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Phenprocoumon – Effects, Dosage and Side Effects

Phenprocoumon is an oral anticoagulant (blood thinner) belonging to the vitamin K antagonist class. It is used to prevent and treat thrombosis and embolism.

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Things worth knowing about "Phenprocoumon"

Phenprocoumon is an oral anticoagulant (blood thinner) belonging to the vitamin K antagonist class. It is used to prevent and treat thrombosis and embolism.

What is Phenprocoumon?

Phenprocoumon is an oral anticoagulant that belongs to the class of vitamin K antagonists (VKA). It reduces the blood´s ability to clot and is widely prescribed in German-speaking countries under the brand names Marcumar and Falithrom. It is one of the longest-established and most thoroughly studied anticoagulant medications in Europe.

Mechanism of Action

Phenprocoumon works by inhibiting the synthesis of specific clotting factors in the liver. These factors – including Factor II (prothrombin), VII, IX, and X, as well as Proteins C and S – are essential for blood coagulation and depend on vitamin K for their activation.

Phenprocoumon blocks the enzyme vitamin K epoxide reductase, which is responsible for recycling vitamin K. This creates a functional vitamin K deficiency in the body, thereby selectively reducing the coagulation capacity of the blood.

Indications

Prevention and treatment of deep vein thrombosis (DVT)
Prevention and treatment of pulmonary embolism
Stroke prevention in patients with atrial fibrillation
Thromboembolism prevention in patients with artificial heart valves
Treatment of certain heart conditions associated with elevated clotting risk

Dosage and Monitoring

The dosage of phenprocoumon is highly individual and must be regularly adjusted. Therapy is monitored using the INR value (International Normalized Ratio), which standardizes the measurement of clotting time. Depending on the indication, a target INR range of 2.0 to 3.0 is typically aimed for (or 2.5 to 3.5 for mechanical heart valves).

Phenprocoumon has a long half-life of approximately 5 to 6 days, which leads to a delayed onset of action and a gradual offset after discontinuation. The usual maintenance dose ranges from 1.5 mg to 4.5 mg daily, though this varies considerably between patients.

Side Effects

The most significant side effect of phenprocoumon is an increased risk of bleeding. Possible bleeding complications include:

Nosebleeds or bleeding gums
Prolonged bleeding from wounds
Blood in urine or stool
Intracranial hemorrhage (rare but serious)
Internal bleeding

Other possible side effects include skin reactions, occasional elevation of liver enzyme levels, and – in very rare cases – coumarin necrosis (skin tissue death due to vascular occlusion at the start of therapy).

Interactions

Phenprocoumon has numerous interactions with other medications and foods:

Vitamin K-rich foods (e.g., spinach, broccoli, kale) can reduce its effect
Antibiotics can enhance its anticoagulant effect
Aspirin and other NSAIDs increase the risk of bleeding
St. John's Wort can reduce its effectiveness
Many other medications may influence the INR value

Contraindications

Phenprocoumon should not be used in the following situations:

Active bleeding or high risk of bleeding
Pregnancy (teratogenic – harmful to the developing fetus)
Severe liver or kidney disease
Known hypersensitivity to the active ingredient

References

Summary of Product Characteristics – Marcumar, Meda Pharma GmbH, current edition.
Schulman S. et al. – Anticoagulant Therapy for Venous Thromboembolism. New England Journal of Medicine, 2021.
European Society of Cardiology (ESC) – Guidelines on Atrial Fibrillation and Anticoagulation, 2023.

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