Introduction of Direct Compression Tablet

Over the past hundred years tablet manufacturers have developed materials and processes that can produce compressed tablets containing a precise amount of an active pharmaceutical ingredient (API) at high speed and at relatively low cost. The development in the field of APIs, excipients and tableting machines during the past decades has made tablet manufacturing a science and the tablets the most commonly used dosage form ,  The ease of manufacturing, convenience in administration, accurate dosing, and stability compared to oral liquids, tamperproofness compared to capsules, safe compared to parental dosage forms makes it a popular and versatile dosage form.

Experts in the art of tableting are aware with the basic art of tableting by the three well-known methods, i.e. wet granulation, roller compaction and direct compression1,2,3. The pros and cons of wet granulation and roller compaction are well documented in the literature , ,  Prior to the late 1950s, the literature contained few references on the direct compression of pharmaceuticals. A great deal of attention has been given to both product and process development in the recent years. The availability of new materials, new forms of old materials and the invention of new machinery has allowed the production of tablets by simplified and reliable methods1 . 

In early 1960’s, the introduction of spray dried lactose (1960) and Avicel (1964) had changed the tablet manufacturing process and opened avenues of direct compression tableting.  Shangraw 4 conducted a survey of 58 products in United States of America for the preference for the granulation process. The results were in favour of direct compression. Of the five processes listed in the survey, the average score (1.0 being the perfect score) for direct compression was 1.5 compared to wet massing and fluid bed drying (2.0), wet massing and tray drying (2.5), all-in-one (3.3) and roller compaction (3.6). About 41% of the companies indicated that direct compression was the method of choice, and 41.1% indicated that they used both direct compression and wet granulation. Only 1.7% of the respondents indicated that they never used direct compression and 15.5% indicated that the process was not recommended. Previously, the word “direct compression” was used to identify the compression of a single crystalline compound (i.e. sodium chloride, potassium chloride, potassium bromide, etc.) into a compact form without the addition of other substances.

Current usage of the term “direct compression” is used to define the process by which tablets are compressed directly from the powder blends of active ingredients and suitable excipients. No pre-treatment of the powder blends by wet or dry granulation is involved (5). The simplicity of the direct compression process is apparent from a comparison of the steps involved in the manufacture of tablets by wet granulation, roller compaction and direct compression techniques (4) (See Table 1). It has been estimated that less than 20 percent of pharmaceutical materials can be compressed directly into tablets (4). The rest of the materials lack flow, cohesion or lubricating properties necessary for the production of tablets by direct compression. The use of directly compressible adjuvants may yield satisfactory tablets for such materials.