What are the dosage forms of drugs?
Today on ePharmacology we will discuss about the different dosage forms of drugs. Let's start!
A patient suddenly develops upper abdominal pain and attends a private clinic in order to relieve pain. The doctor of that clinic advises the patient to chew an antacid tablet (aluminum hydroxide 325 mg). But the pharmacist gives him a tablet, which is 1,200 mg in weight.
Do you think is there any communication gap between the doctor and the pharmacist? Certainly not!
That tablet actually contains 325 mg of aluminum hydroxide as an active ingredient. To prepare that tablet some other pharmacologically inert substances are added which are called excipients. These are mannitol, sodium saccharin, starch paste, peppermint oil, magnesium stearate, corn starch, methylcellulose, and orange. Here, aluminum hydroxide is a drug. The active ingredient sometimes represents only a small amount of the total weight of a tablet (e.g. digoxin) or capsule. A drug for injection requires a fluid vehicle of varying complexity. The purpose of using these excipients are to- solubilize, suspend, thicken, dilute, emulsify, stabilize, preserve, color, or flavor the drug
All drugs are not used in same amount. They vary in amount. Most of them are prescribed in milligram quantities. For example, paracetamol is administered in 500 mg whereas ethinyl estradiol is administered in 0.05 mg. That is, the former drug is 10,000 times greater than the latter drug. It is a difficult task to ensure the supply of 500mg of paracetamol accurately to the patient without dosage formulation. If 505 mg of paracetamol is administered instead of 500 mg, it will not create any problem. But severe adverse effects develop after administering 5.05 mg of ethinyI estradiol instead of 0.05 mg. Thus, how can you ensure the availability of accurate small amount of ethinyl estradiol? Dosage formulation has solved this problem.
There are four varieties of dosage formulations- solid, semi-solid, liquid and gaseous. In addition, liposome-based formulations are promising and will be the future drug delivery system of a lot of drugs
Organizational structure of this hub:
What we will learn today:
(Click on the links to take you to specific sections of the page)
a. Composition of tablet
b. Types of tablet
a. Composition of capsule
b. Types of capsule
iii. Volatile liquids
Why so many dosage forms?
It is quite natural to raise the question - why do we use so many dosage forms?
The answer is simple.
A single formulation does not allow us to administer a drug via different routes.
For example, a drug in tablet form is suitable for oral (swallow) administration. But it can not be administered by parenteral route until it is diluted in a sterile solvent. Even you can not administer a tablet into the rectum. Thus, suppository- especially designed formulation- is prepared for administration into this route (rectal).
The physiochemical properties of a drug can easily be altered by different dosage forms. It conceals the bitter, salty, or offensive taste or odor of the drug. The damage of drug from moisture can also be prevented. It protects the drug from the destructive influence of gastric acid after oral administration. The adverse effects are also reduced.
Different dosage forms provide the time controlled drug effects and increase the acceptability of drug. For example, metronidazole has a bitter taste which can be masked by making the metronidazole tablet film-coated. Film-coated tablets also prevent the damage of a drug from moisture. Benzylpenicillin is not administered orally, as it will be destroyed within the stomach by gastric juice. So, it is always administered parenterally. In case of enteric-coated tablet, the active ingredient will not be released within the stomach when swallowed. So, the drug that damages the gastric mucosa will not be able to get the chance to produce any adverse effect on the stomach. Everybody does not like to swallow the drugs in tablet form? Liquid dosage form of a drug is more acceptable to the children as well as the elder patients.
Solid dosage form
Solid dosage forms include:
Among them tablet and capsule are mainly used and are administered orally. Powder is the oldest dosage form which nowadays has been replaced by tablet and capsule.
Tablet is a solid dosage form in which powder, crystalline, or granular form of drug is compressed in a disk or molded. It is the most frequently used means of administering a drug. Most of the tablets are administered orally. However, tablets for application as solution, vaginal use (e.g. clotrimazole, sulfathiazole), or external use (e.g. potassium permanganate) are also available.
