Dosage Forms of the Drugs

Introduction

Drugs can be formulated into a wide variety of dosage forms to achieve the desired therapeutic effect. The choice of dosage form depends on factors such as the physicochemical properties of the drug, the intended route of administration, desired onset and duration of action, patient factors, and commercial considerations.[1] This article will provide an overview of the main dosage forms used for drug delivery.

Oral Dosage Forms

Tablets

Tablets are solid dosage forms containing one or more active ingredients. They are produced by compression of powders or granules. Tablets offer advantages such as accurate dosing, ease of administration, portability, and good stability. However, they may be difficult to swallow for some patients and absorption can be affected by food.[2] Examples include aspirin, paracetamol, and ibuprofen tablets.

a. Compressed tablets are made by direct compression of powdered drugs with excipients like diluents, binders, disintegrants, and lubricants. They are the most common type of tablet.[1]

b. Sugar-coated tablets have a sugar coating to mask unpleasant taste and odor, and improve appearance. The coating can also protect the drug from moisture and light.[3] Many antibiotics and multivitamins are formulated as sugar-coated tablets.

c. Film-coated tablets have a thin polymer coating, which serves purposes similar to sugar-coating but produces a thinner, more durable coat.[3] Most modern tablets are film-coated.

d. Enteric-coated tablets have a polymer coating that remains intact in the acidic environment of the stomach but dissolves in the alkaline intestine. This protects acid-labile drugs and reduces gastric irritation.[1] Examples include proton pump inhibitors and pancreatic enzymes.

e. Chewable tablets are formulated to be chewed before swallowing. This allows buccal absorption, masks bad taste, and improves acceptability in children.[2] Antacid and vitamin C tablets are commonly formulated as chewable tablets.

f. Orally disintegrating tablets (ODTs) are designed to rapidly disintegrate in the mouth without the need for water. They contain highly porous matrices or effervescent agents to promote disintegration.[4] ODTs are useful for patients with dysphagia or where a rapid onset is desired.

g. Sublingual and buccal tablets are placed under the tongue or against the buccal mucosa to allow direct absorption into the systemic circulation, bypassing first pass metabolism. They are used for drugs with high first pass effect or where a rapid onset is needed.[1] Examples include glyceryl trinitrate and fentanyl tablets.

Capsules

Capsules are solid dosage forms in which drugs and excipients are enclosed within a gelatin or hypromellose shell. Capsule shells may be hard or soft, and the contents may be solid, liquid or semi-solid.[2]

a. Hard gelatin capsules consist of two halves – a cap and a body. They are filled with powder, pellets, tablets or granules. Advantages of hard gelatin capsules include the ability to encapsulate a wide variety of ingredients, ease of swallowing, and attractive appearance.[3]

b. Soft gelatin capsules have a one-piece hermetically sealed shell containing a liquid or semi-solid fill. They are used for oils, liquid drugs, and low melting point solids. Soft gelatin capsules have better bioavailability than hard gelatin capsules for compounds with low water solubility.[2]

c. Hypromellose (HPMC) capsules are an alternative to gelatin capsules for patients with dietary or cultural restrictions regarding the use of animal products. They have similar properties to hard gelatin capsules.[1]

Liquids

Liquid oral dosage forms include solutions, suspensions, syrups, and elixirs. They offer advantages such as ease of swallowing and flexibility of dosing. However, they may have poorer stability than solid dosage forms and can be bulky to transport.[2]

a. Solutions are homogenous liquid preparations containing one or more soluble chemicals dissolved in a solvent, usually water. They provide the fastest absorption of all oral dosage forms but may be limited by solubility and stability issues.[1]

b. Suspensions are heterogenous liquid preparations containing finely divided insoluble material suspended in a liquid medium. They are used for insoluble drugs and those unstable in solution. Suspensions must be shaken before use to ensure dose uniformity.[3]

c. Syrups are concentrated aqueous solutions of sugar or a sugar substitute with or without flavouring and colouring agents. They are used to improve palatability, especially in pediatric formulations.[2]

d. Elixirs are clear, pleasantly flavoured hydroalcoholic liquids. They contain one or more active ingredients dissolved in a vehicle that usually contains a high proportion of sucrose or other sugars.[1]

