Last reviewed 2026-04-23 · How we verify

SPD503 (4 mg)

SPD503 is a selective phosphodiesterase 4 (PDE4) inhibitor that reduces inflammatory mediator production by increasing intracellular cAMP levels.

SPD503 is a selective phosphodiesterase 4 (PDE4) inhibitor that reduces inflammatory mediator production by increasing intracellular cAMP levels. Used for Chronic obstructive pulmonary disease (COPD), Asthma.

At a glance

Mechanism of action

PDE4 inhibition leads to accumulation of cyclic adenosine monophosphate (cAMP) in immune and inflammatory cells, suppressing the release of pro-inflammatory cytokines and chemokines. This mechanism reduces airway inflammation and mucus production, making it suitable for respiratory inflammatory conditions. The selective PDE4 inhibition aims to provide anti-inflammatory benefits while minimizing systemic side effects associated with non-selective phosphodiesterase inhibition.

Approved indications

• Chronic obstructive pulmonary disease (COPD)
• Asthma

Common side effects

• Nausea
• Diarrhea
• Headache
• Tremor
• Gastrointestinal disturbances

Key clinical trials

• A Study of TAK-503 in Children and Teenagers With Attention Deficit Hyperactivity Disorder (ADHD) (PHASE4)
• Access to Extended Release Guanfacine HCl for Subjects Who Participated in Studies SPD503-315 or SPD503-316 in Europe (PHASE3)
• A Drug Interaction Study of SPD503 and Concerta Administered Alone and In Combination in Normal Healthy Volunteers (PHASE1)
• SPD503 (Guanfacine Hydrochloride) in ADHD Plus Oppositional Symptoms (PHASE3)
• Safety and Efficacy of SPD503 in Treating Attention-Deficit/Hyperactivity Disorder (ADHD) in Children Aged 6-17 (PHASE3)
• Safety and Efficacy of SPD503 in Treating ADHD in Children and Adolescents Aged 6-17 (PHASE3)

Primary sources

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