutions",
            "Hypersensitivity to cephalosporins",
        ],
    ),
    "prednisolone": DrugDosing(
        name="Prednisolone",
        generic_name="prednisolone",
        dose_per_kg=1,
        dose_per_kg_max=2,
        frequency="Once daily or divided BID",
        max_single_dose_mg=60,
        max_daily_dose_mg=60,
        route=[RouteOfAdmin.ORAL],
        indication="Asthma exacerbation, croup, allergic reactions",
        concentration="15 mg/5 mL (Prelone) or 3 mg/mL (Orapred)",
        notes=[
            "Asthma exacerbation: 1-2 mg/kg/day x 3-5 days (max 60 mg/day)",
            "Croup: 1 mg/kg single dose (max 60 mg)",
            "Nephrotic syndrome: 2 mg/kg/day (max 60 mg) initially",
            "Short courses (< 7 days) usually do not require taper",
            "Give with food to reduce GI upset",
        ],
    ),
    "ondansetron": DrugDosing(
        name="Ondansetron (Zofran)",
        generic_name="ondansetron",
        dose_per_kg=0.15,
        frequency="Q8H PRN (max 3 doses/day)",
        max_single_dose_mg=4,
        max_daily_dose_mg=16,
        route=[RouteOfAdmin.ORAL, RouteOfAdmin.INTRAVENOUS],
        indication="Nausea and vomiting, gastroenteritis, chemotherapy-induced N/V",
        concentration="4 mg/5 mL oral solution, ODT 4 mg, IV 2 mg/mL",
        notes=[
            "Gastroenteritis: single dose 0.15 mg/kg (max 4 mg) may suffice",
            "Weight-based dosing: 8-15 kg = 2 mg, 15-30 kg = 4 mg, >30 kg = 8 mg",
            "QTc prolongation risk - avoid with other QT-prolonging drugs",
            "ODT can be given without water (dissolves on tongue)",
        ],
        contraindications=["Congenital long QT syndrome"],
    ),
    "albuterol": DrugDosing(
        name="Albuterol (Ventolin, ProAir)",
        generic_name="albuterol",
        dose_per_kg=0,  # Fixed dosing by age
        frequency="Q4-6H PRN or Q20min x 3 for acute exacerbation",
        max_single_dose_mg=0,  # Measured in puffs or mg nebulized
        max_daily_dose_mg=0,
        route=[RouteOfAdmin.INHALED],
        indication="Asthma, bronchospasm, wheezing",
        concentration="MDI 90 mcg/puff; nebulization 2.5 mg/3 mL or 5 mg/mL",
        notes=[
            "MDI + spacer: 4-8 puffs Q20 min x 3 (acute), then Q1-4H",
            "Nebulization: < 20 kg = 2.5 mg; >= 20 kg = 5 mg Q20 min x 3 (acute)",
            "Continuous nebulization: 0.5 mg/kg/hr (max 15 mg/hr) for severe exacerbation",
            "MDI + spacer equally effective as nebulizer for mild-moderate exacerbation",
            "Common side effects: tachycardia, tremor, hypokalemia",
        ],
    ),
}


def calculate_bsa(weight_kg: float, height_cm: float) -> float:
    """
    Calculate Body Surface Area using Mosteller formula.
    BSA (m2) = sqrt((height_cm x weight_kg) / 3600)
    """
    if weight_kg <= 0 or height_cm <= 0:
        return 0.0
    return round(math.sqrt((height_cm * weight_kg) / 3600), 4)


def classify_age(age_months: int) -> AgeCategory:
    """Classify patient into pediatric age category."""
    if age_months < 0:
        return AgeCategory.PRETERM
    elif age_months < 1:
        return AgeCategory.NEONATE
    elif age_months <= 12:
        return AgeCategory.INFANT
    elif age_months <= 144:  # 12 years
        return AgeCategory.CHILD
    else:
        return AgeCategory.ADOLESCENT


def calculate_dose(drug_name: str, weight_kg: float, age_months: int = None,
                   height_cm: float = None, indication: str = None) -> dict:
    """
    Calculate pediatric drug dose with safety checks.

    Args:
        drug_name: Drug name (key in database)
        weight_kg: Patient weight in kilograms
        age_months: Patient age in months (for age-specific validation)
        height_cm: Height in cm (for BSA calculation if needed)
        indication: Specific indication (may alter dosing)

    Returns:
        Calculated dose with safety checks and warnings
    """
    drug = DRUG_DATABASE.get(drug_name.lower())
    if not drug:
        return {
            "error": f"Drug '{drug_name}' not found in database",
            "available_drugs": list(DRUG_DATABASE.keys()),
        }

    warnings = []
    alerts = []

    # Weight validation
    if weight_kg <= 0:
        return {"error": "Weight must be greater than 0 kg"}
    if weight_kg > 150:
        warnings.append("Weight > 150 kg. Verify weight is correct. Consider adult dosing.")

