You are to prepare a 2ml sample of diluted drug for injection.The total amount o

Question

You are to prepare a 2ml sample of diluted drug for injection.The total amount of drug to be injected in this 2ml injection is0.0210mg drug/(kg body mass). The patient's body mass is 70kg. Thelabel tells you that the volume of solution in the drug bottle is30ml. The total mass of the drug in the bottle is 294mg and therest is saline(salt solution). In addition to this bottle ofconcentrated drug, you have an unlimited supply of pure sterilesaline.

(a) What is the concentration (in mg/ml) of drug in thebottle?

(b) What volume of concentrated drug (in ml) and what volume ofsaline (in ml) will you combine to make 2ml of the drug solution ofthe necessary concentration?

(c) The molecular weight of the drug is 15,000 g/mol. What isthe molarity of the injection?

Explanation / Answer

a) 294mg/30mL b) First you must calculate the dosage of the drug in mg neededbased on the recommended dosage. (0.0210 mg drug/kg)(70 kg) = 1.47mg drug Then find out the corresponding volume needed from the stock bottleto equal this amount. (1.47 mg drug)(30 mL/294 mg drug)= 0.15 mL from stockbottle The total mL of the dosage is 2mL. Subtract the previous volumefrom the total volume. The difference will be the volume of salinenecessary to reconstitute the dose. 2mL - 0.15 mL = 1.85mL of sterilesaline (by adding more saline to the drug, wedo not alter the actual amount of moles of the drug, only the molarconcentration) c) We calculated the amount (in mg) of the dosage to be 1.47 mg.Convert this using mg ---> g, then from g ----> mol using themolar mass. (1.47 mg drug)(1 g drug/1000mg drug)(1 mol drug/15000 g drug)= 9.8E-8 mol drug (valueshould be much less than 1 since we calculated the drug amount inmilligrams)

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