Oral tablet is designed to release the drug within the gastrointestinal tract or absorption into the circulation. It may be used for a local effect (antacids, anthelmintics). Tablet is usually swallowed with a cup of water (about 250 ml).
Nowadays most of the tablets are of compressed type. Compression may be single or multiple times. In case of multiple compression (a tablet-within-a-tablet). the inner tablet behaves likes the core and the outer portion as the shell. What is the difference between the compressed and the molded tablets? The molded tablet is softer than the compressed one. The molded tablet dissolves rapidly when administered by placing under the tongue.
To make the tablet well-acceptable to the patient and easier to swallow, the tablet is prepared in different shapes and sizes. The tablet is usually discoid in shape. It may be available in other shapes such as round, oval, triangular or elliptical. Sometimes the tablet may be capsule shaped (called caplet). Caplet is easily swallowed. The upper and lower surfaces of a tablet may be flat or convex. The tablet may be scored or grooved on single side in halves or quadrants to permit the fairly accurate breaking of tablet for administration of a partial amount. Sometimes the tablet may be marked with trade name with or without the amount of the active ingredient. Tablets are produced in different colors to make them further distinctive.
Composition of tablet
The tablet contains not only the active ingredient(s) but also contains a number of inert substances such as diluent (filler), binder (adhesive), disintegrant, lubricant (lubricating agent), coloring agent, sweetening, and flavoring agents
Pharmacologically inert substance is used as diluent when the amount of an active ingredient is inadequate to produce a tablet. For example, it is impossible to make a digoxin tablet of 0.25 mg without adding a diluent. Well-known diluents are dextrose, lactose, starch, powdered sucrose, microcrystalline cellulose. sodium chloride, dicalcium phosphate, calcium sulfate, and kaolin. The selection of diluent is based partly on the experience of the manufacturer in the preparation of other tablets and also on its cost and compatibility with the other ingredients. Calcium salt should not be used in the preparation of tablet or capsule of tetracycline, because the calcium interferes with the absorption of tetracycline from the gastrointestinal tract. Most of the manufacturers prefer lactose as diluent, because of its solubility and compactibility. Microcrystalline cellulose is also preferred, because of its compactibility. compatibility and uniformity of supply.
Binder is the substance used to cause adhesion of powder particles in tablet granulations. It keeps the tablet intact after compression and imparts hardness of the compressed tablet The commonly used binders are starch, acacia, tragacanth, gelatin, liquid glucose, sucrose, lactose, povidone, ethylcellulose, carboxymethyl cellulose, and methylcellulose. The amount of binder used has considerable influence on the characteristics of tablet. The use of excessive or strong binder makes the tablet hard and will not easily disintegrate.
Any substance that is added to the active ingredient(s) of the tablet to facilitate its breakdown into small particles within the gastrointestinal tract after swallow is called disintegrant. So, disintegrant facilitates dissolution. Corn and potato starch. sodium starch glycolate, croscarmellose, carboxymethylcellulose calcium, and microcrystalline cellulose are used as disintegrator. They swell or expand on exposure to moisture and affect the rupture or break up of the tablet after it enters the gastrointestinal tract. Most of the manufacturers prefer croscarmellose and sodium starch glycolate (5 to 20%) as disintegrant for their rapid action.
Lubricant prevents adhesion of tablet materials to the surface of dies and punches. The commonly used lubricants are magnesium stearate, calcium stearate, zinc stearate, stearic acid, purified talc, and mineral oil. Lubricants except purified talc are used at concentration of less than 1%. Purified talc may be used up to 5% of the tablet. The use of excessive amount of lubricant should be avoided since it mav dclcteriously affect the tablet.
Sometimes coloring agent is used to impart elegance to tablet, which also helps to identify the different types of tablet. The coloring agents are brilliant blue, indigoline. last green, erythrosine. tartrazine. and caramel.
Flavorant is generally used to all lozenge, chewable and effervescent tablets to impart a pleasant flavor. The commonlv used flavorants are anise oil. cinnamon oil. cocoa, menthol, orange oil. peppermint oil and vanillin.
