Pharmaceutical Dosage Forms

Introduction

Pharmaceutical or drug dosage form is a combination of an active ingredient with suitable excipients. Active ingredients are the main drug or pro-drug while other substances added are excipients. Dosage forms are pharmaceutical drug products in the form in which they are marketed for use. A particular dosage form has a specific mixture of active and inactive substance (excipients). The route of administration of a drug is dependent on its dosage form. A pharmaceutical dosage form is the entity that it is administered to the patient so that they receive a safe and effective dose of the drug.

Importance of Dosage Forms

1. To protect the active pharmaceutical ingredients from the external destructive influences. Example, enteric coating of dosage forms prevents some drugs from being destroyed by gastric secretions in the stomach.
2. To mask the bitter taste of the active pharmaceutical ingredients usually through, encapsulation, sugar coating, addition of sweeteners and some flavoring agent as excipients.
3. To provide drugs that is stable, effective, and safe under suitable conditions.
4. To provide optimal drug action at its site of administration via targeted drugs administration
5. To achieve drugs with rapid onset of action.
6. To provide drugs that bypass the first – pass metabolism e.g. parenteral
7. To enable easy of adminstration into any desired target
8. To improve patients’ acceptability
9. To allow for accuracy in dosing especially in infants, neonates and drugs with low therapeutic index
10. To control the release pattern of drugs into the system. E.g. sustained release and Controlled release formulations

Factors to Consider in Choosing Dosage Forms

1. Preformulation Studies

These studies are designed to identify those physical and chemical properties of a candidate drug molecule which may affect the development of a safe, stable and efficient dosage forms with good bioavailability.

2. Biopharmaceutical Considerations

The human body is considered here focusing on the absorption and elimination of the drug. For the adsorption, the route of administration is considered. The drug substance must be in a solution form before it can be absorbed into the membrane. Drug administered through buccal, respiratory, rectal, intramuscular or subcutaneous routes passes directly into the absorbing tissues unlike those of oral route that have to undergo first pass metabolism before absorption.

3. Route of Adminstration:

The route of administration is considered before choosing dosage form. The route of administration is determined by the available dosage form. The routes of administrations include: oral, rectal, parenteral, topical, and respiratory. When it comes to oral route, the taste is considered, the dissolution of the drug is considered. Rectal route is mainly used for local effect or when the drug cannot be taken through the oral route. Parenteral route involves use of injection. It includes intramuscular (im), intravenous (IV), subcutaneous (sb). The parenteral route is preferred when rapid absorption and action is essential. Topical route dosage form is meant to be applied on the skin for a local action. Respiratory route is used when drug is inhaled into the airways. The lungs provide an excellent surface for absorption.

4. Drug Factors in Dosage Forms Design

• Particle size and surface area
• Solubility
• Dissolution
• Partition coefficient PKA
• Crystal properties polymorphism
• Stability
• Organoleptic properties
• Other drug properties.

5. Therapeutic Considerations in Dosage Forms Design

The nature of the clinical indication, disease or illness against which the drug is intended is an important factor when selecting the range of dosage form to be prepared.

Classes of Drug Dosage Forms

Drug Dosage Forms can be classified based on

1. Route of administration
2. Physical presentation of the drugs

Classifications of dosage forms based on route of administration

1. Topical dosage forms
2. Oral dosage forms
3. Parenteral dosage form
4. Rectal dosage forms
5. Respiratory (Inhalation) dosage forms
6. Vaginal dosage forms
7. Ophthalmic
8. Nasal
9. Otic

Classification of dosage forms based on Physical presentation

1. SOLID DOSAGE FORMS:

Solid dosage form is the commonest and most used dosage forms. They are not pourable. Solid dosage forms have a definite shape and volume manufactured for the administration of active and inert ingredients.

Example of Solid Dosage Forms

i. CAPSULES:

They are enclosed drugs in a relative stable shell called capsules.
TYPES OF CAPSULES:

• Hard shelled capsules; mainly used to enclose dry, powdered ingredients.
• Soft shelled capsules; mainly used for oils

Both of these classes of capsules are made from aqueous solutions of gelling agents.

ii. TABLETS

They are solid dosage form that comprise of both active and non active ingredients compacted from a powdered mixture or granules into a solid dose unit.
TYPES OF TABLETS

