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REPORT ON CARCINOGENS, ELEVENTH EDITION

Phenolphthalein 

CAS No. 77-09-8

Reasonably anticipated to be a human carcinogen

First Listed in the Ninth Report on Carcinogens (2000)

Carcinogenicity

Phenolphthalein is reasonably anticipated to be a human carcinogen based

on sufficient evidence of increased incidence of malignant and/or

combination of malignant and benign tumors in multiple tissue sites and

in multiple species (IARC 2000). In a two-year B6C3F1 mouse

carcinogenicity study, NTP (1996) concluded that phenolphthalein,

administered in feed, induced significant increases in the incidence of

histiocytic sarcoma and lymphomas of thymic origin in males and

females and malignant lymphoma (all types) and benign ovarian sex cord

stromal tumors in females. In the corresponding Fischer 344 rat dietary

carcinogenicity study, phenolphthalein induced significant increases in

the incidence of benign pheochromocytoma of the adrenal medulla in

males and females and renal tubule adenoma in males (NTP 1996). In a

6-month dietary study with female heterozygous p53-deficient transgenic

mice, phenolphthalein induced a significant increase in the incidence of

malignant lymphoma of thymic origin (Dunnick et al. 1997).

A few epidemiological studies have investigated the association

between the use of phenolphthalein-containing laxatives and colon cancer

or adenomatous colorectal polyps. No consistent association was found.

Cancers at other sites have not been investigated in humans (IARC 2000).

Additional Information Relevant to Carcinogenicity

The malignant thymic lymphomas induced by phenolphthalein in female

heterozygous p53-deficient transgenic mice exhibited a loss of the normal

p53 allele, suggesting the involvement of a mutagenic mechanism in

tumor induction and/or progression (Dunnick et al. 1997).

Phenolphthalein causes enhanced oxygen radical production in in

vitro systems. In vivo, reduction of phenoxyl radicals could allow

reformation of phenolphthalein, establishing a futile cycle of oxidation

and reduction, thereby generating more free radical species. Thus,

phenolphthalein may be a significant source of oxidative stress in

physiological systems.

Although negative for mutagenicity and DNA damage in bacteria,

phenolphthalein exhibits genetic activity in several in vitro and in vivo

mammalian assays. Phenolphthalein was positive for the induction of

chromosomal aberrations in cultured Chinese hamster ovary cells in

the presence of metabolic activation and induced hprt gene mutations,

chromosomal aberrations, and morphological transformation in

Syrian hamster embryo cells. Phenolphthalein was also positive for the

induction of micronucleated erythrocytes in mice following multiple,

but not single, treatments administered by gavage or dosed feed.

Phenolphthalein also induced micronuclei in female heterozygous

p53-deficient transgenic mice exposed via dosed feed for 26 weeks.

Abnormal sperm were induced in male mice, but not male rats,

treated with phenolphthalein via dosed feed for 13 weeks.

Phenolphthalein was negative for Na/K ATPase gene mutations and

aneuploidy in Syrian hamster embryo cells.

No data were available that would suggest that the mechanisms

thought to account for tumor induction by phenolphthalein in

experimental animals would not also operate in humans.

Phenolphthalein causes oxidative stress and also demonstrates the

capability to alter tumor suppressor gene pathways, which are both

mechanisms believed to be involved in human cancer.

Properties

Phenolphthalein is an odorless, white or faintly yellow-white powder

comprising minute, triclinic crystals (Budavari 1996, NTP 1996,

HSDB 2001). It has a melting point of 258 to 262°C. It is almost

insoluble in water, very slightly soluble in chloroform, and soluble in

alcohol, diethyl ether, dilute solutions of alkali hydroxides, and hot

solutions of alkali carbonates. Phenolphthalein-titrated solutions are

colorless at pH <8.5 and pink to deep red at pH >9 (Budavari 1996).