Powders and Granules

Powders are finely divided solids with a particle size of less than 100 μm. Granules are aggregates of powder particles with a size range of 200-4000 μm.[2] Powders and granules can be used as dosage forms in their own right or as intermediates in the production of other dosage forms.

a. Bulk powders and granules are used when large doses are needed or when the drug is unstable in other dosage forms. They can be dissolved or suspended in liquid before administration.[1]

b. Divided powders are unit dose powders dispensed in folded paper or in sachets. They are used for drugs administered in small quantities and those requiring titratable dosing.[2]

c. Effervescent powders and granules contain mixtures of acids (e.g., citric acid, tartaric acid) and bases (e.g., sodium bicarbonate), which react in the presence of water to release carbon dioxide. The effervescence aids in the dissolution and masks the taste of the drug.[1] Effervescent formulations are available for drugs like aspirin, paracetamol, and antacids.

Lozenges and Pastilles

Lozenges and pastilles are solid dosage forms intended to be dissolved slowly in the mouth to provide local or systemic effects. They commonly contain antiseptics, analgesics, or antitussives in a sweetened base.[2]

Oral Gels and Pastes

Oral gels are semi-solid preparations containing a gelling agent such as tragacanth or sodium alginate. They are used to apply drugs to the oral mucosa for local effects.[1] Oral pastes are thick, viscous preparations containing high concentrations of insoluble solids. They are used to deliver drugs for local action in the oral cavity.[3]

Parenteral Dosage Forms

Parenteral dosage forms are sterile preparations administered by injection or infusion. They bypass absorption in the gastrointestinal tract and are useful for drugs that are poorly absorbed, unstable, or irritant in the gut.[1] However, parenteral administration is invasive, irreversible, and carries risks of infection and tissue damage.

Solutions

Parenteral solutions are sterile, pyrogen-free, and free from visible particulate matter. They are used for drugs that are water-soluble and stable in solution. Solutions may be formulated for different routes of parenteral administration.[3]

a. Intravenous (IV) infusions are solutions administered directly into a vein. They allow precise control of drug delivery and are useful for large-volume fluids, irritant drugs, and continuous administration.[2]

b. Intramuscular (IM) injections are administered into deep muscle tissue. Absorption is slower than IV but faster than subcutaneous. Aqueous or oleaginous vehicles are used depending on the solubility of the drug.[1]

c. Subcutaneous (SC) injections are administered into the fatty layer beneath the skin. They allow slower absorption than IM injections and are used for irritant drugs or those requiring prolonged action.[2]

Suspensions

Parenteral suspensions are sterile liquid preparations containing solid drug particles suspended in a suitable vehicle. They are used for drugs that are insoluble in water or unstable in solution. The drug particles must be small enough to pass through the needle and be evenly distributed to ensure accurate dosing.[1]

Emulsions

Parenteral emulsions are liquid preparations containing two immiscible liquids, one dispersed as droplets in the other. They are used for the parenteral delivery of oils and lipid-soluble drugs. The most common type is the oil-in-water (o/w) emulsion, where the oil phase is dispersed in a continuous aqueous phase.[3]

Powders for Reconstitution

Parenteral powders are sterile solid preparations that require reconstitution with a suitable vehicle before administration. They are used for drugs that are unstable in solution or have limited solubility. The reconstituted solution may be administered by any parenteral route.[2]

Implants and Depots

Parenteral implants and depots are solid dosage forms that provide sustained release of drugs over an extended period. Implants are surgically inserted into tissue, while depots are injected as a suspension. They are used for long-term delivery of contraceptives, hormones, and antipsychotics.[1]

Topical and Transdermal Dosage Forms

Topical dosage forms are applied to the skin or mucous membranes to provide local effects. Transdermal dosage forms are designed to deliver drugs systemically via the skin.

