Theophylline interacts with several different types of medications. Therefore, it is important that patients inform their physician and pharmacist about any medications they are taking, including prescriptions, over-the-counter medications, vitamins, supplements and herbal remedies. Patients are encouraged to ask about other drugs that should be avoided when taking theophylline. 

Patients may also benefit from avoiding foods and beverages containing caffeine (e.g., coffee, tea, cocoa, cola, chocolate). Caffeine is known to increase minor side effects associated with theophylline because they are chemically related (especially nervousness, shakiness and headache). Individuals who increase or decrease their caffeine intake while taking theophylline should alert their physician because their medication dosage may need to be adjusted.

Patients who take theophylline must be regularly monitored to ensure the safety of medication levels in the bloodstream. There is a very small difference between a proper dose of the medication and a dangerous, toxic dose. Many drugs and other factors may alter the rate at which theophylline is cleared from the body.

Medications known to increase the levels of theophylline in the bloodstream (thereby potentially triggering a medical emergency) include:

• Cimetidine (used to treat gastrointestinal ulcers)
  
  
• Some antibiotics, including:
• • Ciprofloxacin
  • Clarithromycin
  • Enoxacin
  • Erythromycin
  • Lomefloxacin
  • Norfloxacin
  • Ofloxacin
    
    
• Disulfiram (used to treat chronic alcoholism)
  
  
• Estrogens (used in birth control or hormone replacement medications)
  
  
• Methotrexate (used to treat some cancers and rheumatoid arthritis)
  
  
• Some antiarrhythmics (used to treat abnormal heart rhythms), including:
• • Mexiletine
  • Propafenone
    
    
• Some cox-2 inhibitors (used to treat arthritis)
  
  
• Some antihypertensives (used to treat high blood pressure), including:
• • Propranolol
  • Verapamil
    
    
• Tacrine (used to treat Alzheimer’s disease)
  
  
• Ticlopidine (used to prevent blood clots)

In addition, ingredients contained in certain over-the-counter and prescription cold, allergy and asthma medications may increase the risk for side effects when combined with theophylline. These include:

• Ephedrine
• Epinephrine
• Phenylephrine
• Phenylpropanolamine
• Pseudoephedrine

Other factors known to increase the rate that theophylline is removed from the body (and thus require higher doses of the drug for optimum treatment) include:

• Young age (less than 16)
• Alcohol use
• Smoking (tobacco or marijuana)
• High-protein, low-carbohydrate diets
• Barbecued meat (chemical compounds in grilled meat affect the way the liver processes the medication)

Medications known to decrease the levels of theophylline in the bloodstream (thereby decreasing its effectiveness) include:

• Aminoglutethimide (used to treat tumors and other adrenal disorders)
  
  
• Some anticonvulsants (used to treat seizures and epilepsy), including:
• • Carbamazepine
  • Phenytoin
  • Phenobarbital (also a sedative used to treat anxiety)
  • Isoproterenol (used in the treatment of asthma and other lung diseases)
    
    
• Moricizine (used to treat abnormal heart rhythms)
  
  
• Rifampin (an antibiotic used to treat tuberculosis)
  
  
• Sucralfate (used to treat and prevent ulcers)
  
  
• Allopurinol (used to treat gout)
  
  
• Serotonin uptake inhibitors (SSRIs – used to treat depression and obsessive compulsive disorders), including fluvoxamine
  
  
• Some leukotriene modifiers (used to treat asthma and some allergies), including zileuton

Other factors known to decrease the rate that theophylline is removed from the body and increase the chance of side effects include:

• Advanced age
  
  
• Certain medical conditions, including heart failure, liver disease, pneumonia or viral infection and vaccination
  
  
• High-carbohydrate diets

In addition, taking theophylline in combination with lithium (a drug used to treat bipolar disorder) may decrease the amount of lithium in the bloodstream by increasing the amount of lithium lost through urine output. Increased doses of lithium may be needed when these drugs are used together.