Rectal Ointment

It is used for the symptomatic relief against anal and perianal pruritus, pain and inflammation associated with hemorrhoids, anal fissure, fistulas and proctitis. Rectal ointment should be applied several times in a day according to the severity of the condition. For intrarectal use, the ointment has to be applied with the help of a special applicator.

Creams

Creams Containing Microspheres

Albumin microsphere containing vitamin A can be administered by using creams topically. The in vitro and in vivo drug release of a microencapsulated and nonmicroencapsulated vitamin A cream was studied. The in vivo study in six volunteers revealed that these microspheres were able to remain on the skin for a long period of time and as a consequence they were able to prolong the release of vitamin A.

Lamellar Face Creams

These are liquid paraffin-in-water emulsions prepared from cetrimide or fatty alcohol mixed emulsifiers and ternary systems formed by dispersing the mixed emulsifier in required quantity of water. The cationic emulsifying wax shows phenomenal swelling in water and this swelling is due to electrostatic repulsion, which can be suppressed by the addition of salt and can be reduced by changing the surfactant counter ion.

Creams Containing Lipid Nanoparticles

Occlusion of cream is an important criterion since it increases the penetration of topical drugs. This can be achieved by using oils and fats such as liquid and semisolid paraffin in large quantities. However, such formulations have the limitations of poor cosmetic properties since they have a greasy feel and nonglossy appearance.

The development of a w/o cream containing small particles of solid paraffin was studied. However, this nanodispersion revealed a rough texture when applied. The development of a w/o cream wherein the aqueous phase was divided into small droplets solved this problem. Nanoparticles are incorporated in the aqueous phase. Hence, the oil phase in which the water droplets are dispersed serves as a lubricant for nanoparticles, thereby preventing a rough feel during application.

Gels

Controlled Release Gels

Drug delivery to nasal or ocular mucosa for either local or systemic action suffers from many obstacles. Gel formulations with suitable rheological and mucoadhesive properties increase the contact time at the site of absorption. However, drug release from the gel must be sustained, if benefits are to be gained from the prolonged contact time.

Gelrite gels were formulated in simulated tear fluid at concentrations of polymer as low as 0.1% and it was shown that sodium was the most important gel-promoting ion in vivo.

It was possible to control the release of uncharged drug substances by including surfactants that form micelles in the gel. The release depends on lipophilic interactions between the drug and the polymer and/or the micelles.

Controlled-release formulations of charged drugs could be designed by mixing the drugs with oppositely charged surfactants in certain fixed ratios. In this way, vesicles in which the drug and surfactant constituted the bilayer formed spontaneously. The gels were evaluated using porcine nasal mucosa; from the results it was found that the rate of transport of drugs through the mucosa could be controlled by the rate of release from the formulation.

Organogels

Sorbitan monostearate, a hydrophobic nonionic surfactant, gels a number of organic solvents such as hexadecane, isopropyl myristate and a range of vegetable oils. Gelation is achieved by dissolving or dispersing the organogelator in hot solvent to produce an organic solution or dispersion, which on cooling sets to the gel state. Cooling the solution or dispersion causes a decrease in the solvent–gelator affinities, such that at the gelation temperature the surfactant molecules self-assemble into toroidal inverse vesicles. Further cooling results in the conversion of the toroids into rod-shaped tubules. Once formed, the tubules associate with others and a three-dimensional network is formed, which immobilizes the solvent and thus organogel is formed. The sorbitan stearate and palmitate organogels may have potential applications as delivery vehicles for drugs and antigens.

Extended Release Gels

TIMERx is a controlled release technology consisting of an agglomerated, hydrophilic complex that, when compressed, forms a controlled-release matrix. The matrix, consisting of xanthan and locust bean gums (two polysaccharides) combined with dextrose, surrounds a drug core. In the presence of water, interactions between the matrix components form a tight gel while the inner core remains unwetted. The drug is encapsulated in the pores of the gel, and as the matrix travels through the patient’s digestive system, the tablet swells and begins to erode. This erosion allows the drug to “back-diffuse” out through the gel matrix at a controlled rate until the matrix erodes and a majority of the drug is released. The fundamental component controlling the rate of release lies in the properties of the gel matrix. The advantages of this system include predictable modified release profile such as zero order or first order or initial immediate release kinetics; moreover, it can be produced on standard manufacturing equipment.