Sweetening agent is generally used to all lozenge, chewable and effervescent tablets. The commonly used sweetening agents are mannitol. lactose. dextrose, sucrose, glycerin, sorbitol, and saccharin.
Types of tablet:
Tablets may be uncoated or coated.
Uncoated tablet are chewable tablet, effervescent tablet, lozenge tablet and sublingual tablet.
Coated tablets are enteric-coated tablet, film-coated tablet and modified release tablet.
A broken section of a coated tablet shows a core, which is surrounded by a continuous layer of a different texture. A coated tablet is expensive and a broken coated tablet should not be swallowed. The rate of drug administration into the systemic circulation is slowest.
Then, why a tablet is coated?
It helps to:
- protect the active ingredients from air, moisture, light
- mask the unpleasant tastes, odor
- improve the appearance.
The tablet which is intended to be disintegrated smoothly in the mouth at a moderate rate, either with or without actual chewing. Usually mannitol is added to make the tablet pleasant tasting, no bitter or unpleasant after-taste, a cool taste and mouth-feel. Sometimes, other sweetening agents, such as sorbitol, lactose, dextrose, and glucose, may be substituted for part or all of the mannitol. Antacids, cimetidine, albendazole, and vitamin tablets are usually prepared as chewable tablets. It is given to the children who have difficulty in swallowing and to the adults who dislike swallowing
The tablet that contains acid substances and carbonate or hydrogen carbonate that react rapidly in the presence of water to release carbon dioxide. Sodium bicarbonate, citric acid and tartaric acid are added to the active ingredients to make the tablet effervescent. This preparation makes the tablet fast disintegration and solution when added to water and makes palatable. This preparation is taken as the effervescence subsides. Aspirin, ranitidine, etc. are available as effervescent tablet.
Lozenge (also known as troche; less frequently called pastille) is a disc-shaped, solid dosage form of drug intended to be slowly dissolved in the oral cavity to get localized effects. There is no disintegrating agent. Thus, this kind of tablet is harder than ordinary tablet and dissolves or disintegrates slowly within the mouth. Suitable sweetening (sugar), coloring and flavoring agents must include in this formulation. Gum is used to give strength and cohesiveness to the lozenge and facilitate slow release of the active ingredient. The drugs used for lozenge tablet are nystatin, clotrimazole, benzocaine, dextromethorphan, phenylpropanolamine, etc. This type of tablet is convenient to the patient when compared to the necessity of swishing an oral suspension in the mouth.
The drug which is destroyed or inactivated in the gastrointestinal tract but can be absorbed through the mucosal tissue of the oral cavity is usually given in this formulation. The tablet is placed below the tongue for fast release of drug (dissolve within I to 2 minutes). Nitroglycerin is prepared in this formulation.
Some drugs are destroyed by gastric juice or cause irritation to the stomach. These two factors can be overcome by coating the tablet with cellulose acetate phthalate. This polymer is insoluble in gastric contents but readily dissolves in intestinal contents. So, there is delay in the disintegration of dosage form until it reaches the small intestine. Like coated tablet, enteric-coated tablet should be administered in whole form. Broken or crushed form of the enteric-coated tablet causes destruction of the drug by gastric juice or irritation to the stomach. Enteric-coated tablet is comparatively expensive.
Other substances used for enteric-coating are shellac, hydroxypropyl methylcellulose phthalate, and polyvinyl acetate phthalate. Enteric-coated tablets are aspirin, bisacodyl, etc.
The tablet that is covered with a thin layer of a water- insoluble or water-soluble polymer capable of forming a film over the tablet. This coating is ruptured in the gastrointestinal tract. The film is generally colored and has the advantage over sugar-coating in that it is more durable, less bulky, and less time-consuming to prepare.
The tablet that contains active ingredient(s) of unpleasant taste may be covered with sugar-coating to make it more palatable. This type of tablet should be administered in whole form; otherwise the patient will experience the unpleasant taste of the active ingredient. Disruption of the coating is the rate limiting step in absorption of drug.
