Powders

Powders

Powders are solid dosage form of medicaments which are made for internal and external purposes. They are available in amorphous and crystalline form. Drugs are prepared in different forms and shapes but many of them are prepared by using powder in one way or the other incompatibility (the quality of being discordant).

Advantages and disadvantages of powder:

The various merits and demerits of powders are discussed below;

Advantages:

1.       Many of drugs are available in powder form it become convenient for physician to prescribe specific amount of medicaments.

2.       Powders are less in compatible than liquids. Large quantities of bulky drugs which are difficult to administer can be easily taken with the help of liquid.

3.       They are easier to carry than liquids.

4.       They are more stable than liquids.

5.       Chemical reactions take place more easily in liquids than powders in atmospheric condition.

6.       Small particles of powders produce more rapid dissolution in body fluids than other dosage form.

7.       They are more economical for extemporaneous preparations.

8.       They are convenient for pediatric (child) and geriatric patients (old aged people).

Disadvantages:

1.       Drugs which deteriorate on exposure to atmospheric conditions are not suitable for powders.

2.       Bitter, nauseous, corrosive and unpalatable drugs can’t be dispensed in powder form.

3.       Deliquescent and hygroscopic drugs can’t be dispensed in powder form because they absorb moisture.

4.       Volatile drugs are not suitable for powder form because they lose their efficacy.

Classification of Powders

·         Simple and compound powders for internal use.

·         Granular and effervescent powders for internal use.

·         Bulk powders for external use.

·         Dusting powders, insufflations (used to insert into different body cavities) and tooth powders.

Practice size analysis:

Before the use of powders and other solid materials in pharmaceutical products characterized to determine their physical and chemical properties. It includes morphology, purity, solubility, stability, particle size and impurity.

The particles of pharmaceutical powders may be range from extremely coarse about 10mm in diameter to extremely fine approaching to colloidal dimension of micron or less. To characterized the particle size in USP;

Ø  Very coarse:Powders of vegetable and animal drugs are officially defined as very coarse. All particles pass through the 8 sieve and not more than 20% through a no. 50 sieve

Ø  Coarse:All particles pass through a number 20 sieve and not more than 40% through sieve number 60.

Ø  Moderately coarse:All particles pass through a number 40 sieve and not more than 40% through sieve number 80.

Ø  Fine: All particles pass through a number 60 sieve and not more than 40% through sieve number 100.

Ø  Very fine:All particles pass through a number 80 sieve, there is no limit to to greater fineness.

Blending powers:

These are formed when two or more than two powdered substances are to be combined to form a uniform mixture. It is best to reduce the particle size of each powder before weighing and blending.Depending upon the nature of ingredients amount of powders and equipment, powders may be blended by;

Ø  Spatulation:it involves the using spatula on white papers or slides to decrease the particle size.

Ø  Trituration:It includes the reduction of particle size on small scale by using pestle and mortar i.e. levigation& pulverization.

Ø  Sifting:For sifting process we require sifters i.e. any containers in which two substances are used. It is not used for the substances which produce therapeutic effects in small quantity i.e. potent drugs. In involves the usage of different types of machines for example; V-type, M-type and ribbon type machines.

Ø  Tumbling:Another method of powder mixture is tumbling. In this process powder is mixed in closed chamber by using motorized chamber for example H-type, Ribbon type or U-mixture. H-type total capacity is calculated. The 30% of the volume of total substance is reduced.

Ø Medicated powders:

Some medicated powders are intended to be used internally and externally. Some powders are taken internally with the help of water. Some powders are inhaled for local or systemic purposes; other dry powders are commercially packaged for constitution with liquid solvent and vehicle. Some used for parenteral and others are used as vaginal douches.

Ø Aerosol powders:

Some medicated powders are administered by inhalations with the aid of dry powder inhalers which deliver micronized particles of medication in metered quantities. Most of these products are used in the treatment of Asthma and bronchial disorders, deep lungs for this purpose particle size must be 1 to 6 microns.

Bulk and divided powders:

Ø Divided powders:

After the powder has been properly blended using a geometric dilution method for potent substances. It may be divided into individuals closing units depending on the amounts of medicament taken as single dose.

It includes Bulk powders, antacids and laxatives douches powders and medicated powders for external use.

General methods of preparations of Powders

Since there is a little unavoidable loss of powders during weighing and mixing because some powder will adhere to spatula, pestle and mortar, therefore calculation for one extra powder then required. But if by calculating for extra powder an awkward fraction of weight is involved then a suitable no. of extra powder may be calculated. The dispensing balance is not so sensitive than the quantities less than 2 grains or 130mg must be triturate with a with a suitable inert diluent so that the quantities are made weighable on dispensing balance.

Generally lactose is used as diluent because it is colorless, soluble and compatible with majority of drugs. Mix all ingredients in ascending order of their weighs and mix thoroughly so that a homogenous mixture is formed.

Weight out required no. of powder and wrap in papers. The volatile substance and hygroscopic powders required to be double wrapped. The inner wrapped of which should be of wax paper to prevent volatilization and absorption of moisture.

