Plecanatide
SP-304, uroguanylin analogue
Plecanatide is a 16-amino-acid peptide taken by mouth that is a near-copy of the human hormone uroguanylin, differing by a single amino acid. Like linaclotide it activates guanylate cyclase-C receptors in the gut to increase fluid secretion and speed transit. It is FDA-approved for chronic idiopathic constipation and for irritable bowel syndrome with constipation, but has never been submitted for approval in Europe or the UK.
Mechanism
Plecanatide differs from human uroguanylin by one substitution (aspartate at position 3 is replaced by glutamate), which increases receptor binding affinity. The peptide is bicyclic, held in shape by two disulfide bonds (Cys4-Cys12 and Cys7-Cys15), and binds guanylate cyclase-C on the apical surface of intestinal epithelial cells. Activation raises intracellular cyclic GMP, which activates protein kinase G II, opens the CFTR chloride channel and inhibits the sodium-hydrogen exchanger NHE3. Chloride and bicarbonate move into the lumen, sodium and water follow, stool softens and transit accelerates. As with linaclotide, extracellular cGMP is thought to reduce firing of submucosal afferent nociceptors, which accounts for the abdominal pain endpoint in IBS-C.
The pharmacologically distinctive feature is pH dependence. Uroguanylin (and plecanatide, which mimics it) binds GC-C most avidly at slightly acidic pH, whereas guanylin and the bacterial heat-stable enterotoxins that linaclotide structurally resembles are more active at neutral to alkaline pH. Because the proximal small intestine is mildly acidic, this is proposed to concentrate plecanatide's action in the duodenum and proximal jejunum. This is a real biochemical difference, but whether it translates into a clinically meaningful tolerability advantage has never been tested in a head-to-head trial, and the claim should be treated as a plausible hypothesis rather than an established fact.
What the research shows
For chronic idiopathic constipation, Miner and colleagues randomised 1,394 patients to plecanatide 3 mg, 6 mg or placebo for 12 weeks. Mean weekly complete spontaneous bowel movements increased by 2.5 and 2.2 respectively versus 1.2 on placebo, and durable overall responder rates were 21.0 per cent (3 mg) and 19.5 per cent (6 mg) versus 10.2 per cent on placebo. A second phase 3 trial by DeMicco and colleagues in 1,337 patients replicated this. For IBS-C, Brenner and colleagues reported two identical phase 3 trials enrolling 2,189 patients randomised to placebo or plecanatide 3 or 6 mg for 12 weeks; both met the FDA composite responder endpoint combining a 30 per cent or greater reduction in worst abdominal pain with an increase of at least one complete spontaneous bowel movement per week for at least 6 of 12 weeks.
The honest reading is that plecanatide works, but the therapeutic gain over placebo is in the same modest range as linaclotide (roughly 10 percentage points on responder endpoints), and placebo response rates in these conditions are high. Notably, the 6 mg dose offered no consistent advantage over 3 mg in either indication, which is why 3 mg is the approved strength for both. Diarrhoea rates in the plecanatide trials appear numerically lower than those reported in the linaclotide programme, and this is widely cited as an advantage, but the trials were run years apart in different populations with different definitions; without a randomised head-to-head comparison the difference cannot be attributed to the drug.
Evidence assessment
High-quality evidence
Two large replicated phase 3 randomised controlled trials in chronic idiopathic constipation (n=1,394 and n=1,337) and two in irritable bowel syndrome with constipation (combined n=2,189), all meeting their primary endpoints, plus regulator-approved FDA labelling for both indications. All three citations verified against PubMed with titles, authors, journals and years matching. The absence of European approval reflects a commercial decision not to file rather than a regulatory rejection.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
A randomized phase III clinical trial of plecanatide, a uroguanylin analog, in patients with chronic idiopathic constipation Preclinical only
Both doses beat placebo on the durable overall CSBM responder endpoint (21.0 per cent for 3 mg and 19.5 per cent for 6 mg versus 10.2 per cent, p<0.001 for both), with mean weekly CSBM increases of 2.5 and 2.2 versus 1.2. No advantage was seen for the higher dose. Diarrhoea occurred in about 6 per cent versus 1.3 per cent on placebo.
Randomized clinical trial: efficacy and safety of plecanatide in the treatment of chronic idiopathic constipation Preclinical only
Replicated the efficacy of plecanatide in chronic idiopathic constipation on the durable overall CSBM responder endpoint, supporting the FDA approval alongside the Miner trial.
Efficacy, safety, and tolerability of plecanatide in patients with irritable bowel syndrome with constipation: results of two phase 3 randomized clinical trials Preclinical only
Both trials met the FDA composite responder endpoint requiring a 30 per cent or greater reduction in worst abdominal pain plus an increase of at least one CSBM per week for at least 6 of 12 weeks. These trials supported the January 2018 IBS-C approval.
Safety
Diarrhoea is the commonest adverse effect and the leading cause of discontinuation; in the Miner phase 3 trial it occurred in roughly 6 per cent of treated patients versus 1.3 per cent on placebo. Severe diarrhoea occurs in under 1 per cent. Other reported effects include nausea, abdominal distension, flatulence, sinusitis and upper respiratory tract infection. A boxed warning covers the risk of serious dehydration in young children (in juvenile mice a single oral dose caused deaths from dehydration), and the drug is contraindicated below 6 years of age, with use avoided between 6 and 18 years. It is contraindicated in known or suspected mechanical gastrointestinal obstruction. Systemic drug interactions are not expected given negligible absorption. Because plecanatide has no UK or EU licence, anyone in the UK encountering it is dealing with an unlicensed product outside regulatory oversight; that is a material safety consideration independent of the molecule's own profile.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | Not authorised. Plecanatide has no UK marketing authorisation and has not been submitted to the MHRA. It also has no EMA authorisation. It was never filed in Europe. It is therefore not legally available as a medicine in the UK by any route other than a named-patient import, and any product offered for sale to UK consumers is unlicensed. |
| United States | FDA-approved January 2017 for chronic idiopathic constipation in adults and January 2018 for irritable bowel syndrome with constipation in adults. Prescription-only oral tablet. Carries a boxed warning for risk of serious dehydration in paediatric patients; contraindicated in patients under 6 years of age and in known or suspected mechanical gastrointestinal obstruction. |
| WADA (sport) | Not listed on the WADA Prohibited List. It is minimally absorbed, acts locally in the gut lumen and has no plausible performance-enhancing effect. |
Questions
A single amino acid. Human uroguanylin has aspartate at position 3; plecanatide has glutamate. That substitution increases binding affinity for the guanylate cyclase-C receptor. Otherwise the 16-residue sequence and both disulfide bonds are identical to the natural hormone.
Not as a licensed medicine. Plecanatide has no MHRA or EMA marketing authorisation and was never submitted for European approval. Any plecanatide offered for sale in the UK is an unlicensed product operating outside regulatory oversight.
That claim is common but unproven. Diarrhoea rates in the plecanatide trials were numerically lower, and the pH-dependent binding profile offers a plausible biological reason. But the two drugs have never been compared head-to-head in a randomised trial, and comparing across separate trials run years apart in different populations is not reliable evidence.
Because it did not work better. In both the constipation and IBS-C programmes, 6 mg offered no consistent efficacy advantage over 3 mg (in the Miner trial the responder rate was actually marginally lower) while producing more diarrhoea. The FDA approved 3 mg as the dose for both indications on that basis.