Pharma excipients ‘may affect gastrointestinal tract’, says study

pharmafile | July 31, 2013 | News story | Manufacturing and Production Taylor, excipients 

Excipients used in oral solid dosage forms are typically considered to be inert, but researchers in Japan have found they may an impact on drug therapy. 

The team carried out a study looking at the effects of dosing 20 commonly-used pharmaceutical excipients on the gastrointestinal mucosa of rats, to see if they had an impact on the way drugs are absorbed.  

Their findings suggest formulation scientists should consider the choice of excipients carefully when designing new drugs, and could also explain reports of differing pharmacological effects between generic and brand name drugs. 

The scientists from Tokyo, Tohoku and Tasaaki universities in Japan found that some pharmaceutical excipients – including binders, disintegrants, lubricants, diluents and sustained release substrates – affected the ability of water-soluble drug compounds to cross the GI mucosal membrane.

Specific excipients that showed effects on the GI mucosa included methyl-beta-cyclodextrin, a diluent, and the disintegrants sodium carboxymethyl starch, low-substituted hydroxypropyl cellulose and croscarmellose sodium.

Interestingly, the team also found that excipients could both decrease membrane permeability to drugs and increase it, which suggests that the properties of certain excipients could be exploited to design more effective drug formulations. They also found that excipient sometimes affected permeability in one part of the small intestine and not another.

“Pharmaceutical excipients should not disturb the effects of drug therapy,” say the authors. They note however that in recent years it has been reported in recent years that excipients may induce some changes to the gastrointestinal tract which may affect drug disposition, likely acting on so-called ‘paracellular’ structures such as tight junctions.

Tight junctions hold cells together but also serve as a protective barrier and help control the transfer of molecules by forcing them to be actively taken up and secreted by mucosal cells. Other studies have suggested excipients can also affect P-glycoprotein, a transporter molecule involved in transferring substances across cell membranes.

“Currently, the impact of … excipients on the GI mucosal membrane is not considered in the selection criteria of pharmaceutical excipients in the pharmaceutical industry,” they write.

The study will be published in the 10 September issue of the International Journal of Pharmaceutics.

Phil Taylor

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