Metformin hydrochloride

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

June 24, 1994 - June 29, 1994

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP study performed according to FDA TAD 3.09 (Hydrolysis)

Qualifier:

according to guideline

Guideline:

other: FDA TAD 3.09

GLP compliance:

yes

Radiolabelling:

yes

Analytical monitoring:

yes

Buffers:

0.1 M sodium acetate (NaC2H3O2, formula weight (FW) = 82.03 g/mol): 0.410 g of sodium acetate were dissolved and brought to a final volume of 500 mL with ABC reagent water. The pH was adjusted to 5.00 using 0.1 M acetic acid.

0.067 M potassium phosphate, dibasic (K2HPO4 FW = 174.2 g/mol): 5.836 g of K2HPO4 was dissolved in 500 mL of ABC reagent water.

0.067 M sodium phosphate, monobasic (NaH2PO4, FW = 137.99 g/mol): 4.623 g of NaH2PO4 was dissolved in 500 mL of reagent water. pH 7 buffer was prepared by mixing 165 mL of 0.67 M sodium phosphate and 335 mL of 0.067 M potassium phosphate. A 1:10 dilution of pH 7 buffer was made with ABC reagent water, pH was adjusted to 7.00 with 0.1 M acetic acid.

0.025 M sodium tetraborate (Na2B4O7 x 10H2O, FW = 381.4 g/mol): 4.768 g of sodium tetraborate were dissolved and brought to a final volume of 500 mL with ABC reagent water. The pH was adjusted to 9.00 with 0.1 M acetic acid.

Details on test conditions:

Test Containers
The test containers used for this study were - 7-mL amber glass vials with Teflon-lined screw caps. The test containers were located in a temperature-controlled shaker water bath maintained at 50 ± 1 °C.

Reagent Water
The reagent water used is the product of a multiple-step deionization and purification process that begins by passing feed water over cation, anion, and unibed ion-exchange resin beds (Culligan Corporation, Northbrook, IL). For final purification, the deionized water is plumbed directly to a Millipore (Bedford, MA) Milli-Q system. The system delivers water that has a resistivity of 16-18 megohm • cm. As water leaves the purifiers, it passes through a final 0.2 µm hollow fiber filter. This water was used to prepare the buffer solutions.

Duration:

5 d

pH:

5

Temp.:

50 °C

Initial conc. measured:

10 mg/L

Duration:

5 d

pH:

7

Temp.:

50 °C

Initial conc. measured:

10 mg/L

Duration:

5 d

pH:

9

Temp.:

50 °C

Initial conc. measured:

10 mg/L

Number of replicates:

3

Positive controls:

no

Negative controls:

no

Statistical methods:

standard statistical methods applied

Transformation products:

no

% Recovery:

103

pH:

5

Temp.:

50 °C

Duration:

5 d

% Recovery:

99

pH:

7

Temp.:

50 °C

Duration:

5 d

% Recovery:

98.7

pH:

9

Temp.:

50 °C

Duration:

5 d

Key result

pH:

5

Temp.:

50 °C

Remarks on result:

hydrolytically stable based on preliminary test

Key result

pH:

7

Temp.:

50 °C

Remarks on result:

hydrolytically stable based on preliminary test

Key result

pH:

9

Temp.:

50 °C

Remarks on result:

hydrolytically stable based on preliminary test

Other kinetic parameters:

For details see executive summary

Details on results:

A preliminary study was conducted at a nominal test concentration of 10 ppm with14C-metformin HCl. Test solutions were prepared in aqueous buffers of pH 5, 7 and 9. The purpose of this study was to estimate the percent of 14C-metformin HCl hydrolyzed after 5 days.

Radiochemical Purity
The radiochemical purity of the test chemical was determined to be 99.6 ± 0.0% from triplicate HPLC analyses.

