Oral administration of niclosamide is troublesome unless your target is a tapeworm.  This drug is insoluble in water and barely soluble in alcohol. It also suffers a deleterious  journey through the gut where the enzymes CYP1A2 and UGT1A1 severely degrade this medication.  Little is absorbed into the blood plasma and what’s left fortuitously affects the tapeworm very effectively.  

Consider the fact there are scores of drugs, insoluble in water and with similar molecular weight to niclosamide, delivered by mouth.  For a variety of clinical reasons, among these are many that are compounded into suppository form for delivery within the rectum.   And they work every efficiently.  

A rectal suppository mitigates a drug’s exposure to enteric/first-pass hepatic metabolism, improving its bioavailability. The rectal mucosa, richly vascularized by the inferior and middle veins, connect directly to the systemic circulation.  The more proximal superior rectal vein connects to the portal system.  Thus the distal two-thirds of rectal
mucosa is the optimal target surface area for maximum uptake.

The literature on niclosamide discloses no attempts to employ a rectal suppository as a delivery system, which makes sense.  Oral administration has worked safely and effectively for half a century.  What would motivate any researcher to test suppositories?  Perhaps current attempts to repurpose this unique drug should go beyond nanotechnology and pulmonary sprays and consider this overlooked mode of administration.