TABLE 1.

Potencies, expressed as ED₅₀ or dose ratio (ED₅₀ of combination of fentanyl and alprazolam/ED50 of fentanyl alone), in rhesus monkeys responding under a progressive-ratio schedule (N=6).

ED50 (μg/kg/injection)							Dose Ratio (Combination ED50/Fentanyl Alone ED50)
Alprazolam-Taking (N=3)a
	M-1170b	M-1027	M-42901	mean	S.E.M.			M-1170	M-1027	M-42901	mean	S.E.M.
Fentanyl alone	0.17	0.22	0.55	0.31	0.12			1.00	1.00	1.00	1.00	0.00
3:1	0.13	0.14	0.28	0.18	0.05			0.76	0.64	0.51	0.64	0.07
1:1	0.071	0.036	0.25	0.12	0.07			0.42	0.16	0.45	0.35*,c	0.09
1:3	0.044	0.012	0.25	0.10	0.07			0.26	0.05	0.45	0.26*	0.12
Non-Alprazolam-Taking (N=3)
	M-98-007	M-41123	M-42901	mean	S.E.M.			M-98-007	M-41123	M-42901	mean	S.E.M.
Fentanyl alone	0.20	0.092	0.38	0.22	0.08			1.00	1.00	1.00	1.00	0.00
3:1	0.12	0.22	0.28	0.21	0.05			0.60	2.39	0.74	1.24	0.58
1:1	0.026	–d	0.13	0.08	0.05			0.13	–	0.13	0.13	0.00
1:3	0.072	–	0.38	0.23	0.15			0.36	–	0.38	0.37	0.01

^aPotencies are grouped into monkeys that self-administered alprazolam alone above vehicle levels (“Alprazolam-Taking”) and those that did not (“Non-Alprazolam-Taking”).

^bMonkey identification numbers.

^cNote that *P < 0.05 versus Fentanyl alone, Dunnett’s test.

^dDashes indicate potency could not be calculated due to no significant self-administration above vehicle levels.