Modified-release tablet is commonly referred to as controlled-release, sustained-release, time-release, slow-release, sustained-action, prolonged-action, extended-action, or rate-controlled tablet. It is either uncoated or coated. Modified-release tablet is prepared by various ways.
Conventionally prepared granules are mixed with granules either coated with a poorly soluble material or containing solution-retarding additives. The granules are then compressed together. Thus, an initial release of drug is obtained from the conventionally prepared granules, followed by a sustained release from the treated granules. Modified-release tablet may be formed by preparing a multiple layer tablet, in which the conventional and treated granules are located in separate layers. It prolongs the effect of drug and thus reduces the frequency of administration of drug. Aminophylline and diclofenac are used as modified-release tablets.
In case of elementary osmotic pump, the drug is present in a solid core surrounded by a semipermeable. polymer membrane which selectively allows water to enter the core. Water entering from any part of the gastrointestinal tract gradually dissolves the drug. Since the internal dimensions of the tablet are fixed, the resulting pressure within the core forces the drug solution into the gut lumen through a laser-drilled small orifice. The rate at which this osmotic pump releases drug can be controlled and made constant release for up to 24 hours. The release of drug from this osmotic pump is independent of pH and gut motility. The antihypertensive drug metoprolol can be used in such a dosage form.
A modified-release tablet contains a greater amount of drug than does a conventional form. For example, in case of diclofenac tablet, the conventional form contains 50 mg whereas the modified-release tablet contains 100 mg.
There is usually a great variation in the rate of release of drug among individuals, and even in the same individual at different times. If the release of a drug from a modified-release tablet preparation is more rapid than is assumed, too much drug may be absorbed too quickly and thus leads to adverse effects. On the other hand, if the rate of release is slower than expected, amounts of drug may be provided that are inadequate to produce the desired therapeutic effect. If a modified-release drug leaves the intestine before the drugs have been delivered for absorption, an unused portion will be excreted in the feces.
The term pill is still popularly known to us. Once the idea was to use pill in every ill. Nowadays the term has been only used in contraceptive preparations such as combination pill, mini pill, and morning after pill.
Capsule is a solid dosage form in which one or more active ingredients with or without inert substances are enclosed within a small shell or container generally prepared from gelatin. It is intended for oral administration. The use of capsule overcomes the problem of disintegration, stability, or taste. To make a capsule it is not necessary to use water, which may cause loss of potency of drug. Once a drug is enclosed within a capsule, one cannot experience the taste of the drug.
When a capsule comes in contact with the gastrointestinal fluid, the gelatin starts to dissolve. As the aqueous fluids invade the capsule contents, the capsule rapidly swells, and burst and discharge its contents into the gastrointestinal fluid. Capsule is more expensive than the tablet.
Contents of a capsule:
In addition to active ingredients, the capsule usually contains: diluent, lubricant, and preservative.
Lactose is added to fill the capsule and also causes rapid dispersal of drug into the gastrointestinal fluid.
Magnesium stearate is used to ensure flow of powder during filling into the capsule.
Soft gelatin shell may contain a preservative to prevent the growth of fungi. The commonly used preservatives are methyl- and propylparabens, and sorbic acid.
Types of capsule
The capsules are of two types: hard and soft capsules. In addition, capsule may be modified-release or implant. Most of the capsules are of hard types.
Hard capsule shell has two parts- the body and a tightly fitting cap. The diameter of the cap is slightly larger than the diameter of the body. The gelatin capsule is colorless. It is made colorful or opaque for differentiation by adding a colorant and the opaque-producing substance (such as titanium dioxide). Capsule may be imprinted with monograph of the manufacturer, the strength of the drug in the capsule, a code designation for product identification, or some other symbol to distinguish from. The size of the hard capsule ranges from 12 to 28 mm. The selection of the size of a capsule depends on the amount of drug.
Larger capsules are available for veterinary use. The form of drug within the hard capsule may be either powder or granule. The total weight of the drug varies ranging from 65 to 1,000 mg. When the amount of drug to be administered in a single capsule is large enough to fill a capsule completely, a diluent may not be required.
