Alginic acid

• BPAlginic Acid
• Ph. Eur.Alginic Acid
• USP–NFAlginic Acid

Acidum alginicum; E400; Kelacid; L-gulo-D-mannoglycuronan; polymannuronic acid; Protacid

Alginic acid (linear copolymer of D-mannuronic and L-guluronic acid) · [9005-32-7]

(C6H8O6)n · ≈ 10 000–600 000

Disintegrant, Binder, Gelling agent, viscosity modifier

Typical concentrations: 1–5% · Dosage forms: Solid

Used in oral and topical products as a tablet binder and disintegrant, as a thickening and suspending agent, and in modified-release matrices. Combined with sodium bicarbonate and antacids it forms a floating gel raft in reflux-suppressant products. Typical concentrations: tablet binder 1–5%; tablet disintegrant 1–5%.

A white to yellowish-white, fibrous powder, odourless or almost odourless and practically tasteless. It is a linear polyuronide made of blocks of β-(1→4)-D-mannuronic acid and α-(1→4)-L-guluronic acid in varying proportions and sequence, depending on the seaweed source.

Acidity

pH 1.5–3.5 (3% w/v aqueous dispersion)

pKa

≈ 3.4 (mannuronic acid) and ≈ 3.7 (guluronic acid) units

Loss on drying

not more than 15% w/w (pharmacopoeial limit)

Solubility

soluble in alkali hydroxide solutions, giving viscous solutions; practically insoluble in water (swells) and in ethanol and other organic solvents

Hydrolyses slowly at warm temperatures, with a fall in molecular weight and viscosity. Store in a well-closed container in a cool, dry place.

Incompatible with strong oxidising agents. With calcium and other polyvalent cations it forms insoluble, gelled salts, and it reacts with alkaline drugs and excipients.

Extracted from brown seaweeds (Phaeophyceae), such as Laminaria, Macrocystis and Ascophyllum species, with dilute alkali; the alginate solution is clarified and alginic acid is precipitated by acidification, then washed and dried.

Widely used in oral products and food and regarded as non-toxic and non-irritant. It is not absorbed to a significant extent after oral administration. JECFA has allocated an ADI 'not specified' to alginic acid and its salts.

Observe normal precautions for the quantity handled. Eye protection and a dust mask are recommended; the dust may irritate the eyes and respiratory tract.

GRAS listed. Accepted as a food additive in Europe (E400). Included in the FDA Inactive Ingredient Database (oral preparations) and in non-parenteral medicines licensed in Europe.

Ammonium alginate; calcium alginate; potassium alginate; propylene glycol alginate; sodium alginate.

The ratio and arrangement of guluronic and mannuronic blocks control gel behaviour: alginates rich in guluronic acid form stronger, more rigid calcium gels, whereas mannuronic-rich alginates give softer, more elastic gels.