Dosage calculation help

akulahawkRN, ADN, RN, EMT-P · Nov 2, 2013

If the information you have provided is exactly what is written for the problem, you may be correct... what did you come up with for the answer to the problem? Show us how you came to that answer.

vgut · Nov 2, 2013

the answer key says 0.64 ml but i got 0.84 ml

184lbs/ 2.2lbs= 84kg

84kg x 0.6ml =50.4/60mg = 0.84ml

??

akulahawkRN, ADN, RN, EMT-P · Nov 2, 2013

Not quite there. What's the dose of Lovenox that is needed? Let's start with that first...

vgut · Nov 2, 2013

now i got 1.18 ?

i did the same thing just forgot to multipy wt with dose.

KelRN215, BSN, RN · Nov 2, 2013

the answer key says 0.64 ml but i got 0.84 ml
184lbs/ 2.2lbs= 84kg
84kg x 0.6ml =50.4/60mg = 0.84ml
??

Nope, this isn't how you go about the problem.

First, the patient's weight is 185 lbs not 184 lbs. The weight in kg is 84.09 kg. You then need to multiply the patient's weight by the ordered dose in mg/kg.

akulahawkRN, ADN, RN, EMT-P · Nov 2, 2013

now i got 1.18 ?
i did the same thing just forgot to multiply wt with dose.

This is the correct answer... to a point. You found the right dose and then determined the exact volume at that concentration to achieve that dose. Now you also have to consider whether you need to round... If I had a syringe or some other means of delivery that could measure 1.18 mL, I would use that. If not, I'd have to consider rounding to the nearest 10th of a mL, which is 1.2 mL.

Does that make sense?

Guests · Nov 3, 2013

order: lovenox 1.4mg/kg
pt wt: 185lbs
on hand: 60mg/0.6ml
my answer key says 0.64ml but i think its wrong. :/

The order is giving you the "unit" dose of Lovenox, that is, the dose per 1 kilogram ("unit" means "1" as in "unity" or "united" or the Spanish word "uno" or Latin's "E pluribus unum").

For each kg of the patient's weight, the pt should get 1.4 mg of medication.

Your patient doesn't weigh only 1 kg, now, do they (that is, you're not playing NICU nurse)?

How many kg do they weigh? Hm, they only tell you the weight in lb so you need to convert the weight in lbs to the weight in kg.

One of many conversions that you should just memorize is 1 kg = 2.2 lb.

From basic algebra, you can divide both terms of an expression by the same value and not change the equation (my rule, "Don't Eff with the equal sign") just in the same way that you put the same size kid on each end of a teeter-totter (if you're old enough to remember those) and not disturb its equilibrium.

So, take the equation 1 kg = 2.2 lb and divide each side by 2.2 lb. Now you have 1 kg / 2.2 lb = 2.2 lb / 2.2 lb OR, since anything divided by itself equals one, 1 kg / 2.2 lb = 1

Realize that you can multiply or divide anything by 1 and not change the value. 34 x 1 = 34.... 94/1=94... The value of anything multiplied or divided by one is unchanged.

So, what is 185 lb x 1? 185 lb x 1 = 185 lb... right? Pretty trivial. But just above, we easily showed that 1 kg / 2.2 lb = 1 so we can also write 185 lb x ( 1 kg / 2.2 lb ) since the value in the parentheses equals 1 and therefore does not change the value of the equation. Given that you have lb in both the numerator and the denominator, the "lb" cancels (because anything divided by itself equals one) leaving the units of kg and a magnitude of 185/2.2 = 84.1... That is...

185 lb = 84.1 kg

Now you can utilize your unit dose (remember, "unit" means one... unit dose means dose per unit of weight... 1.4 mg / kg) to determine the dose for your 84.1 kg patient.

84.1 kg x (1.4 mg / kg) = 117.7 mg of Lovenox

Isn't it convenient that they come in 60 mg syringes?

So, now that you know how much Lovenox to give... 117.7 mg, you need need to figure out the volume... that is, how much solution will be in the syringe(s).

The concentration of the medication is 60 mg / 0.6 mL

So, if you were going to give a 60 mg dose, you'd give 0.6 mL, right? The inverse is also true: If you gave a 0.6 mL shot, you'd be delivering a 60 mg dose, right?

That is, 60 mg = 0.6 mL...

Divide both sides of an equation by the same thing and you haven't changed the value

So, divide both sides by 60 mg... 60 mg / 60 mg = 0.6 mL / 60 mg... or, 1 = 0.6 mL / 60 mg.

Since, the value of anything multiplied or divided by one is unchanged, you can multiply your 117.7 mg by your 0.6 mL / 60 mg, which will cancel your mg and leave you with the volume...

117.7 mg x (0.6 mL / 60 mg) = 1.2 mL (or conveniently, two of those 60 mg/0.6 mL syringes).