Unit Converter
Theophylline
(Methylxanthine Bronchodilator - Requires Therapeutic Drug Monitoring)
Synonyms
- Theophylline
- 1,3-dimethylxanthine
- Theo-Dur® (brand)
- Aminophylline (salt form, ~80% theophylline)
- Methylxanthine derivative
Units of Measurement
- µmol/L
- mg/L
- mg/dL
- mg/100 mL
- mg%
- µg/mL
Unit Conversions
Molecular Weight of Theophylline = 180.17 g/mol
µmol/L ↔ mg/L
1 µmol/L=0.180 mg/L1\ \text{µmol/L} = 0.180\ \text{mg/L}1 µmol/L=0.180 mg/L 1 mg/L=5.55 µmol/L1\ \text{mg/L} = 5.55\ \text{µmol/L}1 mg/L=5.55 µmol/L
mg/dL → mg/L
1 mg/dL=10 mg/L1\ \text{mg/dL} = 10\ \text{mg/L}1 mg/dL=10 mg/L
µg/mL → mg/L
1 µg/mL=1 mg/L1\ \text{µg/mL} = 1\ \text{mg/L}1 µg/mL=1 mg/L
mg% = mg/dL
Description
Theophylline is a methylxanthine bronchodilator used in:
- Asthma
- COPD
- Neonatal apnea
- Some cardiac conditions
It has a narrow therapeutic index, meaning toxic effects can occur near therapeutic levels.
Therefore, regular therapeutic drug monitoring (TDM) is essential.
Mechanisms:
- Phosphodiesterase inhibition (↑ cAMP)
- Adenosine receptor antagonism
- Anti-inflammatory effects
- Mild diuresis
Physiological & Pharmacological Effects
- Bronchodilation
- Improved diaphragmatic contractility
- CNS stimulation
- Increased cardiac output
- Mild vasodilation
- Enhanced mucociliary clearance
Clinical Significance
ELEVATED THEOPHYLLINE (Toxicity)
Very important due to narrow safety margin.
Symptoms of Theophylline Toxicity
- Nausea, vomiting
- Tachycardia
- Arrhythmias (PVCs, SVT)
- Hypotension
- Seizures
- Tremors
- Hypokalemia
- Hyperglycemia
- Metabolic acidosis
Risk Factors
- Liver disease
- Fever
- Sepsis
- Older age
- Drug interactions: erythromycin, ciprofloxacin, cimetidine
- Smoking cessation (↓ clearance)
LOW THEOPHYLLINE LEVELS
Indicate:
- Sub-therapeutic dosing
- Poor compliance
- Smoking (↑ clearance)
- Drug interactions (rifampin, carbamazepine, phenytoin)
- Malabsorption
Reference Intervals
(Tietz 8E + ACCP + Mayo + ARUP)
Adults & Children
- 10 – 20 mg/L
(= 10 – 20 µg/mL)
(= 55 – 111 µmol/L)
Toxic Range
- > 20 mg/L → risk of side effects
- > 30 mg/L → high toxicity
- > 50 mg/L → severe toxicity, seizures, arrhythmias
Neonatal Apnea Treatment
- Target: 5 – 10 mg/L
Diagnostic Uses
1. Asthma & COPD Drug Monitoring
Ensures safe and effective dosing.
2. Toxicology
Evaluate acute or chronic overdose.
3. Neonatology
Monitor levels in apnea of prematurity.
4. Drug Interaction Monitoring
Because many medications alter clearance.
5. Liver Disease
Reduced clearance → requires close monitoring.
Analytical Notes
- Blood should be drawn just before next dose (trough level)
- In IV aminophylline infusion: draw 4–8 hours after start
- Avoid hemolysis
- Assays: immunoassay, HPLC
- Half-life varies widely (4 – 9 hours; longer in neonates and elderly)
Clinical Pearls
- Smoking increases clearance → higher doses needed
- Fever reduces clearance → risk of toxicity
- Ciprofloxacin, erythromycin, and cimetidine sharply increase levels
- Seizures from theophylline toxicity are resistant to benzodiazepines - may require barbiturates
- Activated charcoal helps in overdose management
- Hypokalemia is a classic finding in toxicity
Interesting Fact
Theophylline is naturally found in tea leaves and is structurally related to caffeine and theobromine (in chocolate).
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Therapeutic Drug Monitoring
- American College of Clinical Pharmacy (ACCP) - Theophylline Recommendations
- Mayo Clinic Laboratories - Theophylline
- ARUP Consult - TDM for Bronchodilators
- NIH / MedlinePlus - Theophylline Toxicity