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CHAPTER 8 – Tablets

Tablets - solid dosage forms usually prepared with the aid of suitable

pharmaceutical excipients

Majority are administered orally, while others sublingually, buccally or

vaginally contain features most applicable to their routes of administration.

Types of Tablets:

• Compressed Tablets (C.T.) - manufactured with tablet machine

capable of exerting great pressure or compacting the powdered

or granulated tableting material. DILUENTS, BINDERS, DISINTEGRANTS,

ANTIADHERENTS/ GLIDANTS/LUBRICANT, COLORANTS/FLAVORANTS

• Multiple Compressed Tablets (MCT) – prepared by subjecting the

fill material to more than a single compression, the core (inner)

and shell (outer)

• Sugar-Coated Tablet (S.C.T.) – the coating maybe colored or

uncolored sugar layer, water soluble and quickly dissolved after

swallowing. Purposes: to protect the enclosed drug from the

environment and to provide a barrier to objectionable taste and

smell of the drug. Disadvantages: time and expertise needed in

the coating process and increased shipping costs

• Film-Coated Tablets (F.C.T.) – coating is made of thin layer of a

polymer capable of forming a skin-like usually colored film over

the tablet. Polymer is cellulose acetate phthalate. Advantages of

film coating over sugar coating: more durable, less bulky and less

time consuming to apply.

• Gelatin Coated Tablet – capsule-shaped compressed tablet with

1/3 the size of capsule with the same amount of fill, more ease in

swallowing & more tamper evident. (GelCaps)

• Enteric-Coated Tablets (E.C.T.) – have delayed release features,

designed to pass the stomach to the intestines where the tablet

will disintegrate allowing drug dissolution & absorption. Needed

when drug substance:

a) is destroyed by gastric acid

b) is irritating to the gastric mucosa

c) by-passed the stomach enhances the drug

absorption in the intestines

• Buccal tablets – flat, oval tablets intended to be dissolved slowly

in the buccal pouch. It is for oral absorption of drugs destroyed by

gastric acid or poorly absorbed in the GI tract.

• Sublingual Tablets – designed to erode promptly underneath the

tongue for rapid drug effect.

• Lozenges or troches – disc-shaped solid forms containing a

medicinal substance in a hard candy or sugar base. Meant to

dissolve slowly for localized effect or systemic effect

• Chewable Tablets – have rapid disintegration when chewed or

allowed to dissolve in the mouth, have a creamy base usually

specially flavored and colored mannitol. Meant for large-sized

tablets given to children and adults with difficulty in swallowing

solid dosage forms

• Effervescent Tablets – prepared by compressing granular

effervescent salts that release gas when in contact with water.

This tablet contains medicinal substance which dissolves rapidly

when in contact with water.

• Molded Tablet Triturate (M.T.T.) – small & cylindrical, very soft,

soluble & designed to dissolve rapidly.

• Compressed Tablet Triturate (CTT) – prepared by compression

(limited pressure) usually containing potent substance. Sucrose

and lactose are used for diluent.

• Hypodermal Tablet (H.T.) – used by physicians for

extemporaneous preparations of parenterals. It is meant to be

dissolved in suitable vehicle, sterility attained, and the injection

performed. The advent of prefabricated injectable products and

disposable syringes declined its use.

• Dispensing Tablets (D.T.) or compounding tablets – used by

pharmacists when compounding prescriptions and not dispensed

to patients. It contains large amount of potent subs. enabling the

pharmacist to obtain pre-measured amounts. For compounding

multiple dosage units.

• Immediate Release Tablets (I.R.) – designed to disintegrate and

release their medication and therefore are devoid of special rate

controlling features like coating and other ways.

• Instant Disintegrating/Dissolving Tablets – characterized to

dissolve within 10 seconds to 1 minute. This is possible with the

use of lyophilization techniques, soft direct compression, or the

use of water-soluble excipients designed to “wick” water into the

tablet for rapid disintegration.

