Pharmaceutical Dosage Forms: A Review

Brian Staiger Pharm.D" />

​Oral medications are the most common and convenient dosage form available for administration. Most oral medications are intended to be absorbed into the blood stream from the small intestine where they will then be transported throughout the body.

Solid dosage forms have several advantages over other dosage forms including ease of administration, longer expiration dates, ease of packaging, more accurate dosing, the absence of taste and the development of extended release properties. There are several disadvantages as well including difficulty swallowing for some patients and taking longer to absorb than liquid medications.

​Tablets are a solid dosage form that may be administered orally (by mouth) , sublingually (under the tongue), vaginally (as a suppository) or a as pellet under the skin. Tablets can come in many different variations including immediate release, delayed release and extended release. They are the most common type of dosage form due to their ease of administration and manufacturing costs.

Buccal Tablet

A buccal tablets is a solid dosage form that is placed between the teeth and cheek as shown in the picture. Unlike regular tablets, buccal dosage forms are absorbed through the lining of the cheek as opposed to the small intestine. Buccal tablets that are swallowed typically have a much reduced effect due to undesired metabolism in the stomach and liver. Many different drugs are available as a buccal tablet including testosterone, nicotine and pain medications.

Oral Disintegrating

Oral disintegrating dosage forms dissolve in the mouth and the juices/ left over particles are swallowed. The drug is then absorbed through the small intestine. Oral disintegrating dosage forms are very beneficial for those with swallowing problems or those who have severe nausea/vomiting and cannot keep anything down. It is also beneficial for children who cannot or will not swallow medications.

Effervescent dosage forms are typically placed in water or another liquid and allowed to dissolve. After the dissolving action is complete, the liquid is then consumed. Original Alka Seltzer is an example of an effervescent tablet. Effervescent tablets are not very common any longer and are being replaced with powders and dissolving tablets. This is because most effervescent tablets contain a considerable amount of sodium. One tablet of Alka Seltzer contains over 500mg of sodium. It is very important that effervescent tablets are dissolved before consumed. Otherwise, the carbon dioxide that is released in the stomach could cause serious harm.

Powders are typically mixed with a liquid and then consumed. Powders are used when dosages are fairly large and cannot be contained in a tablet or capsule. Fiber supplements are a common example of a medication in a powder form.

Lozenges and troches are typically interchangeable terms. Troches do tend to be softer however. These dosage forms are usually dosed for their topical effect in the mouth. Common drugs that come as lozenges/troches are antifungal medications and numbing agents. There are a small number of drugs such as Actiq (fentanyl) which are intended to be absorbed into the blood stream.

Capsules are the second most common type of solid dosage form behind tablets. They typically contain less inactive ingredients than tablets so they can be a good choice in those with multiple food allergies. The capsule shell is often made of gelatin which usually makes them easier to swallow than tablets. The gelatin shell of capsules are made from animal collagen so vegetarians typically should try to avoid them. Like tablets, capsules are available in immediate release and extended release variations.

Oral Liquid Dosage Forms

Liquids are another very common dosage form and the medications contained in liquids are typically in a water or alcohol vehicle. The medication may either be dissolved or suspended in the vehicle. The consistency of liquids can be as thin as water or a thick as a syrup. There are several advantages of liquids over solid dosage forms including ease of administration for patients with difficulty swallowing, faster absorption than solid dosage forms and the ability of liquid dosages to be altered and changed. Several disadvantages include a shorter shelf life than solid dosage forms, bad taste, difficulty in packaging/transportation and the easier possibility of dosage errors.

A solution is defined as liquid mixture in which a solute is uniformly distributed in a solvent. A good example of this is salt water. You can add a small amount of salt to a glass of water and then stir. The salt will dissolve in the water and becomes evenly distributed throughout. The resulting liquid is known as a solution. Drugs that come as a solution do not need to be shaken and stirred as the liquid has an even distribution of the drug. Solutions usually have the consistency of water and do not contain noticeable particles or undissolved drug. Injectable drugs are very commonly solutions.

A suspension is a liquid in which the ingredients are not soluble. It is very common to see the undissolved drug particles in a suspension. Suspensions need to be shaken prior to administration of the medication or else most of the drug will settle at the bottom. Many different drugs come as suspensions including most antibiotics liquids. Suspensions tend to be much thicker and have a more creamy consistency than liquids.

In most cases, syrups are solutions that are sweetened, usually with sucrose. They have a much thicker consistency than true solutions. They do not need to be shaken or stirred prior to administration, just like solutions.

While not very common, emulsions are another type of liquid medication that is available. An emulsion is technically a suspension of two immiscible liquids held together by an emulsifying agent. Immiscible liquids do not combine together without the aid of an emulsifying agent. For example, water and oil will not mix together and form separate layers when put together. An emulsifying agent can combine and hold the two liquids together.

Topical Dosage Forms

Creams are opaque and typically white to off white in color. They tend to be non-greasy and are smooth. Unlike ointments, creams are absorbed into the skin after application and work from the inner layers of the dermis. Creams are almost always smooth and easy to apply. In addition to the medication contained in creams, they function to sooth, dry and protect the skin. Most patients prefer creams to ointments because they wash off the skin easier and don't leave a greasy residue.

Ointments are designed to deliver medication, lubricate and protect the skin. Unlike creams, most ointments are not absorbed into the skin. The term ointment is very broad as there are multiple types of ointments including water soluble ointments, anhydrous ointments and oleaginous ointments. A common distinction between creams and ointments is that ointments are occlusive and keep moisture from leaving the skin. While this helps protect and moisturize the skin more than creams, it can leave the skin feeling greasy.

Gels are a unique topical dosage form that consists of particles suspended in a non-viscous liquid medium. Gels are considered semi-solid dosage forms as they are technically a liquid that holds together solid drug participles. Drugs produced in gel form are typically considered to be stronger and deliver more medication to the affected area. Many new drugs are being developed as transdermal gels, or gels that go through the skin into the blood stream. Gels typically contain alcohol and provide a cooling feeling after topical administration. Due to the alcohol content, gels can have a significant drying effect.

Pastes are usually very stiff and viscous preparations that do not soften when applied to the skin. They are most commonly intended to be used as a protective covering over areas in which they are applied. Diaper rash preparations are typically manufactured in a paste as they provide protection to sensitive areas.

Lotions are liquid suspensions and are usually not as thick as any other topical dosage form. They are made up of powdered medications in a liquid mixture. Lotions are commonly used as moisturizers. Many patients prefer lotions to other topical dosage forms due to the ease of applying them over large portions of the body. They typically do not leave an oily or greasy feeling on the skin.