Soft capsule is prepared from the shell of gelatin to which glycerin or sorbitol has been added to render the gelatin elastic or plastic-like. These are various in shapes such as round, oval, oblong, tube or suppository. Each contains either liquid, suspension, pastry material or dry powder. The necessity of using soft capsule is to seal the liquid medication within the capsule, to prevent the medication especially susceptible to deterioration in the presence of air and to use the volatile medication. In addition, soft capsule is easily swallowed. The drugs prepared in soft capsule are vitamin A, vitamin E, and demeclocycline.
Modified-release capsule is either hard or soft capsule. The drug in granule form present within the capsule is coated with a variety of substances that are designed to dissolve at different times. So, there is continuous release of a small amount of drug. The period of drug release ranges from 2 to 12 hours depending on the coating used. For example, iron salt available as ordinary tablet is taken orally twice or thrice daily. The frequency of administration may be reduced to once daily using slow release preparation. The slow release formulation is preferable because it improves the patient compliance and reduces the gastrointestinal adverse effects.
Sometimes capsule is placed subcutaneously to provide slow release of drug. For example, levonorgestrel (popularly known to the people as norplant) offers long term contraception (about 5 years), by using this method. It consists of 6 capsules (2.4 mm in diameter and 34 mm in length for each capsule) containing 36 mg of synthetic progestin levonorgestrel. These capsules are inserted in a plane beneath the skin of the upper arm by small incision and special injector. Implant capsule is dependable and totally reversible. There is no question of patient’s compliance.
The word powder is derived from the Latin word pulvis. It is a mixture of finely divided drugs and/or chemicals in dry form. Drugs in powder form are available for both external and internal uses. The advantages of powder as a dosage form are: a) flexibility in compounding and b) relatively good chemical stability. The powder is not suitable for dispensing unpleasant tasting drug.
Powder for external uses:
Powder for external use is also known as dusting powder. The dusting powder is a locally applied non-toxic preparation and should have particle size of less than 100 mesh (150 mm). It includes starch, talc, and zinc stearate. Dusting powders are applied to various parts of the body as lubricants, protective absorbents, antiseptics, and antipruritics. It should not be used on open wound unless the powder is sterilized.
Powder for internal uses:
The powder for internal use is designed for oral or parenteral administration. Some powders are dispensed by the pharmacist to the patient in bulk quantities. Others are provided in divided forms, individually packaged portions, depending primarily on the use, dose, or potency of powder. Each dose is separately wrapped in powder or sealed into a sachet. It is intended to be dissolved in water prior to administration. Antacids and laxative powders are administered in these forms.
The powder for injection is a sterile solid substance to be dissolved or suspended by adding a prescribed volume of appropriate sterile fluid. The solution or suspension is prepared immediately before use to avoid deterioration of the ingredients on storage.Some drugs (such as disodium cromoglycate) are supplied in hard capsules and are inhaled from a device which breaks the capsule and allows the patient to inhale the powder. This type of insufflation is used mainly for drug delivery into the respiratory tract by inhalation.
Granule is small irregular particle ranging from 0.5 to 2 mm in diameter. It is more stable physically and chemically than the corresponding powder from which it is prepared. Some granules are administered by pouring it within the capsule. It may be placed on the tongue and swallowed with water. Some antibiotics (such as ampicillin) unstable in aqueous solution are prepared as granules for reconstitution with purified water just prior to dispensing. The granules not only contain the active ingredient but also the colorant, flavorant, and other pharmaceutic ingredients. Ispaghula husk is also available as effervescent granules.
