Syrups consists of sugar in water. These are highly concentrated, obviously viscous preparations. And they may or may not contain therapeutic agent.
In simple syrup sucrose at the concentration of 85% is dissolved in water. These are sometimes used as a coating on to the surface of the tablets.
If some therapeutic agent is present, then it is called as medicated syrup.
Some syrups does not contain therapeutic agent, instead they consists of flavouring agents. These are called flavoured syrups and are generally used as vehicles. For the preparation of extemporaneous products, flavoured syrups are used as the vehicles.
These are of advantageous as they contain very less amount or no alcohol, it can be administered to small children. But patients who have to take food having less calories should be aware of amount of sugar present in liquid orals.
Effect of concentration on various factors is as follows:
- If the solution is saturated and if the temperature decreases, it results in the crystallization.
- The sugar solution should be nearly to saturation point, but should not be saturated.
- The solution at low concentration flavours the growth of moulds but at higher concentration stops the growth of organism.
Preparation of the syrup:
There are four methods. Based on the physical and chemical properties on the ingredients, the choice of the method is selected.
1. Solution with heat: The temperature of purified water is increased to 80 to 85 C and then taken off from the heat source. Then add sucrose and shake it thoroughly. Those ingredients which are resistant to high temperatures are added. Those substances that are heat sensitive and volatile agents are added after the solution attain the room temperature. But during heating, the sucrose gets hydrolysed, results in the formation of dextrose and fructose, these two sugars together called as invert sugar and the process is known as inversion. This reaction takes place more rapidly in presence of acids. The inversion leads to darkening of the solution.
2. Agitation without heat: This is a simple technique in which a vessel is taken generally made up of stainless steel or glass. The vessel should be larger than the desired volume of syrup required. Then the ingredients according to the formulation are added to watr and mixed. It is better to dissolve solid ingredients in the water first and then to add them to syrup. This results in easy mixing as sugar solution generally retards mixing.
3. Addition of sucrose to liquid medicament: This method is generally used for fluid extracts. But those substances which are soluble in alcohol will precipitate out as soon as the addition of water. An alternation is to first dissolve all the ingredients in water. Now after sometime all the precipitates formed are filtered out. Now add sucrose. But this method is of no use if the precipitates formed has active ingredients.
4. Percolation method: As the name suggest, the principle of percolation is used. A sucrose bed is prepared and then water or vehicle containing therapeutic agent is passed. Here the sucrose bed should be coarse and shape of percolator must be cylindrical or cone shapped.
Sucrose syrups are replaced by agents like sorbital solution or mixture of sorbital and glycerin. Sorbital is osmotic laxative and so it must be administered within the limits. Sorbital solution contains about 64% of sorbital.
They consist of alcohol and water and are sweet in taste and have a nice flavor.
- Flavouring agents
Elixirs have low viscocity than syrups and they can flow more freely as there will be very less use of agents that increase viscocity like sucrose. There is no clear cut difference between elixirs and syrups. To call a formulation as elixir, it must be hydroalcoholic and the amount of alcohol may vary greatly. Elixirsalcohol content
compound benzaldehyde elixir3 to 5%
aromatic elixir USP 21 to 23%
Glycerin and syrup may also used in the formulation. This enhances the solubility of drug, or to increase the sweet taste. Propylene glycol can also be used as solvent.
Elixirs can be prepared more easily than syrups they contain less amount of ingredients that are to be dissolved.
If water soluble and alcohol soluble ingredients are present in formulation then the following procedure is followed.
Add all the water soluble ingredients to water and dissolve them. Now sucrose should be mixed and let it dissolve completely. Take all the alcohol soluble ingredients and dissolve them in alcohol. Then add the first solution to second solution. To make the elixir clear, filter it. Make the final volume with water.
Sucrose will enhance the viscocity and reduces the solubility of water. To make the elixir clear which is compulsory, talc or siliceous earth are used.
Dry elixirs: these are the formulations in which NSAID and alcohol are encapsulated. Dextrin is used for encapsulation. As a result the solubility will be enhanced and so the bioavailability of the drug.
- Alcohol precipitates substances like tragacanth, acacia from water. So incompatibility reactions should be thoroughly checked.
- Alcohol increases the saline taste of bromides etc. so the formulator has to seek some other solvent during these conditions. Syrup is the best choice when taste is the main consideration.
Remington the science and practice of pharmacy, 21st edition, volume 2, Lippincott williams and Wilkins publishers, page no 754 to 757
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