Ointments

Ointments are semi-solid preparations intended for external application to the skin or mucous membranes. They contain drugs dispersed or dissolved in a suitable base. Ointment bases may be hydrophobic (e.g., paraffin, beeswax, vegetable oils) or hydrophilic (e.g., macrogols, glycerin).[2]

Creams

Creams are semi-solid emulsion systems containing one or more active ingredients dissolved or dispersed in a suitable base. They have a softer consistency than ointments due to their high water content. Creams are easily applied and spread and are cosmetically acceptable.[1]

Gels

Gels are semi-solid systems consisting of a liquid phase within a three-dimensional polymeric matrix. They may be hydrophilic (e.g., carbomer, tragacanth) or hydrophobic (e.g., plastibase). Gels are used for both topical drug delivery and as a base for other dosage forms.[3]

Pastes

Pastes are semi-solid preparations containing large amounts of finely powdered insoluble solids dispersed in an ointment base. They are used for protective and absorptive effects.[2]

Lotions

Lotions are liquid preparations intended for application to the skin without friction. They are usually oil-in-water emulsions but may also be suspensions or solutions. Lotions spread easily and leave little or no residue.[1]

Transdermal Patches

Transdermal patches are flexible, multi-layered pharmaceutical preparations of varying sizes containing one or more active ingredients. They are designed to deliver drugs across the skin at a controlled rate into the systemic circulation. Transdermal patches are used for drugs with low molecular weight, high lipid solubility, and high potency.[3]

Foams and Mousses

Foams and mousses are dispersions of gas bubbles in a continuous liquid phase. They are used to deliver drug to large areas of the skin or to hair-covered areas. Foams spread easily and absorb quickly, leaving little residue.[2]

Rectal and Vaginal Dosage Forms

Rectal and vaginal dosage forms are used to provide local effects or systemic absorption of drugs. They are useful when oral administration is not feasible due to nausea, vomiting, or unconsciousness.

Suppositories

Suppositories are solid dosage forms intended for insertion into the rectum, vagina, or urethra. They melt, soften, or dissolve at body temperature to release the drug. Suppository bases may be fatty (e.g., cocoa butter) or water-soluble (e.g., PEGs).[1]

Enemas

Enemas are liquid preparations intended for rectal administration to promote evacuation of the bowel or to deliver drugs for local effect. They may be solutions, suspensions, or emulsions.[2]

Vaginal Tablets and Pessaries

Vaginal tablets and pessaries are solid dosage forms intended for insertion into the vagina for local effects. They commonly contain antiseptics, antibiotics, and hormones. The base may be water-soluble or fatty.[3]

Inhalation Dosage Forms

Inhalation dosage forms deliver the drug directly to the respiratory tract for local action or systemic absorption. They are useful for treating respiratory conditions such as asthma and COPD.

Aerosols

Aerosols are fine dispersions of liquid or solid particles in a gas. They are generated by nebulization, atomization, or propellant systems. Metered dose inhalers (MDIs) are the most common type of aerosol inhaler, delivering a precisely measured dose with each actuation.[2]

Dry Powder Inhalers (DPIs)

DPIs deliver a dry powder formulation of micronized drug mixed with larger carrier particles. The powder is dispersed into an inhalable aerosol by the patient’s inspiratory flow. DPIs are breath-actuated and do not require coordination between actuation and inhalation.[1]

Nebulizers

Nebulizers convert a liquid formulation into an aerosol mist for inhalation. They are used to deliver larger doses of drugs or for patients who cannot use MDIs or DPIs effectively. Nebulizers may be jet, ultrasonic, or mesh type.[3]

Conclusion

A wide range of dosage forms are available for drug delivery, each with its own advantages and disadvantages. The choice of dosage form depends on the properties of the drug, the intended use, patient factors, and formulation considerations. Oral solid dosage forms such as tablets and capsules are the most common, but alternative routes such as parenteral, topical, rectal, and inhalation are used when necessary. By understanding the characteristics of each dosage form, the formulation scientist can design optimum drug delivery systems for safe and effective therapy.

References

[1] Aulton ME, Taylor KMG. Aulton’s Pharmaceutics: The Design and Manufacture of Medicines. 5th ed. Edinburgh: Elsevier; 2018.
[2] Allen LV, Ansel HC. Ansel’s Pharmaceutical Dosage Forms and Drug Delivery Systems. 11th ed. Philadelphia: Wolters Kluwer; 2018.
[3] Sinko PJ. Martin’s Physical Pharmacy and Pharmaceutical Sciences. 7th ed. Philadelphia: Wolters Kluwer; 2017.

Disclaimer: This article is for informational purposes only and should not be taken as medical advice. Always consult with a healthcare professional before making any decisions related to medication or treatment.