Amphiphilic Gels

Amphiphilic gels can be prepared by mixing the solid gelator such as sorbitan monostearate or sorbitan monopalmitate and the liquid phase such as liquid sorbitan esters or polysorbate and heating them at 60°C to form a clear isotropic sol phase, and cooling the sol phase to form an opaque semisolid at room temperature. Amphiphilic gel microstructures consist mainly of clusters of tubules of gelator molecules that had aggregated upon cooling of the sol phase, forming a three-dimensional network throughout the continuous phase. The gels demonstrate thermoreversibility at skin surface temperature and the gels soften considerably, enabling easy topical application. Hence, thixotropic surfactant gels (amphiphilogels) with suitable physical properties are ideal for topical use.

Hydrophilic Gels

An important group of gels used in pharmacy are hydrophilic gels or hydrogels, usually made of hydrophilic polymers, which gellify under certain conditions and polymer concentrations. Attention of pharmaceutical research now concentrates primarily on hydrophilic gels, as this dosage form seems to be prospective for the development of modern drugs based on systems with prolonged and controlled release of active ingredients.

Nonaqueous Gels

Ethylcellulose was successfully formulated as a nonaqueous gel with propylene glycol, dicaprylate or dicaprate. The novel nonaqueous gel exhibited rheological profiles corresponding to a physically cross-linked three-dimensional gel network with suitable mechanical characteristics for use as a vehicle for topical drug delivery. The gel matrices exhibited prominent viscoelastic behavior, yield stress, and thixotropy.

Bioadhesive Gels

Chitosan bioadhesive gel was formulated for nasal delivery of insulin. A nasal perfusion test was carried out to study the toxicity of four absorption enhancers, namely saponin, sodium deoxycholate, EDTA and lecithin. Considering in vitro and in vivo studies, the formulated gel could be a useful preparation for controlled delivery of insulin through the nasal route.

Emulgel

An emulgel is basically a gellified emulsion. It is prepared by mixing an o/w type or w/o type emulsion with a gelling agent. This approach has been applied to numerous drug categories, such as antifungal agents, anti-inflammatory agents, anti-acne agents and corticosteroids. Emulgel formulations offer several advantages over the conventional topical formulations, such as creams, ointments, lotions, and powders. Emulgels allow dual control of drug release from the formulation, that is, emulsion and gel. Incorporation of the emulsion into a gel enhances its stability. It is well suited for the administration of hydrophobic drugs. O/w emulsions may be formulated but a water washable base is intended, such as for cosmetic purposes, whereas w/o type emulsions are a good choice for the treatment of dry skin and emollient application.

Lipid Nanoparticles Incorporated Gel

Solid–lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) are two main types of lipid nanoparticles. Drug delivery from these colloidal systems has unique characteristics when compared to the delivery from traditional topical and dermatological formulations. The small size of lipid nanoparticles ensures close contact with the stratum corneum and increases the amount of encapsulated compounds penetrating into the skin. These nanoparticles have distinct occlusive properties due to the formation of an intact film on the skin surface upon drying, which decreases transepidermal water loss and favors the drug penetrating through the stratum corneum. The advantages of these carriers include negligible skin irritation, controlled release and protection of active substances. They can also be used for controlled drug delivery.

Microemulsion Gel

Microemulsions are thermodynamically stable, isotropically clear dispersion of two immiscible liquids, such as oil and water, stabilized by an interfacial film of surfactant molecules, with a size range of 5200nm and have very low interfacial tension. Because of their unique solubilization properties, microemulsions have attracted increasing attention as potential drug delivery systems, either as vehicles for topical applications or as bioavailability enhancers for poorly water-soluble active pharmaceutical ingredients. The advantages associated with microemulsions include their thermodynamic stability, optical clarity, ease of preparation, and high diffusion and absorption rates when compared with solvents without the surfactant system.

Thermosensitive Sol—Gel Reversible Hydrogels

They are aqueous polymeric solutions at lower temperature and undergo reversible sol-to-gel transformation under the influence of environmental temperature conditions such as room or body temperature. The gels can be prepared using thermoresponsive polymers such as poloxamers.

The advantages of these hydrogels over conventional hydrogels are as follows:

1. Ease of mixing pharmaceutical solutions than semisolids
2. Biocompatibility with biological systems
3. Convenient to administer
4. Controlled manner of release
5. Immobilization of cells
6. Tissue engineering