i) When oral administration of a drug is not suitable as in infants or patients suffering from nausea, vomiting and gastrointestinal disturbances; suppositories serve as an alternate for drug administration.
ii) They have been used for a variety of conditions like hemorrhoids and local infections in vagina and rectum.
iii) Drugs like hypnotics, tranquillizers, antispasmodics etc., are often given as suppositories. This provides the advantage that the biotransformation of drugs in liver, pH conditions and gastrointestinal enzymes are avoided as the portal circulation is bypassed.
iv) Oral administration of phenylbutazone and indomethacin may cause gastric irritation hence these drugs are sometimes administered rectally.
v) Suppositories have also been used for prolongation of drug action.
vi) Absoprtion of drugs from rectal mucosa directly into the venous circulation may bring about a faster onset of action as compared to oral administration.
vii) Undissociated drugs are absorbed more rapidly from gastric mucosa than the ionised ones.
viii) Rate of diffusion of drugs from the dosage form to the site of absorption depends upon nature of the medicament, its lipid/water solubility, physical state of the colon and the amount and nature of the solids and lipids present in the colon.
ix) In general, presence of surfactants may increase the rate of diffusion unless complexation takes place. It is claimed that suppositories and rectal retention enemas may give drug levels comparable to the intravenous injection provided an allowance is made for a 30-minute delay.