Interactions

Other drugs such as heparin, which also acts to prevent blood clots, can enhance the effect of Marcumar. Consequently, the risk of bleeding is also increased. In addition also medicines, which lead to the decreased dismantling of Marcumar increase its effect.

That can be for example Statine, different antibiotics, like Amoxicillin or Anabolika. Other medicines bring the intensified dismantling of the Marcumars with itself and reduce thereby the coagulation inhibition. These are barbiturates, rifampicin, diuretics, metformin or substances that contain vitamin K. In order to be able to control the interaction with other drugs, frequent tests of blood clotting should be carried out.

But also Marcumar can have influence on other drugs. When taken at the same time, it increases the effect of sulfonylureas, a drug used to lower blood sugar levels in type 2 diabetes mellitus. As a result, there is a risk of hypoglycemia, i.e. low blood sugar.

Contraindications

Marcumar must not be taken if there is an allergy to the active ingredient phenprocoumon. Also with hypersensitivities against similar medicines of the same group, i.e. the so-called coumarin derivatives, the taking should be avoided. Furthermore, pregnancy is another contraindication for the use of Marcumar. Furthermore, no therapy with Marcumar should be undertaken if there is a disease in which the risk of bleeding is increased. This could be, for example, severe liver or kidney damage, stomach ulcers or inflammation in which the heart is affected.

Dosage

The active ingredient phenprocoumon, known under the drug name Marcumar®, is a “blood-thinning” drug in the vernacular and belongs to the group of coumarins (vitamin K antagonists). However, “blood-thinning” here does not mean that the blood is thinned, but that blood clotting is inhibited to reduce the risk of thrombus formation. A thrombus is a blood clot that can lead to a stroke or heart attack.

The treating physician draws up a plan for the dosage of Marcumar, which is individually adapted to each patient. At the beginning of each treatment, the patient’s so-called thromboplastin time must first be determined. This is measured in seconds, but is given as a percentage (quick value) or as an integer (INR value).

With its help, a statement can be made about the body’s own coagulation system. It must be measured and monitored at regular intervals throughout the course of treatment. The dosage of Marcumar® is adjusted according to the thromboplastin time.

Nowadays, if possible, it should be indicated as an INR value (INR = International Normalized Ratio). It is determined worldwide in a standardized procedure and is used to determine coagulation. A normalized INR value is 1.

The therapeutic range, depending on the disease, usually covers values of about 2 to 4.5. This is the range that offers the best possible protection against clots, but also represents the lowest risk of bleeding. The quick-value is also a laboratory parameter that allows a statement about the function and disorders of the coagulation system.Its normal range is between 70 and 120 %.

However, it may vary from laboratory to laboratory due to different reagents and has therefore been replaced by the standardized INR value mentioned above. In general, the lower the INR value, the shorter the blood clotting time. A shorter blood clotting time means that the risk of thrombosis increases.

On the other hand, a high INR value indicates a longer clotting time and thus a higher bleeding tendency. For example, an INR of 2 means a clotting time twice as long as normal. The Quick value behaves completely opposite to the INR.

This means that a high Quick value = short coagulation time, a low Quick value = long coagulation time. Anticoagulants, which include Marcumar® as explained above, increase the INR value and thus reduce the risk of thrombus formation. Since the liver stores larger quantities of vitamin K, the effect of Marcumar® does not start immediately, but takes a few days to fully develop.

For immediate effect, the patient must therefore be additionally treated with heparin in an overlapping manner until the respective target value/range is reached. Marcumar® is dosed very highly at the beginning of the treatment (approx. 2-4 tablets of 3mg each) in order to build up an effective level.

As a result, the INR value rises sharply in the first few days (even to values above 3). A high INR value normally indicates a reduced ability to clot. However, high INR values in the first days of medication only feign this.

One reason for this is the different degradation times of the individual coagulation factors. In the case of the so-called factor VII, the half-life is approx. 5-6 hours, in the more significant factor II it is 40-60 hours.

Looking at these hourly figures, it can be seen that in the first day there is almost only an increased turnover of factor VII. Therefore, it takes some time until one can rely on the INR values with regard to coagulation ability. It is also important to note that the values can still fluctuate greatly in the first period of taking Marcumar® , so regular checks are extremely important in order to reduce both the risk of bleeding and the risk of thrombus formation.

After the initially high doses, the daily dose is slowly reduced until the INR is within its therapeutic range for the respective disease. In the case of deep vein thrombosis or atrial fibrillation, the target range is between 2 and 3. In the case of a mechanical heart valve, the target range is then already somewhat higher, namely 3 to 4.5.

Thus, the physician must adjust the daily dose individually for each patient, taking into account the existing disease, while controlling the values. Initially, the coagulation values are determined daily, after a certain time and when the values do not fluctuate so much any more, only weekly and at some point only once a month. Every patient receives a so-called “Marcumar® passport”, which he should always carry with him. This contains the measured INR values and the corresponding dosage of his tablets as well as the existing illness that led to the therapy. If the value is now in the therapeutic range, the Marcumar® dosage is approximately 1 tablet (3mg) per day.