Effects on the human central nervous system of two isomers of ephedrine and triprolidine, and their interaction.

1 D(-)ephedrine is four times as potent as L(+)pseudoephedrine in producing both tachycardia and a rise in systolic blood pressure. No changes in diastolic blood pressure occurred in 12 subjects with doses of up to D(-)ephedrine (50 mg) and L(+)pseudoephedrine (180 mg). 2 Significant evidence of stimulation of the central nervous system occurred only after D(-)ephedrine in that tapping rates were increased and subjects could reliably detect that they had received an active drug. While mean performance rates in an auditory vigilance test were higher following both ephedrine isomers these changes were not significant. 3 Impairment of both tapping rates and auditory vigilance occurred following triprolidine in another group of 12 subjects. The effect was generally related to dose of antihistamine given and lasted up to 7.25 hours. Subjective effects were reliably recognized by subjects following all treatments containing triprolidine (2.5 mg or more) for up to 4.75 hours. Using analogue lines for self rating the subjective effects following triprolidine indicated both mental and physical impairment differing significantly from scores after lactose and L(+)pseudoephedrine (60 mg). 4 Combination of triprolidine (2.5 mg) and L(+)pseudoephedrine (60 mg) produced effects similar to triprolidine alone on both subjective measures and the auditory vigilance test. It is suggested that these objective tests and subjective scales could be used to measure effects on the central nervous system produced by antihistamines together with similar drugs, and their interaction with other compounds administered concurrently.