Meds and you

27 September 2013

Isosorbide mononitrate

Isosorbide mononitrate is a nitrate vasodilator. Nitrate vasodilators are drugs that widen and relax blood vessels to reduce the workload on the heart.


Isosorbide mononitrate is the active ingredient Elantan tablets (Nappi code: 793418-001, 003), Elantan LA capsules (Nappi code: 860115-003), Imdur CR tablets (Nappi code: 821500-007), Ismo tablets (734055-005, 013), Monicor SR tablets (Nappi code: 710251-001).

General information
Isosorbide mononitrate is a nitrate vasodilator. Nitrate vasodilators are drugs that widen and relax blood vessels to reduce the workload on the heart, and thereby also improve the supply of oxygen- rich blood to the heart.

In South Africa isosorbide mononitrate is registered for the prevention of angina, a suffocating chest pain which results when partially clogged arteries restrict the flow of oxygen-rich blood to the heart.

Isosorbide mononitrate does not cure this condition, but merely keeps its symptoms under control. For this drug to be effective, it has to be taken regularly.

The first few doses of this drug may cause dizziness if you get up suddenly from sitting or lying down. It is advised to get up carefully until you know how this drug affects you.

Treatment should not be stopped abruptly, especially if you have been taking this drug for a prolonged period of time. To prevent the return of symptoms you should decrease your dose gradually only as directed by your doctor.

How does isosorbide mononitrate work?
Vasodilators relax smooth muscle within blood vessels via a direct effect it has on these arterial muscles. As a result it widens and relaxes blood vessels to reduce the workload on the heart, and to increase the supply of oxygen-rich blood to the heart. This leads to chest pain subsiding.

Fast facts

Drug schedule: schedule 3
Available as: isosorbide mononitrate is available as tablets, controlled release tablets and long- acting capsules.
What does it do? Isosorbide mononitrate widens blood vessels to reduce chest pain.
Overdose risk: low
Dependence risk: low
Is isosorbide mononitrate available as a generic? yes
Is isosorbide mononitrate available on prescription only? yes

User information

Onset of effect: within 30 minutes
Duration of action: 4 - 8 hours depending on formulation
Dietary advice: take tablets with water 1 hour prior to a meal, or 2 hours after a meal.
Stopping this medicine: do not stop using this medication abruptly as it may cause a recurrence of the original symptoms being treated. It is advised that you decrease your dose gradually as directed by your doctor.
Prolonged use: some patients may develop a tolerance to the effect of isosorbide mononitrate, which causes its effects to be reduced over time. Speak to your doctor if you suspect your treatment to be losing its efficacy.

Special precautions
Consult your doctor before using this drug if:

  • you have anaemia
  • you have glaucoma
  • you have history of a head injury
  • you have history of heart attack
  • you have low blood pressure
  • you have an underactive thyroid

Pregnancy: avoid. Potential risk to the foetus has been reported. Consult your doctor before use, or if you are planning to fall pregnant.
Breastfeeding: avoid. It is unknown how this medication may affect your baby. Consult your doctor before use.
Porphyria: avoid. This medication may cause serious adverse effects. Consult your doctor before use.
Infants and children: this medication is not intended for use in children.
The elderly: no special precautions need to be taken.
Driving and hazardous work: caution is advised as use of this medication may lead to dizziness, light-headedness and/or sedation. Avoid such activities until you know how this medication affects you.
Alcohol: avoid concomitant use of alcohol with this medication.

Possible side effects

Side Effect
Consult your doctor

Only if severe
In all cases








heart rhythm disturbances


skin rash


eye pain




Drug interactions

alcohol reduced blood pressure - risk of dizziness and fainting
medication for high blood pressure reduced blood pressure - risk of dizziness and fainting
heparin blood-clotting effect of heparin is reduced
sildenafil causes life-threatening lowering of blood pressure and should be avoided at all times when taking nitrates
sumatriptan possible vasospasm of coronary arteries which may worsen angina

Overdose action
A small overdose is no cause for concern. In case of intentional large overdose, seek emergency medical attention.

Recommended dosage
Adults, angina. Sublingual: 2.5 - 15mg daily in divided doses 2 - 3 hours apart; oral: 10 - 20 mg 6 - 8 hourly.

This material is not intended to substitute medical advice, but is for informational purposes only. Please consult a physician for specific treatment and recommendations.


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