Methylnaltrexone Bromide

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Cat Number

API0232149

CAS Number

73232-52-7

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Product Detail Description Scientific Support Customer Q&A

CAS Number

73232-52-7

EINECS

615-932-9

Storage

Store at room temperature

Synonyms

N-Methylnaltrexone Bromide; Naltrexone methobromide; MRZ-2663BR; MOA-728; bromuro de metilnaltrexona; DTXSID30868236

Molecular Formula

C21H26BrNO4

Molecular Weight

436.3

Smiles

C[N+]1(CC[C@]23[C@@H]4C(=O)CC[C@]2([C@H]1CC5=C3C(=C(C=C5)O)O4)O)CC6CC6.[Br-]

Appearance

Typically exists as solid at room temperature

Melting Point

237-239°C

General Description

Methylnaltrexone bromide is a quaternary ammonium derivative of naltrexone, with a methyl group added to the tertiary amine of the parent molecule. This positive charge restricts its ability to cross the blood‑brain barrier, confining it to peripheral tissues. The bromide salt improves solubility. The molecule retains the cyclopropylmethyl group characteristic of opioid antagonists.

Mechanism of Action

Methylnaltrexone acts as a selective, competitive antagonist at peripheral mu‑opioid receptors located in the gastrointestinal tract. It reverses opioid‑induced constipation (OIC) by blocking the inhibitory effects of opioids on gut motility, gastric emptying, and fluid secretion. Unlike naltrexone or naloxone, it does not cross into the central nervous system, so it does not precipitate opioid withdrawal or reverse analgesia.

Application

Methylnaltrexone is indicated for the treatment of opioid‑induced constipation in patients with advanced illness receiving palliative care and in adults with chronic non‑cancer pain when other laxatives have failed. It is also used for postoperative ileus. The peripheral selectivity allows effective bowel motility restoration without compromising central analgesia.

Pooled analysis of four randomized double‑blind trials (1,627 patients with opioid‑induced constipation) compared methylnaltrexone (a peripherally acting µ‑opioid antagonist) with placebo, stratifying by age (<65 vs. ≥65 years). Pain intensity scores did not differ significantly from placebo in either age group, and opioid withdrawal symptoms were not statistically different from baseline. Treatment‑related adverse events (abdominal pain, flatulence, nausea) declined after the second dose and were comparable to placebo. Rescue‑free laxation within 4 hours was significantly increased with methylnaltrexone in both age cohorts. Age did not compromise pain control or safety. Further research is needed on factors that alter blood‑brain barrier permeability (e.g., dementia, stroke).

Fig. 1 Percentage of responders with rescue-free laxation within 4 h after the first dose. SC subcutaneous. (Liao SS, et al., 2021)

References

Liao SS, et al. The Influence of Age on Central Effects of Methylnaltrexone in Patients with Opioid-Induced Constipation. Drugs Aging. 2021;38(6):503-511.

Does Methylnaltrexone Bromide require protection from light during storage?

Yes, it is photosensitive. UV light can cause photodegradation and isomerization. Store in light-resistant containers, preferably amber glass or original packaging.

What is the recommended storage temperature for Methylnaltrexone Bromide?

Store at controlled room temperature (15-25°C). Avoid excessive heat above 30°C, which can accelerate oxidation of the phenolic hydroxyl group.

Is Methylnaltrexone Bromide stable in solution for subcutaneous injection?

Formulated solutions are stable when stored at room temperature and protected from light.

How is the impurity methylnaltrexone N-oxide (an oxidative degradation product) monitored?

This degradation product is quantified using a stability-indicating HPLC method, ensuring it remains within ICH qualification thresholds.