LIQUID DOSAGE FORM
The liquid form of a drug dose for administration or consumption. Route of administration may be oral, intravenous, intramuscular, cutaneous, subcutaneous, etc.
Advantages of Liquid Dosage Form
- Most suitable dosage form for patients who have difficulty taking tablets or capsules, as might be the case with pediatric or geriatric patients.
- Attractive in appearance gives beneficial psychological effects.
- Drugs with bitter unpleasant taste can be given in sweetened, colored, flavored vehicles.
- Measuring flexibility as needed.
- If given orally, the liquid dosage is rapidly absorbed than tablets and capsules.
- Hygroscopic and deliquescent medicaments can easily be given in liquid dosage form.
- Products like adsorbents and antacids are more effective in this form.
- The liquid dosage form is expected for products like cough medicaments.
Disadvantages of Liquid Dosage Form
- Liquid dosage forms are usually more susceptible to chemical degradation when compared to solid dosage forms.
- Inconvenient to transport and store.
- Accidental breakage of the container results in loss of whole dosage form.
- The shelf-life of a liquid dosage form is often much shorter than that of solid preparation due to low stability.
- A solution often provides suitable media for microbial growth.
- Liquid dosage forms e.g. vaccines may require special storage conditions
- The taste of a drug that is usually unpleasant is more prominent in solution form.
- There is a higher chance of dose variability since the delivery of the dose depends upon the patient measuring the proper volume. This can be a significant issue for patients with vision-impaired, arthritis, unable to read the numbers on measuring cups.
Excipients used in formulation-
- Vehicles= vehicles are major components used as a base in which drugs and other excipients are dissolved or dispersed.
- Aqueous– (e.g. Water, polyhydric alcohols, hydro-alcoholic solutions, and buffers)
- Oily– (e.g. Vegetable or mineral oils, organic oily bases, emulsified bases, etc.),
- Buffers= Buffers are added to regulate the pH when an acid or alkali is added to the liquid dosage form. (e.g. Monobasic sodium acetate, sodium citrate, potassium phosphate, etc)
- Tonicity modifier= to make the solution iso-osmotic with tissue fluid to avoid pain and irritation (e.g. dextrose, NaCl)
- Preservatives= preservatives are added for fungistatic action to avoid microbial growth in the formulation. (E.g. benzoic acid, sod. Benzoate, alcohol, propylparaben, methylparaben)
- Antioxidant= Antioxidants are used to prevent oxidation which may lead to unpleasant taste, odor, taste, precipitation, discoloration, or even loss of activity. (E.g. sod. Sulfite, sod. Bisulfite, ascorbic acid, citric acid)
- Viscosity modifier= Used to minimize interparticle attraction and aggregation by functioning as energy barrier thus retarding particle settling. (e.g. methylcellulose, microcrystalline cellulose, carboxymethylcellulose, etc)
- Sweetening agent= Used to mask the bitter taste of the formulation (e.g. sucrose, sorbitol, mannitol, glycerol)
- Flavors & perfumes = Used to give a specific flavor to improve patient compatibility. (e.g. cinnamon oil, lemon oil, peppermint oil)
- Colours= Used to improve the attractiveness of the product and easy identification of the formulation. (e.g. Amaranth sol.-RED, tartrazine sol.- YELLOW,)
Solubility enhancement Techniques:-
Strongly ionized drugs are freely soluble in water over a wide pH range, for unionized drugs/weak electrolytes at pH that are unfavorable for extensive ionization some techniques can be used to improve aq. Solubility,
- Cosolvency = Solubility of poorly soluble drugs can be improved by using cosolvents, cosolvents are a mixture of water and one or more water-miscible solvents.
- pH control= The solubility of the weak base can be increased by lowering pH & the solubility of a weak acid is increased by increasing pH.
- Solubilization=By addition of surface-active agents micelle is formed. Non-polar molecules will dissolve in lipophilic moiety and hydrophilic surfactant HLB value above 15 is valuable as solubilizing agents.
- Hydrotropy= Addition of large amt. of a second solute increase aq. Solubility of existing solute.
- Particle size reduction=As a particle size is reduced using micronization technique the surface area increases and that allows greater interaction with a solvent which causes increase insolubility.
- Nanonization= It improves the dissolution and bioavailability of numerous drugs which are poorly soluble in water. The technique used is wet milling, homogenization, spray drying, etc.
- Solid dispersion= It increases dissolution, absorption & therapeutic efficacy of a drug. Solid dispersion is a group of solid products consisting of at least 2 diffs. components as hydrophilic matrix and hydrophobic drugs.
- Complexation= Complexation of drugs with cyclodextrins has been used to enhance aq. Solubility and drug stability. It relies on relatively weak forces such as London forces, hydrogen bonding & hydrophobic interactions.