Medication Dosage Calculator

mg/kg (weight-based) dosing calculates medication based on body weight and is commonly used for most medications, especially antibiotics, pain relievers, and maintenance drugs. mg/m^2 (BSA-based) dosing uses Body Surface Area and is primarily used for chemotherapy agents, some cardiac medications, and drugs with narrow therapeutic windows. BSA dosing is considered more accurate for drugs that distribute throughout the entire body because it accounts for both height and weight, providing better correlation with metabolic processes and organ size. Children and adults with significantly different body compositions may receive more appropriate doses with BSA-based calculations.

Maximum dose limits exist for patient safety and are based on pharmacokinetic studies, clinical trials, and post-market surveillance. Reasons include: toxicity prevention (higher doses may cause organ damage or severe side effects), therapeutic ceiling (beyond a certain dose, there's no additional benefit), saturation of drug receptors (body can't utilize more drug), and risk-benefit ratio considerations. For example, acetaminophen has a maximum daily dose of 4000mg to prevent liver damage, and many antibiotics have caps to prevent resistance and adverse effects. Always respect maximum doses even in obese patients - this is where adjusted body weight calculations become important.

Medication dosing in obesity is complex because different drugs distribute differently in adipose tissue. For obese patients (>20% above ideal body weight), consider these approaches: (1) Use actual body weight for hydrophilic drugs that don't penetrate fat well (like aminoglycosides), (2) Use adjusted body weight (AdjBW = IBW + 0.4 * (ABW - IBW)) for many drugs, (3) Use ideal body weight for some drugs with narrow therapeutic windows, (4) Use dosing caps/maximum doses when specified. Our calculator helps with basic calculations, but pharmacists and physicians should make final dosing decisions for obese patients, often using therapeutic drug monitoring when available.

This calculator is educational and helps understand dosing principles, but you should ALWAYS consult healthcare professionals for: actual medication prescribing, pediatric dosing (especially infants), chemotherapy or high-alert medications, patients with renal or hepatic impairment, drug interactions or contraindications, calculating complex regimens (e.g., vancomycin, warfarin), and any time you're uncertain. Pharmacists are medication experts who consider factors this calculator cannot: patient-specific factors, drug-drug interactions, organ function, allergies, and special populations. This tool assists with calculations but never replaces clinical judgment. Medical errors from dosing mistakes can be fatal - when in doubt, always consult qualified professionals.