Disodium fluorophosphate

Specific investigations: other studies

Administrative data

Endpoint:

specific investigations: other studies

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Scientifically sound study

Data source

Reference

Reference Type:

publication

Title:

Chemical stability and mode of gastrointestinal absorption of sodium monofluorophosphate.

Author:

Setnikar I, Arigoni R.

Year:

1988

Bibliographic source:

Arzneimittelforschung. 1988 Jan;38(1):45-9. PMID: 3365276

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The ability of different body fluids and tissue homogenates to catalyse the hydrolysis of monofluorophosphate was tested

GLP compliance:

no

Type of method:

in vitro

Endpoint addressed:

basic toxicokinetics

Test material

Test material information

Constituent 1

Reference substance name:

Disodium fluorophosphate

EC Number:

233-433-0

EC Name:

Disodium fluorophosphate

Cas Number:

10163-15-2

Molecular formula:

FH2O3P.2Na

IUPAC Name:

disodium fluorophosphate

Details on test material:

- Name of test material (as cited in study report): sodium monofluorophosphate (sodium MFP)
- Analytical purity:
sodium MFP, USP grade;
Formulation 1: tablets (Tridine®, manufacturer: Opfermann Arzneimittel, Wiehl (Fed.Rep. of Germany)) containing Na2FPO3 38 mg, calcium gluconate
500 mg, calcium citrate 500 mg;
Formulation II: tablets (experimental , formulation) containing
Na2FPO3 76 mg, calcium carbonate 1203 mg, calcium glycerophosphate
358 mg.
- Impurities (identity and concentrations): see above
- Composition of test material, percentage of components: see above
- Stability under test conditions: not reported, expected to be stable
- Storage condition of test material: not reported

Test animals

Species:

other: rats, dogs, humans

Strain:

other: rat: Sprague Dawley, dog: mongrel

Sex:

not specified

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: rats: 250 - 320 g
- no further details given

Administration / exposure

Route of administration:

other: not applicable

Vehicle:

other: not applicable

Details on exposure:

not applicable

Analytical verification of doses or concentrations:

not specified

Details on analytical verification of doses or concentrations:

not applicable

Duration of treatment / exposure:

not applicable

Frequency of treatment:

not applicable

Post exposure period:

not applicable

Doses / concentrations

Remarks:

Doses / Concentrations:
not applicable
Basis:

No. of animals per sex per dose:

not applicable

Control animals:

no

Details on study design:

not applicable

Examinations

Examinations:

not applicable

Positive control:

not applicable

Results and discussion

Details on results:

- Acid phosphatase is practically ineffective in MFP hydrolysis (Table 1)
- Alkaline phosphatase is highly effective in MFP hydrolysis at neutral and alkaline conditions (Table 1)
- MFP is not significantly hydrolysed in gastric juices neither in human nor dog (Tables 2 and 3) except for the basic hydrolysis rate due to low pH
- MFP is hardly hydrolysed in human blood, plasma or haemolysed cells (Table 4)
- MFP hydrolysis is fast in rat intestine homogenates and the activity is inhibited by denaturation of proteins (boiling) (Table 5)
- MFP hydrolysis is very fast in rat liver homogenates (kcat= 71.5 µmol x mL/(min x mg protein), KM given without parameter) and the activity is inhibited by denaturation of proteins (boiling) (data only available as graph)
- MFP hydrolysis is pH-dependent, with complete hydrolysis within 4 h at pH < 0.8, while at pH > 2.2 only 0.1 to .1 % are hydrolysed (Table 6)
- Formulation I and II both raise the pH of human gastric fluids above 2.6 thereby impairing the hydrolysis of MPF (Table 3 and 7)
- The pKas of fluorophosphoric acid at 37 °C are ca. 0.8 and 5.08
- metabolic fate of sodium MFP:
Based on the presented results the authors conclude that sodium MFP passes the gastric environment almost un-hydrolysed if the pH is raised above 2.2 by administration with food or in appropriate formulations. MFP is absorbed readily in the intestine and then cleaved there or in the liver by phosphatase (e. g. alkaline phosphatase). Serum MFP cleavage is negligible. Co-administration of Calcium salts is proposed to inactivate the traces of fluoride formed in the gastric tract by precipitation as calcium fluoride.

Any other information on results incl. tables

Table 1: Hydrolysis rate of MFP (µmol/min) in the presence of 1 U/mL of alkaline phosphatase (ALP) at pH 11.2 or pH 7.2, or of 0.4 U/mL of acid phosphatase (AcP) at pH 4.8 or pH 7.2.

Concentration of NaFPO3 (mrnol/B	ALP 1 U/mL		AcP 0.4 mU/mL
	pH 11.2	pH 7.2	pH 4.8	pH 7.2
0.28	2.3	9.3	<0.1	<0.1
0.28	2.2 a	10.8 a	<0.1	<0.1
178	10.2	80.6	<0.1	<0.1
27.79	55.6	190.8	<0.1	<0.1
27.79	57,4 b	179.4 b	<0.1	<0.1
277.87	463.1	528.0	<0.1	<0.1

a: in the presence of 0.28 mmol/L NaF; b: in the presence of 27.79 mmol/L of NaF

Table 2: Hydrolysis rate of MFP (% hydrolysed/min) in human gastric juice at 37 °C.

