Products
Phenolphthalein has been included in many laxatives in the past, for example in Reguletts tablets (100 mg) in many countries. Sales of the last drug containing phenolphthalein (Paragar Emulsion) will be discontinued in many countries in 2018.
Structure and properties
Phenolphthalein (C20H14O4, Mr = 318.3 g/mol) exists as a white powder that is practically insoluble in water. It is a benzofuran and phenol derivative. It is synthesized with phthalic anhydride and phenol. The solutions are colorless below a pH of about 8.2. At a basic pH above 8.2, the solution becomes pink. In chemistry, phenolphthalein is therefore used as an indicator for acid-base titrations.
Effect
Phenolphthalein (ATC A06AB04) has laxative properties. It increases the secretion of electrolytes and water into the intestinal lumen, causing an increase in volume and filling pressure in the colon. This stimulates the movement of the colon. The effects occur about 6 to 10 hours after ingestion.
Indications for use
Phenolphthalein has been used in the past for the short-term treatment of constipation.
Contraindications
For complete precautions, see the drug label.
Adverse effects
Possible adverse effects include gastrointestinal symptoms such as diarrhea and abdominal pain. Phenolphthalein may cause a harmless pink or red discoloration of the urine. Long-term therapy is not indicated. Disturbances of the electrolyte balance may occur. Phenolphthalein is controversial as a laxative. It is considered to be possibly carcinogenic based on animal studies conducted primarily in mice and rats. The corresponding publication by Dunnick and Hailey was published in 1996. In the USA, phenolphthalein subsequently lost its GRAS status and was reclassified by the FDA to “not generally recognized as safe.” Laxatives containing the active ingredient were withdrawn from the market in many countries. For humans, the data are not as clear as for rodents. However, ingestion should be avoided and phenolphthalein should be replaced with other, noncritical agents.
