Concentrations of Drug Products Concentrations are expressions of the strength of drugs in aqueous solutions or suspensions Concentrations of drugs in solid dosage forms like creams or ointments Concentrations are ratios of amount of drug (A) per volume that the drug occupies (V) or C= A/V or C*V = A mg/ml, mcg/ml, mg/L, mg/dl and % w/v or % v/vfor solutions and suspensions % w/w for solid dosage forms like creams

Concentrations of Drug Products Concentrations are the amount of drug in the volume it occupies for solutions or amount of vehicle or product in weight if cream or ointment There is 100 mg of morphine in this whole vial of 10 ml of drug product This product has 80 mg of drug in 80 g tube Courtesy of :http://medlibrary.org/lib/rx/meds/triamcinolone-acetonide-29/page/2/ Courtesy of : Westward pharmaceuticals

Percentage Concentrations X % w/v is by definition X g of drug/100 ml solution 5% is 5 g/100 ml (very important is pharmacy) 0.9% is 0.9 g/100 ml (NS) X% v/v is by definition X ml of drug/100 ml solution If a cream or ointment X% w/w is by definition X g of drug/100 g of product

Dose Formula C * V= D C= concentration V= volume D= Dose To use this formula make sure all units match i.e. if C= mg/ml V must be ml and D is mg

Sample Calculations A patient in the hospital develops an acute supraventricular tachycardia with a HR of 130 at rest. MD orders a STAT order of Diltiazem 10 mg IVP. If you have a vial of Diltiazem 50 mg/10 ml , how much do you draw into the syringe to deliver this dose? Courtesy of: http://www.hospira.com/en/products_and_services/drugs/DILTIAZEM_HYDROCHLORIDE_INJECTION

Sample Calculations A patient in the hospital develops an acute supraventricular tachycardia with a HR of 130 at rest. MD orders a STAT order of Diltiazem 10 mg IVP. If you have a vial of Diltiazem 50 mg/10 ml , how much do you draw into the syringe to deliver this dose? Answer: C * V= D C is 50 mg/10 ml or 5 mg/ ml D is 10 mg 5 * V = 10 V= 2 ml Answer 2 you can use ratios and proportions 50 mg= 10 mg 10 mL X x= 2 ml

Sample Calculations A patient is experiencing a DVT and requires a Heparin Drip with a loading dose of 8,000 units. You have a vial of heparin 1,000 units/ml, what volume do you use to deliver this loading dose? Answer C*V=D C= 1000 units/ml D=8,000 units 1000*V=8000 V= 8 ml

Sample Calculations What is the magnitude of the error? A patient required a dose of insulin for hyperkalemia. The dose was supposed to be 10 units. 30 minutes later, patient develops profound hypoglycemia (30 mg/dl) and is comatose. Dextrose was given and patient recovers with no permanent brain damage. (Thank God). It was determined that the order was written as : regular Insulin .1 ml IVP stat. The pharmacist profiled the order as 1 ml IVP stat. If you have Humulin R (which is 1000 units/ 10 ml) and draw this volume what was the dose given? C*V=D C= 1000 unit/10 ml or 100 units/ml V= 1 ml 100 units/ml * 1 ml= 100 units What is the magnitude of the error? Dose given is 100 units Actual dose is 10 units 10 fold overdose How can such error be avoided? Write the order as : regular insulin 10 units IVP or 0.1 ml IVP

Sample Calculations A patient requires an amiodarone drip. The concentration of the drip is 450 mg/250 ml in D5W. You are asked to compound this drip. Using a 250 ml D5W and amiodarone 150 mg/ 3 ml vial how do you prepare this drip? http://www.nursingconsult.com/nursing/drugs/monograph?tab=generic&drug_id=25

Sample Calculations If C= 150 mg/3 ml it is 50 mg/ml Dose is 450 mg (this is what must be added to the 250 ml bag) 50 * V = 450 V= 9 ml If each vial is 3 ml and you need 9 ml you need 3 vials 1 vial/ 3 ml = x vials/9 ml X= 3 vials

Dilutions A dilution is the process of reducing the concentration of a solution, suspension, cream or ointment by the addition of water (for solutions and suspension) or addition of a unmedicated base for an ointment or cream to produce a product of a lesser concentration

Dilution process The amount of drug in container S is Cs* Vs The amount of drug in container D is Cd* Vd The amount of drug does not change you are adding only water, if that is the case, amount of drug in A and B does not change thus Cs * Vs = Cd* Vd Adding water

Example You get an Rx that reads Digoxin solution 10 mcg/ 5 ml Sig: take 1 tsp daily Dispense 100 ml You have Digoxin 50 mcg/ 5 ml available in your pharmacy. How can you make this Rx?

It’s a dilution problem If you need 100 ml of 10 mcg/5 ml elixir and you have a 50 mcg/5 ml elixir you can add water to a given volume of your stock solution to make it. How much of the stock solution do you need and how much water? Cs* Vs = Cd* Vd where Cd= 10 mcg/ 5ml and Vd= 100 ml and Cs is the concentration of your stock solution Thus (50 mcg/5 ml) Vs = (10 mcg/5 ml) (100 ml) Vs = 20 ml. You start with 20 ml and you get 100 ml the difference is the amount of water you add

Another prescription Dexamethasone 0.5 % ointment Sig: apply to affected area BID Qnty 100 grams You have Dexamethasone 2% in stock How can you dispense this ? It is a dilution where we take our stock product and add some hydrophilic petrolatum to lessen its concentration. How much stock ? And how much ointment base?

It’s another dilution problem Cs * Ws= Cd* Wd (we use weight for solid dosage forms) Cs= 2%, Ws = ? (we need to find this) we know that we need to make Cd=0.5% and Wd is 100 grams 2 * Ws= (0.5) X (100) 2 *Ws= 50 grams Ws= 25 grams So we take 25 grams of stock product and via geometric dilution add how much base? Wd- Ws or 100 -25 or 75 grams of base