Bosentan Zentiva: Uses, Dosage & Side Effects

What Is Bosentan Zentiva and What Is It Used For?

Bosentan Zentiva is a generic formulation of bosentan, originally developed and marketed as Tracleer. It belongs to a class of medications known as endothelin receptor antagonists (ERAs), which represent one of the three major drug classes specifically developed for pulmonary arterial hypertension. The medication works by blocking the effects of endothelin-1 (ET-1), a peptide produced by endothelial cells that is the most potent vasoconstrictor identified in humans. In patients with PAH, circulating and lung tissue levels of ET-1 are markedly elevated, contributing to the progressive narrowing, stiffening, and remodeling of pulmonary arteries that characterizes the disease.

Pulmonary arterial hypertension is a serious and progressive condition in which the blood pressure in the pulmonary arteries — the vessels carrying blood from the right side of the heart to the lungs — is abnormally high. This increased pressure forces the right ventricle to work harder to pump blood through the lungs, eventually leading to right heart failure if left untreated. Symptoms of PAH include breathlessness (dyspnea), fatigue, dizziness, chest pain, and fainting (syncope), particularly during physical exertion. The World Health Organization (WHO) classifies PAH severity by functional class (I through IV), based on the degree to which symptoms limit physical activity.

Bosentan is a dual receptor antagonist, meaning it blocks both the endothelin A (ETA) and endothelin B (ETB) receptor subtypes. The ETA receptor is found predominantly on vascular smooth muscle cells and mediates vasoconstriction and cell proliferation. The ETB receptor is found on both endothelial cells (where it promotes vasodilation via nitric oxide and prostacyclin release) and smooth muscle cells (where it can mediate vasoconstriction). In PAH, the balance of ET-1 signaling is heavily shifted toward vasoconstriction and vascular remodeling. By blocking both receptor subtypes, bosentan achieves comprehensive antagonism of the deleterious effects of endothelin-1 in the pulmonary vasculature.

The clinical evidence supporting bosentan in PAH comes from several landmark randomized controlled trials. The pivotal BREATHE-1 trial (Bosentan Randomized trial of Endothelin Antagonist THErapy) demonstrated that bosentan significantly improved exercise capacity (as measured by 6-minute walk distance), WHO functional class, time to clinical worsening, and hemodynamic parameters compared with placebo in patients with PAH functional class III and IV. The EARLY trial further established the benefit of bosentan in patients with less severe (WHO functional class II) PAH, showing improvements in pulmonary vascular resistance and a delay in clinical worsening.

Bosentan Zentiva is approved for the following indications in most markets:

• Pulmonary arterial hypertension (PAH): Treatment of PAH to improve exercise capacity and symptoms in patients with WHO functional class II and III disease. PAH may be idiopathic (of unknown cause), heritable (genetic), associated with connective tissue diseases (such as systemic sclerosis or scleroderma), or related to congenital heart disease with Eisenmenger physiology.
• Digital ulcers in systemic sclerosis: In the European Union and some other markets, bosentan is also approved to reduce the number of new digital ulcers in patients with systemic sclerosis who have ongoing digital ulcer disease. The RAPIDS-2 trial demonstrated that bosentan significantly reduced the number of new digital ulcers compared with placebo, although it did not accelerate healing of existing ulcers.

What Should You Know Before Taking Bosentan Zentiva?

Before starting treatment with Bosentan Zentiva, your physician will conduct a thorough assessment of your medical history, current medications, and overall health status. There are several critical safety considerations that must be evaluated, and ongoing monitoring requirements that must be understood and agreed upon before the first dose. Understanding these precautions is essential for safe and effective use of this medication.

Contraindications

Bosentan Zentiva must not be taken in any of the following circumstances:

• Pregnancy: Bosentan is classified as a known teratogen (Pregnancy Category X in the US). Animal studies have demonstrated severe birth defects including craniofacial malformations, cardiovascular abnormalities, and skeletal defects. There is no safe dose of bosentan during pregnancy. A negative pregnancy test must be confirmed before starting treatment.
• Hypersensitivity: Known allergy to bosentan or any of the excipients in the tablet formulation.
• Severe hepatic impairment: Patients with moderate-to-severe liver disease (Child-Pugh class B or C) or with baseline liver aminotransferases (ALT/AST) greater than 3 times the upper limit of normal (ULN) must not take bosentan.
• Concomitant use with cyclosporine A: Co-administration is contraindicated because cyclosporine dramatically increases bosentan plasma levels (up to 30-fold) and bosentan reduces cyclosporine levels by approximately 50%, creating an unacceptable safety risk.
• Concomitant use with glyburide (glibenclamide): Co-administration increases the risk of elevated liver enzymes and is contraindicated. Additionally, the glucose-lowering effect of glyburide may be reduced.

