Alprostadil
Synthetic prostaglandin E1 (PGE1) and one of the first FDA-approved treatments for erectile dysfunction. Works locally by directly relaxing smooth muscle in penile blood vessels to produce erection, independent of sexual arousal or desire. Also FDA-approved to maintain patent ductus arteriosus in neonates with congenital heart defects. Available as intracavernosal injection (Caverject) and urethral suppository (MUSE).
Typical Dosage
Intracavernosal (Caverject): 2.5-40 mcg per injection, dose titrated in physician's office. Urethral suppository (MUSE): 125-1000 mcg per application. Maximum 1 dose per 24 hours, 3 doses per week.
Administration
Intracavernosal injection or urethral suppository
Mechanism of Action
Alprostadil is synthetic prostaglandin E1 (PGE1), a 20-carbon oxygenated fatty acid derived from dihomo-gamma-linolenic acid (DGLA) through the cyclooxygenase pathway. It acts locally on penile vascular and trabecular smooth muscle through two prostaglandin E receptor subtypes: EP2 and EP4, both of which are Gs-coupled GPCRs that increase intracellular cAMP upon activation.
Elevated cAMP activates protein kinase A (PKA), which phosphorylates multiple targets in smooth muscle cells to produce relaxation. PKA phosphorylates myosin light chain kinase (MLCK), reducing its affinity for the calcium-calmodulin complex and decreasing its ability to phosphorylate myosin light chains — the final step in smooth muscle contraction. PKA also activates calcium-ATPase pumps and opens potassium channels, reducing intracellular calcium concentration. The net effect is relaxation of both the helicine arterioles (which supply blood to the corpora cavernosa) and the trabecular smooth muscle (which forms the spongy erectile tissue). As these relax, blood flows into the sinusoidal spaces of the corpora cavernosa, expanding the tissue against the tunica albuginea and compressing the subtunical veins — trapping blood and producing an erection.
The critical distinction of alprostadil's mechanism is its direct, local action independent of central sexual arousal pathways and independent of nitric oxide. PDE5 inhibitors (sildenafil, etc.) work by preventing cGMP breakdown downstream of nitric oxide release, which requires sexual arousal to generate the initial NO signal. Alprostadil generates its own second messenger (cAMP) at the injection site regardless of arousal state, which is why it produces erections reliably even in patients with neurogenic erectile dysfunction (spinal cord injury, radical prostatectomy) where the nerve-mediated NO pathway is damaged. The extremely rapid pulmonary metabolism (80% cleared in a single pass through the lungs) ensures that systemic effects are minimal when administered locally.
Regulatory Status
FDA approved. Caverject/Edex (injection), MUSE (urethral). Prescription required. Also available compounded in combination formulations (TriMix).
Risks & Safety
Common: penile pain (37% with injection, 30% with MUSE), prolonged erection, urethral burning (MUSE), minor urethral bleeding (MUSE). Serious: priapism — erection lasting more than 4 hours is a medical emergency requiring immediate treatment to prevent permanent tissue damage, penile fibrosis and Peyronie's disease with repeated injections. Rare: penile fracture, infection at injection site. Contraindicated in patients with sickle cell disease or coagulation disorders. FDA approved.
Research Papers
7Published: November 6, 2025
Abstract
This study aimed to investigate the regulation of chloride channels in proliferative vitreoretinopathy (PVR) both in vitro and in vivo using a rabbit model and to explore the underlying mechanism.
Published: January 29, 2026
Abstract
Chronic constipation reduces quality of life and imposes a significant economic burden. The introduction of novel agents in Japan has expanded treatment options. This study aimed to establish a cost-effective treatment strategy, considering clinical utility and patient satisfaction.
Published: October 20, 2025
Abstract
Chronic idiopathic constipation (CIC) is a common disorder associated with socioeconomic burden. The aim of this study was to quantify the socioeconomic burden of CIC, including non-traditional value elements, and to compare the cost-effectiveness of 3 treatments for CIC with unique mechanisms of action: elobixibat 10 mg, linaclotide 0.5 mg, and lubiprostone 48 μg.
