Theophylline belongs to the class of medications called bronchodilators. It is used to treat respiratory conditions such as asthma, emphysema, and chronic bronchitis. It relaxes the muscles in the lungs, which opens the airways. This helps to relieve symptoms associated with breathing problems such as cough, wheezing, and shortness of breath.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are being given this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The dose of theophylline sustained release is determined based on individual needs and may vary depending on the specific product used. Your doctor will adjust your dose depending on your response to the medication and the levels of theophylline in your blood.

Theophylline sustained release tablets are taken every 12 hours. Try to take the medication at the same time each day. Tablets may be cut in half if a score line appears on the tablet, but do not crush, chew or dissolve the tablets when you are taking them. Theophylline sustained release tablets that are not swallowed whole release the medication too quickly and may cause serious side effects.

Do not use theophylline to relieve sudden breathing attacks. It would take too long to start working.

Many things can affect the dose of a medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose and remember within several hours, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature and keep it out of the reach of children.

Do not take this medication if you:

• are allergic to theophylline, any of the xanthines, or any ingredients of the medication
• have coronary artery disease (when, in the opinion of the doctor, it would be harmful to stimulate the heart)
• have peptic ulcers
• are taking ephedrine and are a child

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• diarrhea
• dizziness
• flushing
• headache
• heartburn
• irritability
• itching
• loss of appetite
• nausea
• rash
• restlessness
• stomach pain
• trembling
• trouble sleeping
• unusual tiredness or weakness
• upset stomach

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if the following side effects occur:

• irregular heartbeat
• rapid, pounding heartbeat
• vomiting

Stop taking the medication and seek immediate medical attention if any of the following occur:

• confusion or change in behaviour
• convulsions (seizures)
• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• signs of bleeding in the stomach (e.g., bloody, black, or tarry stools; spitting up of blood; vomiting blood or material that looks like coffee grounds)
• signs of having taken too much theophylline (e.g., hearing changes, vision changes, unusually fast breathing or heartbeat, headache, fever, flushing, extreme thirst, change in urination)
• nervousness or restlessness (continuing)
• trembling (continuing)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Cystic fibrosis: People with cystic fibrosis break theophylline down more quickly than people without cystic fibrosis. If you have cystic fibrosis, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Heart disease: For people with certain types of heart disease, such as congestive heart failure, theophylline may build up in the body and cause side effects. If you have heart disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Heart rhythm: This medication can cause an irregular heartbeat or make an irregular heartbeat worse. If you have a history of irregular heartbeat (arrhythmia), discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Kidney function: Kidney disease or reduced kidney function may cause this medication to build up in the body, causing side effects. If you have reduced kidney function or kidney disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Laboratory tests: There a small difference between the amount of theophylline in your body that makes it an effective medication and the amount that makes it toxic. Your doctor may ask you to have your blood tested to check your blood levels of theophylline. It is very important to keep these appointments, to make sure that you are not receiving too much medication.

Liver function: Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. Your doctor may want to test your liver function regularly with blood tests while you are taking this medication.

Medical conditions: Any of the following medical conditions can affect how theophylline is processed and used by your body (metabolized): fever or viral infections, low oxygen levels, high blood pressure, a known or suspected ulcer, acute pulmonary edema, pneumonia, severe fever, chronic obstructive pulmonary disease, impaired kidney function, or following a high-carbohydrate and low-protein diet. Some of these conditions may also be affected by theophylline. If you have any of these medical conditions, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Overdose: An overdose may lead to serious side effects such as racing heart rate, abnormal heart rate, and seizures. It is important to take the medication exactly as prescribed by your doctor. From time to time, your doctor may ask you to have your blood tested to check your blood levels of theophylline.

Seizures: Theophylline may cause an increase in the number or length of seizures for people who have a medical history that includes seizures. If you have a history of epilepsy or medical conditions that increase the risk of seizures, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Smoking: Tobacco smoking causes your body to process theophylline faster than if you were a non-smoker. If you are a smoker and quit smoking, inform your doctor, as your dose may need to be adjusted. Likewise, if you start smoking while you are taking theophylline, you should also let your doctor know.

Thyroid disease: People with an underactive thyroid gland are more likely to experience side effects of theophylline because the medication may build up in the body. People with an overactive thyroid gland may clear theophylline from the body too quickly for it to be very effective. In both cases, it is important to have blood tests done when your doctor orders them, to make sure you are getting the right amount of medication to treat your illness.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are breast-feeding and are taking theophylline, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: Children are very sensitive to theophylline, as the margin of safety above therapeutic doses is small. This medication is not recommended for children under 12 years of age, as proper dosages for this age group have not been established.

Seniors: Seniors may be more likely to experience side effects and high levels of theophylline in the blood due to the body's decreased ability to clear this medication.

There may be an interaction between theophylline sustained release and any of the following:

• acyclovir
• adalimumab
• alcohol
• allopurinol
• amiodarone
• amphetamines (e.g., dextroamphetamine, lisdexamfetamine)
• atomoxetine
• barbiturates (e.g., butalbital, pentobarbital, phenobarbital)
• benzodiazepines (e.g., diazepam, lorazepam)
• beta-adrenergic blockers (e.g., atenolol, propranolol, sotalol, timolol)
• birth control medications
• bronchodilators: fast-acting (e.g., salbutamol, terbutaline) and long-acting (e.g., formoterol, indacaterol, salmeterol)
• bupropion
• caffeine
• cannabis
• carbamazepine
• cimetidine
• decongestant cold medications (e.g., phenylephrine, pseudoephedrine)
• decongestant eye drops and nose sprays (e.g., naphazoline, oxymetazoline, xylometazoline)
• dexmethylphenidate
• deferasirox
• digoxin
• diltiazem
• dipivefrin
• disulfiram
• epinephrine
• estrogens (e.g., conjugated estrogen, estradiol, ethinyl estradiol)
• febuxostat
• fluconazole
• fluvoxamine
• glecaprevir and pibrenasvir
• influenza vaccine
• isoniazid
• leflunomide
• linezolid
• lithium
• macrolide antibiotics (e.g., clarithromycin, erythromycin)
• methimazole
• methotrexate
• methylphenidate
• mexiletine
• modafinil
• nabilone
• nondepolarizing muscle relaxants (e.g., pancuronium, atracurium)
• pentoxifylline
• phenytoin
• propafenone
• propylthiouracil
• quinine
• quinolone antibiotics (e.g., ciprofloxacin, ofloxacin, norfloxacin)
• riociguat
• ritonavir
• stiripentol
• teriflunomide
• thyroid hormones (e.g., levothyroxine, liothyronine, thyroid)
• ticlopidine
• valacyclovir
• vemurafenib
• verapamil
• zafirlukast

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.