Noxap (Nitric Oxide)

Noxap is used in the management of conditions that involve elevated pulmonary vascular resistance and impaired gas exchange.

• Pulmonary hypertension: reduces pulmonary arterial pressure and improves exercise capacity.
• Acute respiratory distress syndrome (ARDS): enhances oxygenation by dilating pulmonary vessels.
• Neonatal persistent pulmonary hypertension of the newborn (PPHN): lowers pulmonary artery pressure to support transition to extra‑uterine life.
• Peri‑operative pulmonary vasodilation: stabilises haemodynamics during cardiac surgery.
• Right‑heart failure secondary to pulmonary hypertension: alleviates right‑ventricular afterload.
• Chronic obstructive pulmonary disease (COPD) exacerbations: improves ventilation‑perfusion matching.

• Nitric oxide diffuses across cell membranes and activates soluble guanylate cyclase in vascular smooth‑muscle cells, increasing cyclic GMP levels. Elevated cGMP leads to relaxation of pulmonary arterial smooth muscle, producing selective vasodilation of the pulmonary circulation without systemic hypotension. This mechanism improves blood flow to ventilated lung regions and enhances oxygen uptake.

Adverse reactions to inhaled nitric oxide are generally related to its vasodilatory activity and the delivery system.

Common Side Effects

• Methemoglobinemia: dose‑dependent increase in methemoglobin levels.
• Nitrogen dioxide (NO2) formation: irritant gas produced when NO reacts with oxygen.
• Rebound pulmonary hypertension: rise in pulmonary pressure after abrupt discontinuation.
• Hypotension: systemic blood pressure reduction if high doses are used.
• Headache: mild, transient headache associated with vasodilation.
• Cough or throat irritation: local airway discomfort during inhalation.

Serious or Rare Side Effects

• Severe methemoglobinemia: symptomatic levels requiring treatment.
• Persistent rebound pulmonary hypertension: may need rescue therapy.
• Acute kidney injury: reported in rare cases with prolonged high‑dose exposure.
• Hemolysis: especially in patients with glucose‑6‑phosphate dehydrogenase deficiency.
• Pulmonary edema: rare accumulation of fluid in the lungs.
• Allergic reaction: anaphylaxis or severe hypersensitivity to the delivery system.

When using inhaled nitric oxide, clinicians should observe specific safety measures and patient monitoring.

• Dose titration: adjust to the lowest effective concentration to achieve target oxygenation.
• Methemoglobin monitoring: regularly check levels to keep them below 5 %.
• NO2 monitoring: ensure nitrogen dioxide concentrations remain below safe limits.
• Abrupt discontinuation: avoid sudden cessation to prevent rebound pulmonary hypertension.
• Contraindications: do not use in patients with known hypersensitivity to nitric oxide or its delivery components.
• Store at ambient temperature: keep the gas cylinders in a well‑ventilated, dry area, protected from direct sunlight and extreme temperatures.

Inhaled nitric oxide may interact with other agents that affect vascular tone or hemoglobin.

Major Interactions (Avoid)

• Phosphodiesterase‑5 inhibitors (e.g., sildenafil): additive pulmonary vasodilation may cause severe hypotension.
• Methylene blue: can reverse methemoglobinemia but may interfere with nitric oxide’s efficacy.

Moderate Interactions (Monitor Closely)

• Inhaled bronchodilators (e.g., albuterol): may enhance vasodilatory response, requiring blood pressure monitoring.
• Hemoglobin‑modifying agents (e.g., nitrites): increase risk of methemoglobinemia.
• General anesthetics (e.g., volatile agents): may potentiate systemic hypotension.
• Anticoagulants: monitor for bleeding if pulmonary pressures change rapidly.
• High‑flow oxygen therapy: can increase NO2 formation, necessitating careful gas monitoring.