Theophylline µg/mL → µmol/L
Convert theophylline from µg/mL to µmol/L
Sources last checked: 2026-11-03
Theophylline µg/mL → µmol/L
Convert theophylline from µg/mL to µmol/L
Converts units only; reference ranges depend on the laboratory, the assay and the patient.
What is the Theophylline µg/mL → µmol/L?
Theophylline levels are reported in µg/mL (identical to mg/L) by most laboratories in Germany, Austria, Turkey and the USA, and in µmol/L by some SI-reporting laboratories. This converter multiplies by 5.551, the factor that follows from the molar mass of theophylline (180.16 g/mol). It applies equally to levels measured during aminophylline therapy, because the assay measures theophylline.
When to use it
- Comparing a theophylline level in µg/mL with a source written in µmol/L
- Documenting therapeutic drug monitoring for a patient moving between laboratories
- Pharmacokinetic exercises in SI units
- Exam questions on narrow-therapeutic-index drugs
When not to use it
- Converting an aminophylline dose — aminophylline is a theophylline salt, and doses are not concentrations
- Caffeine levels in neonates, which need caffeine's own molar mass
- Interpreting a level without knowing the formulation, the time since the last dose or whether an infusion is running
How it is calculated
Theophylline (µmol/L) = theophylline (µg/mL) × 5.551
Clinical pearls and limitations
- Converts units only; reference ranges depend on the laboratory, the assay and the patient.
- 1 µg/mL = 1 mg/L = 5.551 µmol/L; conversely 1 µmol/L = 0.1801 µg/mL.
- Theophylline clearance changes with smoking (including stopping smoking), heart failure, liver disease, fever, age and many interacting drugs such as some fluoroquinolones and macrolides.
- With modified-release tablets, the timing of the sample relative to the dose matters; with continuous infusion, levels reflect steady state only after it has been reached.
- In neonates theophylline is partly converted to caffeine, which some assays do not detect and which also has pharmacological effect.
Frequently asked questions
How do I convert theophylline from µg/mL to µmol/L?
Multiply by 5.551. For example, 13 µg/mL × 5.551 = 72 µmol/L.
Why is the theophylline factor 5.551?
Theophylline has a molar mass of 180.16 g/mol. 1 µg/mL equals 1 mg/L, and 1000 ÷ 180.16 = 5.551 µmol/L.
Is an aminophylline level converted differently?
No. The laboratory measures theophylline itself, so the same factor applies. Aminophylline matters only when converting doses.
Evidence and guidelines
Have a follow-up question?
Medelix answers clinical questions from current guidelines and studies — every statement with its source.
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<p><a href="https://medelix.ai/en/calculators/theophylline-ug-ml-to-umol-l">Theophylline µg/mL → µmol/L calculator by Medelix</a></p>For healthcare professionals and medical students. These tools support, and do not replace, clinical judgement. Always check results against the original source and your local protocols.