Disposition, metabolism and mass balance of [¹⁴C]apremilast following oral administration

Figures & data

Figure 1.  Structure of apremilast, with the site of the ¹⁴C label indicated (*).

Figure 2.  Cumulative elimination of radioactivity in urine and faeces after a single oral 20-mg dose of [¹⁴C]apremilast in male healthy subjects (• urine, ○ faeces, ▪ total). Values are mean ± standard deviation.

Table 1.  Plasma and whole blood total radioactivity pharmacokinetic parameters following a single oral 20-mg dose of [¹⁴C]apremilast.

PK parameter	Whole-blood total radioactivity^a	Plasma total radioactivity^a	Blood-to-plasma ratio
Cmax (ngEq/mL)	303 ± 77	527 ± 127	0.57
Tmax (h)	2.0 (1.0–3.0)	1.5 (1.0–3.0)	NA
AUC0–t (ngEq*h/mL)	3489 ± 509	6201 ± 937	0.56
AUC0–∞ (ngEq*h/mL)	3664 ± 556	6632 ± 653	0.55
t½ (h)	16.3 ± 5.2	50.4 ± 8.7	NA

NA, not applicable; ngEq, ng [¹⁴C]apremilast equivalent.

^aValues are reported as mean ± standard deviation except T_max values, which are reported as median (min-max).

Table 2.  Mean ± standard deviation plasma pharmacokinetic parameters for apremilast and circulating metabolites after a single oral 20-mg dose of [¹⁴C]apremilast.

	TRA	Apremilast^a	Apremilast^b	M11	M12	M13	M14	M16
Cmax (ngEq/mL)	527 ± 127	333 ± 76	321 ± 134	20.2 ± 7.6	111 ± 36	7.5 ± 6.8	9.4 ± 4.3	27.6 ± 26.0
Tmax (h)	1.5 (1.0–3.0)	1.5 (1.0–3.0)	1.8 (1.0–2.5)	1.0 (0.5–2.5)	2.5 (1.0–2.5)	2.5 (1.0–24)	2.5 (1.0–24)	5.3 (1.0–8.0)
AUC0–t (ngEq*h/mL)	5483 ± 825^c	1913 ± 339	2455 ± 690	139 ± 89	2124 ± 331	133 ± 125	269 ± 146	363 ± 54
AUC0–∞ (ngEq*h/mL)	6632 ± 653	1970 ± 343	2636 ± 705	232 ± 151	2446 ± 416	n/c^d	n/c	389 ± 91
t½ (h)	50.4 ± 8.7	6.8 ± 2.6	7.1 ± 2.7	10.7 ± 10.2	15.8 ± 3.9	n/c	n/c	11.0 ± 2.4

T_max, median and range; TRA, total radioactivity.

^aApremilast concentrations in plasma determined using a Chiral LC/MS/MS assay.

^bApremilast and metabolite concentrations in plasma calculated using plasma radioactivity concentrations and radiochromatography. ^cAUC_0–48 was used for TRA for these calculations.

^dNot calculated.

Figure 3.  Concentration versus time curves for radioactivity in plasma (○), apremilast in plasma (•) and radioactivity in blood (▪) following a single oral 20-mg dose of [¹⁴C]apremilast in healthy male subjects. Values are mean ± standard deviation.

Figure 4.  Concentration versus time curves for total radioactivity (TRA), apremilast, M11, M12, M13, M14 and M16 in plasma following a single oral 20-mg dose of [¹⁴C]apremilast in healthy male subjects. Values are mean ± standard deviation.

Figure 5.  Representative radiochromatograms of (A) 0–24-h pooled plasma, (B) 0–24-h pooled urine and (C) 0–48-h pooled faeces after a single oral 20-mg dose of [¹⁴C]apremilast in healthy male subjects.