Published: October 14, 2025
Abstract
Nephronophthisis (NPHP) is a recessive tubulointerstitial nephropathy and a leading genetic cause of kidney failure in children and young adults. The most common genetic cause is a homozygous deletion of NPHP1, which encodes nephrocystin-1, a protein essential for primary cilium structure and cell junctions. Using personalized medicine and deep phenotyping, we investigated a family with three siblings carrying a homozygous NPHP1 deletion. We compared kidney biopsy tissue and human urine-derived renal epithelial cells (hURECs) from these individuals. Bulk RNA-seq on patient hURECs revealed altered expression in EGFR signalling, extracellular components and adherens junctions, which is consistent with the known roles for nephrocystin-1. Treatment with alprostadil, a proposed NPHP therapy, increased ciliation but worsened ciliary elongation. By contrast, the EGFR kinase inhibitor AG556 rescued of ciliary length and morphology. Transcriptional profiling post-treatment showed AG556 reversed the disease signature more effectively that alprostadil. These findings suggest that EGFR inhibition might offer a more promising therapeutic strategy for NPHP1-associated renal ciliopathy, warranting further testing in in vivo models before clinical application.
Published: July 24, 2025
Abstract
Chronic constipation is one of the most common digestive diseases encountered in clinical practice. Constipation manifests as a variety of symptoms, such as infrequent bowel movements, hard stools, feeling of incomplete evacuation, straining at defecation, a sense of anorectal blockage during defecation, and use of digital maneuvers to assist defecation. During the diagnosis of chronic constipation, the Bristol Stool Form Scale, colonoscopy, and a digital rectal examination are useful for objective symptom evaluation and differential diagnosis of secondary constipation. Physiological tests for functional constipation have complementary roles. They are recommended for patients who have failed to respond to treatment with available laxatives and those who are strongly suspected of having a defecatory disorder. As new evidence on diagnosing and managing functional constipation emerged, the need to revise the previous guideline was suggested. Therefore, these evidence-based guidelines have proposed recommendations developed using a systematic review and meta-analysis of the treatment options available for functional constipation. The benefits and cautions of new pharmacological agents (such as lubiprostone and linaclotide) and conventional laxatives have been described through a meta-analysis. The guidelines consist of 34 recommendations, including 3 concerning the definition and epidemiology of functional constipation, 9 regarding diagnoses, and 22 regarding management. Clinicians (including primary physicians, general health professionals, medical students, residents, and other healthcare professionals) and patients can refer to these guidelines to make informed decisions regarding managing functional constipation.
Published: April 24, 2025
Abstract
Irritable bowel syndrome with predominant constipation (IBS-C) is a functional gastrointestinal disorder characterized by abdominal pain with chronic constipation and abdominal bloating, which could significantly impair the quality of life of patients and bring substantial socio-economic burdens. Pharmacology treatment is central to managing patients with IBS-C, aiming to alleviate symptoms and improve patient treatment outcomes. Guanylate cyclase-C agonists (linaclotide and plecanatide) enhance intestinal fluid secretion and motility, normalize bowel movements, and reduce abdominal pain. Na+/H+ exchanger inhibitors (e.g., tenapanor) decrease sodium absorption, increase fluid secretion, and alleviate visceral pain. Lubiprostone activates the chloride channels to facilitate bowel movements, while polyethylene glycol laxatives regulate osmotic pressure to improve stool consistency and ease defecation. Highly selective 5-HT4 agonists, such as prucalopride, accelerate gastrointestinal and colonic transit and improve stool frequency and consistency without increasing the cardiovascular risks raised in earlier agents such as tegaserod. Neuromodulators, including selective serotonin reuptake inhibitors and tricyclic antidepressants, help manage visceral hypersensitivity and chronic abdominal pain in selected patients. These pharmacology agents have shown efficacy and safety in clinical studies, but drug availability, adverse effects, and variable patient responses are still challenging. Effective strategies to manage IBS-C require a personalized approach, considering the patient's symptom profile, treatment goals, and safety concerns.
Published: May 27, 2025
Abstract
Irritable bowel syndrome with constipation (IBS-C) and chronic idiopathic constipation (CIC) are common functional intestinal disorders which impact all age groups, yet there is limited comparative evidence on the economic benefits of treatment of these conditions on the elderly. We assessed differences in healthcare resource utilization (HCRU) and total costs of care among Medicare-insured patients initiating linaclotide, lubiprostone, or plecanatide after 1 year.
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