How amiodarone works
Amiodarone is a so-called multichannel blocker that interacts with numerous ion channels important for the excitation of the heart and in this way influences the electrical stimulation of the heart muscle.
In order for the heart muscle to regularly pump blood through the body, its cells must be evenly excited. This excitation always recedes in between.
Different types of ion channels are involved in these processes. During excitation and de-excitation, certain charged particles (ions) flow through them into and out of the cells.
In cardiac arrhythmias, this regular alternation between excitation and de-excitation is disturbed. As a result, the heart muscle can no longer contract rhythmically – an irregular heart rate is the consequence.
If such irregularities occur more frequently, sufficient blood flow to the body is no longer guaranteed. Treatment with so-called antiarrhythmics (drugs against cardiac arrhythmias) may then be necessary.
Absorption, degradation and excretion
Amiodarone is absorbed into the blood from the intestine in varying amounts (25-80 percent). It is then broken down in the liver and excreted mainly in the stool.
Because the active ingredient accumulates in fatty tissue, it can take up to 100 days after stopping the drug for amiodarone to be completely eliminated from the body.
When is amiodarone used?
Amiodarone is used for various cardiac arrhythmias (such as atrial fibrillation) when other antiarrhythmic drugs have been ineffective or may not be used.
How Amiodarone is used
Amiodarone can be injected in acute cases, but treatment is usually in the form of tablets.
The dosage is 600 milligrams daily (= saturation dose) for the first eight to ten days. In some cases, up to 1200 milligrams per day may be necessary. Thereafter, the dose is gradually reduced to 200 milligrams (= maintenance dose).
As a rule, amiodarone is taken five days a week in the maintenance phase.
For the same reason, the effect only occurs after about two weeks. Particularly in older patients, this special active ingredient “distribution” in the body requires regular monitoring by the attending physician.
This control is carried out either by long-term electrocardiogram (LZ-EKG) or programmed ventricular stimulation (measurement of refractory period and conduction time). Determination of plasma concentration is inappropriate in the case of amiodarone.
What are the side effects of amiodarone?
Very often, that is, more than ten percent of those treated, amiodarone can cause side effects such as skin rashes and veil vision due to deposits on the cornea.
Frequently (in one to ten percent of patients), blackish-purple, reversible skin discoloration, thyroid disorders, tremors, sleep disturbances, slowed pulse rate (bradycardia), low blood pressure (hypotension), muscle weakness, and pulmonary changes with nonproductive cough and difficulty breathing occur.
What should be considered when taking amiodarone?
Contraindications
Amiodarone must not be taken in certain cases:
- Low pulse rate (less than 55 beats per minute, so-called “bradycardia”)
- Thyroid disease
- Certain congenital or acquired changes in the ECG (QT time prolongation).
- Potassium deficiency (hypokalemia)
- concomitant treatment with so-called MAO inhibitors, such as tranylcypromine, moclobemide, selegiline, and rasagiline (for depression and Parkinson’s disease)
- Simultaneous use of drugs that prolong the QT interval
- Iodine allergy
- pregnancy, unless clearly needed
- Breastfeeding
Drug Interactions
Amiodarone affects several degradation mechanisms important for other drugs. These include the enzymes CYP2C9, CYP2D6, and CYP3A3, as well as P-glycoprotein (P-gp).
Because amiodarone is excreted from the body very slowly, interactions with other drugs must be expected for up to six months after discontinuation of the active substance.
Amiodarone potentiates the effects and side effects of the following agents:
- Phenytoin (drug for epilepsy)
- Cholesterol-lowering drugs (statins)
- Midazolam (for anesthesia)
- Dihydroergotamine, ergotamine (for migraine)
The following substances potentiate the amiodarone effect:
- Digitalis (for cardiac dysfunction)
- Grapefruit juice
Concomitant use of the following drugs and amiodarone may cause a potentially life-threatening cardiac arrhythmia (“torsade de pointes tachycardia”):
- Certain agents against bacterial, parasitic, and fungal infections (such as erythromycin, cotrimoxazole, pentamidine, moxifloxacin)
- Agents against malaria (such as quinine, mefloquine, chloroquine)
Laxatives, diuretics, glucocorticoids (“cortisone”), or amphotericin B (antifungal agents) cause decreased blood potassium levels. Simultaneous use with amiodarone may also cause “torsade de pointes tachycardia” or other cardiac arrhythmias.
Because of the many possibilities for interactions, inform your doctor or pharmacist about your amiodarone therapy before you are prescribed a new medication or purchase over-the-counter.
Trafficability and operation of machines
Age restrictions
There is insufficient experience to date on the use of the active substance in children and adolescents. The dosage is based on the body surface area or body weight.
Pregnancy and lactation
Amiodarone should be taken by pregnant women only in urgent emergencies, as there are indications that the active substance may cause harm to the unborn child. However, very few data are available on its use during pregnancy.
In the event of a planned pregnancy, amiodarone should be discontinued six months in advance to ensure that no amiodarone residues remain in the body at the time of fertilization.
If use during breastfeeding is unavoidable or if amiodarone was taken during pregnancy, the newborn must not be breastfed because the active substance passes into breast milk.
Restrictions
While taking amiodarone, the skin is particularly sensitive to light (“photosensitization”). Therefore, extensive sunbathing should be avoided and adequate sun protection should be used.
How to obtain medication with amiodarone
How long has amiodarone been known?
Amiodarone was developed in 1961. In the meantime, other antiarrhythmic drugs or measures (e.g. implantable cardioverter defibrillator) have become available.
Amiodarone is therefore now only used as a second-choice agent for cardiac arrhythmias. However, due to its good efficacy in case of failure of other measures, it is still an important reserve drug.