The word suppository is derived from the Latin supponere, meaning “to place under” as derived from sub (under) and ponere (to place). It is a solid medicated preparation designed for insertion into the rectum. It is tapered at one or both ends usually weigh between 1 and 4 gm. Rectal suppositories are shaped like a — bullet, torpedo, or little finger. It is usually 32 mm in length and is cylindrical. Usually cocoa butter, glycerinated gelatin, polyethylene glycol are used as suppository bases. These bases are non-toxic, non-irritant to the mucous membrane, and melt quickly at body temperature. Suppository should be kept in a well-closed container and stored at temperature not exceeding 30° C. Drugs in suppositories are used for systemic or local effect. Analgesics, aminophylline, and sedatives are used for systemic effect. Example of local effect is the use of drug for the treatment of constipation or hemorrhoid. Bisacodyl or glycerin suppository is used to relieve from constipation. Suppository should be moistened with water before use.
The solid medicated preparation designed for insertion into the vagina is called pessary. It melts or dissolves and exerts a local or systemic effect. There are three types of pessaries- molded pessary, compressed pessary (vaginal tablet), and vaginal capsule. Molded pessary is cone shaped and is prepared in a similar way to molded suppository. Compressed pessary is of different shapes and is prepared by compression in a similar way to oral tablet. Vaginal capsule is similar to soft gelatin oral capsule. It differs only in size and shape. Methylparaben is used as a preservative.
Others include ocular insert, intrauterine device and transdermal patch.
Ocular insert is a special device for modified-release of pilocarpine at the eye for the treatment of glaucoma. Traditionally 2% pilocarpine eye drops are used every 6 hourly. To replace this method, ocular insert can be placed either under the eyelid or in the cul-de-sac of the eye. It consists of a wafer-like pilocarpine core held between two transparent rate-controlling membranes (ethylene-vinyl acetate copolymer). Pilocarpine is released at a rate of 20 or 40 µg/hour for 1 week. A single weekly administration of drug is obviously more convenient than periodic daily administration of eye drops.
This is a small, T-shaped, flexible, multicomponent unit consisting of a polymeric membrane-enclosed drug reservoir that delivers progesterone (65 µg/day) to the lining of the uterus for more than one year. Within the drug reservoir, progesterone is present with barium sulfate and silicone oil.
Transdermal patch is a multilayer disk comprising a reservoir of drug sandwiched between an impermeable backing membrane and a rate-controlling microporous membrane. There is an adhesive gel on the dermal side of the patch which serves to secure the system to intact skin. It is usually applied to the post-auricular area of the skin. The rate of drug absorption is controlled by the patch and not the skin. Drugs being considered for transdermal delivery are scopolamine (to counteract motion sickness), clonidine (to control hypertension), estradiol (for the treatment of postmenopausal syndrome), and nitroglycerin (for treatment and prevention of angina).
Drugs suitable for this type of administration should have molecular weights below 800 to 1000, adequate solubility in oil and water, good skin permeability, and no history of skin irritation. In case of scopolamine, 500 µg of drug is to be released within 72 hours when in contact with skin.
Semisolid dosage form
Semisolid dosage form of drug is presented as:
Here, the active ingredients dissolved in a suitable base. Some excipients such as emulsifier, viscosity increasing agent, antimicrobial agent, antioxidant and stabilizing agent may be used.
The following points should be considered before selecting a base-
- Does it irritate or sensitize the skin?
- Does it delay the wound healing?
- Should it be smooth, stable, inert, and odorless?
- Semisolid dosage form should normally be of such a consistency that it spreads and softens. Cream is more acceptable than ointment for cosmetic purpose.
Ointment is a semisolid greasy preparation which is normally anhydrous and insoluble in water. It is more occlusive than cream. Ointment is used for external application to the skin or mucous membrane. It usually contains medicinal substances. However, there may be some ointments without any medicinal substance. The effectiveness of drug and the absorption of it through skin may be superior when using a hydrocarbon base. Petroleum jelly is used for moistening the skin as because it is occlusive and increases the hydration of skin by reducing the rate of loss of surface water. Suitable preservatives are used and may vary from preparation to preparation.
Paste is a semisolid preparation to be intended for external application to the skin. It differs from ointment primarily in that it generally contains a larger percentage of solid material and as a consequence is thicker and stiffer than ointment. Paste is generally more absorptive and less greasy than ointment prepared with the same component. Paste is preferred over ointment for acute lesions that have a tendency toward crusting, vesiculation, or oozing. It should not be applied to hairy parts of the body due to its stiffness and impenetrability. Some examples of pastes are zinc oxide paste, triamicinolone acetonide dental paste.
