Registration Dossier

Administrative data

Endpoint:
basic toxicokinetics in vivo
Type of information:
other: Publication
Adequacy of study:
weight of evidence
Study period:
no information
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: No details as to whether the study was conducted to GLP. Limited details on the purity of the test article.

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
1949
Report Date:
1949

Materials and methods

Objective of study:
metabolism
Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
The principle of the published data was to demonstrate the ability to determine β-Naphthoxyethanol levels in biological materials of animals that had been intravenously administered with the substance, using UV absorption spectroscopy, and to determine the metabolites of β-Naphthoxyethanol excreted in Rabbit urine using UV absorption spectroscopy.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): β-Naphthoxyethanol
Radiolabelling:
no

Results and discussion

Main ADME results
Type:
metabolism

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
β-Naphthoxyacetic acid - accounts for 25% of the β-Naphthoxyethanol dosed (by spectrophotometric estimation)
Conjugated β-Naphthoxyethanol (approx 0.5%)
Conjugated β-Naphthol (approx 0.1%)

Any other information on results incl. tables

Determination of β-Naphthoxyethanol in Blood: Summary of publication (A. Spinks 1950)

The validity of the procedure using CHCl3 has been established in three ways:

1. The recovery of β-Naphthoxyethanol from blood and urine has been examined.

2. The specificity of the method has been checked by establishing the identity of the ratio d273/d325 for β-Naphthoxyethanol extracted from the blood of experimental animals with that for authentic β-Naphthoxyethanol.

3. The method has been used for some time to determine β-Naphthoxyethanol in the blood of of sheep, horse and rabbit.

β-Naphthoxyethanol is rapidly eliminated from the blood, in conformity with it's use as a short acting anaesthetic.

Metabolism of β-Naphthoxyethanol in the Rabbit: Summary of publication (A. Spinks 1950)

Test animals: Rabbits (Chinchilla bucks) weighing 2 -3kg.

Dosage: β-Naphthoxyethanol was administered as a 10% (w/v) dispersion, in a typical experiment two rabbits received a total of 1.7 g of

β-Naphthoxyethanol intraperitoneally.

The combined 24 hour urine total of the two dosed rabbits was 222 mL.

Free non-acidic metabolites.

Urine (1 ml) was treated with 1 ml of 0.2m Na2HPO4and shaken for 5 min with 40 ml of CHCI3. The extract was seperated, dried over Na2SO4and examined in the spectrophotometer. The spectrum non-characteristic and showed no evidence of the presence of any naphthalene derivative. In this fraction would have appeared β-naphthoxyethanol, solvent soluble phenolic compounds and quinones of low molecular weight. All could therefore be present only in negligible amount.

Free acidic metabolites.

Urine (0.5 ml) was treated with 1ml of N-HCI and extracted with 40 ml of CHCl3as described above. The absorption spectrum B (a chloroform extract of urine acidified with HCl) was very similar to that of β-naphthoxyethanol itself, suggesting the presence in the urine either of an acid of similar chromophoric structure, presumably, β-naphthoxyacetic acid, or of a conjugated derivative of, β-naphthoxyethanol, immediately hydrolysed on adding HCl. The former possibility was established by extracting fraction B with an equal volume of % Na2CO3(w/v). The CHCl3residue was similar in spectrum to A (a chloroform extract of urine buffered to pH 8.5), but the spectrum of the carbonate extract (C) clearly indicated the presence of an acid. By comparing the extinction coefficients from spectra B and C with those of authentic β-naphthoxyacetic acid in the corresponding solvents it was found that approximately 25% of the drug could be accounted for as β-naphthoxyacetic acid.

Conjugated non-acidic metabolites.

Urine (5 ml) was treated with 5 ml of N-HCl and heated at 100° for 1.5 hr. On cooling, 5 ml of N-NaOH were added and the volume was adjusted to 20 ml with distilled water. The filtered solution (4 ml), equivalent to 1 ml of the original urine, was treated with 4 ml of 0.2m-Na2HPO4and extracted with 40 ml of CHCl3. The absorption spectrum D (a chloroform extract of hydrolysed urine buffered to pH 8.5) showed some evidence of maxima at the same wavelengths as β-naphthoxyethanol. The extract was purified by removal of phenols with N-NaOH. It then gave spectrum E (the same as D after washing with N-NaOH) which showed maxima at 263, 272, 314 and 327-5 mµ, and a marked inflexion at 282 mµ, suggesting that, β-naphthoxyethanol was present. The amount was difficult to assess because the spectrum was clearly affected by other absorbing materials, but it did not seem that more than 1-2% of the drug could be accounted for in this fraction. The spectrum of the phenolic fraction was inferred by subtracting E from D. It was clearly due to a complex mixture of compounds, and no further spectrophotometric study was made until isolation had been attempted.

