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Can anyone tell me oral dose equivalence for subcutaneous scopolamine? I'm
examining the cognitive and electrophysiological responses to cholinergic
drugs in humans.
My question stems from the following: Safer and Allen (Biol. Psychiatry 3
;347-355,1971) suggest that the ratio of oral to i.v. effective dose for
frequency of hallucinations is .aaa. 4 to 1. Intrusion errors on memory tests
linearly increase with doses starting from 0.5mg s.c., but rarely below
(e.g., Wesnes et al, Annals NYAS: 268-271, 1991), whereas Broks et al
(Neuropsychologia 26: 685-700) found a linear increase in memory intrusions
with oral doses of 0.3mg, 0.6mg and 1.2 mg. Other studies have found linear
decrements in cognition (vigilance, memory, sedation) with low oral doses
(0.15-1.2mg; e.g. Parrott, Psychopharm 89:347-54). There is no equivalent
dose response data for i.v. The discrepency could be due to the higher level
of sensitivity of the tasks in the oral studies, but maybe S&A underestimate
oral scopolamine's effectiveness. Alternatively, is s.c. a much less
effective route than i.v. ?
The only PK study I've found is by Putcha et al. (Pharm. Res. 6: 481-5) who
found mean peak plasma concentrations of 0.4mg to be >5 times higher i.v.
versus oral. Can anyone refer me to PK data on s.c. versus oral? Also, can
anyone shed some light on the above results. I know that no relationship
between peak plasma concentrations & cogniton has been established, but
would appreciate any input.
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