How many milliliters of a thimerosal 25% stock solution must be used to prepare 100 ml of thimerosal topical solution of 1:1000 ratio strength?A diphenhydramine elixir contains 12.5 mg drug in one teaspoon. The volume of oral vehicle that is to be added to 100 ml of this elixir to reduce its strength by one half its original strength is:When preparing an ounce of 1% hydrocortisone cream the technician made an error and added 200 mg of hydrocortisone in the preparation. Calculate the additional amount of hydrocortisone powder that should be added to the 1 ounce cream to make the strength 1%.Onabotulinumtoxin A (BOTOX) is available in a 100 units vial for reconstitution. 2.5 ml of sterile preservative free normal saline was added to this vial and reconstituted. How many units of botox is present in 0.1 ml of the dilution? (ignore any volume changes during reconstitution)

For the first question, the objective is to find out how much of the 25% thimerosal stock solution is needed to prepare a 100 ml solution with a 1:1000 ratio strength. The 1:1000 ratio strength means that there is 1 gram of thimerosal in 1000 ml of solution. Therefore, we need 0.1 gram (or 100 mg) of thimerosal for the 100 ml solution. Since the stock solution is 25% thimerosal, it contains 250 mg of thimerosal per ml. Therefore, we need 100 mg / 250 mg/ml = 0.4 ml of the stock solution.For the second question, the objective is to find out how much oral vehicle needs to be added to the diphenhydramine elixir to reduce its strength by half. Since the elixir currently contains 12.5 mg of drug per teaspoon (or 5 ml), it contains 12.5 mg/5 ml = 2.5 mg/ml. To reduce the strength by half, we need to dilute it to 1.25 mg/ml. Therefore, we need to add enough oral vehicle to double the volume of the elixir. Since the current volume is 100 ml, we need to add another 100 ml of oral vehicle.For the third question, the objective is to find out how much additional hydrocortisone powder needs to be added to the cream to make the strength 1%. Since 1 ounce is approximately 28.35 grams, a 1% hydrocortisone cream would contain 0.01 * 28.35 g = 0.2835 g (or 283.5 mg) of hydrocortisone. Since the technician has already added 200 mg, an additional 283.5 mg - 200 mg = 83.5 mg of hydrocortisone needs to be added.For the fourth question, the objective is to find out how many units of botox are present in 0.1 ml of the dilution. Since the vial contains 100 units of botox and was reconstituted with 2.5 ml of saline, the concentration of botox is 100 units/2.5 ml = 40 units/ml. Therefore, 0.1 ml of the dilution would contain 40 units/ml * 0.1 ml = 4 units of botox.In summary, 0.4 ml of the 25% thimerosal stock solution is needed to prepare a 100 ml solution with a 1:1000 ratio strength. 100 ml of oral vehicle needs to be added to the diphenhydramine elixir to reduce its strength by half. An additional 83.5 mg of hydrocortisone needs to be added to the cream to make the strength 1%. 0.1 ml of the botox dilution contains 4 units of botox.