Conjugated acid metabolites.

The hydrolysed and neutralized urine (1 ml), equivalent to 0.25 ml. of original urine, was acidified with 1 ml. of N-HCI, and extracted with 40 ml. of CHCl3. The chloroform extract was shaken with an equal volume of 1% Na2CO3(w/v), and the spectrum of the latter was constructed F (a carbonate extract of acids from a chloroform extract of acidified, hydrolysed urine). It was consistent with the presence in this fraction of the presumed β-naphthoxyacetic acid of the un-hydrolysed urine, together with a mixture of other acids liberated by hydrolysis. The extinction coefficients did not suggest the formation by hydrolysis of further amounts of β-naphthoxyacetic acid.

 

The spectrophotometric study indicated the presence of β-naphthoxyacetic acid and conjugated β-naphthoxyethanol. These deductions were confirmed by isolation, and in addition, β-naphthol was isolated as an azo derivative.

(I) Isolation of β-Naphthoxyacetic acid.

 

The main bulk of the urine (200 mL) was acidified with an equal volume of N-HCl and extracted with 3 x 100 ml. of ether. The aqueous residue was retained for hydrolysis (see II below). The combined ether extracts were shaken with 3 x 30 ml. of 1 % Na2CO3w/v) and the ether was discarded. The combined carbonate extracts were acidified with conc HCl. After standing overnight the dark, crystalline deposit was filtered, washed with water and dissolved in 25 ml of boiling water. Charcoal (0-5 g, DY3) was added, boiling continued for 5 min. and the charcoal removed by filtration. The pale yellow filtrate was evaporated to incipient cloudiness and allowed to stand overnight. The colourless plates were filtered, washed with distilled water and dried in vacuo overCaCl2. The yield was 130 mg m.p. 151-153°; mixed with authentic β-naphthoxyacetic acid, m.p. 152-154°. One recrystallization from benzene gave rosettes (85 mg), m.p. 154°C (Found C, 70-5; H4.95. Calc. for

C12H10O3: C,71-2; H, 4.95%). The mother liquors were not further examined.

(II) Isolation of β-naphthoxyethanol

 

The acid urine residue from (I) was heated for 1.5 hr at 100°C and allowed to cool. It was then extracted with 3x150 ml of ether. The urine was discarded, and the combined ether fraction washed with 2 x 50 ml of water,

and then extracted with 3 x 20 ml. of 1% Na2CO3. This extract did not give any crystalline product and was discarded. The ether residue was extracted with 2 x 20 ml of 2N NaOH and the combined aqueous fraction examined for phenolic metabolites (see III below). The ether fraction, now free from phenols and acids, was dried over Na2SO4and the solvent removed on the steam bath. The tarry residue was dissolved in boiling light petroleum b.p. 40-60°, 2 ml.) and the filtered solution allowed to stand overnight at room temperature. The precipitated solid weighed 8-10 mg and melted at 62-66°. Recrystallization from light petroleum (b.p. 60-80°, 1 ml.) gave 6 -7 mg. of almost pure, β-naphthoxyethanol, m.p. 70-72°, mixed with an authentic specimen, m.p. 72-73°. The yield of crude material was equivalent to about 0.5% of the dose.

(III) Isolation of β-naphthol as an azo derivative.

