The Different Dosage Forms Manufactured In The Industry
A pharmaceutical drug, often referred to as medication or medicine, may be defined as a substance that is used to treat cure, prevent or diagnose a disease or to promote well-being. Traditionally drugs were obtained through extraction from medicinal plants, but more recently they are synthesised from organic precursors. Pharmaceutical drugs may be used for a limited duration, or on a regular basis for chronic disorders. The can be supplied as liquids or as various sold forms to help health care providers and patients to administer the drug safely. Each form of drug has certain benefits in terms of its effectiveness, ease of use and safety. Some of the issues that need to be addressed when considering the different forms are:
- To protect the active compound in the drug from exposure to the atmosphere, to ensure a long shelf-life
- For drugs that are taken orally, to protect the drug active ingredient from stomach acids or other enzymes so that it can be absorbed in the lower intestinal tract.
- To extend the drug reaction time through controlled release action in the body
- For drugs that are taken orally, to mask any bitter taste of the drug to make it palatable for the patient
Different agents that may be used to make oral drugs palatable include:
- Vehicles. These components are used to suspend or dissolve the drug and even to mask its taste.
- Colouring agent. Application of colour to the drug form can make it visually appealing to the patient
- Sweetener. Sweetening agents are added usually to liquid forms of medicine to make them palatable to the patient. Examples of agents include sucrose, cane sugar, saccharin and aspartame. Saccharin is 5 times sweeter than sugar but is non-caloric and therefore acceptable for diabetic patients to help them curb their carbohydrate intake. That said, there are some reports that saccharin is carcinogenic. Aspartame is another sweetener, which is 200 times sweeter than sugar but is cleared as safe to use. It is metabolized like protein by the body but loses its sweetness when exposed to heat. Stevia, which is a plant extract, is 150 times sweeter than sugar but was banned in the USA in 1991 because of concerns that it is carcinogenic. More recently the extracted glycoside steviol has been approved both in the USA and Europe as a permitted sweetening agent. It has the advantage over aspartame that it is heat stable, and also pH stable.
- Flavourings. These can be added to the drug to mask the taste. Common flavourings added to oral medication include orange and strawberry fruit extracts.
Different Drug Forms
Drugs can be delivered in two liquid forms. The first is an aqueous solution of one or more active drug ingredient dissolved in water or a saline solution (a solution of sodium chloride). These liquids are intended for injection and are shipped in appropriate sterile containers. Small quantities for injection are supplied in vials or glass ampoules. For administering via intravenous drips, the solutions of drugs are typically metered into a saline solution.
It is possible, in the case of drug compounds that are not soluble or poorly soluble in water, to create a suspension of the drug in an aqueous solution. Suspensions are more commonly used for medicines that are intended for oral administration.
Suspensions can be provided in the following forms:
- Emulsions. A suspension of oil or fat in water can be prepared with the aid of emulsifying agents, often an anionic surfactant – a material whose molecule is hydrophobic at one end and hydrophilic at the other. An example surfactant commonly used in pharmaceutical preparations is sodium stearate. In an emulsion, the sub-microscopic oil particles are coated by the emulsifying agents to create what chemists call a micelle. Unlike an oil globule which tends to separate out from water on account of a massive difference in surface tension of the two liquids, a micelle of oil is stable in water. Using emulsifying agents therefore helps stabilize the suspension of oil in water. Suspensions are often used for oral medications.
- Gels. Gels are quasi-solid materials that have a large number of cross-linked molecules usually holding aqueous solutions of the active pharmaceutical ingredient. Gels are commonly used for topical application as ointments or lotions.
- Magmas. Magmas are a combination of bulky suspension of poorly soluble substances in an aqueous liquid. Magmas are also known as “milks” due to their resemblance to conventional dairy milk. An example of a pharmaceutical magma is milk of magnesia. Magmas and gels are somewhat similar except that the particles suspended in magmas are generally larger and bulkier. Due to this, magma suspensions require shaking before administration.
- Mixtures are usually aqueous liquid preparations which contain suspended, insoluble, solid substances/drugs and are intended for internal use. The insoluble particles may be held in suspension by suitable suspending or thickening agents. The insoluble substance must be in a very finely divided states and it must be uniformly distributed throughout the preparation. This is accomplished by using a colloid mill, special methods of precipitation and suspending agents. There are three main reasons for having the insoluble substance as finely divided as possible:
- If the mixture approaches the colloidal state by including kaoli, magnesium trisilicate, or magnesium phosphate, the more active the particles become when in contact with inflamed surfaces.