Cream is a semisolid preparation consisting of opaque emulsion system and is essentially miscible with the skin secretion. It should be sterile when intended to be used on open wound. Cream is cosmetically more acceptable than ointment as it is less greasy and easier to apply. It may be either oil-in-water (aqueous cream) or water-in-oil (oily cream) type.
Aqueous cream includes saving cream, hand cream, and foundation cream. It is relatively non-greasy. It may be used to moisture the skin or to deliver drug for transdermal absorption. Oily cream includes cold cream and emollient cream.
Liquid dosage form
Liquid dosage form of drug is presented as:
Several terminologies used for liquid preparation in clinical practice are mixture, syrup, elixir, lotion, tincture, linctus, etc. Though the acceptability of oral liquid preparation is more, there remains a problem of taking accurate dose. Once the container is opened, it must be used within a certain period.
Solution is a homogenous liquid preparation containing one or more dissolved ingredients. It may be used either internally or externally. Some antibiotics such as cloxacillin, nafcillin, benzylpenicillin are relatively unstable in aqueous solution. So, these antibiotics are supplied to the patients as dry powder or granule in combination with sweetening agent, suitable buffer, flavorant, colorant, and preservative. Flavorant and colorant are used to make the medication more palatable and attractive to the patient. When these antibiotics are prepared into solution by adding water the prepared products are suitable for use for a period of up to 14 days when kept at 4°C. Thus, this period is sufficient to complete the medication. If the drug remains after the patient completes his course of treatment, he should be instructed to discard the remaining portion, which would be unfit for use at a later date.
Aqueous solution for intravenous infusion is free from pyrogens and usually made isotonic with blood. Buffering agent is not added to the solution. Aqueous solution for external use is nasal solution, otic solution, and eye drop. An example of nasal solution is ephedrine nasal drop, which is used to reduce nasal congestion. Examples of otic solution are glycerin otic solution and corticosteroid otic solution.
suspension is a heterogeneous system of liquid dosage form of drug in which the finely divided solid particles ranging from 0.5 to 5.0 µm are suspended or dispersed in a liquid vehicle. The solid microsized particle constitutes the dispersed or internal phase whereas the liquid vehicle constitutes the continuous phase. The suspension is chemically more stable than the solution and is mainly used for oral administration, external application or parenteral use.
A suspension is an ideal dosage form for patient who has difficulty in swallowing tablet or capsule. Oral suspension is made palatable by adding some sweetening and flavoring agents and thereby masking the unpleasant taste and odor of medicament.
The solid particles remain suspended in the liquid medium by adding some suspending agents, which will reduce the interfacial tension between two phases as well as increase the viscosity of liquid vehicles. In an ideal suspension, the particles should not aggregate and should remain uniformly distributed throughout the dispersion. Practically this situation is seldom realized, so it is desirable to get a suspension where the particles do settle slowly and should be readily re-dispersed on minimum shaking.
Suitable preservative should be incorporated in order to minimize microbial contamination. The suspension prepared for external use should have very fine particle size to avoid gritty feeling to the skin.
Examples of suspensions given by the oral route are antacids, cotrimoxazole, and benzoyl metronidazole. Occasionally they may be in dry form and to be made suspension by adding water before use- e.g. oral antibiotic syrup.
The suspension can also be administered by intramuscular or subcutaneous injection. Another important consideration in case of suspension for injection is its pH. If the suspension is too acidic or too alkaline it may cause irritation and even tissue damage at the site of injection.
An emulsion is a two-phase system prepared by intimate mixture of immiscible liquids, one of which is uniformly dispersed as globules throughout the other. The system is stabilized by the presence of an emulsifying agent.
The emulsifying agent reduces the interfacial tension between the two phases, i.e. aqueous phase and oily phase and thus make them miscible with each other and form a stable emulsion. The type of emulsion produced also depends on the type of emulsifying agents. To prepare a stable emulsion two or more emulsifying agents are usually used.