Dose Solution Analysis and Dose Verification
The nominal concentration of 10 ppm was confirmed by measuring concentration of radiolabeled test samples. The measured concentration (by LSC of test solutions) in pH 5, 7, and 9 buffers at the initiation (day 0) were 9.79, 10.2, and 10.6 µg/mL, respectively. The measured concentrations of the 14C-metformin HCl were determined to be 9.71, 9.97, and 10.4 µg/mL, respectively based on HPLC analysis.

Characterization of Test Chemical
Following 5 days of hydrolysis at 50 °C, the mean percent of14C-metformin HCl in solution was 103%, 99.0%, and 98.7% of time 0 for the pH 5, 7 and 9 test systems, respectively. The percent of the initial concentration hydrolyzed [(Co-Cs/Co) x 100%] of 14C-metformin HCl was negative for pH 5 test system. At pH 7 and 9 the percent of the initial concentration hydrolyzed was 1.04% and 1.27%, respectively. The UV-detector and radiodetector profiles show similarity in the hydrolysis patterns as seen in the HPLC chromatograms of selected sampling points. The hydrolysis rate test was not preformed since the test chemical concentration is greater than 90% or more of the initial concentration. The test chemical is considered to be hydrolytically stable. The half-life would be equal to or greater than a year at 25 °C.

Confirmational Analysis
In order to confirm the results obtained with the analytical method developed by ABC Laboratories, representative samples were analyzed by the method supplied by the study sponsor. One replicate sample for each pH was analyzed. The results of those analyses support the results of the original analyses.

14C-Mass Balance
The radioactivity mass balance at the study termination following 5 days of hydrolysis was 103%, 98.6%, and 98.9% for the pH 5.0, 7.0, and 9.0 test systems, respectively.

pH of the Test Solutions
The pH of the test solutions remained stable during the course of the study with less than 5% change in pH values between initiation and termination of the test.

For details see executive summary

Validity criteria fulfilled:

yes

Conclusions:

14C-metformin was shown to be hydrolytically stable at 50 °C. Therefore, the hydrolysis rate test was not performed since, based on the preliminary results, the test chemical concentration in the preliminary investigation was greater than 90% of the initial concentration.

Executive summary:

Study Design

The hydrolysis of the test item was determined in a GLP study according to FDA TAD 3.09.
In detail, the study with ¹⁴C-metformin HCl was conducted at a nominal test concentration of 10 ppm in three aqueous buffer solutions in a shaking water bath maintained at 50 ± 1 °C. The buffer systems were pH 5 (0.010 M acetate buffer), pH 7 (0.05 M phosphate buffer), and pH 9 (0.025 M borate buffer). The concentration of ¹⁴C-metformin HCl in each test sample at day 0 and day 5 was measured using high-performance liquid chromatography (HPLC). Liquid scintillation counting was used to determine the total radioactivity of the test chemical at each sample point.

Results

The data generated during this study confirmed that the test chemical, ¹⁴C-metformin HCl, did not hydrolyze in the pH range between 5 and 9. Following 5 days of hydrolysis at 50 °C, the mean percent of  ¹⁴C-metformin HCl in solution was 103%, 99.0%, and 98.7% of time 0 for the pH 5, 7, and 9 test systems, respectively. The percent of the initial concentration of  ¹⁴C-metformin HCl hydrolyzed [((Co-Cs)/Ca) x 100%] was negative for pH 5 test system. At pH 7 and 9 the percent of the initial concentration hydrolyzed was 1.04% and 1.27%, respectively.

Conclusion

¹⁴C-metformin was shown to be hydrolytically stable at 50 °C. Therefore, the hydrolysis rate test was not performed since, based on the preliminary results, the test chemical concentration in the preliminary investigation was greater than 90% of the initial concentration.

Description of key information

14C-metformin was shown to be hydrolytically stable at 50 °C. Therefore, the hydrolysis rate test was not performed since, based on the preliminary results, the test chemical concentration in the preliminary investigation was greater than 90% of the initial concentration.