Fundamental Operations in Compounding: Weighing Techniques in Pharmacy
Compounders and dispensers rely on precise weighing techniques in pharmacy operations to ensure accurate preparation of medicines. This involves placing the balance in a well-lit, dust-free area, using clean pans and weights, and following meticulous steps to weigh medicinal ingredients correctly. Proper weighing is crucial for the success of compounding and dispensing activities in pharmaceutical settings.
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FUNDAMENTAL OPERATIONS IN COMPOUNDING Dr. Marriam Zaka Lecturer Institute of Pharmacy, Faculty of Pharmaceutical and Allied Health Sciences LCWU, Lahore.
FUNDAMENTAL OPERATIONS IN COMPOUNDING COMPOUNDING & DISPENSING IS CONCERNED WITH THE PREPARATION OF MEDICINES FROM BASICINGREDIENTS IN SMALL QUANTITIES. THE ACCURATE & ELEGANT COMPOUNDING OFMEDICINES REQUIRES EXPERTISE IN SEVERAL FUNDAMENTAL OPERATIONS WHICH ARE FOLLOWING : 1. WEIGHING, 2. MEASUREMENT OF LIQUIDS, 3. DISSOLUTION, 4. FILTRATION, 5. MIXING, 6. SIZE REDUCTION, 7. SIZE SEPARATION
1. WEIGHING: MOST IMPORTANT STEP UPON WHICH SUCCESS OF ALL THESE OPERATIONS IN PHARMACY DEPENDS. PROPER WEIGHING DEPENDS ON A THOROUGH KNOWLEDGE OF BALANCE, ITS PRINCIPLE, ITS CARE &PROPER USE. DURING COMPOUNDING & DISPENSING OF MEDICINES,WEIGHING IS CARRIED OUT ON A DISPENSING BALANCE. ALLOF YOU HAVE BEEN PROVIDED WITH SUCH A BALANCE. WHEN THE LOAD IS PLACED ON THE PANS OF THE BALANCE,THE HORIZONTAL METAL BEAM MOVES AROUND THECENTRAL FULCRUM AND DEFLECTION FROM THEHORIZONTAL IS INDICATED BY THE MOVEMENT OF APOINTER FIXED IN THE CENTER OF THE BEAM WHICH COMESIN THE CENTER WHEN THE WEIGHTS IN THE TWO PANS ARE EQUALLY BALANCED.
WEIGHING IN PHARMACY FOLLOWING TECHNIQUE SHOULD BE FOLLOWED WHILEWEIGHING THE MEDICINAL INGREDIENTS: PLACE THE BALANCE IN A WELL LIT AREA FREE FROM DUST& PLACE IT OVER THE RUBBER SHEET TO PROTECT THE BALANCE FROM CORROSION, ADJUST THE LEVEL OF THE BALANCE CLEAN THE BALANCE PANS WITH A DRY DUSTER BEFOREUSE, KEEP EQUAL SIZE PIECE OF CLEAN WHITE PAPER IN EACHPAN & BALANCE THE PANS, PLACE THE REQUIRED WEIGHTS ON THE LEFT HAND SIDEPAN WITH THE HELP OF FORCEPS SO THAT SWEAT, DUST &GREASE FROM HANDS MAY NOT MAKE THE WEIGHTS INACCURATE, THE DRAWER OF THE BALANCE IN ORDER TOPREVENT SPILLAGE OF INGREDIENTS ON THE WEIGHTS LYING IN THE DRAWER,
WEIGHING IN PHARMACY ADD OR REMOVE THE MEDICAMENT IN THE RIGHT HAND PAN WITH THE HELP OF THE SPATULA UNTIL THE POINTER RETURNS TO THE NULL POINT. REMEMBER IN PHARMACY RIGHT HAND PAN IS USED FOR WEIGHING THE MEDICAMENTS, WHEN THE WEIGHING IS COMPLETED PUT THE BALANCE BEAM AGAIN IN FIXED POSITION, TRANSFER THE WEIGHED INGREDIENT IN A CONTAINER OR A PIECEOF PAPER, AS PER REQUIREMENT, RETURN THE WEIGHTS TO THE DRAWER WITH FORCEPS ANDCAREFULLY CLEAN THE BALANCE PAN & THE SPATULA, RETURN THE EXCESS LEFT OVER INGREDIENT TO THE STOCKBOTTLE AFTER CAREFULLY READING ITS NAME ON THE LABEL.SIMILARLY WEIGH ALL OTHER INGREDEINTS. WITH THE DISPENSING BALANCE PROVIDED TO YOU THE MINIMUM WEIGHABLE QUANTITY IS 100 MG.
