Topical medication

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A topical medication is a

topikos, "of a place".

Justification

Topical drug delivery is a route of administering

need to be considered. There are some novel topical drugs in the market which can utilise the system as much as possible.

This localized system provides topical therapeutic effects via

to provide topical treatment.

Factor affecting topical drug absorption

Topical drug absorption depends on two major factors – biological and physicochemical properties.

The first factor concerns body structure effects on the

.

The other factor concerns metabolism of medications on

of the drugs can affect this diffusion rate too. If the drug shows lower degree of ionization, it is less polar. Therefore, it can have a faster absorption rate.

Local versus systemic effect

The definition of the topical

In other cases, topical is defined as applied to a localized area of the body or to the surface of a body part regardless of the location of the effect.^[5][6] By this definition, topical administration also includes transdermal application, where the substance is administered onto the skin but is absorbed into the body to attain systemic distribution. Such medications are generally hydrophobic chemicals, such as steroid hormones. Specific types include transdermal patches which have become a popular means of administering some drugs for birth control, hormone replacement therapy, and prevention of motion sickness. One example of an antibiotic that may be applied topically is chloramphenicol.

If defined strictly as having local effect, the topical

Choice of base formulation

A medication's potency often is changed with its base. For example, some topical steroids will be classified one or two strengths higher when moving from cream to ointment. As a rule of thumb, an ointment base is more occlusive and will drive the medication into the skin more rapidly than a solution or cream base.^[8]

The manufacturer of each topical product has total control over the content of the base of a medication. Although containing the same active ingredients, one manufacturer's cream might be more acidic than the next, which could cause skin irritation or change its absorption rate. For example, a vaginal formulation of

However, in a simple base like an ointment, much less variation between manufacturers is common.

In dermatology, the base of a topical medication is often as important as the medication itself. It is extremely important to receive a medication in the correct base, before applying to the skin. A pharmacist should not substitute an ointment for a cream, or vice versa, as the potency of the medication can change. Some physicians use a thick ointment to replace the waterproof barrier of the inflamed skin in the treatment of eczema, and a cream might not accomplish the same clinical intention.

Formulations

There are many general classes, with no clear dividing line among similar formulations. As a result, what the manufacturer's marketing department chooses to list on the label of a topical medication might be completely different from what the form would normally be called.

Cream

A

Foam

Foam can be seen with topical steroid marketed for the scalp.^{[citation needed]}

Gel

Gels are thicker than liquids. Gels are often a semisolid emulsion and sometimes use alcohol as a solvent for the active ingredient; some gels liquefy at body temperature. Gel tends to be cellulose cut with alcohol or acetone. Gels tend to be self-drying, tend to have greatly variable ingredients between brands, and carry a significant risk of inducing hypersensitivity due to fragrances and preservatives. Gel is useful for hairy areas and body folds. In applying gel one should avoid fissures in the skin, due to the stinging effect of the alcohol base. Gel enjoys a high rate of acceptance due to its cosmetic elegance.^[9]

Lotion

in nature than solution. They are usually oil mixed with water, and more often than not have less alcohol than solution. Lotions can be drying if they contain a high amount of alcohol.

Ointment

An ointment is a homogeneous, viscous, semi-solid preparation; most commonly a greasy, thick water-in-oil emulsion (80% oil, 20% water) having a high viscosity, that is intended for external application to the skin or mucous membranes. Ointments have a water number that defines the maximum amount of water that they can contain. They are used as

or for the application of active ingredients to the skin for protective, therapeutic, or prophylactic purposes and where a degree of occlusion is desired.

Ointments are used topically on a variety of body surfaces. These include the skin and the mucous membranes of the eye (an eye ointment), chest, vulva, anus, and nose. An ointment may or may not be medicated.

Ointments are usually very moisturizing, and good for dry skin. They have a low risk of sensitization due to having few ingredients beyond the base oil or fat, and low irritation risk. There is typically little variability between brands of drugs. They are often disliked by patients due to greasiness.^[9]

The vehicle of an ointment is known as the ointment base. The choice of a base depends upon the clinical indication for the ointment. The different types of ointment bases are:

• Absorption bases, e.g.,
  wool fat
• Emulsifying bases, e.g., cetrimide and emulsifying wax
• Hydrocarbon bases, e.g.,
  ceresine, microcrystalline wax, hard paraffin, and soft paraffin
• Vegetable oil bases, e.g.,
  almond oil, coconut oil, olive oil, peanut oil, and sesame oil
• Water-soluble bases, e.g., macrogols 200, 300, 400

The medicaments are dispersed in the base and are divided after penetrating the living cells of the skin.

The water number of an ointment is the maximum quantity of water that 100g of a base can contain at 20 °C.

Ointments are formulated using hydrophobic, hydrophilic, or water-emulsifying bases to provide preparations that are immiscible, miscible, or emulsifiable with skin secretions. They can also be derived from hydrocarbon (fatty), absorption, water-removable, or water-soluble bases.

Evaluation of ointments:^{[citation needed]}

1. Drug content
2. Release of medicament from base
3. Medicament penetration
4. Consistency of the preparation
5. Absorption of medicament into blood stream
6. Irritant effect

Properties which affect choice of an ointment base are:^{[citation needed]}

1. Stability
2. Penetrability
3. Solvent property
4. Irritant effects
5. Ease of application and removal

Methods of preparation of ointments:

• Fusion: In this method the ingredients are melted together in descending order of their melting points and stirred to ensure homogeneity.^{[citation needed]}
• Trituration: In this finely subdivided insoluble medicaments are evenly distributed by grinding with a small amount of the base followed by dilution with gradually increasing amounts of the base.^{[citation needed]}

Paste

Paste combines three agents – oil, water, and powder. It is an ointment in which a powder is suspended.