Subject	pH	Hydrolysis rate
		Found	Expected a
1 (basal)	1.51	0.03	0.01
1 (pentag.) b	0.96	0.22	0.27
2 (basal)	1.93	0,01	0.00
2 (pentag.)	1.03	0,17	0.19
3 (basal)	2.06	0.00	0.00
3 (pentag.)	1.13	0.12	0.10
1 ( + HCl)	0.70	0.65	0.75
2 (+ HC1)	0.80	0.48	0.53
3 (+ HCI)	0.90	0.35	0.35

a: according to hydrolysis due to pH (see Table 7); b: pentagastrin

Table 3: Hydrolysis rate of MFP (% hydrolysed/min) in canine intestinal fluid adding Na2FPO3, Formulation I or Formulation II

Dog No.	pH				Hydrolysis rate.
	Before	After addition of			Before	After addition of
		Form. I	Form. II	5 mol/L HCI		Form. I	Form. II	5 mo1/1
1	6.4	6.7	7.2	0.95	<0.001	<0.001	<0.001	0.21
2	6.8	7.1	7.5	1.03	<0.001	<0.001	<0.001	0.16
3	5.9	6.3	6.9	1.01	<0.001	<0.001	<0.001	0.19
4	6.3	6.5	7.1	0.98	<0.001	<0.001	<0.001	0.22
5	6.6	6.8	7.3	0.99	<0.001	<0.001	<0.001	0.18

Table 4: Hydrolysis rate of MFP (% hydrolysed/h) in human blood, plasma or hemolyzed red cells with 2 concentrations of Na2FPO3. Averages and standard deviations of 4 subjects.

Medium	Na2FPO3 (mg/m1)
	0.1	1
Blood	7.4±2.4	2.5±1.4
Plasma	5.9± 1.6	± 1.2
Red cells	9.2±1.5	6.5± 1.9

- Table 5: Hydrolysis rate of MFP (µmol/min) with rat intestine homogenate, 4 mg/ml protein.

Concentration of Na2FPO3 (mmo1/L)	Hydrolysed FPO3 (µmol/min)
0.14	4.6
0.47	15.7
1.56	52.1
5.21	119.8
17.36	126.2
34.73	119.3
69.46	112.3
138.94	107.4
277.87	117.6

Table 6: Hydrolysis rate of MFP (% hydrolysed/min) at different pH values and at 37 °C in a solution of 0.7557 mg/mL of Na2FPO3

pH adjustment	Time (h)
	0		0.5		2		4
	pH	% fluoride	pH	% fluoride	pH	% fluoride	pH	% fluoride
HCl	0.43	8.6	0.38	56.6	0.34	85,1	0,31	100
	0.78	8.1			0,73	43,4	0.67	100
	0.98	8.1			0.92	23_	0,89	67,5
	1.12	7.4			1.08	13.8	1.05	34.1
	132	7.7			1.31	10,3	1.29	19.2
	1,56	7.9					1,55	16.6
	1.64	7.5					1.62	12.3
Citrate	2.28	7.6					2.28	7.7
	3.02	7.3					3.01	7.5
	3.98	6.7					3.97	7.7
Phosphate	6.81	7.8					6.80	8.3
	7.50	8.0					7.48	8.4
NaOH	13,03	6.9					13.01	8.0

Table 7: Hydrolysis rate of MFP (% hydrolysed/min) in human gastric juice to which Formulation I or Formulation II were added

Subject	pH			Hydrolysis rate
	Before	After		Before	After
		Form. I	Form. II		Form. I	Form. II
1	0.96	2.78	3.15	0.22	<0.001	<0.001
2	1.03	2.85	3.22	0.17	<0.001	<0.001
3	1.13	2.66	3.18	0.12	<0.001	<0.001

Applicant's summary and conclusion

Conclusions:

The kinetics of sodium monofluorophosphate (sodium MFP) hydrolysis was analysed. pH dependence of the un-catalysed reaction was determined and the ability of different body fluids, tissue homogenates and solutions of alkaline phosphatase and acid phosphatase to catalysed the reaction was determined.
Sodium MPF is stable in solutions with a pH > 2.2. In liver an intestine mark able protein based catalytic activity is present while blood shows hardly any such activity and no activity was found in gastric juices.

Executive summary:

In the present study (Setnikar, 1988) the kinetic of sodium monofluorophosphate (sodium MFP) hydrolysis was analysed using the detection of formed fluoride ions potentiometrically by a fluoride ion specific electrode. The catalytic activity of the following body fluids, homogenates and purified enzymes was tested: rat liver homogenate; rat intestine homogenate; dog intestinal juice; human gastric juice; human whole blood, serum and blood cells; purified alkaline phosphatase; purified acid phosphatase. In addition the pH dependence of the un-catalysed reaction was determined.

It was found that sodium MPF is stable in solutions with a pH > 2.2. In liver an intestine mark able protein based catalytic activity is present while blood shows hardly any such activity and no activity was found in gastric juices. Alkaline phosphatase has a mark able activity to cleave MFP both at neutral and alkaline pH while the catalytic activity of acid phosphatase for this reaction is negligible both at neutral and acidic pH.

Concerning the metabolic fate of MFP based on the presented results the authors conclude that sodium MFP passes the gastric environment almost un-hydrolysed if the pH is raised above 2.2 by administration with food or in appropriate formulations. MFP is absorbed readily in the intestine and then cleaved there or in the liver by phosphatase (e. g. alkaline phosphatase) which leads to the release of fluoride. Serum MFP cleavage is negligible. Co-administration of calcium salts is proposed to inactivate the traces of fluoride formed in the gastric tract by precipitation as calcium fluoride.