2.MEASUREMENT OF LIQUIDS 2. MEASUREMENT OF LIQUIDS IS GENRALLY DONE WITH THE HELP OF VARIOUS CYLINDRICAL OR CONICAL MEASURESPROVIDED TO YOU. BUT THE CONICAL MEASURES AREPREFERRED BECAUSE IT IS EASY- TO FILL THEM WITHOUT SPILLAGE,- TO DRAIN OUT WHOLE LIQUID,- TO RINSE OUT THE RESIDUE AFTER DRAINING OUT LIQUID SESPECIALLY, VISCOUS LIQUIDS AND- ALSO EASY TO CLEAN THEM AS COMPARED TO CYLINDRICAL MEASURES. THE MINIMUM MEASUREABLE QUANTITY IS 1 ml. USING A 10ml, CONICAL MEASURE. UPTO 0.1 ml, LIQUID CAN BE MEASURED USING A GRADUATED GLASS PIPETTE.
MEASUREMENT OF LIQUIDS Measuring technique for conical measures: Always use clean & dry measures Always choose the smallest measure that will hold the required volume to be measured. Do not split the volume into two measurements as this would double the error, Check the label of the stock bottle for the correct name of the liquid to be measured, Hold the bottle in the right hand with label in the upper side so that it is visible during measurement & also to prevent its spoilage if some liquid trickles down, Remove the stopper of the bottle and hold it between the little finger and palm of the left hand, Straighten the conical measure with the graduated side in front and put it on a flat surface or a tile,
3.DISSOLUTION IT INVOLVES DISSOLVING SOLIDS IN TO LIQUID TO PREPARE A SOLUTION. IT IS NECESSARY TO KNOW THE SOLUBILITY OF THE MEDICAMENTS INTO VARIOUS LIQUIDS OR SOLVENTS. THE SOLUBILITY OF A LIQUID IN A GIVEN LIQUID CAN BE INCREASED BY FOLLOWING WAYS: - POWDER THE SOLID INTO FINE PARTICLES, THIS INCREASES THE SURFACE AREA FROM WHICH MOLECULES CAN DIFUSE INTO LIQUID, - BY AGITATING THE SOLUTION IN A CONICAL FLASK WHICH HELPS RAPID DIPERSION OF THE SOLUTE THROUGHOUT THE LIQUID, AND - BY INCREASING THE TEMPERATURE WHICH DECREASES THE VISCOSITY & INCREASES THE DIFFUSION CO-EFFICIENT AND ALSO INCREASES THE SOLUBILITY OF MOST OF THE DRUGS
DISSOLUTION TECHNIQUE OF DISSOLUTION: GENERALLY A CONICAL FLASK IS SELECTED AS A VESSEL FOR MAKING A SOLUTION BECAUSE OF FOLLOWING ADVANTAGES: -THE CONTENTS CAN BE EASILY AGITATED BY SHAKING WITHOUT ANY SPILLAGE, - THE CONTENTS CAN BE READILY HEATED IF DESIRED, -THE CONTENTS CAN ALSO BE READILY COOLED UNDER RUNNING TAP WATER WITHOUT CONTAMINATION
FOLLOWING STEPS ARE TAKEN IN DISSOLUTION TECHNIQUE - POWDER THE DRUG IN MORTAR & WEIGH THE REQUIRED QUANTITY OF THE POWDERED DRUG, -PUT THE DRUG WITH THE LITTLE VOLUME OF THE SOLVENT IN THE CONICAL FLASK AND STIR WITH A GLASS ROD & AGITATE BY SHAKING OR BY USING A MECHANICAL STIRRER, - HEAT THE SOLUTION IF NEEDED AND OBTAIN A CLEAR SOLUTION, -BRING THE SOLUTION TO ROOM TEMPERATURE BY COOLING, - TRANSFER THE SOLUTION TO A CONICAL MEASURE AND ADD MORE SOLVENT TO MAKE THE REQUIRED VOLUME OF THE SOLUTION
4.FILTRATION FILTRATION IS THE PROCESS BY WHICH THE SOLID PARTICLES ARE REMOVED FROM LIQUID OR GAS BY PASSING IT THROUGH APOROUS MEDIUM WHICH RETAINS THE SOLID PARTICLES BUT ALLOWS THE LIQUID TO PASS. THE RATE OF FILTRATION CAN BE INCREASED BY FOLLOWING WAYS: - INCREASING THE SURFACE AREA OF THE FILTER, - REDUCING THE VISCOSITY OF THE LIQUID BY HEATING THELIQUID, - INCREASING THE PRESSURE ACROSS THE FILTERING DEVICEEITHER BY APPLYING VACCUM BELOW IT OR BY INCREASING THE PRESSURE OVER THE LIQUID BEING FILTERED, - BY USING HIGH POROSITY FILTERING MEDIUMS SUCH AS SINTERED GLASS FILTER OR MEMBRANE FILTERS. GENERALLY A NO.3 FILTER IS USED FOR SMALL VOLUMES FOR FILTRATION BY GRAVITY AND NO.4 FILTER FOR LARGE VOLUMES BY VACCUM OR PRESSURE. SINTERED GLASS FILTERS ARE MADE FROM BOROSILICATE, VERY EXPENSIVE, NOT USED IN PHARMACY LAB. OR FOR ROUTINE USE
FILTRATION A HIGH DEGREE OF CLARITY IS REQUIRED IN CASE OF ORAL SOLUTIONS AND SOLUTIONS FOR APPLICATION TO SKIN OR MUCOUS MEMBRANES OR ULCERATED AREAS. IT IS NECESSARY TO ADJUST SOLUTIONS TO VOLUME THROUGH THE FILTER AS FOLLOWS; - WASH THROUGH THE FILTER USING A LITTLE OF THE VEHICLE AND DISCARD THE WASHINGS, - MAKE THE SOLUTION TO VOLUME AND PASS THROUGH THE FILTER INTO A MEASURING DEVICE, -RINSE THROUGH THE FILTER WITH THE SUFFICIENT QUANTITY OF VEHICLE TO MAKE THE FINAL REQUIREDVOLUME.
