Stability of apomorphine in solutions containing selected antioxidant agents

Figures & data

Figure 1 Chromatographs and mass spectra produced by liquid chromatography–mass spectrometry.

Notes: (A) apomorphine HCl; (B) Compound 1.

Table 1 Mean residual concentration (μg/mL) of apomorphine HCl solutions, mean residual concentration (%), and color observed after specificity assay/forced degradation

Reagent	Temperature (°C)	Time (min)	Mean residual apomorphine HCl concentration (μg/mL)	Mean residual apomorphine HCl concentration (%)	Observed color changes
Water	25	0	50.0	100.0	Colorless
		10	49.9	99.7	Very light green
		60	48.5	97.1	Light green
	45	0	50.0	100.0	Colorless
		10	49.7	99.4	Light green
		60	47.5	95.0	Green
0.02 M NaOh	25	0	50.0	100.0	Colorless
		10	0	0	Brown
		60	0	0	Brown
	45	0	50.0	100.0	Colorless
		10	0	0	Brown
		60	0	0	Brown
0.02 M HCl	25	0	50.0	100.0	Colorless
		10	50.0	100.0	Colorless
		60	49.7	99.4	Colorless
	45	0	50.0	100.0	Colorless
		10	49.8	99.6	Colorless
		60	49.4	98.8	Colorless
1.2% H2O2	25	0	50.0	100.0	Colorless
		10	43.8	87.6	Colorless
		60	26.2	52.5	Colorless
	45	0	50.0	100.0	Colorless
		10	17.8	35.5	Colorless
		60	4.7	9.3	Colorless

Note: Apomorphine HCl sample solutions for each assay were prepared in duplicate (n=2).

Abbreviation: min, minutes.

Figure 2 Chromatographs of specificity assay/forced degradation of apomorphine HCl.

Notes: (A) Apomorphine HCl solution (without additive) (60 minutes at 45°C); (B) reaction of apomorphine HCl in 0.02 M NaOH (60 minutes at 45°C), no apomorphine HCl peak detected in the forced degradation by 0.02 M NaOH. (C) reaction of apomorphine HCl with 0.02 M HCl (60 minutes at 45°C); and (D) reaction of apomorphine HCl in 1.2% H₂O₂ (60 minutes at 45°C). The peak labels illustrate the retention times.

Figure 3 Natural logarithm (ln) of mean residual concentration (%) of apomorphine HCl solutions (50 μg/mL) in different antioxidant solutions over 336 hours at 25°C.

Notes: Apomorphine HCl sample solutions for each assay were prepared in duplicate (n=2). *Linear trend line of 0.1% AA solution (pH 4.00) did not include data points at 96 hours, 168 hours, and 336 hours as the rate of reaction decreased significantly after 96 hours. ^#Value from apomorphine HCl in 0.1% SMB solution (pH 4.00) at 336 hours was not included as the value was zero (or approximately zero).
Abbreviations: AA, L-ascorbic acid; SMB, sodium metabisulfite.

Figure 4 Natural logarithm (ln) of mean residual concentration (%) of apomorphine HCl solutions (50 μg/mL) in different antioxidant solutions over 336 hours at 32°C.

Notes: Apomorphine HCl sample solutions for each assay were prepared in duplicate (n=2). *Linear trend line of 0.1% AA solution (pH 4.00) did not include data points at 96 hours, 168 hours, and 336 hours as the rate of reaction decreased significantly after 96 hours. ^#Values from apomorphine HCl in 0.1% SMB solution (pH 4.00) at 168 and 336 hours were not included as the values were zero (or approximately zero).
Abbreviations: AA, L-ascorbic acid; SMB, sodium metabisulfite.

Figure 5 Natural logarithm (ln) of mean residual concentration (%) of apomorphine HCl solutions (50 μg/mL) in different antioxidant solutions over 336 hours at 37°C.

Notes: Apomorphine HCl sample solutions for each assay were prepared in duplicate (n=2). *Linear trend line of 0.1% AA solution (pH 4.00) did not include data points at 96 hours, 168 hours, and 336 hours as the rate of reaction decreased significantly after 96 hours. ^#Values from apomorphine HCl in 0.1% SMB solution (pH 4.00) at 72, 96, 168, and 336 hours were not included as the values were zero (or approximately zero).
Abbreviations: AA, L-ascorbic acid; SMB, sodium metabisulfite.