    # Age-based validation
    age_category = classify_age(age_months) if age_months is not None else None
    if drug.age_restrictions and age_months is not None:
        warnings.append(f"Age restriction: {drug.age_restrictions}")

    # Calculate weight-based dose
    dose_low = round(drug.dose_per_kg * weight_kg, 1)
    dose_high = round(drug.dose_per_kg_max * weight_kg, 1) if drug.dose_per_kg_max else dose_low

    # Apply maximum single dose cap
    capped = False
    if drug.max_single_dose_mg > 0:
        if dose_low > drug.max_single_dose_mg:
            dose_low = drug.max_single_dose_mg
            capped = True
        if dose_high > drug.max_single_dose_mg:
            dose_high = drug.max_single_dose_mg
            capped = True

    if capped:
        warnings.append(f"Dose capped at maximum single dose: {drug.max_single_dose_mg} mg")

    # BSA calculation if applicable
    bsa = None
    bsa_dose = None
    if height_cm and drug.dose_per_bsa > 0:
        bsa = calculate_bsa(weight_kg, height_cm)
        bsa_dose = round(drug.dose_per_bsa * bsa, 1)

    # Contraindication check
    if drug.contraindications:
        alerts.append({
            "type": "contraindication_check",
            "message": "Review contraindications before prescribing",
            "contraindications": drug.contraindications,
        })

    # Build result
    result = {
        "drug": drug.name,
        "generic_name": drug.generic_name,
        "patient": {
            "weight_kg": weight_kg,
            "age_months": age_months,
            "age_category": age_category.value if age_category else None,
            "bsa_m2": bsa,
        },
        "calculated_dose": {
            "dose_range": f"{dose_low} - {dose_high} mg per dose" if dose_low != dose_high
                          else f"{dose_low} mg per dose",
            "dose_per_kg": f"{drug.dose_per_kg} mg/kg" + (
                f" to {drug.dose_per_kg_max} mg/kg" if drug.dose_per_kg_max else ""
            ),
            "frequency": drug.frequency,
            "route": [r.value for r in drug.route],
            "max_single_dose": f"{drug.max_single_dose_mg} mg" if drug.max_single_dose_mg else "See notes",
            "max_daily_dose": f"{drug.max_daily_dose_mg} mg" if drug.max_daily_dose_mg else "See notes",
            "bsa_based_dose": f"{bsa_dose} mg (based on BSA {bsa} m2)" if bsa_dose else None,
        },
        "concentration": drug.concentration,
        "indication": drug.indication,
        "clinical_notes": drug.notes,
        "warnings": warnings,
        "alerts": alerts,
        "dose_adjustments": {
            "renal": drug.dose_adjustment_renal or "See product labeling",
            "hepatic": drug.dose_adjustment_hepatic or "See product labeling",
        },
        "verification_required": True,
        "disclaimer": "ALL doses must be independently verified by a pharmacist or "
                      "physician before administration. This calculator is a decision "
                      "support tool only.",
    }

    return result


def list_drugs(category: str = None) -> dict:
    """List available drugs in the database."""
    drugs = []
    for key, drug in DRUG_DATABASE.items():
        drugs.append({
            "key": key,
            "name": drug.name,
            "indication": drug.indication,
            "route": [r.value for r in drug.route],
        })
    return {"drugs": drugs, "total": len(drugs)}


def run_dosing_calculator(action: str, **kwargs) -> str:
    """
    Main entry point for the Pediatric Drug Dosing Calculator.

    Actions:
        calculate: Calculate dose (drug_name, weight_kg, age_months, height_cm)
        list: List available drugs
        bsa: Calculate BSA (weight_kg, height_cm)
    """
    if action == "calculate":
        result = calculate_dose(
            kwargs.get("drug_name", ""),
            kwargs.get("weight_kg", 0),
            kwargs.get("age_months"),
            kwargs.get("height_cm"),
            kwargs.get("indication"),
        )
    elif action == "list":
        result = list_drugs()
    elif action == "bsa":
        bsa = calculate_bsa(kwargs.get("weight_kg", 0), kwargs.get("height_cm", 0))
        result = {"bsa_m2": bsa, "formula": "Mosteller: sqrt((H x W) / 3600)"}
    else:
        result = {
            "error": f"Unknown action: {action}",
            "available_actions": ["calculate", "list", "bsa"],
        }

    return json.dumps(result, indent=2)


if __name__ == "__main__":
    print("=== Amoxicillin Dosing (20 kg child) ===")
    print(run_dosing_calculator("calculate", drug_name="amoxicillin",
                                 weight_kg=20, age_months=60))
    print()
    print("=== Ceftriaxone Dosing (8 kg infant) ===")
    print(run_dosing_calculator("calculate", drug_name="ceftriaxone",
                                 weight_kg=8, age_months=6))