Case study II

PK Modeling, Oral delivery

1.� An HIV positive patient was seen at the ER with lesions that biopsy showed were not� Kaposi's Sarcoma but rather bacillary angiomatosis, that may look like KS.  While KS is treated with chemotherapy and or radiation therapy, bacillary angiomatosis is treated with erythromycin.�� A 250 IV bolus dose of erythromycin was given to a patient prior to sending him home with a handful of prescriptions and samples.��� Erythromycin is partially excreted as parent drug and as a primary metabolite.� Draw the black box diagram that would represent this system.� Write the differential equations that would model the amount of erythromycin� in the body and urine at any time (t).� The patient was dosed with 30 mg.� The rate constant to form the metabolite is 0.493 hr^-1,� the rate constant for the excretion of metabolite is 0.09� hr^�1 and the ^�rate constant for excretion of unchanged parent drug is 0.087hr ^-1.^�

^�What is the amount of metabolite and parent drug in this person at 2 hours?�

What should you be aware/alert for with this type of patient?

2. A person on oral Valproate, an anticonvulsive medication, wants to know when they should expect a maximum therapeutic effect.� They just took a 250mg tablet.
1. �Calculate the time to reach a maximum Cp based on the manufacturer�s� (Abbott) literature that the absorption rate constant is 0.7 hr^-1 �and the� elimination rate constant is 0.065 hr^-1.

b. If another formulation has ka= 0.493 and ke=0.0655h^{-1� are} the formulations bioequivalent?