Tesamorelin gelling and reconstitution: an evidence audit

Verified against PubChem PUG-REST (CID 16137828, formula and synonym list); UniProt P01286 for the somatoliberin sequence; DailyMed EGRIFTA SV prescribing information; PubMed. Fields marked “not verified” are ones we could not confirm against a primary chemical database — we leave them blank rather than guess.

What the identity record actually supports

Tesamorelin is a synthetic analogue of human growth hormone-releasing hormone, built on the GHRH(1-44) backbone with a trans-3-hexenoyl group acylating the N-terminus and an amide capping the C-terminus. PubChem CID 16137828 records the molecular formula C221H366N72O67S and an average mass near 5,136 g/mol. The same record carries CAS 218949-48-5 for the free peptide, the UNII MQG94M5EEO, and CAS 804475-66-9, which resolves to the identical CID and denotes a salt form.

FDA labeling for the marketed article states the formula as C221H366N72O67S with approximately seven acetate equivalents and a mass of 5,135.9 Da, identifying the drug substance as an acetate salt of the same peptide. UniProt P01286 supplies the somatoliberin precursor from which the 44-residue segment YADAIFTNSYRKVLGQLSARKLLQDIMSRQQGESNQERGARARL derives. Formula, mass and residue count reconcile across all three sources.

One value did not reconcile. The NCBI LiverTox monograph lists CAS 901758-09-6 for this compound. A PubChem name query on that number returns no record, while both 218949-48-5 and 804475-66-9 resolve to CID 16137828. This page carries the two resolvable numbers and flags the third rather than silently picking one.

No primary literature describes tesamorelin gelling

The gelling account is the reason this page exists, so it was searched first and directly. A PubMed query combining tesamorelin with isoelectric point, solubility, aggregation and formulation returned zero records. A second query combining tesamorelin with reconstitution, stability and diluent returned zero records. A third, restricted to the Journal of Pharmaceutical Sciences - the journal most often named when specific degradation percentages are quoted for this molecule - returned zero records for the compound.

Open web searching surfaced the same figures repeatedly. The pages carrying them were research-supplier catalogues and supplier blog posts, none citing a study, several citing wording close enough to one another to suggest a single origin. No peer-reviewed characterisation of tesamorelin solubility behaviour, no measured isoelectric point, and no stability study on a reconstituted solution were located in any indexed source.

That absence is itself the finding, and it is the reason this page is published rather than dropped. Everything downstream of the missing measurement - the pH mechanism, the diluent selection, the storage windows - rests on supplier documentation rather than data. The sections below separate the parts of that account that can be checked against a verified structure or a regulatory document from the parts that cannot be checked at all.

The near-neutral pI premise does not survive the sequence

The mechanism as usually told runs in four steps: the isoelectric point sits near neutral pH, a near-neutral diluent therefore strips the molecule of net charge, charge-charge repulsion collapses, and hydrophobic association produces the gel. Every step after the first depends on the first, and the first has no measurement behind it.

The verified composition argues the other way. Across the 44 residues, eight are lysine or arginine and four are aspartate or glutamate. There is no histidine. Both termini are blocked - the N-terminus by the hexenoyl acyl group, the C-terminus by amidation - which removes the free amine and free carboxylate that would otherwise contribute ionisable groups. What remains titratable is six arginines, two lysines, four acidic side chains and two tyrosines.

Running a standard Henderson-Hasselbalch charge calculation across that composition places the isoelectric point near pH 11.3 and holds net charge at roughly +4 from pH 5 through pH 8. This is a computed estimate derived from a verified sequence, not a measured value, and it is published here as an estimate. It nonetheless points hard away from the stated premise: in a near-neutral diluent the molecule would sit far from its isoelectric point carrying substantial positive charge, which is the condition the account itself describes as favouring dissolution.

What the regulatory labeling specifies

One handling document for this molecule carries regulatory weight: the FDA prescribing information for the marketed formulation. It diverges from research-supply guidance at nearly every point that matters.

The label directs reconstitution with a single named diluent, instructing that only the supplied Sterile Water for Injection be used, at 0.5 mL into a 2 mg vial. Mixing is specified as rolling the vial gently in the hands for 30 seconds, with shaking prohibited. The stated acceptance criterion is a solution that is clear, colorless and without particulate matter. On the mixing point, supplier guidance and the label agree.