- Finely divided particles suspend more easily than large particles, enabling the mixture becoming more homogenous. This is especially desirable when administering medication to form an evenly distributed, soothing, protective coating on the gastrointestinal tract.
- The palatability of many preparations is enhanced by using colloidal suspending agents.
- Tinctures. A tincture is typically an alcoholic extract of plant or animal material or solution of such, or of a low volatility substance (such as iodine and mercurochrome).
Below are the different solid dosage forms available in the market today.
- Powder is the most common solid form; most drugs can be dried and divided into portions that can be used in internal and external applications. Effervescent powders are popular as oral medications as when the powders are dissolved in water, they release gaseous carbon dioxide, which makes the medicine palatable.
- Another solid form is that of capsules made from gelatin or a non-animal substitute. Capsules may contain dry materials, oil or liquid ingredients. The thin capsule material dissolves fast enabling the drug to be absorbed quickly by the body. Some capsules are coated to prevent them from dissolving immediately when exposed to the stomach’s acid. Such capsules are said to have an enteric coating – they disintegrate and release the drug once when pH of the surrounding fluids reaches a certain value, typically above pH 5, in the small intestines. Capsules are usually taken orally, though in certain instances they can be administered through the rectum or vagina.
- Tablets are another popular solid form of drug delivery. In this form the drug is mixed with various other ingredients such as binders, diluents and lubricants that enable the material to be moulded and compressed into the desired shape. Binders are agents that help the material particles to stick together. Depending on the size, weight and shape of a particular tablet, diluents may or may not be added. Lubricants are necessary to prevent the granules from sticking to the mixing machine and the pill or tablet press. Tablets, like capsules, may also be coated to improve their palatability or to create enteric tablets.
- Pellets. Pellets are sphere-shaped drugs formed through compression.
- Pills. Pills were powdered drugs that featured the active ingredients mixed with adhesive substances to create small dosage forms for oral administration; capsules and tablets have generally replaced pills nowadays.
- Lozenges and Troches. These forms are usually provided in flat, round shapes that can be dissolved by saliva in the mouth.
Other External Forms of Drug Administration
- Liniment. Liniments are liquid forms of drug that are applied by rubbing into the skin. These forms often contain anodyne compound to alleviate pain and a rubifacient, which reddens the skin e.g. by causing dilation of the capillaries and an increase in blood circulation.
- Ointments. These drug forms are often semi-solid preparations in which the drug is incorporated into a base material. Ointment bases fall into four general classes: 1) hydrocarbon bases (oleaginous ointment bases) - these keep medicaments in prolonged contact with the skin, act as occlusive dressings, and are used chiefly for emollient effects; 2) absorption bases that either permit the incorporation of aqueous solutions with the formation of a water-in-oil emulsions, or are water-in-oil emulsions that permit the incorporation of additional quantities of aqueous solutions; such bases permit better absorption of some medicaments and are useful as emollients; 3) water-removable bases (creams) – these are oil-in-water emulsions containing petrolatum (petroleum jelly), anhydrous lanolin, or waxes; they may be washed from the skin with water and are thus more acceptable for cosmetic reasons; they favour absorption of serous discharges in dermatologic conditions; and 4) water-soluble bases (greaseless ointment bases) containing only water-soluble substances.
- Lotions. Lotions are liquid forms, which are applied to the skin to protect, cool, cleanse, act as emollient and even provide antipruritic treatment.
- Paste. Pastes are ointment-like type of form where drugs and other solid substances (e.g., zinc oxide) are mixed together with an adhesive fatty base (e.g., petroleum jelly). Pastes are semi-solid preparations intended for topical application affected areas of the skin. Usually they are thick (contain 25% of solids by weight) and do not melt at normal temperature. Remain on the area for longer duration than ointments and are therefore generally more effective.
- Suppositories. A form where drugs are mixed together and molded into the desired shape to be inserted into the body cavity.
- Sprays. Sprays contain drugs in liquid form and are administered using an atomizer.
- Inhalants. These devices contain drugs and are administered by inhaling the vapour sent out from the inhalant and directly to the patient’s nasal passage.