Powders require special consideration:

The considerations which should be kept under observation for powders are written below;

1.     Hygroscopic and delinquent:

The substances which absorb moisture from the atmosphere are not suitable for dispensing in powder papers because they absorb moisture and promote the chemical degradation of drugs. In case of effervescent preparation the acid may completely react with sodium bicarbonate (NaHCO₃), ammonium chloride (NH₄Cl), sodium bromide (NaBr), sodium iodide (NaI) and talc.

Hygroscopic powders are usually supplied in granular form in order to expose less surface area to atmosphere. They should not be finely powdered. They should be doubly wrapped. In humid weather Aluminum foil or plastic is used.

2.     Eutectic mixtures:

When two or more than or substances are mixed together they tend to liquefy due to the formulation of new compound which has a lower melting point than room temperature for example Acetamide, Methnol, thymol, phencetin, camphor, aspirin, phenol etc.

They may be dispensed as a separate set of powders. They may be incorporated in powder by adding invert absorbent like light magnesium carbonate (MgCO₃) or magnesium oxide (MgO).

3.     Efflorescent powders:

These are crystalline substances that liberate water of crystallization completely or partially due to change in relative humidity or during trituration, causing the powder to become wet or liquefy. This difficulty may be overcome by using either corresponding anhydrous salt or inert substances mixed.

Granular powders

Sometimes it is difficult to present solid medicaments and large suitable forms. The tablets and capsules cannot be prescribed because a large number of them will be required to take a single dose which is not feasible liquids cannot be prepared because of stability problems.Choice remains to powders but bitter nauseous and unpleasant powders are different to dispense as such. These powders are prepared in the form of granules.

Ø Vegetable powders:

Contain volatile oils should not be subjected to heavy grinding in the mortar. When it is necessary to powder them lightly in the mortar to prevent the loss of volatiles oils present in them. In dispensing vegetable powders and other volatile substances they must be doubly wrapped inner wrapper of which should be of wax paper.

Ø Effervescent granules:

These are specially prepared solid dosage form of medicament meant for internal use. They usually contain a soluble medicinal agent mixed with citric acid, tartaric acid, sodium bicarbonate.

Method of preparations of Granules

Granules are prepared by several of the following methods;

§  Heat method

§  Wet method

    Heat method:

A large porcelain or stainless steel evaporating dish is placed over water bath which is being heated to boiling point and must ensure that the evaporating dis is not when the powder are added to it. Failing to do so will not provide sufficient water needed for granulation which will be liberated by citric acid on heating.

    Wet method:

In this method the mixed ingredients are moistened with suitable liquid (for which alcohol is most suitable) in dish in which alcohol is added in small portion with continuous stirring until a coherent mass is formed. The mass is then passed through a no. 6 sieve and the granules are dried on 59⁰C temperature not exceeding 60⁰C.The dried granules are again passed through the sieve break the lumps which may have formed during drying. They are packed in wide mouth air tight containers.

Ø Bulk powders:

They are supplied in bulk quantities and the patient measured the dose according to need. The bulk powders are meant for internal use is supplied in wide mouthed containers in which a tea spoon can be entered easy removal of the contents. Only the non-potent substances are supplied as bulk powders. Example: Antacids, laxatives etc.

Bulk powders meant for external use like antiseptic and dusting powders are supplied in card board glass or plastic containers, which are often designed for specific method of application.

Ø Dusting powders:

These are meant for external appropriate to the skin for antiseptic, antipruritic, antiperspirant, absorbent, protective and lubricant. The powder must be homogenous and in a very fine state of subdivision to enhance the effectiveness and minimize local irritation.

Ø Insufflations:

These are finely divided powders meant for the introduction into body cavities such as ear, nose, vagina, and tooth sockets with the help of an apparatus known as insuff.

Ø Snuffs:

Snuffs are finely divided solid dosage form of medicaments which are inhaled into nostrils for their antiseptic, decongestion or bronchodilators action. Snuffs should be dispensed in flat metal boxes.

Ø Dentifrices:

Dentifrices are the substances which are generally used with the help of tooth brush for cleaning the surface of teeth.

Ø Explosive powders:

When an oxidizing agent and a reducing agent are triturated in mortar then are changes of explosion which may lead of serious consequences, such substances are referred to as explosive powders.

Ø Potent drugs:

Substance having a maximum dose of less than are grain and poisonous substance should be regarded as potent substances. Small quantities of drugs should not be weighed on dispensing balance. The best method to prepare potent drugs is trituration.

Ø Cachets:

Cachets are classical dosage form. Cachets are the solid unit dosage form of medicaments in which the drug is enclosed in a tasteless sheet made by pouring a mixture of rice flour and water between not polished revolving cylinders since flour and water mixture treat easy digestible, disintegrate in stomach.

Advantages of Cachets:

1.       They are easy to prepare because no complicated machinery is required.

2.       Drugs can be extemporaneously and quickly dispensed in cachets.

3.       Comparatively large dosage of drug can be dispensed because one they have been softened by dipping in water even a large size can swallowed easily.

4.       They quickly disintegrate in stomach.