Warnings and Precautions

Several important warnings apply to patients taking bosentan. The most clinically significant concern is hepatotoxicity. Bosentan is associated with dose-dependent elevations in liver aminotransferases (ALT and AST). In clinical trials, approximately 11% of patients receiving bosentan 125 mg twice daily experienced aminotransferase elevations greater than 3 times the upper limit of normal. These elevations are typically asymptomatic and reversible with dose reduction or discontinuation, but cases of liver failure, including cases requiring transplantation, have been reported in the post-marketing setting, though the causal relationship has not been definitively established.

The mandatory liver monitoring schedule requires measurement of ALT and AST levels before starting treatment and then at monthly intervals throughout therapy. If aminotransferases rise above 3 times the ULN, the dose should be reduced or the medication stopped, with intensified monitoring. Patients should be alert for signs and symptoms of liver injury, including unexplained nausea, vomiting, fever, abdominal pain, jaundice, unusual fatigue, or dark urine, and should report these to their physician immediately.

Bosentan can cause a dose-related decrease in hemoglobin concentration and hematocrit. In clinical trials, decreases in hemoglobin to below 10 g/dL were observed in approximately 3-6% of bosentan-treated patients compared with 1-3% of placebo-treated patients. The mechanism is thought to involve hemodilution rather than bone marrow suppression. Hemoglobin levels should be checked at baseline, at 1 and 3 months after starting treatment, and quarterly thereafter. Clinically significant anemia may require a reduction in dose or discontinuation of treatment.

Fluid retention and edema, particularly in the lower extremities, are common with bosentan. In patients with pre-existing heart failure, fluid retention can lead to clinical decompensation and requires careful monitoring. Patients should be advised to weigh themselves regularly and to contact their physician if they experience rapid weight gain or increased swelling.

Pregnancy and Breastfeeding

Bosentan is absolutely contraindicated in pregnancy. It is a known human teratogen based on animal data showing severe birth defects at clinically relevant doses. Women of childbearing potential must meet the following requirements before and during treatment:

• A negative pregnancy test must be obtained within the first 11 days of starting treatment.
• Monthly pregnancy tests are mandatory throughout the duration of treatment and for one month after stopping bosentan.
• Reliable contraception must be used at all times. Because bosentan induces CYP3A4 and CYP2C9 enzymes, it reduces the effectiveness of hormonal contraceptives (oral pills, implants, injections, patches, and hormonal intrauterine devices). Therefore, hormonal contraception alone is not considered reliable. Women should use a non-hormonal method (such as a copper intrauterine device) or a combination of a hormonal method with a barrier method (such as a condom).

It is not known whether bosentan is excreted in human breast milk. Animal studies have shown excretion in milk. Breastfeeding is not recommended during treatment with bosentan due to the potential for serious adverse effects in the nursing infant.

Male fertility may also be affected. Bosentan has been shown to impair spermatogenesis in animal studies, and decreased sperm counts have been observed in some male patients receiving endothelin receptor antagonists. Men considering fatherhood should discuss this with their specialist before starting treatment.

How Does Bosentan Zentiva Interact with Other Drugs?

Bosentan is extensively metabolized in the liver by the cytochrome P450 enzymes CYP2C9 and CYP3A4. Importantly, bosentan also acts as an inducer of these same enzymes, meaning that it increases the activity of CYP2C9 and CYP3A4 over time. This dual role as both a substrate and inducer creates a complex interaction profile that requires careful attention when prescribing or reviewing a patient’s medication regimen. At steady state (typically reached after 3-5 days of dosing), bosentan’s enzyme-inducing effects are fully established and can significantly alter the plasma levels of co-administered drugs.

Additionally, bosentan inhibits the bile salt export pump (BSEP) in hepatocytes, which is believed to contribute to its hepatotoxic potential. Drugs that also inhibit BSEP or are hepatotoxic themselves may compound this risk when given together with bosentan.

Major Interactions (Contraindicated)

Significant Interactions (Caution Required)

What Is the Correct Dosage of Bosentan Zentiva?

Bosentan Zentiva dosing follows a mandatory titration schedule designed to minimize the risk of hepatotoxicity and allow the body to adapt to the medication. The starting dose is lower than the target maintenance dose, and dose escalation should only proceed if the lower dose is well tolerated and liver function remains satisfactory. Your specialist will guide this process and may adjust the schedule based on your individual clinical response and laboratory results.

Adults

Children

Bosentan has been studied in pediatric patients with PAH. In the European Union, bosentan is approved for use in children aged 1 year and older with pulmonary arterial hypertension. Dosing in children is based on body weight. A dispersible tablet formulation (32 mg) is available specifically for pediatric use, allowing weight-based dosing. The target dose in children is typically 2 mg/kg twice daily, following the same 4-week initiation period at a lower dose. The prescribing specialist will determine the appropriate dose based on the child’s weight and clinical condition.

For children weighing 10-20 kg, the initiation and maintenance doses are typically 31.25 mg twice daily. For children weighing 20-40 kg, the doses are 31.25 mg twice daily during initiation and 62.5 mg twice daily for maintenance. For children over 40 kg, adult dosing applies. Regular weight-based dose review and liver function monitoring are essential in the pediatric population.