Powder

powder used in nasal surgery).

Shake lotion

A shake lotion is a mixture that separates into two or three parts over time. Frequently, an oil mixed with a water-based solution needs to be shaken into suspension before use and includes the instructions: "Shake well before use".^[citation needed]

Solid

Medication may be placed in a solid form. Examples are deodorant, antiperspirants, astringents, and hemostatic agents. Some solids melt when they reach body temperature (e.g. rectal suppositories).

Sponge

Certain contraceptive methods rely on

embedded in a sponge has been used as a primitive contraception in some cultures.

Tape

Cordran tape is an example of a topical steroid applied under occlusion by tape. This greatly increases the potency and absorption of the topical steroid and is used to treat inflammatory skin diseases.

Tincture

A tincture is a skin preparation that has a high percentage of alcohol. It would normally be used as a drug vehicle if drying of the area is desired.

Topical solution

Topical solutions can be marketed as drops, rinses, or sprays, are generally of low viscosity, and often use alcohol or water in the base.^[11][12][13] These are usually a powder dissolved in alcohol, water, and sometimes oil; although a solution that uses alcohol as a base ingredient, as in topical steroids, can cause drying of the skin.^{[14][page needed]} There is significant variability among brands, and some solutions may cause irritation, depending on the preservative(s) and fragrances used in the base.

Some examples of topical solutions are given below:

1. Aluminium acetate topical solution: This is colorless, with a faint acetous odour and sweetish taste. It is applied topically as an astringent after dilution with 10-40 parts of water. This is used in many types of dermatologic creams, lotions, and pastes. Commercial premeasured and packed tablets and powders are available for this preparation.^{[citation needed]}
2. Povidone iodine topical solution: This is a chemical complex of iodine with polyvinylpyrrolidone. The agent is a polymer with an average molecular weight of 40,000. The povidone iodine contains 10% available iodine, slowly released when applied to skin. This preparation is employed topically as a surgical scrub and non irritating antiseptic solution; its effectiveness is directly attributed to the presence and release of iodine from the complex. Commercial product:
   Betadine solution.^{[citation needed}
   ]

Transdermal patch

Transdermal patches can be a very precise time released method of delivering a drug. Cutting a patch in half might affect the dose delivered. The release of the active component from a transdermal delivery system (patch) may be controlled by diffusion through the adhesive which covers the whole patch, by diffusion through a membrane which may only have adhesive on the patch rim or drug release may be controlled by release from a polymer matrix. Cutting a patch might cause rapid dehydration of the base of the medicine and affect the rate of diffusion.

Vapor

Some medications are applied as an ointment or gel, and reach the mucous membrane via vaporization. Examples are nasal topical decongestants and smelling salt.

Topical Drug Classification System (TCS)

Topical drug classification system (TCS) is proposed by the

Advantages of topical drug delivery systems

In the early 1970s, the

]

Disadvantages of topical drug delivery systems

The site of putting the patches for topical drugs may get irritated and have rashes and feel itchy. Hence, some topical drugs including nicotine patches for smoking cessation are advised to change places for each application to avoid continuous irritation of the skin. Also, since the drug needs to penetrate the skin, some drugs may not be able to pass through the skin. Some drugs are then “wasted” and the bioavailability of the drug will decrease.

Challenges for designing topical dosage form

Skin penetration is the main challenge for any topical dosage form. The drug needs to penetrate the skin in order to get into the body to apply its function. The drug follows the Fick’s first law of diffusion.^[17] One of the most common versions of Fick’s first law of diffusion is:

${\displaystyle J=-D{dc \over dx}}$

where

• J is the
  diffusion flux
  .
• D is the
  diffusion coefficient
  .
• dc/dx is the
  concentration gradient
  .

For D is described by the

. The equation is:

${\displaystyle D={\frac {RT}{6\pi \eta rN_{A}}}}$

where

• R is the gas constant.
• T is the temperature.
• η is the viscosity.
• r is the radius of the solute.
• ${\displaystyle N_{A}}$ is the Avogadro constant.

Assuming

New developments

There are many factors for drug developers to consider in developing new topical formulations.

The first one is the effect of the drug vehicle. The medium to carry the topical drugs can affect the penetration of the drug

In order to enhance drug penetration into the skin, scientists have several ways to achieve their purposes by using chemical, biochemical, physical and

See also

• Finger tip unit
• Liniment
• Topical anesthetic
• Topical antibiotic
• Topical corticosteroids
• Unguent

References

• Goodman & Gilman's The Pharmacological Basis of Therapeutics
• Dr. David Edwards – Dentistry Microbiology Lecture series

External links

• History of ointments

Skin	Intradermal Subcutaneous Injector pen Transdermal implant	Organs	Intracavernous Intravitreal Intra-articular
Central nervous system	Intracerebral Intrathecal Epidural
Circulatory, musculoskeletal	Intravenous Intracardiac Intramuscular Intraosseous Intraperitoneal Nanocell injection Patient-controlled analgesia pump PIC line