5.MIXING & MIXTURES MANY PHARMACEUTICAL PREPARATIONS CONSIST OFHOMOGENOUS MIXTURES OF TWO OR MORECOMPONENTS & DEPENDING UPON THE COMPONENTSTHE MIXTURES ARE DIVIDED INTO FOUR CLASSES: I.MIXTURES OF LIQUIDS, II. MIXTURES OF LIQUIDS AND SOLIDS, III. MIXTURES OF SOLIDS, IV. MIXTURES OF SEMISOLIDS.
MIXTURES OF LIQUIDS THESE ARE OF TWO TYPES: A. HOMOGENOUS MIXTURES OF LIQUIDS CALLED SOLUTIONS: Contain readily miscible liquids, a mechanical stirrer or glass rod may be needed to mix them. Sometimes, an electric stirrer may be needed to mix liquids of high viscosity B. HETEROGENOUS MIXTURES OF LIQUIDS OR EMULSIONS: THESE INVOLVE MIXING OF TWO IMMISCIBLE LIQUIDS WITH THE HELP OF SUSPENDING AGENTS OR EMULGENTS AND BY LOCAL MIXING IN WHICH SHEAR IS APPLIED TO THE GLOBULES OF LIQUIDSI N A MORTAR & PESTLE ON SMALL SCALE.
II. MIXTURES OF LIQUIDS & SOLIDS THESE ARE ALSO OF TWO TYPES: A. HOMOGENOUS MIXTURE OR SOLUTIONS: IT INVOLVES SIMPLE DISSOLUTION OF A SOLUBLE SOLID INTO A LIQUID WHICH MAY BE ACHIEVED BY SHAKING OR STIRRING. B. HETEROGENOUS MIXTURES OR SUSPENSIONS: IN THIS VARIETY THE DISPENSED SOLID TENDS TO SEPARATE FROM DISPERSION MEDIUM SO PROPER MIXING IS REQUIRED TO OBTAIN A STABLE SUSPENSION. THIS IS GENERALLY DONE USING A MORTAR & PESTLE ON SMALL SCALE.
III. MIXTURES OF SOLIDS: IT INVOLVES HOMOGENOUS MIXING OF SOLIDS IN POWDER STATE WHICH IS GENERALLY DIFFICULT TO ACHIEVE BECAUSE SOLIDS DO NOT MIX READILY AND ESPECIALY SO WHEN MINUTE QUANTITIES OF ONE SOLID IS TO BE MIXED WITH THE LARGER QUANTITIES OF OTHERS. THIS IS GENERALLY DONE IN MORTAR & PESTEL AND FOLLOWING STEPS ARE OBSERVED IN THE PROCESS: - ADD TO THE MORTAR THAT INGREDIENT FIRST WHICH IS PRESENT IN THE SMALLEST QUANTITY AND POWDER, - ADD A QUANTITY OF THE SECOND SOLID THAT WILL APPROXIMATELY DOUBLE THE BULK OF MEDICAMENTS ALREADY PRESENT IN THE MORTAR,MIX LIGHTLY TO OBTAIN A POWDER WITHOUT ALLOWING PRESSURE WHICH MAY CAUSE CAKING OF INGREDIENTS. - EVERY ADDITION OF INGREDIENT SHOULD BE SUCH THAT IT DOUBLES THE QUANTITY ALREADY PRESENT IN THE MORTAR. THIS ASSISTS HOMOGENOUS MIXING OF SOLIDS. REPEAT THE PROCESS UNTIL ALL THE SOLIDS HAVE BEEN CONSUMED, - SEPARATE THE POWDER FROM THE BASE & SIDES OF THE MORTAR USINGA SPATULA AND TRANSFER IT ON TO A CLEAN PAPER AND PEPARE THE REQUIED NUMBER OF DOSES BY ACCURATE WEIGHING
IV.MIXTURES CONTAINING SEMISOLIDS: IT INVOLVES MIXING A SOLID AND / OR A LIQUID INTO A BASE CONSISTING OF ONE OR MORE SEMISOLIDS. FOR EXAMPLE: - OINTMENT, - PASTE, - SUPPOSITORIES. THE FOLLOWING PROCEDURE IS ADOPTED: 1. PREPARE THE BASE OF OINTMENT OR PASTE WHICH MAY CONTAIN LIQUIDS, SUCH AS LIQUID PARAFFIN, SEMI-SOLIDS SUCH AS WOOL FAT & SOFT PARAFFIN AND ALSO SOLIDS SUCH ASCETOSTEARYL ALCOHOL & HARD-PARAFFIN. - THE INGREDIENTS ARE MELTED TOGATHER IN A DISH OVER A WATER BATH AND STIRRED WELL TAKING CARE TO AVOID OVERHEATING. THIS IS DONE TO OBTAIN A HOMOGENOUS MIXTRURE.