Use

Phenolphthalein in 1% alcoholic solution is used as a visual indicator in

titrations of mineral and organic acids and most alkalies (Budavari

1996). It is also used in a variety of ingested products as well as in some

scientific applications. Because phenolphthalein is odorless and tasteless,

it can be incorporated easily in tablets, powder, and liquid. It has been

commonly used as a laxative, available worldwide as an over-the-counter

chocolate or gum laxative product. The typical oral dose is 30 to 200

mg for adults and children ≥12 years of age. A dose of 270 mg should

not be exceeded. The dosages for children aged 6 to 11 years or 2 to 5

years are 30 to 60 mg and 15 to 30 mg, respectively (IARC 2000).

Bedridden patients require 500 mg doses (Sollman 1957).

Production

As reported in 1997, only one company produced phenolphthalein in

the United States, with an annual production of 250 tons (197 metric

tons) (SRI 1997a). Twenty manufacturers of phenolphthaleincontaining laxatives were identified in 1997 (FDA 1997). There are 39

current suppliers of phenolphthalein in the United States (Chem

Sources 2001). Combined sales of the top three phenolphthaleincontaining drugs, Correctol, Phillips, and Ex-Lax, totaled 16.4% of

the laxative market in 1989 (Drug Store 1990), 23.9% in 1992 (Advert

Age 1993), and 19.9% in the period July 1993 to July 2, 1994

(DeNitto 1994). The three drugs were still among the top-selling

laxatives in 1995 (SRI 1997b). Ex-Lax, which continued to hold a

top-three position in 1996, accounted for approximately 7% of the

brand-name sales (Suplee 1997, Drug Top 1997). The use of

phenolphthalein in laxatives has decreased since the FDA proposed the

reclassification of its use in over-the-counter laxative products (FDA

1997). Producers of Correctol and Feen-a-Mint brand products

replaced phenolphthalein with bisacodyl in January 1996. Bayer’s

Phillips’ GelCaps was voluntarily removed from the market in mid

1997. Novartis AG, the marketer of Ex-Lax, announced in late August

1997 that its product would be reformulated, substituting senna for

phenolphthalein (Suplee 1997, Drug Top 1997).

Exposure

The major routes of human exposure to phenolphthalein are ingestion,

dermal contact, and inhalation of contaminated air originating from

process units manufacturing the compound. The general population is

exposed to phenolphthalein through its common application as an

over-the-counter drug, particularly as a laxative. Many studies show that

the use of laxatives to relieve constipation and to maintain regularity in

bowel habits is widespread in the United States; however, few studies

report on the prevalence of phenolphthalein laxative use.

From studies of four U.S. populations (Harari et al. 1996, Everhart

et al. 1989), it would appear that no more than 10% of the U.S.

population has used phenolphthalein-containing laxatives as often as

once per month, but up to 5% may have used them weekly or more

often. In one study of 424 cases of invasive adenocarcinoma of the colon

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and 414 controls in Washington state, ages 30 to 62 years, it was found

that 13.6% of the subjects reported constipation requiring treatment (use

of a laxative, enema, or prunes), 4.7% reported ever using

phenolphthalein laxatives, and 3.5% reported use of phenolphthalein

laxatives at least 350 times in their lifetimes (Jacobs and White, 1998). In

three U.S. populations of 268 to 813 persons comprising approximately

equal numbers of cases of adenomatous colorectal polyps and controls,

0.97 to 5.1% of the subjects used phenolphthalein laxatives at least once

per week. The two North Carolina groups included subjects aged 30 to

89 years, 58% and 53% of which were female; the group in Los Angeles,

California, included subjects aged 50 to 74 years of which 34% were

female. Mean ages of the three groups were comparable (59 to 62 years).

The frequent phenolphthalein laxative users represented 8% to 30% of

all frequent laxative users. The overuse of phenolphthalein laxatives in

the two North Carolina groups was 17.5% and 25%, with 10% and 7%

using them at least once per month (Longnecker at al. 1997).

Potential occupational exposure could occur through inhalation or

dermal contact for workers involved in the manufacturing,

formulating, packaging, or administering of drugs containing

phenolphthalein. The National Occupational Exposure Survey

(NOES), conducted by NIOSH between 1981 to 1983, listed 75,243

workers (26% female) as being potentially exposed to phenolphthalein.

