What prostacyclin (PGI2) analogues are used for primary pulmonary arterial hypertension and how should they be initiated and titrated?

Prostacyclin Analogues in Primary Pulmonary Arterial Hypertension

Initial Treatment Selection by WHO Functional Class

For WHO FC II-III patients without high-risk features, start with oral combination therapy (ambrisentan + tadalafil) and reserve parenteral prostanoids for disease progression or high-risk patients. 1, 2

WHO Functional Class II-III (Lower Risk)

• Oral combination therapy with ambrisentan 10 mg daily + tadalafil 40 mg daily is the preferred first-line regimen, avoiding parenteral prostanoids in this population 1, 2
• Start ambrisentan at 5 mg daily; uptitrate to 10 mg after 4 weeks if tolerated 2
• Initiate tadalafil at the full 40 mg once-daily dose from the start 2
• Parenteral prostanoids should not be used as initial therapy in WHO FC II patients due to higher cost, administration complexity, and lack of supporting evidence 2

WHO Functional Class III with Rapid Progression or Poor Prognosis

Initiate parenteral prostanoid therapy without delay in these patients. 1

Intravenous epoprostenol is the gold standard and only prostanoid with proven mortality benefit in randomized trials. 1, 3, 4

Epoprostenol Initiation Protocol:

• Starting dose: 2 ng/kg/min via continuous IV infusion through a central venous catheter 1
• Titration schedule: Increase by 1-2 ng/kg/min every 15-30 minutes during initial titration until side effects develop (nausea, diarrhea, jaw pain, bone pain, headache) 1
• Target maintenance dose in children: 40-150 ng/kg/min (average ~80 ng/kg/min); pediatric patients typically require higher doses than adults 1
• Requires continuous refrigeration with ice packs; half-life is 2-5 minutes, creating risk of rebound pulmonary hypertensive crisis if interrupted 1
• Over time, uptitrate as needed to maintain effect, but avoid excessive doses that create high-output state requiring downtitration 1

Alternative Parenteral Prostanoids:

• Continuous IV treprostinil: Starting dose 1.25 ng/kg/min (or 0.625 ng/kg/min if not tolerated), increase by 1.25 ng/kg/min per week for first 4 weeks, then 2.5 ng/kg/min per week thereafter 1, 5
• Continuous subcutaneous treprostinil: Same dosing as IV; avoids central line infection risk but causes intractable infusion site pain in many patients 1, 6, 7
• Transition from epoprostenol to treprostinil: Start treprostinil at 10% of current epoprostenol dose, then follow structured 7-step protocol reducing epoprostenol while increasing treprostinil 5

WHO Functional Class IV

Initiate monotherapy with continuous IV epoprostenol immediately. 1, 3

• Epoprostenol is the treatment of choice for WHO FC IV patients with proven improvements in functional class, 6-minute walk distance, and hemodynamics 1
• In the only randomized trial, zero deaths occurred in the epoprostenol group versus 8 deaths in conventional therapy (p=0.003) 3
• Long-term observational data show survival rates of 85%, 70%, 63%, and 55% at 1,2,3, and 5 years respectively 3
• For patients unable or unwilling to manage parenteral therapy, consider inhaled prostanoid (iloprost or treprostinil) combined with an endothelin receptor antagonist 1

Adding Inhaled Prostanoids to Existing Oral Therapy

For WHO FC III patients with disease progression despite one or two oral agents, add inhaled prostanoid therapy. 1

Inhaled Treprostinil:

• Initial dose: 3 inhalations (18 mcg) every 6 hours 1
• Titration: Increase up to 9 inhalations (54 mcg) every 6 hours for optimal effect 1
• Improves 6-minute walk distance when added to stable endothelin receptor antagonist or PDE5 inhibitor 1

Inhaled Iloprost:

• Improves WHO functional class and delays time to clinical worsening 1
• Requires 6-9 administrations daily, which limits adherence 6, 7

Critical Safety Considerations

Bloodstream Infection Risk with IV Epoprostenol:

• Chronic IV infusion via external pump carries approximately 1 bloodstream infection per 3-5 years of use 5
• Use high pH glycine diluent rather than neutral diluents (sterile water, 0.9% saline) to reduce infection risk 5
• Implantable pump systems have lower infection rates (2 infections in 265 patient-years) 5

Abrupt Withdrawal:

• Never abruptly discontinue or make sudden large dose reductions—this causes rebound worsening of PAH symptoms and potential crisis 5
• The 2-5 minute half-life of epoprostenol means any interruption creates immediate risk 1
• Patients must have immediate access to backup infusion pump and supplies 5

Hypotension:

• All prostanoids cause systemic vasodilation; monitor blood pressure closely, especially in patients with baseline low systemic arterial pressure 5

Hepatic/Renal Impairment:

• Titrate slowly in patients with hepatic or renal insufficiency due to higher systemic drug exposure 5

Common Pitfalls to Avoid

• Do not use parenteral prostanoids as first-line therapy in WHO FC II patients—oral combination therapy is appropriate and effective 2
• Do not delay parenteral prostanoid initiation in WHO FC III patients with rapid progression or WHO FC IV patients—mortality benefit is time-sensitive 1, 3
• Do not use peripheral IV access for more than a few hours with treprostinil—this increases thrombophlebitis risk; place central line promptly 5
• Do not transition patients from epoprostenol to other prostanoids outside the hospital—requires constant observation of walk distance and symptoms 5
• Do not start bosentan simultaneously with IV epoprostenol—unknown mechanism of concern per guidelines 8