Do you know the method of drying for pharmaceutical formulations?

Unknown to many, pharmaceutical formulations are dried using microwave drying. This method has been used since the 1930s when the development of magnetron presented a challenge to the worlds of engineering and science during the Second World War to develop industrial applications for this technology.

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Major Developments In Microwave Technology
The decades that followed saw major developments in the extensive investigation of material properties and the design of magnetrons which led to the adoption of microwave applications in several industry sectors including rubber, paper, ceramics, and food. In addition, as early as the 1950s, medical applications for microwaves were simultaneously developed.

Microwave Technology And Pharmaceutical Industry
While other industries have started benefiting from microwave technology early, the pharmaceutical industry is a late adopter. The pharmaceutical industry showed some interest in the technology around 1979 when:

  • the first prototypes of static-bowl microwave dryer were developed
  • the concept of vacuum and microwave combination was proposed by ICI
  • the microwave vacuum dryer belt to dry plant extract was developed

The slow uptake rate of microwave technology by the pharmaceutical industries may be attributed to the fact that drying conditions, especially for pharmaceutical powders that are temperature sensitive are mainly dictated by strict and rigid quality criteria.

Drying conditions for pharmaceutical powders require strict and rigid quality criteria.

Microwave Heating
The technology of microwave heating involves dielectric materials. An electrical insulator that gets polarized caused by the action of applied electrical field is a dielectric. Electrons move freely through a conductor but a dielectric in electric fields displace electrons slightly from their normal positions. A separation of the negative charge from the positive charge is caused by the electric field.

Heating Effect Of Microwave On Material Or Substance
The dielectric loss factor controls the heating effect of microwaves on a material. Some of the common pharmaceutical excipients and active ingredients’ loss factors for single and two-component systems were determined through an experimental atmospheric microwave drying system. High loss factors are observed from formulations with a high percentage of ammonium acetate as against the low loss factors exhibited by Aspirin-based samples. Both were significantly less than that of water which was the solvent used in the experiment.

Microwave Drying And Sterilization
Microwave technology in drying and sterilization not only shortens drying time but also reduces drying defects and damages. This also increases the potential for product innovation to provide seamless integration into manufacturing systems in automated mode.

When moist material is subjected to microwave heating, the molecules and ions are excited which cause them to align with the rapidly alternating electric field. Evaporation of water is promoted by the frictional heat generated as a result of the quick molecular rotations. Microwave dryers combine vacuum and microwave heating which provides high-quality drying and sterilization of substances and materials.

Conventional Drying Problems Avoided
The high level of sterilization and drying at relatively low temperatures avoid problems that usually result from conventional drying such as:

  • contamination of the products with combustion products of gas or oil
  • change of composition and structure of materials
  • undesired agglomeration, sintering, and induration
The advent of microwave technology in the pharmaceutical industry has prevented conventional drying problems.

Benefits Of Microwave Drying
Using microwave drying as an industrial heating and drying process for the pharmaceutical industry brings about the following advantages:

  • reduced drying time
  • ability to dry very fine structures and large dimensions
  • can be easily integrated into automated systems
  • increased productivity and flexibility
  • reduced handling error and production costs

The introduction of microwave drying in pharmaceutical applications has led to its use in single-pot processes that incorporate the dryer and granulator. Using this method allows for a faster and continuous process which ultimately reduces the loss of product during the process change.

Do you know of other drying methods used in the pharmaceutical industry?

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2 thoughts on “Microwave Drying And The Pharmaceutical Industry”

  1. I guess we’ve come a long way with microwave technology since that first bulky microwave melted a candy bar. I recall the big bulky first generation of microwave ovens that hit the consumer market in the 1970’s. The only thing I know about this subject is that the ultimate breakdown strength of a dielectric material is found to decrease as the dielectric-constant k increases. It’s a highly technical subject best left for the engineers.

  2. Although the application of microwave dryers has proven successful in many industries, the uptake rate of microwave technology by pharmaceutical companies has been slow, particularly in the primary manufacturing sector. Pharmaceutical powders are temperature sensitive thus, drying conditions are primarily dictated by stringent quality criteria. The advent of microwave technology, in my opinion, has only intensified the search for pharmaceuticals amenable to microwave processing. There are studies that investigat the drying characteristics of microwave freeze-drying (MFD)/microwave vacuum drying of banana/potato restructured chips of varying proportion and microwave power

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