Sodium sulfate Isoniazid

Sodium sulfate and castor oil used as laxatives can cause a modest but probably clinically unimportant reduction in isoniazid absorption. 

In an experimental study of the possible effects of laxatives on isoniazid absorption, healthy subjects were given 10 to 20 g of oral sodium sulfate or 20 g of castor oil (doses sufficient to provoke diarrhoea). Absorption, measured by the amount of isoniazid excreted in the urine, was decreased by 50% with castor oil and by 41% with sodium sulfate at 4 hours. However, serum levels of isoniazid were relatively unchanged. The overall picture was that while these laxatives can alter the pattern of absorption, they do not seriously impair the total amount of drug absorbed. ... 

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