Table 3.  Fragment ions and relative amounts for apremilast metabolites characterized in plasma, urine and faeces

Metabolite Characterization				Plasma (% AUC relative to TRA)^d	% of dose excreted
Number	Pathway	[M + H]^+ a	Fragment Ions		Urine	Faeces
Apremilast	Unchanged	461	257, 205, 178, 163, 150	44.8	2.8	4.1
M1/M2	Hydrolysis products of apremilast	479	274, 257, 223, 206, 178	D	0.9	0.5
M3	O-Demethylation	447	243, 164, 136	D	D	4.6
M4	O-Demethylation, N-deacetylation	405	243, 164	ND	ND	2.4
M7	N-Deacetylation	419	257, 178, 163	D	D	0.1
M8	Hydroxylation, O-demethylation, N-deacetylation	421	243, 179, 164	ND	ND	1.0
M9	Hydrolysis product of M3	465	260, 243, 223, 206, 164	ND	ND	7.7
M10	Hydroxylation, O-demethylation	463	243, 221, 164, 163, 136	ND	ND	1.3
M11	Hydroxylation, N-deacetylation	435	257, 179, 178	2.5	ND	1.4
M12	O-Demethylation, glucuronidation	623	447, 243	38.7	33.7	ND
M13	O-Deethylation, glucuronidation	609	488, 433, 229, 205, 150	2.4	2.0	ND
M14	O-Demethylation, N-deacetylation, glucuronidation	581	405, 243	4.9	4.0	ND
M15	Hydrolysis product of M12	641	465, 436, 260, 243, 164	ND	3.3	ND
M16	Hydroxylation, glucuronidation	653	477, 397, 257	6.6	0.6	ND
M17	Hydroxylation	477	257, 221, 178, 163	D	1.2	0.9
M18	Hydrolysis	222^c	178, 136, 134, 92	ND	ND	1.4
M19	O-Demethylation, O-deethylation	419	215, 205, 163, 136	ND	ND	0.8
M20^b	O-Demethylation, O-deethylation, N-deacetylation	377	215, 163, 136	ND	ND	0.5
M21^b	Hydroxylation, O-demethylation, O-deethylation	435	221, 215, 163, 136	ND	ND
M22	Hydrolysis, O-deethylation	451	246, 229, 223, 206, 150, 135	ND	ND	0.6
M23	Hydrolysis, hydroxylation	238^c	194, 150, 136, 92, 74	ND	ND	3.0

ND, not detected; D, detected by MS, but at concentrations too low to accurately quantify by radiochromatography.

^aMany compounds were observed as [M + H]⁺ and [M + NH₄]⁺.

^bM20 and M21 coeluted under the HPLC conditions used.

^cCharacterized in negative mode, so values are [M – H]^–.

^dAUC_0–t (unchanged drug or metabolite)/AUC_0–48 (TRA) * 100%.

Figure 6.  Mass spectral fragmentation of apremilast.

Figure 7.  Metabolic scheme of apremilast in humans. For hydrolysed phthalidomide ring products, only one of two possible forms is shown. [M5, O–desethyl apremilast, was not observed in this study and is a proposed intermediate metabolite] (GLU: glucuronic acid, * site of ¹⁴C label).

Table 4.  Phosphodiesterase type 4 and tumour necrosis factor-α inhibitory activities of apremilast and its metabolites.

Compound	PDE4 IC50 (μM)	TNF-α IC50 (μM)
Apremilast (S-isomer)	0.074	0.077
M1/M2; Hydrolysis products of apremilast (S-isomer)	120	77
M3; O-Desmethyl apremilast (S-isomer)	8.3	5.6
M5; O-desethyl apremilast (racemate)	44	4.9
M7; N-deacetyl metabolite (S-isomer)	0.16	0.13
M12; O-Desmethyl apremilast glucuronide (S-isomer)	>100	>10
M14; O-Desmethyl, N-deacetyl apremilast glucuronide	>80	>10
M16; Acetamide hydroxylation glucuronide (S-isomer)	6.5	>10
M17; Acetamide hydroxylation (S-isomer)	0.094	0.021