The common emulsifying agents are acacia, gelatin, Tween 80. span 80, and span 20. The particle diameter of the dispersed phase generally extends from about 0.1 to 100 µm.
The emulsion may be of two types: oil-in-water (o/w) and water-in-oil (w/o) emulsion.
When the oil phase is dispersed as globules throughout an aqueous phase, the system is called o/w emulsion. Benzylbenzoate lotion is an example of o/w emulsion. When the oil phase serves as the emulsion phase, w/o emulsion is produced. The emulsion for oral administration is usually o/w type and requires the use of an o/w emulsifying agent. These include synthetic nonionic surface acting agents such as acacia, tragacanth, and gelatin.
O/w type emulsion is preferred for internal use because the unpleasant taste and odor is masked by emulsification and the oil being in a finely dispersed state is more quickly absorbed into the body. For example, cod liver oil and castor oil belong to this group. The activity of certain drugs can be increased and the action can be prolonged by emulsifying the drugs in a suitable vehicle. The emulsion containing amino acid, fat, carbohydrate, and vitamin in sterile condition can be used as total parenteral nutrition (TPN) to patient who is unable to take food by oral route.
The emulsion for external uses may be o/w or w/o type, but w/o emulsion is used almost exclusively for external use.
The aqueous phase of emulsion favors the growth of microorganisms and it is necessary to add chlorocresol, benzoic acid, sorbic acid, or salicylic acid as preservative.
Various Liquid Dosage Forms
Gaseous dosage form
Gaseous preparations are available in gas form present within:
- Volatile liquid
Therapeutically active liquid or solid can be formulated in this form by making colloidal dispersion. The active ingredient when packaged in pressurized dispenser is popularly known as aerosol. The container is so designed that, by depressing a valve, some of the contents are expelled due to pressure inside the container. The large expansion of the propellant at room temperature and atmospheric pressure produces a dispersion of the drug in air. Fluorinated hydrocarbons, nitrogen, and carbon dioxide are usually used as propellant in the formulation of aerosol. Pressure ranging from 1 to 6 atmospheres at room temperature can be achieved by varying the proportions of the various propellants.
Aerosol spray is of several types:
- Surface spray
- Spray on dusting powder
- Foam dispenser
- Metered dose aerosol.
Surface spray produces droplets of 100 µm or more. It may be used to relieve muscle ache, irritation of bites and sting, as surface disinfectant, as wound or burn dressing. Foam spray is used for some spermicidal preparations. Metered dose aerosol is used for the delivery of glycerol trinitrate in droplet form to the buccal mucosal.
The use of aerosol is continually increasing since it frequently offers distinct advantages over other dosage forms.These are:
- Antiseptic materials can be sprayed onto the abraded skin
- Minimum irritation
- Administration of the drug in the formulation, via the respiratory tract may increase the efficiency of the drug
- Protection from contamination
- Regulation of dosage by the use of metered valve.
Only a few gases such as oxygen, nitrous oxide, and carbon dioxide are used in clinical practices.
Halothane, ether, and chloroform are present in liquid form and are used during induction and maintenance of general anesthesia.
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Liposome-based drug formulation
Liposomes are-water-filled, vesicular structures composed of several phospholipid layers surrounding an aqueous core, and with the outer shell capsule providing directions to specific target cells (e.g. tumors).
They will concentrate the drugs in cells of the reticuloendothelial system of the liver and spleen, and will reduce drug intake in the heart, kidney, and gastrointestinal tract.
Several drugs (amphotericin B, doxorubicin, tretinoin, vincristine, cisplatin, nystatin, prostaglandin E, and amikacin) containing liposome system have been developed for the delivery of drugs by various routes of administration including inhalation, ocular, injectable, dermal, and oral. The use of doxorubicin in liposome
For example, following injection, large size liposome can have the tendency to settle in the lungs whereas smaller particles may concentrate in other body sites, such as the liver.
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