Syrup is commonly given sweet taste, but sachets are given sour taste because syrup is supplied as a viscous liquid and viscous liquid stays in oral cavity for longer time. If they are made sour, then that sour taste cannot be endured for longer time while sweet taste is bearable. While in case of sachet sour taste provides good feel to mouth while its solution stays for short time due to being dilute. On the other hand, sachets are also commonly manufactured with citric acid as a main ingredient as it provides effervescence & convert many salts into their easy to absorb form and since citric acid is sour in taste; the sachets, when constituted, have a sour taste.
Effervescence on
one hand converts many salts into their easy to absorb form while on other hand
when sachet with effervescent properties is poured into water it results in a
distinct reaction that improves patient compliance that by their perception
that this product is something powerful so results in attraction of customer
towards product. These characteristics coupled with good drug absorption
results in a successful product.
Effervescence
caused by sodium bicarbonate is quick while effervescence caused by calcium
carbonate is slow because reactions of sodium are faster than calcium. There
are many formulations which are supplied in combination of various acids (citric
acid, tartaric acid, ascorbic acid) and bases (sodium bicarbonate, calcium
carbonate). If these acids and bases are
kept dry in the sachet then there will be minimum chance of reaction but if
there is presence of moisture (as moisture provides media for acid base
reaction due to providing mobility to molecules), it will lead to reactions
that results in the production of basic salts, water and carbon dioxide. This
carbon dioxide during shelf-life results in swelling of sachet and failure of
product stability.
NaHCO3
has the property to adsorb high quantity of moisture (may be more than 30% LOD)
and interaction of moisture between sodium and water is also strong so removal
of this moisture from sodium bicarbonate is also a challenging process.
On the other hand, calcium carbonate takes
less moisture. It is commonly less than 1% so in formulation of calcium
carbonate there is lesser risk but in case of sodium bicarbonate it may have
moisture up-to 35% or more so it should be sufficiently dried to take its
moisture to less than 1%; in that case there will be minimum chance of reaction.
Reaction of calcium carbonate with citric
acid is single step reaction. While potassium sorbate which is good
preservative for sachet also results in effervescent reaction, but effervescent
reaction of potassium sorbate happens in two steps; first it is converted into
sorbic acid and then sorbic acid is converted to calcium sorbate and there is
release of carbon dioxide. So in case of sodium bicarbonate, you will feel
immediate effervescence while in case of calcium carbonate you will see these
reactions to happen within formulations for various minutes.
Effervescence
has advantage of converting product into easy to absorb form; for example,
calcium carbonate has no solubility in water in acids etc. but in glass of
water calcium carbonate reacts with citric acid to result in calcium citrate
which has a good lipophilic absorption due to its specific structure. So, if an
effervescence reaction is undergone before intake then calcium will easily be
absorbed empty stomach but if there is no effervescent reaction then calcium
carbonate will need food in stomach because presence of food results in
production of HCl. Calcium carbonate
reacts with acid to form calcium chloride while chloride has good dissolution
in HCl, so on dissolving it gets absorbed through stomach but old people who
needs calcium supplement doesn't have good acid production in stomach so they
cannot absorb calcium carbonate without effervescence.
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