Table 2 Mean residual concentration (%), color changes, and final pH values of apomorphine HCl sample solutions (which were colorless initially) after 336 hours

Apomorphine HCl in different solutions	Experimental temperature (°C)	Mean residual concentration at 336 hours (%)*	Color of solution at 336 hours	Time (day) when color change was first observed	Period of time where mean residual concentration was within 95%–105% (hours)	pH at 336 hours#
0.1% AA	25	50.02	Copper	2	10	3.88
	32	50.98	Copper	1	10	3.93
	37	43.69	Copper	1	5	3.93
0.1% SMB	25	0.53	Very light yellow	11	<5	3.84
	32	0.05	Very light yellow	5	<5	3.63
	37	0.06	Light yellow	3	<3	3.45
0.1% EDTA	25	99.20	Light blue	4	>336	4.02
	32	90.17	Light blue	2	200	3.98
	37	84.58	Emerald	0	120	3.92
0.1% AA +0.1% SMB	25	99.73	Colorless	–	>336	3.94
	32	98.66	Colorless	–	>336	3.81
	37	95.86	Colorless	–	>336	3.64
0.1% AA +0.1% EDTA	25	85.26	Colorless	–	130	3.91
	32	70.12	Yellow	4	45	3.98
	37	74.51	Yellow	4	50	3.91
0.1% SMB +0.1% EDTA	25	88.37	Colorless	–	95	4.02
	32	77.53	Colorless	–	70	3.90
	37	70.72	Colorless	–	50	3.91
Water (without antioxidant)	25	94.68	Light blue	2	310	4.08
	32	81.23	Light blue	1	100	3.87
	37	56.84	Emerald	0	25	3.96

Notes: Apomorphine HCl sample solutions for each assay were prepared in duplicate (n=2). The initial concentration of sample solutions was 50 μg/mL.

* The acceptable limit of mean residual concentration at the end of period of stability study is between 95% to 105%.

# Initial pH was buffered by acetate buffer to pH 4.

Abbreviations: AA, L-ascorbic acid; SMB, sodium metabisulfite.

Table 3 Mean residual concentration (μg/mL), mean residual concentration (%), color changes, initial pH and post-study pH of 10 mg/mL and 50 μg/mL apomorphine HCl solutions (purged with nitrogen) after 168 hours

Experimental conditions	Experimental temperature (°C)	Mean residual concentration (%) at 168 hours*	Mean residual concentration at 168 hours	Color of solution at 168 hours	Initial pH	pH at 168 hours
Apomorphine HCl (10 mg/mL) in 0.1% SMB (buffered by acetate buffer)	25	102.2	10.2 mg/mL	Colorless	4.00	3.81
Apomorphine HCl (10 mg/mL) in 0.1% SMB (no buffer)	25	100.0	10 mg/mL	Colorless	2.71	2.27
Apomorphine HCl (50 μg/mL) in 0.1% SMB (buffered by acetate buffer)	25	20.8	10.4 μg/mL	Colorless	4.00	3.88
Apomorphine HCl (50 μg/mL) in 0.1% SMB (no buffer)	25	41.8	20.9 μg/mL	Colorless	3.44	3.04

Notes: Apomorphine HCl sample solutions for each assay were prepared in duplicate (n=2).

* The acceptable limit of mean residual concentration at the end of period of stability study is between 95% and 105%.

Abbreviation: SMB, sodium metabisulfite.

Figure 6 Natural logarithm (ln) of mean residual concentration (%) of 10 mg/mL and 50 μg/mL apomorphine HCl in 0.1% SMB solutions (with and without buffer; both purged with nitrogen) over 168 hours at 25°C.

Notes: Apomorphine HCl sample solutions for each assay were prepared in duplicate (n=2). *Linear trend line of 50 μg/mL apomorphine HCl in 0.1% SMB solutions (without buffer) did not include data points at 168 hours as the rate of reaction decreased significantly after 72 hours.
Abbreviation: SMB, sodium metabisulfite.

Table 4 Mean residual concentration (%), mean residual concentration (mg/mL) and color observation, initial pH and post-study pH of 10 mg/mL apomorphine HCl (without nitrogen purging) in 0.1% AA solution and 10 mg/mL apomorphine HCl in 0.1% EDTA solution at 25°C after 72 hours

Experimental conditions	Experimental temperature (°C)	Mean residual concentration at 72 hours (%)	Mean residual concentration at 72 hours (mg/mL)	Color of solution at 72 hours	Initial pH (buffered by acetate buffer)	pH at 72 hours
10 mg/mL apomorphine	25	99.4	9.9	Colorless	4.00	3.89
HCl in 0.1% AA	37	99.6	10.0	Colorless	4.00	3.92
10 mg/mL apomorphine	25	99.5	10.0	Colorless	4.00	4.01
HCl in 0.1% EDTA	37	100.50	10.1	Colorless	4.00	3.98

Note: Apomorphine HCl sample solutions for each assay were prepared in duplicate (n=2).

Abbreviation: AA, L-ascorbic acid.