• Extended Release Tablet (E.R.) /Controlled Release (C.R.) –

designed to release their medication in a predetermined manner

over an extended period of time.

• Vaginal Tablet/Inserts – uncoated and bullet- or ovoid- shaped

tablets for localized effect. Prepared by compression and shaped

to fit smugly into plastic inserter devices. They contain

antibacterials (against Hemophilia vaginitis) and antifungals

(against Candida albicans)

The physical features of compressed tablets are varied; its

diameter and shapes are determined by the die and punches used

in the compression. The less concave the punch, the more flat the

resulting tablets. Punches with raised impressions will have

recessed impressions on the tablets.

Quality Standards and Compedial Requirements:

• USP Weight Variation Test: 10 tablets are individually weighed

and average weight calculated.

• Content Uniformity: Dosage units are assayed individually and

requires that each dosage unit is 85% - 115% of the label claim

(S.D. is less than 6%)

• Tablet thickness is determined by

a. the diameter of the die

b. the amount of fill

c. the compactibility of the fill material

d. the force of pressure applied during compression.

Uy, Alyssa V.

2BPh

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• Tablet thickness is measured by a hand gauge.

• Tablet hardness affects its disintegration & drug absorption. The

greater the pressure, the harder the tablet. It should be hard

enough to resist breaking during the normal handling and yet soft

enough to disintegrate properly after swallowing.

• A force of 4 kilograms as determined by hardness tester is

minimum requirement for a satisfactory tablet.

• Tablet friability – the tendency to crumble by allowing it to roll

and fall within the rotating machine (friabilator). A maximum

weight loss of not more than 1% of the weight of the tablets being

tested is acceptable.

• Tablet Disintegration Test – uses a basket-rack assembly

containing 6 open ended transparent tubes held vertically upon a

10-mesh stainless steel wire screen.

The basket is raised and lowered in the immersion fluid (water at

37oC) at a frequency of 29-32 times per minute. Result: the

residue of the tablet on the screen is a soft mass having no

palpable inner core. Disintegration time ranged from 2 mins. to 4

hours depending upon the monograph.

For enteric coated tablets, test is done in a simulated gastric fluid

for 1 hr. No sign of disintegration must be seen. They are

immersed in a simulated intestinal fluid for the time stated in the

monograph where they disintegrate completely.

• Tablet dissolution test - Uses:

a. guides formulation and product development

b. performance of manufacturing process can be

monitored by it (quality assurance)

c. Consistent results assure bioequivalence from batch

to batch

d. As a requirement for regulatory approval

– Its goal to provide a reasonable prediction or correlation with

the product’s in vivo bioavailability.

a) High Solubility and High Permeability – IVIVC

b) Low Solubility and High Permeability – IVIVC

c) High Solubility and Low Permeability – limited IVIVC

d) Low Solubility and Low Permeability – none

In (a) IVIVC is expected if the dissolution time is slower then

gastric emptying time (limiting factor).

• Dissolution Test Apparatus consists of:

1. variable stirrer motor

2. stainless basket on a stirrer shaft (Apparatus I) or a

paddle as stirrer (Apparatus II)

3. 1-L vessel glass with a cover having the shaft of the

stirrer fitted at the center port, with 3 ports for

samples and 1 port for the thermometer

4. Water bath to maintain the temp. of the medium in

the vessel

Dissolution medium is placed in the vessel at 37oC + 0.5o C. The stirrer is

rotated at speed specified and at stated intervals; samples of the medium

are withdrawn for chemical analysis. Samples must meet the requirement

stated in the monograph.

Pooled dissolution testing – samples coming from different batches placed

in individual dissolution vessel in the apparatus or multiple dosage units in a

single vessel. This recognizes the concept of batch characteristics.

3 methods for compressed tablet:

Wet Granulation: Weighing and blending of ingredients (A.I. &

adjuvants) + liquid binder screen the damp mass (Sieve 6-8)

dry size the granules (Sieve 12-20) + lubricant and blend

compress

Fillers – lactose and microcrystalline cellulose

Binder – to facilitate adhesion of powder particles.

