Alora is a transdermal system designed to deliver estradiol continuously and con

Question

Alora is a transdermal system designed to deliver estradiol continuously and consistently over a 3-4 day period when placed on the skin. Alora provides systemic estrogen replacement theory in postmenopausal women. For a 36 cm^2 patch, the release rate of the drug is 0.1 mg of estradiol per d ay. Clinical trials have provided the following pharmacokinetic data. In one study, following applications of the patch, the peak concentration of the estradiol was found to be 144 pg mL^-1 (10^12 pg = 1 g) and the half life of estradiol was found to be 1 h. Over an 84 h dosing interval, the plasma clearance for estradiol from the Alora patch was found to be 61 L h^-1. What is the apparent volume of distribution in liters?

Explanation / Answer

From the above given data Half life of thedrug = 1h

Plasma clearence (CL) = 61Lh-1

Volume of distribution (Vd) = ?

We know that t1/2 = ln (2) * Vd / CL

Because t1/2 depends upon plasma clearence and volume of distribution

Therefore:

1h = ln (2) * Vd / 61 L h-1

=> 1h = 0.693 * Vd / 61 L h-1

=> 1h * 61 L / h * 0.693 = Vd

=> Vd = 42 L

Therfore the apparent volume of distribution of drug is 42L

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