Storage is where they part. The label stores the lyophilised 2 mg vial at room temperature, 20 to 25 degrees C, protected from light in its original carton - not frozen. For reconstituted material it states that the solution must not be frozen or refrigerated, and directs that unused solution be discarded rather than held. Supplier guidance describing dilute acetic acid diluents, storage of the lyophilisate at minus 20 or minus 80 degrees C, and reconstituted windows extending to 28 days at 2 to 8 degrees C is not a more conservative reading of this document. It contradicts it. Trial protocols also excluded participants with known hypersensitivity to tesamorelin or mannitol, indicating the study formulation was not peptide alone.

One methionine, not two

Methionine oxidation is a genuine degradation route for peptides that contain methionine, and this one contains a methionine. Counting the verified GHRH(1-44) sequence places it at position 27. Position 42 is alanine.

Supplier documentation describing oxidation-prone methionine residues at positions 27 and 42 is therefore wrong against the sequence, and wrong against the molecular formula independently. C221H366N72O67S carries a single sulfur atom. One sulfur permits exactly one sulfur-bearing residue and excludes cysteine altogether. Two methionines would require two sulfurs. The formula and the sequence constrain each other, and both give the same answer.

The quantitative claims attached to that account fare no better. Figures of 40 to 60 percent activity loss on oxidation, 12 percent potency loss over 72 hours at 4 degrees C, and near-complete degradation within 48 hours at ambient temperature appear on supplier pages attributed to the Journal of Pharmaceutical Sciences. No article on tesamorelin is indexed in that journal.

What can be stated is narrower. The molecule has one oxidisable thioether side chain. Peptide-bond hydrolysis and physical aggregation are general degradation routes for peptides of this class. Neither the rates nor the pH dependence quoted for this specific compound trace to a measurement anyone has published.

What the clinical record established

The compound is well documented clinically, which makes the formulation gap more conspicuous rather than less. Falutz and colleagues randomised 412 adults with HIV and abdominal fat accumulation to 2 mg subcutaneous tesamorelin or placebo for 26 weeks; visceral adipose tissue measured by CT fell 15.2 percent in the tesamorelin arm and rose 5.0 percent in the placebo arm (N Engl J Med, 2007). A pooled analysis of two phase 3 trials covering 806 randomised participants reported a visceral adipose tissue treatment effect of minus 15.4 percent at week 26, alongside an IGF-1 change of 108 plus or minus 112 ng/mL against minus 7 plus or minus 64 on placebo (J Clin Endocrinol Metab, 2010).

In HIV-associated fatty liver disease, Stanley and colleagues randomised 61 participants for 12 months and reported a hepatic fat fraction difference of minus 4.1 percentage points, a 37 percent relative reduction, with 35 percent of the tesamorelin arm and 4 percent of the placebo arm below a 5 percent fat fraction at 12 months (Lancet HIV, 2019).

Outside HIV, Baker and colleagues randomised 152 adults aged 55 to 87, of whom 66 had mild cognitive impairment, to 1 mg daily tesamorelin or placebo for 20 weeks and reported a favourable effect on a composite cognitive outcome at P = .03, with IGF-1 rising 117 percent (Arch Neurol, 2012). Two further trials are registered and separate: a completed phase 2 study of NAFLD in obesity without HIV (NCT03375788) and an ongoing phase 2 peripheral nerve injury study at Johns Hopkins (NCT03150511), which was still recruiting and had posted no results at the time of writing.

What is not known

No published study characterises the physical behaviour of tesamorelin in solution. There is no measured isoelectric point, no solubility-versus-pH curve, no aggregation kinetics, and no forced-degradation study in the indexed literature. Nothing is established about how concentration, ionic strength, buffer identity or shear rate affect association of this specific molecule, and the diluents named in supplier guidance - dilute acetic acid in particular - have not been compared against water for this compound in any published experiment. The stability windows quoted for reconstituted material rest on no measurement at any temperature. Separately, the clinical evidence base is narrower than its volume suggests: the large randomised trials enrolled adults with HIV on antiretroviral therapy and excess visceral fat, a population selected for reduced growth hormone secretion, so the visceral fat and liver fat findings do not transfer to unselected populations. The cognition trials were small, short (10 to 20 weeks) and have not been replicated at scale; NCT02553603 completed in 2019 without posting results. The peripheral nerve injury trial remains in recruitment with no results posted. Long-term outcome data, paediatric data, and pregnancy data are absent throughout.

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