Bosentan contains bosentan, a dual endothelin receptor antagonist used in the management of pulmonary arterial hypertension. It works by blocking both endothelin-A and endothelin-B receptors, preventing the potent vasoconstriction and vascular remodelling driven by endothelin-1. Bosentan reduces pulmonary vascular resistance, improves exercise capacity, and slows disease progression in pulmonary arterial hypertension. Always use Bosentan exactly as directed by your doctor.

Bosentan contains bosentan, the first orally active dual endothelin receptor antagonist approved for clinical use in pulmonary arterial hypertension.

Endothelin-1 is a potent vasoconstrictor peptide produced primarily by vascular endothelial cells. In pulmonary arterial hypertension, endothelin-1 levels are markedly elevated and contribute to sustained pulmonary vasoconstriction, vascular smooth muscle proliferation, fibrosis, and progressive obliteration of the pulmonary vascular bed. These changes increase pulmonary vascular resistance, raise right ventricular afterload, and ultimately lead to right heart failure.

Bosentan competitively antagonises both endothelin receptor subtypes. ETA receptor blockade reduces vasoconstriction and smooth muscle proliferation. ETB receptor blockade reduces endothelin clearance and endothelial nitric oxide synthase stimulation, though the net clinical effect of dual blockade is vasodilation and reduced vascular remodelling.

Bosentan is metabolised hepatically by CYP2C9 and CYP3A4 enzymes and is a potent inducer of these pathways, making drug interactions clinically significant. It is available as oral tablets and dispersible tablets for paediatric use, and requires regular liver function monitoring due to hepatotoxicity risk.

The uses of Bosentan are as follows:

Pulmonary Arterial Hypertension (WHO Group I)

Bosentan is used to improve exercise capacity, reduce symptoms, and slow disease progression in WHO functional class II and III pulmonary arterial hypertension.

Systemic Sclerosis-Associated Pulmonary Arterial Hypertension

It is used in connective tissue disease-associated pulmonary arterial hypertension, a common and serious complication of systemic sclerosis.

Digital Ulcers in Systemic Sclerosis

Bosentan reduces the frequency of new digital ulcers in systemic sclerosis patients through its vasodilatory and anti-fibrotic effects.

Paediatric Pulmonary Arterial Hypertension

Dispersible tablet formulations are used in children with pulmonary arterial hypertension under specialist supervision.

Here are the benefits of Bosentan:

• Dual Endothelin Receptor Blockade: Simultaneous ETA and ETB antagonism provides more comprehensive inhibition of endothelin-driven vasoconstriction and vascular remodelling than selective receptor blockade.

• Improves Exercise Capacity: Clinical trials have demonstrated significant improvement in six-minute walk distance in pulmonary arterial hypertension patients.

• Slows Disease Progression: Bosentan delays clinical worsening and reduces the rate of hospitalisation in pulmonary arterial hypertension.

• Reduces Digital Ulcer Formation: Vasodilatory and anti-fibrotic effects reduce the frequency of new digital ulcers in systemic sclerosis.

• Oral Administration: Once or twice daily oral dosing offers a practical alternative to parenteral pulmonary arterial hypertension therapies.

Like all medicines, Bosentan may cause side effects in some individuals.

Common Side Effects

• Liver Enzyme Elevation: Dose-dependent increases in hepatic transaminases occur in a significant proportion of patients and require regular monitoring.

• Headache: Commonly reported, particularly during early treatment.

• Flushing: Vasodilatory effects may cause facial flushing and warmth.

• Peripheral Oedema: Ankle swelling is frequently reported and related to vasodilatory effects.

Uncommon Side Effects

• Anaemia: Bosentan reduces haemoglobin levels, likely through haemodilution and reduced erythropoiesis stimulation.

• Palpitations: Mild increase in heart rate may be noticed.

• Nasal Congestion: Vasodilatory effects in the nasal mucosa may cause congestion.

Serious Side Effects (Require Immediate Medical Attention)

• Significant Hepatotoxicity: Marked elevation of liver enzymes or symptoms of liver injury including jaundice require immediate discontinuation and medical review.

• Severe Anaemia: A significant fall in haemoglobin may require treatment interruption and haematological assessment.

• Severe Allergic Reaction: Swelling of the face, lips, or throat with difficulty breathing requires urgent medical care.

• Teratogenicity: Bosentan is highly teratogenic; pregnancy must be excluded before and during treatment.

Always consult your doctor if side effects persist or worsen.