The NaOH fraction from (II) was acidified and extracted with 3 x 100 ml of ether. The combined extracts were dried over Na2SO4, and the solvent was removed on the steam bath. The residue (20 mg) was tarry and resisted attempts at crystallization. It was therefore decided to convert the phenols to azo dyes and to attempt a separation by chromatography. The residue was dissolved in 1 ml of 2N-NaOH and treated with a solution of naphthalene-1-diazonium chloride from 150 mg of recrystalized α-naphthylamine hydrochloride). The mixture was acidified and shaken vigorously with 100 ml of CHCl3. The lower layer was separated, dried over Na2SO4and passed through a column of activated alumina (7x1 cm), the column being washed with 100 ml of CHCl3to remove the last traces of dye. Some tarry impurities remained strongly adsorbed. The eluate gave an absorption spectrum (total eluate from the first chromatogram) which showed some similarity in position of the main maximum to that of 1-(naphthalene-1 -azo)-2 naphthol. The volume was reduced to 10 ml and the solution rechromatographed on alumina (14x2 cm). A faint bluish band and a faint orange band at the top of the column were discarded. The remaining bands, a weakly adsorbed broad pink band, and a more strongly adsorbed purple band were passed through the column by washing with 200 ml ofCHCl3and collected separately. The purple band and pink band were obviously mixtures however the pink band agreeing best with the spectrum of authentic 1-(naphthalene-1'-azo)-2-naphthol. This fraction was therefore evaporated to dryness, and the semi-crystalline residue dissolved in 10 ml of benzene and chromatographed on alumina (14x2 cm), the column being developed with benzene. Five main bands were observed as follows (in decreasing strength of adsorption): faint purple, purplish blue, orange, strong red, orange. The lower three bands were passed through the column by washing with 200 ml of benzene, and collected separately. The red fraction was retained and the solvent removed to give a crystalline residue (4.3 mg). A trace dissolved in CHCl3gave a spectrum identical with that of authentic 1-(naphthalene-1-azo)-2-naphthol. The remainder of the material was crystallized from ethanol CHCl3(70-30 (v/v) 0.5 ml) to give needles (2.8 mg) of 1-(naphthalene-1-azo)-2-naphthol. (Found C, 80.3; H, 5.4. Calc. for C20H14ON2: C, 80-4; H, 4.7%); m.p. 227-228°, mixed with an authentic specimen, m.p. 227-228°. The yield was equivalent to about 0-1% of the dose. The absence of, β-naphthol from the free phenol fraction of the urine (and from the α-naphthylamine used) was readily demonstrated, no characteristic pink band being observed in the chromatograms.

Applicant's summary and conclusion

Conclusions:
β-naphthoxyethanol is shown to be metabolized by three routes. Route 1 to β-naphthoxyacetic acid, accounts for about 25% of the drug (by spectrophotometric estimation. Route 2 to a conjugate of β-naphthoxyethanol (approx 0.5%) and Route III to a conjugate of β-Naphthol (approx 0.1%). 75 % of the β-Naphthoxyethanol dosed remains unaccounted for, some of this may have been present as polyphenolic compounds (which could remain in the aqueous phase under the conditions of extraction used) and their coloured oxidation products, but it is probable that much of the drug was either burned completely or converted to metabolites not specifically sought during these experiments e.g. phthalic acid. The trace of β-Naphthol isolated is considered negligible from the standpoint of toxicity. The most notable feature of the various degradative reactions known and unknown is their rapidity. Together they result in the reduction of blood concentrations of 5 mg or more of the drug per 100 mL to zero within half an hour to an hour.
Executive summary:

Summary: Determination of β-Naphthoxyethanol in Blood (A. Spinks 1950).

1. β-Naphthoxyethanol has been determined in blood by extracting it with chloroform and measuring the optical densities of the extract at the absorption maxima of 272 and 325 mµ.

2. β-Naphthoxyethanol is rapidly eliminated from the blood in conformity with its use as a short acting anaesthetic.The rate of elimination of β-Naphthoxyethanol was then determined over time. It was demonstrated that β-Naphthoxyethanol is rapidly removed from the blood after intravenous administration of 80 mg/kg to sheep and rabbit.

Summary: Metabolism of β-Naphthoxyethanol in the Rabbit (A. Spinks 1950)

1. β-Naphthoxyethanol was not detected in the urine of rabbits receiving large doses intravenously or

intraperitoneally.

 

2. Three metabolites have been identified as β–naphthoxyacetic acid (approx. 25%), conjugated

β -naphthoxyethanol (approx. 0-5%) and conjugated β -naphthol (approx. 0-1 %).

 

3. It is suggested that part of the missing drug appears in the urine as coloured oxidation products

of , β -naphthol or other phenolic metabolites, but much must be degraded by unknown routes.