For patient conveniency and their acceptance tablets are
often coated, also to protect drug from gastric acid etc but the tendency of
formulations to adhere can be affected by coatings themselves. The result of
using isolated oesophageal preparations in In vitro studies is that the hard
gelatin capsules had greatest tendency to adhere. While the film coated
tablets, uncoated tablets, sugar coated tablets show minimum adhesion.Calculations
show that the tendency of adhesion of hard gelatin capsules is 6 times than the
tendency of sugar coated tablets and when calculated per unit area it is 1.5
times than that of soft gelatin capsules.
Normally, human studies do not accept the difference of hard
and soft gelatin capsules in their tendency to adhere.Though there is shorter
oesophageal passage time of coated tablets
than plain tablets but it take longer for them to break, if they do
lodge. Coatings having low tendency to adhere are made up from cellulose
acetate phthalate, shellac, methacrylate copolymer and a copolymer composed
from of vinyl acetate and crotonic acid.
In order to improve
the adhesion tendency of
hydroxypropylmethylcellulose, sucrose is incorporated which helps to reduce the
surface stickness; while the addition of titanium oxide, lactose and talc
increases the tendency to adhere. On the other hand , greatest tendency to
adhere is shown by polyethylene glycol 6000 coating .A variety of studies in
humans show that capsules get stuck in the oesophagus with a much higher rate
than tablets. Hard gelatin capsule can become adherent to mucosa by absorbing sufficient
water, if its passage through the oesophagus is hindered for more than two
minutes. Besides gelatin, cellulose derivatives and guargum are materials that
become sticky as hydrated. According to recent studies,guargum when transformed
into a slimming product hydrated and developed a large sticky mass which was
enough to cause oesophageal barrier.
Not only the pharmaceuticals dosage forms get stuck into the
oesophagus but neutraceuticals can also cause this hazard as reported by recent
researches where an anhydrous protein health food tablet get stuck to the
oesophagus so strongly that it had to be removed by endoscopy.
With the newly developed Dosage forms there will be no need
of drinking water for swallowing . although these dose forms are retained in
mouth and oesophagus yet saliva is needed for clearance.
One of the example of quickly disintegrating solid dosage
forms is the Zydis® formulation (Scherer DDS Ltd) that can be taken without
water.the fast dissolving dosage forms can be cleared through buccal cavity by
either of two methods; to clear with the help of several swallows after
dissolving or to pass the whole through oesophagus.
OF ADHESION OF DOSAGE FORMS
Drug absorption can be delayed due to withholding of dosage
form in oesophagus and thus the commencement of action.it becomes difficult for
drugs to pass through the strarified squamous epithelium of oesophageal mucosa.
Disintegration time of the unit in oesophagus is the factor on which the passage of the drug into the stomach and
through the small intestine depends.