Dosage forms are the final form of a medicine which is available to the patients. Pharmaceutical researchers developed different types of dosage forms for the same medicines considering the patient acceptability, convenience to use and achieving best results from given drugs with least adverse effects. Liquid dosage forms are one of the oldest and important types of pharmaceutical dosage forms. It helps in administering medicines to the childrens and other patients who have difficulty swallowing dosage forms like tablets.
Liquid dosage forms are pourable dosage forms where drugs and other excipients dissolved or dispersed in a suitable liquid vehicle. Most of the traditional systems of medicines are using this form from ancient times to deliver medicines to the patients.
Read more about What is dosage form
We can check some advantages and disadvantages of liquid dosage forms
Advantages of liquid dosage forms
- Easy administering:
Liquid dosage forms can be administered easily without the need of water. It is more important in case of patient groups who cannot swallow other types of dosage forms like pediatric patients, geriatrics etc.
- Flexibility in dosage adjustment and dispensing:
Dosage of medicines in liquid forms can be easily adjusted for different patients compared to solid forms. Doctors can prescribe medicines in milliliters or in drops count depending on the body weight or other conditions of patients. Dispensing pharmacists can also adjust the strength of medicine easily by mixing with suitable solvents.
- Faster results:
Medicines in liquid forms are absorbed faster because they don’t need the steps like disintegration and dissolution.
- Can mask unpleasant taste and odor by mixing with suitable vehicles like syrup or other sweetened and flavored vehicles. It will improve patient acceptability.
- Some medications like cough preparations and antacids are more effective in liquid form
- Parenteral preparations like injections and eye ear and nose preparations are more preferred in liquid form.
- Administering medicines to unconscious and non co-operating patients is more easy with liquid forms.
- Liquid preparations are more suitable for the application of drugs or other preparations in a large skin area.
Disadvantages of liquid dosage forms
- Stability:
Medicines in liquid forms are less stable than in solid form. There are more chances of chemical reactions and contamination in liquid dosage forms. Therefore liquid dosage forms usually need addition of preservatives in their formulation.
- Difficulties in storage and transportation:
Liquid preparations are heavy and bulky. Storage of these needs a large area and special care. Usually liquid dosage forms are stored in special containers like glass, so there are high chances of breakage and other losses during transportation.
- Increased production cost:
Production, standardization and packaging of liquid dosage forms need more steps and materials as compared to different other types of formulations. It leads to an increased production cost.
- Dosage accuracy;
Usually liquid dosage forms are made in multiple dose packaging and patients have to take medications by measuring themselves. So here dosage accuracy depends on the ability of individual patients to measure and take.
- Less shelf life:
Compared to other forms, shelf life of liquid dosage forms is less.
- There are many medicines and ingredients that cannot be made into liquid forms.
Classification of liquid dosage forms
Now we can explain different types of liquid dosage forms
Monophasic liquid dosage forms
Monophasic liquid dosage forms are liquid preparations containing two or more components mixed together to form a single phase system. There will be a liquid solvent which acts as a vehicle and liquid or solid solutes which are dissolved in it.
Different types monophasic liquid dosage forms are as follows
- Mixtures:
Mixtures are liquid dosage forms containing more than one component that may be dissolved, dispersed or suspended in a suitable liquid vehicle. Most of the time mixtures are extemporaneously prepared and must be used within a limited time period like one weak or one month.
Examples of mixtures include some cough preparations antibiotics etc
- Syrups:
Syrups are concentrated aqueous solutions of sucrose or other sugar substitute with or without flavoring agent. Syrups may be medicated or non medicated. Non medicated syrups are used as vehicles for other medications.
Examples of syrups: Cough syrups, antibiotic syrups etc
- Linctuses:
Linctuses are viscous monophasic liquid dosage forms containing medicaments usually used for its local action in mucus membranes of the throat. They generally contain medications having demulcent, cough suppressant and expectorant action.
Examples: Codeine linctus, Ammonium chloride linctus etc.
- Elixirs:
Elixirs are clear, sweetened, aromatic hydro-alcoholic liquid preparations intended for oral use. There are medicated and non medicated elixirs available. Medicated elixirs usually contain potent medications like antibiotics, sedatives, antihistamines etc. Non medicated elixirs are well flavored and usually used as flavoring agents for other formulations.
Examples: Antihistaminic elixirs, Phenobarbital elixir, Digoxin elixir.
- Liniments:
Liniments are liquid preparations containing medicaments meant for application to skin. Liniments usually contain ingredients having analgesic, rubefacient, counter irritant or soothing properties. Liniments are generally applied to skin with rubbing or friction to promote absorption of medicines contained in it.
