Nitroglycerin belongs to the class of medications called antianginals. Nitroglycerin ointment is used to prevent angina attacks (chest pain). Nitroglycerin reduces the number of angina attacks by relaxing blood vessels and increasing the oxygen and blood supply to the heart. Nitroglycerin ointment is not intended for immediate relief of angina.

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 using 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 use this medication if their doctor has not prescribed it.

Nitroglycerin ointment may be applied every 3 to 8 hours if necessary, but one application at bedtime is often sufficient for the entire night. The usual dose is 2.5 cm to 5 cm as squeezed from the tube onto the applicator.

You may use the ointment on any convenient skin area – many people prefer to apply it to the chest. Place the applicator with the ointment side down onto the desired area. Spread the ointment over at least a 5 cm by 7.5 cm area in a thin, uniform layer. Do not rub the nitroglycerin into the skin. Cover the ointment with the supplied paper, plastic kitchen wrap, or other suitable material. This can be held in place with adhesive or transparent tape. Before applying your next dose of nitroglycerin, wipe off any remaining ointment from the area where the previous dose was applied.

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 applying the medication without consulting your doctor.

It is important to use this medication exactly as prescribed by your doctor. If you miss a dose, apply 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 apply 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.

Do not use nitroglycerin ointment if you:

• are allergic or sensitive to nitroglycerin or any of the ingredients of the medication
• are allergic or sensitive to any organic nitrates
• are taking a PDE-5 inhibitor for erectile dysfunction (e.g., sildenafil, tadalafil, vardenafil)
• are taking the medication riociguat
• have acute circulatory failure associated with severe lowering of blood pressure (states of collapse or shock)
• have extremely low blood pressure
• have increased eye pressure (glaucoma)
• have increased pressure within the head (e.g., after an accident)
• have reduced heart function due to obstruction (e.g., narrowing of the heart valves)
• have severe anemia

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.

• dizziness or lightheadedness, especially when getting up from a lying or sitting position
• fast heartbeat
• flushing of the face and neck
• headache
• nausea or vomiting
• restlessness
• sore, reddened skin

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

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

• blurred vision
• dryness of the mouth
• headache (severe or prolonged)
• increased blood pressure
• irregular heartbeat

Contact a doctor at once if any of the following signs of overdose occur:

• bluish-coloured lips, fingernails, or palms of the hands
• convulsions (seizures)
• dizziness (extreme) or fainting
• feeling of extreme pressure in head
• fever
• shortness of breath
• unusual tiredness or weakness
• weak and fast heartbeat

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

• signs of a heart attack (e.g., chest pain or pressure, pain extending through shoulder and arm, nausea and vomiting, sweating)
• signs of methemoglobinemia (e.g., shortness of breath, blue to purplish lips, fingers or toes, severe headache, fatigue, dizziness or loss of consciousness)
• symptoms of a serious allergic reaction (such as swelling of the face, lips, tongue, or throat; skin rash; hives; or difficulty breathing)

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.

Acute angina attacks: Nitroglycerin ointment is not intended for immediate relief of acute attacks of angina. Sublingual (under the tongue) nitroglycerin preparations (spray or tablets) should be used for this purpose.

Dizziness/reduced alertness: People using this medication may experience faintness or dizziness and reduced reaction time when driving or operating machinery, especially at the start of treatment. Avoid these and other hazardous tasks until you have determined how this medication affects you.

Heart attacks: Not enough information exists on the safety of using nitroglycerin ointment during the early phase of a heart attack. If you suspect you are having a heart attack, call 9-1-1.

Low blood pressure: Headaches or symptoms of low blood pressure such as weakness or dizziness, particularly when getting up suddenly from a sitting or lying down position, may result from taking too much nitroglycerin. If these symptoms occur, your doctor may reduce the dose or stop the use of nitroglycerin. People who might be negatively affected by low blood pressure should use nitroglycerin ointment with caution. People who take diuretics or have preexisting low blood pressure may be at more risk of being negatively affected.

PDE-5 inhibitors: PDE-5 inhibitors (e.g. sildenafil, tadalafil, vardenafil) should never be taken with nitroglycerin. Blood pressure may suddenly drop to life-threatening levels if these medications are combined. They may cause dizziness, fainting spells, heart attack, or stroke.

Tolerance: People taking nitroglycerin may develop tolerance to the medication, resulting in it not working as well. Tolerance to other nitrates or nitrites can also develop, especially if a medication-free period is not observed each day.

Withdrawal: Dependence may occur with chronic use. To avoid possible withdrawal effects, reduce nitroglycerin ointment use gradually over 4 to 6 weeks.

Pregnancy: This medication has not been studied for use by pregnant women. Be sure to tell your doctor if you are pregnant or planning to become pregnant.

Breast-feeding: It is not known if this medication passes into breast milk. Be sure to discuss with your doctor the risks and benefits of using this medication before breast-feeding.

Children: The safety and effectiveness of this medication for children have not been established.

There may be an interaction between nitroglycerin ointment and any of the following:

• alcohol
• aldesleukin
• alpha blockers (e.g., alfuzosin, doxazosin, tamsulosin)
• alpha agonists (e.g., clonidine, methyldopa)
• alteplase
• angiotensin converting enzyme inhibitors (ACEIs; captopril, enalapril, ramipril)
• angiotensin receptor blockers (ARBs; e.g., candasartan, irbesartan, losartan)
• barbiturates (e.g., butalbital, pentobarbital phenobarbital)
• beta-adrenergic blockers (e.g., atenolol, propranolol, sotalol)
• aripiprazole
• brimonidine
• bromocriptine
• cabergoline
• calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
• clonidine
• dipyridamole
• diuretics (water pills; e.g., furosemide, hydrochlorothiazide, triamterene)
• ergot derivatives (e.g., dihydroergotamine, ergotamine, ergonovine, methylergonovine)
• duloxetine
• guanfacine
• heparin
• hydralazine
• other nitrates (e.g., nitroglycerin, isosorbide dinitrate, isosorbide mononitrate)
• quetiapine
• reserpine
• riociguat
• risperidone
• rosiglitazone
• phosphodiesterase -5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
• riociguat

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.