• Enteric coated tablets: They are compressed tablets with delayed release properties which are coated with polymeric substance (e.g. cellulose acetate phthalate) that resist dissolution and absorption in the intestine.
• Chewable tablets: These are big sized tablets which are difficult to swallow, thus are chewed within the buccal cavity prior to swallowing. They are especially useful for the administration of large tablets to children and adults who have difficulties in swallowing conventional tablets or antacid formulation.
• Buccal and sublingual tablets: Small, flat, oral tablets that are intended to be dissolved with the buccal punch or beneath the tongue as in sublingual for absorption through the oral mucosa to produce a systemic effect. They are used to achieve rapid absorption into the systemic circulation or drug that are destroyed by gastric juice and are poorly absorbed by GIT.
• TABLET TRITURATES: Thes are small, usually cylindrical compressed tablets containing small amount of usually potent drugs mixed with a combination of sucrose and lactose or any suitable diluents. They are prepared from a moist material using triturate mould that gives the shape of cut sections of a cylinder. One major disadvantage is finding a lubricant which is completely water soluble.
• Hypodermic tablets: These are soft, readily soluble tablets that were originally used by physicians in extemporaneous preparation of parental solution. These tablets are dissolved in suitable vehicle and administered through the parenteral route. The major disadvantage of this is difficulty in maintaining sterility.
• Dispensing tablets: Dispensing or compounding tablets are tablets supplied primarily for extemporaneous compounding. These tablets contain highly potent API’S and thus are used by pharmacists to compound prescriptions that can be incorporated readily into powders and liquids, thus circumventing necessity to weigh small quantities of theses potent drug substance. They are no longer in use.
• Gelatin coated tablets: These are compressed tablets coated with either one or two tuned colour gelatin. The gelatin coating impacts the same general characteristic as sugar coating and film coating with the added advantage of improving the stability of photosensitive API.
• COMRESSION TABLETS: Compression coated tablets; usually referred to as dry coated or press coated tablets are tablets with 2 parts, internal core and surrounding cores. The tablets are prepared by feeding previously compressed tablets into a special tablet press and compressing another granulation layer around a preformed tablet core. These tablets are also used to separate incompatible drug substance and masking taste.
• Layered tablets: This is tablet composed of two or more layers of ingredients prepared by compressing additional tablets granulation on a previously compressed granulation to form two layered or three layered tablet.
• In lay tablets: popularly known as dot or bull. Tablets are variation of compressed tablets with partially surrounded core.
• Rapid release tablets: Rapidly dissolving tablets are characterized by disintegration dissolution in the mouth within a minute leaving an easy to swallow residue
• Extended release: Tablets are designed to release their medication in pre determined time over a prolonged period of time
• Vaginal tablets/ inserts: They are uncoated bullet shaped or ovoid shaped tablets designed for vaginal administration. They are prepared by compression and are shaped to fit tightly on a plastic inserter device.
• Implantation tablets: long lasting sterile tablets designed to provide continuous release of the drug often over a period of months or a year. They are placed subcutaneously.

iii. PELLETS

Pellets are multi particulate dosage forms which was formed by agglomeration of fine powdered excipient and drugs together that leads to formation of small free flowing spherical or semi spherical particles

iv. PILLS:

Pills are medicinal substances in a small round or oval mass meant to be swallowed.

v. LOZENGES:

It is a small, typically medicated tablets intended to be dissolved slowly in the mouth to temporally stop cough, lubricate, and soothe irritated tissues of the throat, possibly from common cold or flu.

vi. SPRAYS:

Sprays are pressurised dosage forms containing one or more active ingredients which upon activation emit a fine dispersion of liquid and solid materials in a gaseous
SUPPOSITORIES: it is a small, round or cone shaped substances that are put into the body usually through the rectum or vagina

2. LIQUID DOSAGE FORMS:

These are dosage forms in liquid phase. They involve active pharmaceutical ingredients and excipients i.e. the inactive part in a liquid form. Liquid dosage forms are pourable pharmaceutical formulations which contain a mixture of active and inactive substances.
There are two types of liquid dosage form based on the phases;

1. Monophasic liquid form
2. Biphasic liquid form

Monophasic Liquid Dosage Forms

Mono phasic form have only one phase. It’s a homogenous mixture of substance both the active and inactive ingredients in one phase.
Monophasic Liquid dosage forms include

• Mixtures: they are aqueous liquid preparations which contain suspended, insoluble solid substances intended for external use
• Linctuses: A syrup like medicinal formulation taken to relieve cough and sore throat.
• Droughts: A drought is an older term used to describe a liquid preparation formulated as a single dose in a volume which is larger than generally utilized in traditional mixture formulations.
• Elixer: elixers are sweetened hydro- alcoholic (water and alcohol) liquids for oral use.
• Syrup: A thick, sweet liquids made by dissolving sugar in boiling water. 85% of sugar is usually used.
• Drops: A liquid medication applied by means of a dropper.
• Lotions: A low viscosity topical preparation intended for application to the skin.
• Liniments: A liniment is a liquid dosage form that is rubbed into the skin in order to reduce pain or relieve stiffness. Liniments are solutions or mixtures of various substances in oil, alcoholic solution of soap or emulsions, intended for external use.
• Colloids: It has dispensed phase and dispersion medium. It is the mixture of two substances which one form the dispersed phase and the other forms the dispersion medium.
  Gargles: They are aqueous solution employed for treating the pharynx and nasopharynx by forcing air from the lungs through gargle which is held in the throat.
• Mouth wash: Liquid which is held in the mouth passively or swilled around the mouth by the contraction of the parietal muscles and movement of the head. It is used as antiseptic.
  Throat paint: They are solutions or dispersions of one or more active ingredients intended for application to the mucosa of the throat or mouth. It is viscous due to high content of glycerin which sticks it to affected part for prolonged actions.
• Douches: A douche is liquid dosage form introduced into the appropriate body cavity for cleansing purposes. They are referred to as irrigation possessing antiseptic.
• Enemas: They are rectal injections used to evacuate the bowel, influence the general system by absorption or to affect local seat of disease.
• Parenteral solutions: They are sterile liquid dosage form meant to be administered using syringes through venous route, muscular route or subcutaneous route.
• Solution: it is a homogenous mixture of two or more substances in a relative amount that can be varied continuously. A solution is a homogenous mixture of one or more solutes dissolved in a solvent.
• Magma: It is a suspension of inorganic solid such as clay in water where there is tendency for strong hydration and aggregation of solid giving rise to gel like consistency.

Biphasic Liquid Forms

They are heterogeneous mixtures of substances to form two phases.
Biphasic Liquid Dosage Forms Include:

• Suspension: It is a heterogeneous mixture that contain solid particles sufficiently large for sedimentation in the solvent like phase.
• Emulsion: It is a mixture of two substance especially oil and water that are normally immiscible but emulgent or emulsifying agent is added to mix them. They are of two types that is oil in water and water in oil emulsion.

Conclusion

In conclusion, a drug is a substance used for diagnosis, prevention and treatment of disease. Dosage form of a drug is the form in which the drug appeared physically.
Recent advancement in technology helps to provide varieties of dosage forms suitable for a specific drug and convenience of the target patients are also considered especially children and elderly patients.