To ensure safe use:

• Use exactly as prescribed by your doctor.

• Usually taken orally twice daily with or without food.

• Do not crush or split standard tablets unless specifically instructed.

• Do not discontinue without consulting your doctor as abrupt withdrawal may cause clinical deterioration.

• Attend all scheduled liver function and pregnancy test monitoring appointments.

Bosentan competitively and reversibly blocks both ETA and ETB endothelin receptors on vascular smooth muscle cells and endothelial cells.

In pulmonary arterial hypertension, endothelin-1 binds ETA receptors on pulmonary vascular smooth muscle, causing sustained vasoconstriction and proliferation. ETA blockade by bosentan prevents this, reducing pulmonary vascular tone and inhibiting smooth muscle cell proliferation and fibrosis.

ETB receptors on endothelial cells normally clear endothelin-1 from the circulation and stimulate nitric oxide and prostacyclin release. ETB blockade by bosentan reduces endothelin clearance but the dominant net effect of dual blockade is a reduction in pulmonary vascular resistance and right ventricular afterload, improving haemodynamics and exercise capacity.

Bosentan is hepatically metabolised by CYP2C9 and CYP3A4 and is a potent inducer of both enzymes, significantly reducing plasma levels of co-administered medicines metabolised by these pathways.

A few practical measures can help ensure safe and effective use of Bosentan:

• Never miss liver function monitoring: Monthly liver function tests are mandatory during bosentan therapy. Elevated transaminases may require dose reduction or treatment interruption.

• Use reliable contraception throughout treatment: Bosentan is highly teratogenic and requires dual contraception in women of childbearing potential, combined with monthly pregnancy testing.

• Do not stop treatment abruptly: Sudden discontinuation may cause rebound pulmonary vasoconstriction and clinical deterioration. Always taper under specialist supervision.

• Inform all treating doctors and pharmacists: Bosentan induces CYP2C9 and CYP3A4 and significantly reduces plasma levels of many co-administered medicines including contraceptives and anticoagulants.

• Monitor haemoglobin periodically: Bosentan reduces haemoglobin levels; regular blood counts are advisable during treatment.

Proper storage is important to maintain the stability and effectiveness of Bosentan:

• Store at room temperature: Keep away from heat, moisture, and direct sunlight.

• Keep in original packaging: Protects tablets from humidity and light.

• Keep out of reach of children: Store securely to prevent accidental ingestion.

• Check expiry before use: Do not use after the expiry date printed on the packaging.

Bosentan may generally be taken without strict dietary restrictions. However:

• Avoid excessive alcohol: Compounds hepatotoxicity risk and may worsen vasodilatory hypotension.

• Avoid grapefruit juice: May inhibit CYP3A4 metabolism and alter bosentan plasma levels unpredictably.

• No significant food effect on absorption: Tablets may be taken with or without food.

Bosentan may interact with the following medicines:

• Hormonal Contraceptives: Bosentan induces CYP3A4 and significantly reduces plasma levels of oestrogen and progestogen contraceptives, rendering them unreliable. Dual non-hormonal contraception is required.

• Cyclosporin A: Markedly increases bosentan plasma levels through CYP inhibition; concurrent use is contraindicated.

• Warfarin and Other Anticoagulants: CYP induction reduces anticoagulant levels; INR monitoring and dose adjustment are required.

• Sildenafil and Other PDE5 Inhibitors: Bosentan reduces plasma levels of sildenafil through CYP3A4 induction; dose adjustments may be required in combination therapy.

• Statins: Bosentan reduces statin plasma levels through CYP induction, potentially reducing lipid-lowering effectiveness.

• Glibenclamide: Concurrent use increases hepatotoxicity risk and is contraindicated.

Bosentan should be used carefully in the following conditions:

• Hepatic Impairment: Bosentan is contraindicated in moderate to severe liver disease due to hepatotoxicity risk and impaired metabolism.

• Anaemia: Pre-existing anaemia may be worsened by bosentan-induced haemoglobin reduction.

• Hypotension: Vasodilatory effects may compound pre-existing hypotension or haemodynamic instability.

• Pulmonary Veno-Occlusive Disease: Bosentan may cause pulmonary oedema in this condition and is generally avoided.

Usually initiated at a lower dose and titrated to the maintenance dose after four weeks as directed by your specialist. Dose is taken twice daily with or without food.

If a dose is missed, take it as soon as remembered. However, if it is close to the time of the next scheduled dose, skip the missed dose and resume the regular schedule. Do not double the dose to make up for a missed one.