Solutions
Part -1
Solutions
Solutions
Solutions are:
Dosage forms prepared by dissolving the active ingredient(s) in an
aqueous or non-aqueous solvent.
Solutions can be formulated for different routes of administration
Orally: Syrups, elixirs, drops
In mouth and throat: Mouth washes, gargles, throat sprays.
In body cavities: Douches, enemas, ear drops, nasal sprays.
On body Surfaces: Collodions,
lotions.
Advantages of Solutions
Easier to swallow (for children - old age).
More quickly effective than tablets and capsules.
Homogenous therefore give uniform dose than suspension or
emulsion which need shaking.
Dilute irritant action of some drugs (aspirin, Kl, KBr) minimize
adverse effects in the GIT like KCl.
Disadvantages of solutions
Bulky therefore difficult to transport and store.
Unpleasant taste or odours are difficult to mask.
Needs an accurate spoon to measure the dose.
Less stable than solid dosage forms.
Major signs of instability:
Colour change, Precipitation Microbial growth Chemical
gas formation
Additives
A.Buffers To resist any change in pH
B.Isotonicity modifiers
• Solutions for injection and ophthalmic application
• Application to mucous membrane
• E.g.: dextrose and NaCl
C. Viscosity enhancement
It is difficult for aqueous-based topical solutions to remain on the
skin or in the eye (why?) therefore low concentrations of jelling
agents are added to increase the viscosity of the product.
D. Preservatives
Solution may become contaminated for a number of reasons:
1. Raw materials used in the manufacture of solutions are excellent
growth media for bacterial substances
2. Equipment, environment and personnel contribute to product
contamination.
3. Consumer use may result in the introduction of microorganism
a preservative should be added to the product
Preservative used should be:
effective against a wide spectrum of microorganisms
stable for its shelf life
non toxic, non sensitizing
compatible with the ingredients in the dosage form
free of taste and odor
Preservatives may be used alone or in combination to prevent the
growth of microorganisms.
E.g. of preservative
A. Alcohols
Ethanol is useful as a preservative when it is used as a solvent. It
needs a relatively high concentration (> 10%) to be effective.
Propylene glycol also used as a solvent in oral solutions and topical
preparations. It can function as a preservative in the range of (15 to
30%). It is not volatile like ethanol.
B. Acids
Benzoic acid and sorbic acid have low solubility in water.
They are used in a concentration range from (0.1 % to 0.5%).
Only the non-ionized form is effective and therefore its use is
restricted to preparations with a pH below 4.5 (WHY?).
C. Esters
Parabens are esters (methyl, ethyl, propyl and butyl) of
phydroxybenzoic acid.
They are used widely in pharmaceutical products and are effective
and stable over a pH range of 4 to 8 with concentrations up to
about (0.2%). So that 2 esters are used in combination in the same
preparation WHY?
- To achieve a higher total concentration
- To be active against a wider range of microorganisms.
D. Quaternary Ammonium Compounds
Benzalkonium chloride is used at a relatively low concentration
(0.002 to 0.02%).
with an optimal activity over the pH range of 4 to 10
Because of the cationic nature of this type of preservative it is
incompatible with many anionic compounds.
E. Antioxidants
Vitamins, essential oils & almost all fats and oils can be oxidized.
Oxidation reaction can be initiated by:
1. heat: maintain oxidizable drugs in a cool place
2. light: use of light- resistant container
3. heavy metals (e.g. Fe, Cu): effect of trace metals can be
minimized by using citric acid or ethylenediamine tetraacetic
acid (EDTA)
E.g.
• propyl & octyl esters of gallic acid,
• tocopherols or vitamin E,
• sodium sulfite,
• ascorbic acid (vit. C) can be used.
F. Sweetening agents
Sucrose is the most widely used sweetening agent.
Advantages:
Colorless, highly water soluble, stable over a wide pH range (4-
8), increase the viscosity, masks both salty and bitter taste, has
soothing effect on throat.
Polyhydric alcohols (sorbitol, mannitol and glycerol) possess
sweetening power and can be used for diabetic preparations.
G. Flavors and perfumes
Mask unpleasant taste or odor
Enable the easy identification of the product.
Natural products: fruit juices, aromatic oil (peppermint, lemon)
Artificial perfumes are cheaper, more readily available and more
stable than natural products.
Stability of solutions
Both physical and chemical stability of solutions in their
containers is very important
A solution must retain its clarity, colour, odour, taste and viscosity
over its shelf life.
