Stimulant laxatives:
(1) bisacodyl (Ex-Lax, Correctol, Dulcolax)
(2) anthraquinones
(2a) senna (Senokot, Castoria, Black Draught)
(2b) cascara
Usual screening method of detection: thin layer chromatography on urine or stool
Causes of a false negative test:
(1) intermittent use of the laxative
(2) single specimen tested
(3) testing only urine or stool (not both)
(4) use of senna (the metabolite Rhein is not detected at clinical levels by TLC)
False positive results for bisacodyl may occur, so a single positive result should not be used alone to make the diagnosis.
If the results of the TLC screen are in doubt, then alternative testing (HPLC, other ) should be performed.
