Table 1.

N-(4-hydroxyphenyl)retinamide (4-HPR), N-(4-methoxyphenyl)retinamide (4-MPR) and 4-oxo-N-(4-hydroxyphenyl)retinamide (4-oxo-4-HPR) levels in plasma of neuroblastoma patients

	Mean ± standard deviation (µM)
Hours after treatment (n = 3)	4-HPR	4-MPR	4-oxo-4-HPRa
0	7.04 ± 4.75	4.03 ± 2.98	0.91b
2	9.69 ± 7.30	4.91 ± 3.69	1.27b
4	12.82 ± 8.08	5.72 ± 4.21	0.86 ± 0.66c
6	13.11 ± 8.50	6.61 ± 5.75	0.43b
8	8.55 ± 6.42	4.69 ± 3.92	1.00 ± 0.72d

Blood was taken from three patients treated at the 595 mg·m⁻² per day dose level. All blood samples were collected on day 6 of cycle 1, just before and after the first dose of the day, and plasma was prepared as described. Doses of 4-HPR were given twice a day, 12 h apart and the zero time value represents blood taken just before the first dose of day 6, that is, 12 h after the last dose on day 5.

^aNot all patients were analyzed for 4-oxo-4-HPR at the indicated hour.

^bn = 1

^cn = 2

^dn = 3.