Examples : Camphor liniment, Sloans liniment, Methyl salicylate liniment
- Lotions:
Lotions are liquid preparations meant for application to the skin. They are generally applied by hand, cotton wool or brush and without rubbing or friction. Lotions may be medicated or non-medicated. Non medicated lotions are generally used for moisturizing, protecting and soothing purposes. Medicated lotions contain medicines like antibiotics, steroids, antihistamines etc.
Examples: Calamine lotion, salicylic acid lotion.
- Collodions
Collodions are liquid preparations for external use containing nitrocellulose dissolved in ether and alcohol. When this preparation is applied to skin using a suitable applicator ether and alcohol will evaporate leaving a film of nitrocellulose in the skin. It is generally used as a protective surgical dressing for small wounds and burns. It is also used to keep medicines in contact with the affected area for a long time.
Examples: Salicylic acid-lactic acid collodion
- Gargles and mouthwashes
Gargles are liquid dosage forms intended for the treatment of throat infections like sore throat. These preparations are usually kept in the throat for some seconds by air movements and then spit out.
Mouthwashes are liquid dosage forms having pleasant taste and odor which is used to clean and deodorize buccal mucosa.
Examples: Chlorhexidine mouthwash, povidone iodine mouthwash gargle.
- Throat paints:
Throat Paints are viscous liquid dosage forms used for the treatment of mouth and throat infections. Usually glycerine is used as the base in the preparation of throat paints. Glycerine adheres to the mucus membrane for a long time and provides a long contact time for the medicines in the infected area.
Example: Glycerine borax throat paint, Povidone iodine throat paint.
- Eye drops:
Eye drops are liquid dosage forms intended to be instilled directly into the eyes usually in small quantities like one or two drops. Eye drops are generally prepared with saline solution having the same osmotic pressure as of eye secretions to prevent any irritation to the eye. There are different types of eye drops based on their uses
Examples: lubricating eye drops, antibiotic eye drops, steroid eye drops etc.
- Ear drops:
Ear drops are liquid preparations for instilling to the ear using a dropper. Ear drops are used for different purposes like removing ear wax, treating infections, easing pain etc.
Examples: clotrimazole ear drops, glycerin ear drops, chloramphenicol ear drops.
- Nasal drops and nasal sprays:
Nasal drops and sprays are liquid dosage forms used to deliver medications directly to the nasal cavities. These preparations are generally used for their local effects like decongestion, treatment of infection etc. These are also used for the delivery of drugs to systemic circulation. Nasal preparations are generally prepared using saline solutions having the same osmotic pressure as nasal secretions. It also contains buffering agents to make preparation neutral pH.
Examples: saline nasal drops, oxymetazoline nasal spray etc.
- Douches:
Douches are liquid preparations intended for rinsing body cavities. They are used to clean, irrigate or remove forien particles or secretions from body cavities. Douches are most commonly used in vaginal as irrigations but they are also used in body cavities like the eye, ear, nose etc.
- Enemas:
Enemas are aqueous or oily liquid preparations that are introduced into the rectum. Enemas are most commonly used for evacuating the bowel before medical examinations. Enemas are also used for treatment of constipation, some infections and delivery of drugs to systemic circulation.
- injections:
Injections are liquid dosage forms intended to be administered directly to blood or other body tissues. Injections help deliver medications directly to the blood circulation.
There are different types of injections
- Intravenous injections
- Intramuscular injection
- Subcutaneous injection
- Intraperitoneal injections etc.
Biphasic liquid dosage forms
Biphasic liquid dosage forms contain two phases, one continuous phase and one dispersed phase. Here insoluble solid or liquid components are dispersed in suitable vehicles and are stabilized using another stabilizing agent.
Generally there are two types of biphasic dosage forms. They are suspensions and emulsions
- Suspensions:
Suspensions are biphasic liquid dosage forms in which finely divided solid particles are uniformly dispersed in a suitable vehicle. Suspensions are stabilized using suspending agents like methyl cellulose, sodium carboxymethyl cellulose, sodium alginate tragacanth etc
Examples: paracetamol suspensions, metronidazole suspensions, antacid suspensions
- Emulsions:
Emulsions are biphasic liquid dosage forms containing two immiscible liquids in which one liquid is dispersed as minute globules in the other liquid. Emulsions are made stable by using emulsifying agents like acacia, starch, wool fat, gelatine, methyl cellulose, cholesterol, lecithin etc.
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