Clinical Trial Finder

Inclusion Criteria:

• - ≥6 months to <18 years of age at screening.

• - Currently have a diagnosis of PAH that is either: - idiopathic, including hereditary.

• - related to connective tissue disease.

• - related to anorexigen use.

• - associated with surgical repair of at least 6-month duration of congenital systemic to pulmonary shunt (eg, atrial septal defect, ventricular septal defect, patent ductus arteriosus) - Have a history of a diagnosis of PAH established by a resting mean pulmonary artery pressure (mPAP) ≥25 millimeter of mercury (mm Hg), pulmonary artery wedge pressure ≤15 mm Hg, and a pulmonary vascular resistance (PVR) ≥3 Wood units via right heart catheterization (RHC).

In the event that a pulmonary artery wedge pressure cannot be obtained during RHC, participants with a left ventricular end diastolic pressure (LVEDP) <15 mm Hg, with normal left heart function, and absence of mitral stenosis on echocardiography can be eligible for enrollment.

• - Have a World Health Organization (WHO) functional class value of II or III at the time of screening.

• - All participants must be receiving an endothelin receptor antagonist (ERA) (such as bosentan or ambrisentan) and must be on a maintenance dose with no change in dose (other than weight-based adjustments) for at least 12 weeks prior to screening and have a screening aspartate transaminase (AST)/alanine transaminase (ALT) <3 times the upper limit of normal (ULN) - If on conventional PAH medication, including but not restricted to, anticoagulants, diuretics, digoxin, and oxygen therapy, the participant must be on stable doses with no changes (other than weight-based adjustments) for at least 4 weeks before screening.

• - Female participants of childbearing potential must test negative for pregnancy during screening.

Furthermore, female participants must agree to abstain from sexual activity or to use two different reliable methods of birth control as determined by the Investigator during the study. Examples of reliable birth control methods include true abstinence as a lifestyle choice (periodic sexual abstinence method is not acceptable); the use of oral contraceptives; a reliable barrier method of birth control (diaphragms with contraceptive jelly; cervical caps with contraceptive jelly; condoms with contraceptive foam; intrauterine devices)

• - Written informed consent from parents (and written assent from appropriately aged participants) will be obtained prior to any study procedure being performed.

Exclusion Criteria:

• - Have pulmonary hypertension related to conditions other than specified above, including but not limited to chronic thromboembolic disease, portal pulmonary hypertension, left-sided heart disease or lung disease and hypoxia.

• - History of left-sided heart disease, including any of the following: - clinically significant [pulmonary artery occlusion pressure (PAOP) 15-18 mm Hg] aortic or mitral valve disease (ie, aortic stenosis, aortic insufficiency, mitral stenosis, moderate or greater mitral regurgitation) - pericardial constriction.

• - restrictive or congestive cardiomyopathy.

• - left ventricular ejection fraction <40% by multigated radionucleotide angiogram (MUGA), angiography, or echocardiography.

• - left ventricular shortening fraction <22% by echocardiography.

• - life-threatening cardiac arrhythmias.

• - symptomatic coronary artery disease within 5 years of study entry.

• - Unrepaired congenital heart disease.

• - Have a history of angina pectoris or other condition that was treated with long- or short-acting nitrates within 12 weeks before administration of study drug.

• - Have severe hepatic impairment, Child-Pugh Grade C.

• - Have severe renal insufficiency, defined as receiving renal dialysis or having a measured or estimated creatinine clearance (CC) <30 millimeter per minute (mL/min) (Schwartz Formula) - Diagnosed with a retinal disorder (eg, hereditary retinal disorders, retinopathy of the preterm participant and other retinal disorders) - Have severe hypotension or uncontrolled hypertension as determined by the Investigator.

• - Have significant parenchymal lung disease.

• - Have bronchopulmonary dysplasia.

• - Concurrent phosphodiesterase type 5 (PDE5) inhibitor therapy (sildenafil or vardenafil) or has received PDE5 inhibitor therapy within 12 weeks prior to the first study drug dosing.

• - Concurrent therapy with prostacyclin or its analogues within 12 weeks of screening.

• - Commenced or discontinued a chronic conventional PAH medication including but not restricted to: diuretics, anti-coagulants, digoxin, and oxygen therapy within 4 weeks of screening.

• - Currently receiving treatment with doxazosin, nitrates, or cancer therapy.

• - Current treatment with potent Cytochrome P450 3A4 (CYP3A4) inhibitors, such as antiretroviral therapy (protease inhibitor), systemic ketoconazole, or systemic itraconazole, or chronic use of potent CYP3A4 inducers, such as rifampicin.

• - Are nursing or pregnant.

• - Have previously completed or withdrawn from this study (LVHV), or any other study investigating tadalafil.

• - Have received tadalafil therapy within 12 weeks prior to the first study drug dosing or are hypersensitive to tadalafil.

• - Have allergy to the excipients, notably lactose.

• - Are currently enrolled in, or discontinued within the last 30 days from, a clinical trial involving an investigational product or non-approved use of a drug or device, or concurrently enrolled in any other type of medical research judged not to be scientifically or medically compatible with this study by the Sponsor.

• - Unable to take orally administered tablets (without chewing, crushing or breaking) or suspension.

• - Are Investigator site personnel directly affiliated with this study or their immediate families.

Immediate family is defined as a spouse, parent, child or sibling, whether biological or legally adopted. - Diagnosis of Down syndrome

Arms

Experimental: Tadalafil

Period 1: 20 mg or 40 mg administered orally by tablets once a day. Period 2: 20 mg for middle weight and 40 mg for heavy weight administered orally by tablets once a day. Final tadalafil doses for Period 1 (6-month double-blind) were assigned after the weight cohort completion from H6D-MC-LVIG (NCT01484431).Tadalafil doses would range from 5 milligram (mg) to 40 mg depending on body weight cohorts. Heavy weight cohort ≥40 kilogram (kg), Middle weight cohort ≥25 kg to <40 kg: administered orally by tablets once a day. Light weight cohort <25 kg: administered orally by suspension once a day. Participants receiving tadalafil in Period 1 continued to receive tadalafil during Period 2 (2-year open-label extension).

Placebo Comparator: Placebo

Period 1: Participants received placebo orally by tablets once a day. Period 2: 20 mg for middle weight and 40 mg for heavy weight administered orally by tablets once a day. Final placebo dose for Period 1 (6-month double-blind) was be assigned after the weight cohort completion from H6D-MC-LVIG (NCT01484431) to maintain blinding depending on body weight cohort. Participants receiving placebo in Period 1 Period 2 (2-year open-label extension) would receive tadalafil in Period 2 at the corresponding tadalafil dose in that participant's weight group.

Interventions

Drug: - Tadalafil

Administered orally by tablet form for heavy and middle weight participants. Administered orally by suspension for light weight participants.

Drug: - Placebo

Administered orally by tablet for heavy and middle weight participants. Administered orally by suspension for light weight participants.

Drug: - ERA as specific PAH treatment

All participants were taking endothelin receptor antagonist (ERA) (such as bosentan, ambrisentan and macitentan).