IV.MIXTURES CONTAINING SEMISOLIDS 2. INCORPOATE ANY SOLID INGREDIENTS BY FIRST RUBBING THEM INTO A SMALL QUANTITY OF THE BASE. THE REST OF THE BASE IS ADDED GRADUALLY AND MIXING CONTINUED UNTIL THE MEDICAMENTS ARE THOROUGHLY MIXED. 3. INCORPORATE ANY LIQUIDS WITH THE BASE AFTER COOLING IT TO THE ROOM TEMPERATURE. VOLATILE LIQUIDS AND HEAT LABILE LIQUIDS SHOULD NOT BE ADDED UNTIL THE TEMPERATURE OF THE BASE IS BELOW 40-C. THE SOLIDS AND LIQUIDS INGREDIENTS ARE GENERALLY ADDED WITH THE BASE ON LARGE WARM TILE USING A FLEXIBLE SPATULA OR IN A WARM MORTAR USING PESTLE.
6.SIZE-REDUCTION SIZE REDUCTION OR COMMUNITION: IS THE PROCESS OF REDUCING DRUGS INTO SMALLER PIECES WHICH MAY BE COARSE PARTICLES OR FINE POWDERS. THE ADVANTAGES OF SIZE REDUCTION ARE FOLLOWING: PROMOTES MIXING, PROMOTES SUSPENDING, FACILITATES DISSOLUTION, INCREASES RATE OF ABSORPTION FROM GIT, YIELDS PREPARATION SUITABLE FOR USE ON MUCUSMEMBRANES OR SKIN BECAUSE IT PREVENTS GRITTINESS AND IRRITATION ON APPLICATION. ON SMALL SCALE THIS IS ACHIEVED BY THE PROCESSES OF: 1. 2. 3. 4. 5. 6. -DRY GRINDING, AND - WET GRINDING OR LEVIGATION
SIZE-REDUCTION 1. DRY GRINDING: IT INVOLVES BREAKING THE INGREDIENT IN A MORTAR & PESTLE. SIZE REDUCTION IS DONE BY COMPRESSION BETWEEN THE FLAT HEAD OF PESTLE AND BOTTOM OF THE MORTAR AND ATRITION BY SHEARING ACTION OF THE PESTLE. 2. WET GRINDING OR LEVIGATION: THIS INVOLVES PREPARING AQUEOUS SUSPENSIONS. THE INGREDIENTS ARE MADE INTO PASTE WITH WATER AND GROUND IN MORTAR. IN CASE OF PREPARATION OF SEMI- SOLID PREPARATIONS, THE MEDICAMENT IS RUBBED DOWN WITH THE WARM BASE ON A WARM TILE OR IN WARM MORTAR
7.SIZE SEPARATION SIZE SEPARATION IS DONE TO SEPARATE PARTCLES OF THE SPECIALIZED SIZE FROM A MEDICAMENT BY SIFTING. GENERALLY WIRE MESH SIEVES ARE USED. FOR DUSTING POWDERS FINE POWDERS ARE PASSED THROUGH THE APERTURE OF 180 MICRO-MILIMETER (NO. 85 SIEVE). FOR ORAL POWDERS OR FOR POWDERS FOR EXTERNAL USE MESH SIZE OF 250 MICRO MILIMETER OR SIEVE NO. 120 IS USED. FOR ABRASIVE TOOTH POWDERS A NO. 60 SIEVE IS USED.
