2.a drug muct be in solution before ti can be absorbed.a drug administered in the form of a solution immediatley available for abosorption.
3. a solution is a homogenous system; the drug will be uniformly distributed thoughout the preparation.
4.some drugs can irritate and damage the gastric mucosa particularly if localized in one area as often occurs after ingestion of a solid dosage form. irritation is reduced by administration of a solution of a drug, because of the immediate dilution by the gastric contents.
disadvantages of solutions
1.bulky and inconvenient to transport and store.
2. the stability of ingredients in aqueous solution is often poorer than if they were formulated as a tablet or capsule.
3.solutions provide suitable media for growth of microorganisms.
4.accurate dosage usually demped on the ability of the patient to use a 5 ml spoon or volumetric dropper.
5.the taste of a drug, which is usually unpleasent is always more pronounced when in solution than when in a solid form.
homogeneous mixtures that are prepared by dissolving a solid, liquid or gas in an aqueous media ( vehicle=water)
advantages of water as a vehicle and solvent for ingredients.
1. lack of toxicity
2. lack of pharmacological activity
4. ability to dissolve wide range of materials
not permitted to use tap water for the dispensing of pharmaceutical dosage forms due to possible bacterial contamination and the presence of dissolved salts that destroy the active ingredients or enhance their decomposition.
freshly boiled or cooled water
boiling is seldom used to destroy vegtative bacteria. however; on storage for long time spores may yield microorganisms
must be used for most pharmaceutical operation and in all the tests.
such water is prepared by a suitable process:
distillation, ion exchange or reverse osmosis.
ultraviolet energy, heat or filtration can be uset to remove or kill the microorganisms present in the water.
contain no added substances
not for parenteral adinistration.
water for injection
must be used for the formulation of parenteral solution.
obtained by sterilizing pyrogen-free distilled water.
contains no added substances.
bacteriostatic water for injection
prepared from sterilized water for injection.
contains one or more antimicrobial agents
it is used to dilute ore dissolve a particular medicinal substance to be used for as parenteral solutions.
oldest method of water purification.
1.water is first heated to boiling
2. the water vapor rises to a condenser where cooling water lowers the temperature so the vapor is condensed, collected and stored.
3. most contaminants remain behind in the liquid phase vessel.
advantages of distilled water
remove broad range of contaminants.
disadvantage of distilled water
1. some contaminants can be carried to the condensate.
2.requires careful maintenace to ensure purity.
3.consumes large amount of energy and water.
ion exchange method
it removes dissolved salts.
io-exchange equipment passes water through a column of cation and anion exchanger consistinng of water-insoluble synthetic resins type.
resins of 2 types:
cation exchange resin: resins made of styrene and divinylbenzene containing containing sulfonic acid groups which exchange a hydrogen ion for any cation (Na++ , Ca++ ,Al++++ )
anion exchange resins: resins made of styrene and containing quaternary ammonium groups which exchange a hydroxyl ion for any anion (Cl-- ,CO3-- ).
advantages of ion-exchange method over distilation method.
1. no heat required
3. ease of operation
4. minimal maintenance
disadvantages of ion-exchange method over distilation method.
does not effectively removes particles, pyogens or bacteria.
it is a process known as cross-flow membrane filtration.
it works by using pressure in excess of the osmotic pressure to force a solution through a membrane, retaining the solute on one side and allowing the pure solvent to pass to the other side.
this is the reverse of the normal osmosis process which is the natural movement of solvent from an area of low solute concentration through a semi-permeable membrane, to an area of high solute concetration when no external pressure is applied.
advantage of reverse osmosis
effectively removes all types of contaminants to some extant( particles, pyogen, mo, dissolved salts)