The number of Health Services employees potentially exposed to the

compound was 20,122 (65% female) (NIOSH 1990).

Regulations

FDA

Drug products containing phenolphthalein can no longer be marketed

REFERENCES

AdvertAge. 1993. Brand Scorecard: Laxatives. Advertising Age. 12.

Budavari, S., ed. 1996. The Merck Index. 12th ed. Whitehall, NJ, Merck & Company, Inc.

ChemSources. 2001. Chemical Sources International, Inc. http://www.chemsources.com.

DeNitto, E. 1994. Brand Scorecard: Laxatives. Advertising Age: 28 pp.

DrugStore. 1990. Eighty-three Laxatives Carry 91% of Sales. Drug Store News: IP25.

DrugTop. 1997. Laxative Alert? Fifteen of 17 Members of FDA Carcinogenicity Assessment Committee

Believe Laxative Element Phenolphthalein May Be Carcinogenic. Drug Topics June 16: 16.

Dunnick, J. K., J. F. Hardisty, R. A. Herbert, J. C. Seely, E. M. Furedi-Machacek, J. F. Foley, G. D. Lacks, S.

Stasiewicz and J. E. French. 1997. Phenolphthalein induces thymic lymphomas accompanied by loss

of the p53 wild type allele in heterozygous p53-deficient (+/-) mice. Toxicol Pathol 25(6): 533-40.

Everhart, J. E., V. L. Go, R. S. Johannes, S. C. Fitzsimmons, H. P. Roth and L. R. White. 1989. A longitudinal

survey of self-reported bowel habits in the United States. Dig Dis Sci 34(8): 1153-62.

FDA. 1997. Laxative drug products for over-the-counter human use; Proposed amendment to the tentative

final monograph. Fed Regist 62: 46223-46227.

Harari, D., J. H. Gurwitz, J. Avorn, R. Bohn and K. L. Minaker. 1996. Bowel habit in relation to age and gender. Findings from the National Health Interview Survey and clinical implications. Arch Intern Med

156(3): 315-20.

HSDB. 2001. Hazardous Substances Data Base. National Library of Medicine. http://toxnet.nlm.nih.gov/

cgi-bin/sis/htmlgen?HSDB.

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Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Humans, vol. 76. Lyon, France:

International Agency for Research on Cancer. 522 pp.

Jacobs, E. J. and E. White. 1998. Constipation, laxative use, and colon cancer among middle-aged adults.

Epidemiology 9(4): 385-91.

Longnecker, M. P., D. P. Sandler, R. W. Haile and R. S. Sandler. 1997. Phenolphthalein-containing laxative use

in relation to adenomatous colorectal polyps in three studies. Environ Health Perspect 105(11): 1210-2.

NIOSH. 1990. National Occupational Exposure Survey (1981-83). Unpublished provisional data as of

7/1/90. Cincinnati, OH: U. S. Department of Health and Human Services.

NTP. 1996. Toxicology and Carcinogenesis Studies of Phenolphthalein (CAS No. 77-09-8) in F344/N Rats

and B6C3F1 Mice (Feed Studies). Technical Report Series No 465. NIH Publication No. 97-3390.

Research Triangle Park, NC: National Toxicology Program. 354 pp.

Sollman, T. 1957. Cathartics. In A Manual of Pharmacology, 8th ed. Philadelphia, PA: W.B. Saunders Company.

SRI. 1997. Gastrointestinal Agents and Therapeutic Nutrients. In Chemical Economics Handbook. Menlo

Park, CA: SRI International.

SRI. 1997. Phthalic Anhydride. In Chemical Economics Handbook. Menlo Park, CA: SRI International.

Suplee, C. 1997. Firm to Pull Ex-Lax from Store Shelves. The U.S. Plans to Ban Phenolphthalein, a

Component. It's Been Linked to Cancer in Mice. Philadelphia Inquirer [from the Washington Post].

Philadelphia, PA: A1.

REPORT ON CARCINOGENS, ELEVENTH EDITION