Elderly

No specific dose adjustment is required for elderly patients based on age alone. However, elderly patients may have decreased hepatic function, reduced renal clearance, or be taking multiple medications that could interact with bosentan. These factors should be carefully considered, and liver function monitoring should be particularly diligent. The initiation and titration schedule remains the same as for younger adults.

Missed Dose

If you miss a dose of Bosentan Zentiva, take it as soon as you remember. However, if it is nearly time for your next scheduled dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a forgotten tablet. Consistency in dosing is important for maintaining stable blood levels and optimal therapeutic effect. If you frequently forget doses, discuss strategies with your specialist or pharmacist.

Overdose

There is limited clinical experience with bosentan overdose. In healthy volunteers who received single doses up to 2,400 mg, the most prominent symptoms were headache, nausea, and vomiting. A marked decrease in blood pressure with dizziness and potential loss of consciousness may occur with significant overdose. In the event of an overdose, standard supportive measures should be instituted. Due to its high protein binding, bosentan is unlikely to be removed by dialysis. If overdose is suspected, contact your local poison control center or seek emergency medical attention immediately.

What Are the Side Effects of Bosentan Zentiva?

Like all medications, Bosentan Zentiva can cause side effects, although not everyone experiences them. The side effects described below are based on data from clinical trials and post-marketing surveillance. The frequency categories follow European Medicines Agency conventions. The most common and clinically significant adverse effect is hepatotoxicity, manifesting as elevated liver aminotransferases, which necessitates the mandatory monthly liver function monitoring described earlier.

Many side effects of bosentan are related to its vasodilatory mechanism of action (such as headache, flushing, and hypotension) or to its effects on fluid balance (edema, fluid retention, and decreased hemoglobin). Most adverse effects are dose-related and may improve with dose adjustment. It is important to report any new or worsening symptoms to your specialist, as some side effects require medical evaluation or treatment modification.

The liver enzyme elevations associated with bosentan deserve particular attention. In clinical trials, aminotransferase elevations greater than 3 times ULN occurred in approximately 11% of patients receiving the 125 mg twice daily dose compared with approximately 2% of patients on placebo. These elevations were generally asymptomatic and detected on routine monthly blood tests. The mechanism is thought to involve inhibition of the bile salt export pump (BSEP) and potentially direct hepatocellular injury. When aminotransferases are elevated, the following guidelines apply:

If you experience any of the following symptoms while taking Bosentan Zentiva, contact your specialist immediately: unexplained nausea or vomiting, fever, abdominal pain, yellowing of the skin or eyes (jaundice), unusual fatigue, dark-colored urine, or flu-like symptoms. These may indicate liver problems that require urgent medical evaluation.

How Should You Store Bosentan Zentiva?

Proper storage of Bosentan Zentiva is important to ensure the medication remains effective and safe throughout its shelf life. Film-coated tablets should be stored at a temperature not exceeding 30°C (86°F). The medication should be kept in its original packaging, as the blister or container provides protection from moisture and light. Do not transfer the tablets to a different container unless specifically designed for medication storage.

Keep Bosentan Zentiva out of the sight and reach of children. Because bosentan is teratogenic, extra care should be taken to prevent accidental exposure, particularly in households where women of childbearing age may be present. Unused or expired medication should not be disposed of in household waste or flushed down the toilet. Return any unused tablets to your pharmacist for safe disposal in accordance with local regulations.

Check the expiry date on the outer packaging before taking each dose. Do not use the medication after the expiry date, which refers to the last day of the month indicated. If the tablets appear discolored, damaged, or show signs of deterioration, do not take them and consult your pharmacist.

What Does Bosentan Zentiva Contain?

The active substance in Bosentan Zentiva is bosentan, present as bosentan monohydrate. Each film-coated tablet contains 62.5 mg of bosentan. Bosentan monohydrate is a white to slightly yellowish crystalline powder with the molecular formula C₂₇H₂₉N₅O₆S·H₂O. It is a synthetic compound classified as a sulfonamide derivative that acts as a competitive antagonist at both ETA and ETB receptors.

The excipients (inactive ingredients) typically found in bosentan film-coated tablets include:

• Tablet core: Maize starch, pregelatinized starch, sodium starch glycolate, povidone, glycerol dibehenate, magnesium stearate
• Film coating: Hypromellose, glycerol triacetate (triacetin), talc, titanium dioxide (E171), iron oxide yellow (E172), iron oxide red (E172), ethylcellulose

The 62.5 mg tablets are typically round, biconvex, orange-white film-coated tablets. The exact appearance may vary depending on the specific generic manufacturer and market. Patients with known hypersensitivity to any of the listed excipients should discuss alternative formulations with their specialist. Note that some bosentan formulations contain a small amount of lactose; patients with rare hereditary galactose intolerance, Lapp lactase deficiency, or glucose-galactose malabsorption should check the specific product information with their pharmacist.