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About

Therapeutic Drug Monitoring (TDM) and toxicology often require switching between molar units (umol/L) and mass units (mg/L). While chemists prefer molarity to understand stoichiometry, clinicians and pharmacists often work with mass concentrations to align with dosing guidelines (mg/kg).

This conversion is impossible without the substance's Molecular Weight (MW). For instance, a blood alcohol concentration of 21.7 mmol/L is equivalent to 100 mg/dL (0.1%), but this relationship is unique to Ethanol. This tool bridges that gap by providing a comprehensive database of pharmaceuticals, toxins, and heavy metals, allowing for instant, error-free conversion.

toxicology pharmacology drug monitoring molar mass concentration

Formulas

To convert from a molar count (micromoles) to a physical weight (milligrams), we multiply by the molar mass and adjust the prefix.

Cmg/L = Cumol/L × MW1000

This derivation comes from:

1 umol = 10-6 mol × MW (g/mol) = Mass (g)

Since we need the result in mg (10-3 g), we divide the result by 1000.

Reference Data

SubstanceMolecular Weight100 umol/L converts to
Paracetamol (Acetaminophen)151.16 g/mol15.1 mg/L
Salicylic Acid (Aspirin metabolite)138.12 g/mol13.8 mg/L
Ethanol46.07 g/mol4.6 mg/L
Phenytoin252.27 g/mol25.2 mg/L
Theophylline180.16 g/mol18.0 mg/L
Lithium6.94 g/mol0.7 mg/L
Lead (Pb)207.20 g/mol20.7 mg/L
Digoxin780.95 g/mol78.1 mg/L
Vancomycin1449.30 g/mol144.9 mg/L
Cyclosporine1202.61 g/mol120.3 mg/L

Frequently Asked Questions

A micromole is a specific number of molecules (approx 6.022 x 10^17). The weight of that pile of molecules depends entirely on how heavy each individual molecule is. Lead atoms are much heavier than Lithium atoms, so 100 umol of Lead weighs far more than 100 umol of Lithium.
Not directly. This tool outputs mg/L. To get mg/dL, you would divide the result by 10. For example, 100 mg/L = 10 mg/dL.
The database includes common anti-epileptics (Phenytoin, Carbamazepine), antibiotics (Gentamicin, Vancomycin), cardiac drugs (Digoxin), and common toxicology agents (Ethanol, Salicylates, Paracetamol).
While accurate, this tool is for concentration conversion (lab results), not dosing. Always consult official pharmacopoeia or hospital guidelines for patient dosing.