Classification of solutions according to vehicle
(a) Aqueous solutions (b) Non-aqueous solutions
Aqueous Solutions
Aqueous solutions are homogeneous mixtures that are prepared by
dissolving a solid, liquid or gas in an aqueous medium (vehicle).
Vehicle: This may be water, aromatic water or extracts.
Water
Water is used both as vehicle and as a solvent for the desired
flavoring or medicinal ingredients.
Advantages: Tasteless, odourless, lack of pharmacological activity,
neutral and very cheap
Tap Water
It is not permitted to use tap water for the dispensing
of pharmaceutical dosage forms due to
o its possible bacterial contamination
o the presence of dissolved salts that destroy the
active ingredients or enhance their decomposition.
Freshly Boiled and Cooled Water
Boiling is seldom used due to on storage for long time spores may
yield vegetative microorganism.
Purified Water
o Must be used for most pharmaceutical operations
o It is prepared by distillation, deionization or reverse osmosis.
"Hard" waters are those that contain the Ca and Mg cations.
“Alkaline" waters are those that contain bicarbonates as the
major impurity.
Ultraviolet energy, heat or filtration (Millipore filtration) can be
used to remove or kill the microorganisms present in the water
Water for injection
Must be used for the formulation of parental solutions. It is obtained
by sterilizing pyrogen-free distilled water.
Aromatic Waters
Aromatic waters (medicated waters) are clear, saturated
aqueous solution of volatile oils or other aromatic or
volatile substances.
o They are used as flavored vehicles.
o Volatile oils solutions represent an incompatibility problem of
salting out. This occurs after the incorporation of a very soluble salt
in their solution.
o Aromatic water will deteriorate with time therefore:
- should be made in small quantities
- protected from intense light and excessive heat
If they become cloudy; they should be discarded.
o Deterioration may be due to volatilization, decomposition or mould
growth.
o There are 2 official methods of preparation:
a) Distillation process
(Stronger Rose Water NF)
Adv.: most satisfactory method
Dis.: slow and expensive
• The drug should be coarsely ground
and mixed with sufficient quantity of
purified water in the distillation unit.
• After distillation any excess oil in the
distillate is removed by filtration.
• Drug should not be exposed to the
action of direct heat during
distillation; otherwise, the odor of the
carbonized substance will be
noticeable in the distilled aromatic
water.
b) Solution process (Peppermint water)
Aromatic water may be prepared by shaking volatile substance
with purified water.
The mixture is set aside for 12 hours & filtered.
Talc (inert) may be used to increase the surface of the volatile
substance, insure more rapid saturation of the water and act as a
filter aid.
Methods of Preparation of Solutions
(a)Simple Solution
(b)Solution by Chemical Reaction
(c)Solution by Extraction
(a) Simple Solution
Solutions of this type are prepared by dissolving the solute in a
suitable solvent (by stirring or heating).
(b) Solution by Chemical Reaction
These solutions are prepared by reacting two or more solutes with
each other in a suitable solvent e.g. Calcium carbonate and lactic
acid used to prepare Calcium lactate mixture.
(c) Solution by Extraction
Plant or animal products are prepared by suitable extraction
process. Preparations of this type may be classified as solutions
but more often, are classified as extractives.
Extraction Methods for Preparing Solutions
1- Infusion
An infusion is a dilute solution of the readily soluble constituents of
crude drugs. Fresh infusions are prepared by macerating the solids
for a short period of time with either cold or boiling water.
Concentrated infusions
Are preparations which, when diluted with seven times their volume of
water, yield products representing approximately the corresponding
infusions of the British Pharmacopoeia.
2- Decoction
A decoction is an herbal preparation similar to an herbal infusion
except that it more potent in its strength and therapeutic properties.
Some parts of an herb cannot be completely extracted in a solution
with an ordinary infusion processes, especially when you are using
tougher herbal parts like the root, bark, seeds, dry fruits.
Decoction is a method of extraction by boiling herbal or plant
material (which may include stems, roots, bark and rhizomes) to
dissolve the chemicals of the material.
3- Maceration Process
4- Percolation
It is a process in which a comminuted drug is
extracted of its soluble constituents by the slow
passage of a suitable solvent through a column of
the drug.
The drug is packed in a percolator, with the
collected extractive called the percolate.
Most drug extractions are performed by percolation.
In the process of percolation the flow is generally downward to the
exit orifice by the force of gravity
In certain percolation apparatus, additional pressure on the column is
exerted with suction at the outlet.
Percolators employed in the large-scale are generally stainless steel
but on a small scale generally are glass percolators
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