Starch, povidone, methylcellulose.

Flavorant and colorant are added to binder.

Lubricant – to improve the flow of granules from the

hopper to the die; prevent adhesion to the punches

and die during compression; reduce friction between

tablet and die’s wall during tablet ejection and provide

tablet sheen. Calcium and magnesium stearate are

examples.

All-In-One Methods:

1) Fluid-bed Process – fluid-bed granulator

which performs the blending, granulating,

drying into 1 continuous process

2) Microwave Vacuum Process – powder mix

is mixed, wetted, agglomerated and dried

using microwave

Dry Granulation – the powder mixture is compacted to large

pieces and broken down or sized into granules

Active ingredient or diluent must have cohesive

properties.

Advantages: For materials that are degraded by

moisture or by elevated temperature during drying

Steps in Dry Granulation: Weighing & blending powder

mix slugging sizing + lubricant compression

Tableting machine – compress tablet formulation

within a steel die cavity by the pressure exerted by the

movement of the two steel punches (upper and

lower).

Imperfections of tablets:

a) a)Laminations – horizontal striations

b) Tablet capping – the top of tablet

separates from the whole

c) Tablet splitting

Reasons:

a) particles has no time to bond due to

fast high speed production

b) air is entrapped during direct

compression

c) punches not clean

d) aging

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Direct Compression – appropriate for chemicals with flowing and

cohesive properties

Tablet Deduster – to remove traces of loose powder

adhering to the tablets following compression.

Tablets are coated:

1) to protect from air and/or humidity

2) mask the taste

3) provide characteristics of drug release

4) to provide aesthetics or distinction to the product

Sugarcoating – tedious, time-consuming and needs

expertise of qualified technician and the product

doubles the size and wt.

Film coating – provides a thin, skin-tight coating of a

plastic material over the compressed tablet.

Components:

a) Film former – to produce thin smooth film. Cellulose

acetate phthalate

b) Alloying substance – to provide water solubility/

permeability for body fluids to penetrate through and

make the drug available. Polyethylene glycol

c) Plasticizer – to produce elasticity/flexibility to the

coating & provide durability. Castor oil

Advantages: Size and wt. almost the same as the

tablet, more resistant to destruction by abrasion,

markings can be embossed on the coating.

Enteric coating – maybe accomplished through coating

with enough thickness or coating which allow

dissolution at a pH 4.9 or higher. Example is shellac

Fluid –Bed or Air Suspension Coating – spray coating of

powder, pellets, granules or tablets held in suspension

by a column of air

Depending where the coating solution come from:

a) Wurster – the bottom of the cylinder

b) Top spray –sprayed downward

c) Tangential – spray techniques – rotary fluid

bed coater

Top spray – recommended for taste masking, enteric

release and barrier film on tablets.

Bottom spray – for sustained release and enteric

release

Tangential – layering coating, sustained and enteric

releases

Compression Coating – the coating material

(granulation or powder form) is compressed into the

tablet core.

Advantages:

a) It is anhydrous process appropriate for

drugs affected by moisture

b) more uniform coating

c) uses less coating material resulting to

lighter, smaller and easy to swallow

tablets

d) less expensive to package and ship

Packaging and Storage:

a) Use tight, light resistant (amber) containers,

if adversely affected by light

b) Store in places of low humidity and protected

from extreme temperature

c) Use desiccant pellet is affected by moisture

Oral administration of solid dosage forms

Lozenges – by compression or molding. Meant to dissolve slowly in the

mouth for localized effect.

Impact of Changes on Solid dosage forms:

1. Changes in formulation

a) active ingredients

b) excipients

c) their quantities

d) addition of new excipients

2. Changes in methods of manufacturing

a) new machineries

b) different steps in manufacturing

c) different in process controls, tests or assay methods

d) production of different batch sizes

e) use of different product reprocessing procedures

f) suse of different manufacturing sites