Different Types Of Pharmaceuticals Taken Via The Mouth Biology

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In general terms, the formation of a tablet requires a mixture of active substances and excipients which are compacted together to help formulate it into the shape of a tablet. The effectiveness of the tablet is largely dependent on the various excipients added in order to make it into a suitable oral dosage form. The definition of a tablet in the Pharmacopeia (PhEur, 2002) states that a tablet is a "Solid preparation with each containing a single dose of one or more than one active ingredients which is usually obtained via compression of a uniform volume of particles.

Tablets have been around for centuries and mainly originate from the 19th century; where the Royal Pharmaceutical Society explain using their fact sheet, how they saw a progress of increased plant use via extracting the active ingredients from the plant roots and leaves to formulate it, into a much more convenient, easy and compressible dosage form i.e. a tablet (Homan, P. 2002).

There are 2 ways of tableting namely; direct compression and wet granulation. Each way is dependent on the amount of drug required for each dosage form. Low dose tablets are mostly manufactured via a method known as Direct Compression whereas the manufacturing of a high dose tablet requires a process known as Wet granulation (Wet massing). An example of a low dose tablet is e.g. Levothyroxine 25 mcg tablet. An example of a high dose tablet is e.g. Metformin 850mg tablet.

Direct Compression

Direct compression is mainly used for low dose tablets. The advantages of using direct compression is that less material is lost, due to direct compression requiring fewer steps in comparison to Wet granulation. No heat or water involved also therefore the stability of the drug is also not affected. Some disadvantages of using direct compression may be that difference in particle size and bulk density of the diluent and the active substance may result in stratification and variation in drug content. Static charges can also develop during mixing and is limited to certain materials (Shoyele, S. 2009).

The manufacturing of tablets via the method of Direct Compression is best described by analysing the flow chart below. There are only two stages to direct compression; powder blending and power compression. The excipients used in Direct compression include; the active pharmaceutical ingredient, a filler, a disintegrant, lubricant and a glidant (Shoyele, S. 2009).

Generally low dose tablets are formulated using the direct compression method. These drugs are very potent and less than 50mg in weight per unit dose. This method is therefore preferred in order to avoid loss in the numerous steps required in wet granulation.

Filler is required in low dose tablets to increase the bulk volume of the tablet. The properties of good filler are that it should be inert and should meet some requirements such as being chemically inert, non-hygroscopic, have good biopharmaceutical properties, good taste and be cost effective. Examples of fillers include lactose, sucrose, microcrystalline cellulose, calcium phosphate. The most common filler used in industry is Lactose (Shoyele, S. & Wells, J. 2009). It fulfils all characteristics of a good filler e.g. dissolves in water, good taste, is non-hygroscopic and inert.

Disintegrants are used in tablet formulation so that when the tablet comes into contact with a liquid, it breaks into small fragments which would result in rapid drug dissolution. Some examples of such disintegrants used in tableting would be; Starch, Cellulose, Cross linked polyvinyl pyrrolidone, sodium starch glycolate and Sodium carboxymethyl cellulose (Aulton, M.E (2007).

The addition of a lubricant in tableting is to ensure that the tablet formation and ejection can occur with low friction between the solid and the die wall (Wells, J. 2008). Examples of lubricants are magnesium stearate, stearic acid and polyethylene glycol (Wells, J. 2008).

Glidants are used to improve the flow ability of the powder, hence decreasing the angle of repose. Examples of a Glidants used in industry are; Silica, magnesium stearate and talc (Wells, J. 2008).

The method of direct compression firstly requires all the excipients to be weighed. Next the active ingredient is mixed with the filler in a mixer. After mixing, the binder, disintegrant and glidant is added to the mixture and mixed again using a mixer. The resulting powder is then used and mixed with the lubricant. The mixer mostly used in direct compression is diffusive mixing.

Wet Granulation

Wet granulation is the process at which high dose tablets can be formulated. This process is also known as wet massing. Granulation is the process where primary powder particles are made to adhere to form larger multi-particle entities known as granules. Wet granulation is a technique used routinely in the pharmaceutical industry when formulating a tablet. It is chosen routinely as a method, as granulation prevents segregation of powder mix; improves flow; improves the compaction characteristics of the mix; and provides uniformity in weight of the ingredients used in the powder mix.

Wet granulation involves the massing of a mix of dry primary powder particles using a granulating fluid. Granulating fluid contains a solvent that is both non-toxic and volatile so that it may be removed by the process of drying. Examples of solvents used include water ethanol and Isopropanol or a combination. The granulating fluid may also contain a binder (examples could be Polyvinyl pyrrolidone/ Polyethylene glycol (Rowe et al (2009) which is an agent that ensures that the particles adhere when the granule is dry. The most commonly used solvent is water. Advantages of this are that it's economical, readily available, and environmentally friendly and doesn't require expensive equipment. The disadvantages are that water can have an effect on the drug stability, if the drug is susceptible to hydrolysis. Water requires an extended drying time in comparison to organic solvents, which may affect the stability due to extended exposure to heat. Ethanol and Isopropanol can be used as an organic solvent. The advantages of using an organic solvent are that it can be used for drugs which are water sensitive and it reduces drying time rapidly. The disadvantages are that expensive equipment and safety apparatus is required.

Wet granulation involves the following stages: blending, wetting, drying, sizing, blending and compression as described in the flow chart below (Shoyele, S. 2009).

Following the blending process, the final step is tableting which involves the use of a tablet press machine. The process of tableting can be split into 3 stages:

Die filling

Tablet formation

Tablet ejection

Die filling is when the upper punch is raised and the lower punch is dropped. The hopper shoe moves forward over the die and the powder falls into the die.

Tablet formation is where the upper punch moves down and compresses the powder, forming the tablet. The lower punch remains stationary or can also move up.

One die and one pair of punches

Can produce up to 200 tablets per min

Produces small batches of tablets

Number of dies and punches

Can produce up to 10,000 tablets per minute

Produces Large batches of tabletsTablet ejection is where the upper punch moves up and the lower punch rises until its tip reaches the top of the die and the tablet is removed.

[4](Shoyele, Sunday, (2009). Lecture Notes- Tablet Testing and Tableting, Huddersfield: School of Pharmacy, University of Huddersfield).

Capsules

As explained above there are many routes by which pharmaceutical dosing can be taken place. The use of capsules is interesting as they are another solid dosage form similarly to tablets that can be taken via the oral route however it has been noted that there are products that have been formulated into a hard gelatin capsule which are not used for oral administration, but used for the administration via the inhaled route therefore counselling patient becomes essential.

The word capsule is derived from the Latin word "capsula" meaning a small box (Aulton, M.E (2007). There are 2 types of capsules that are commercially available; soft gelatin capsules and hard gelatin capsules. The soft gelatin capsule is often referred to being described as one-piece whereas the hard gelatin capsule is referred to as two-piece incorporating the cap and the shell body as two separate pieces (Aulton, M.E (2007).

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