Table 2

ED₅₀ values (95% confidence limits; milligrams per kilogram, s.c.) of four currently available antipsychotics for the induction of prolactin release, the antagonism of apomorphine-induced abnormal behaviour, and the occupancy of D2 receptors in the pituitary and the striatum

Compound	ED₅₀ for Elevating Prolactin > 20 ng/ml		ED₅₀ for D2 Receptor
Compound	Prolactin Release	Apomorphine Antagonism	Ratio	Pituitary	Striatum	Ratio
	mg/kg, s.c.; 95% CL^2-a			mg/kg, s.c.; 95% CL^2-b
Amisulpride	0.0017	37	21764	0.026	17	654
	(0.00074–0.0037)	(28–51)		(0.017–0.038)	(15–19)
				[r ²: 0.90; p: 0.12]	[r ²: 0.98; p: 0.76]
Risperidone	0.0050	0.070	14	0.081	0.89	11
	(0.0032–0.0077)	(0.047–0.102)		(0.053–0.122)	(0.68–1.17)
				[r ²: 0.90; p: 0.14]	[r ²: 0.96; p: 0.94]
Quetiapine	0.55	5.8	10	4.1	24	6
	(0.30–1.00)	(4.6–7.1)		(2.4–7.1)	(14–40)
				[r ²: 0.84; p: 0.063]	[r ²: 0.88; p: 0.063]
Olanzapine	0.10	0.17	1.7	0.43	0.30	0.7
	(0.058–0.19)	(0.12–0.23)		(0.37–0.49)	(0.26–0.36)
				[r ²: 0.98; p: 0.75]	[r ²: 0.98; p: 0.27]

CL, confidence limits.
↵2-a ED₅₀ values were determined from the fraction of rats achieving a biologically significant (>20 ng/ml) prolactin elevation using two to three doses over a 4- to 16-fold range.
↵2-b ED₅₀ values were determined from the sigmoidal log dose-receptor occupancy curve (Fig. 1) of best fit by nonlinear regression analysis with the GraphPad Prism program. Note a p value >0.05 means that the data does not systematically deviate from the sigmoidal curve.