_{PHA 5127}

_{Case Study 1}

_{I. Mr J.S., a 41 yr old, 60 kg, double amputee patient with G-ve pneumonia, was being treated with gentamicin and ampicillin. Gentamicin had been given as an iv bolus (0.5 mg/kg). Serum samples were obtained at 1 and 8 hours post injection, and the lab reported concentrations of 3 and 0.5 m g/ml, respectively. Assume one compartment, first-order elimination for gentamicin.}

1. _{Calculate ke and half-life of gentamicin in this patient.}
2. _{Calculate Vd. Knowing that Vd in normal subjects=0.25 L/kg, explain any observed deviations for this patient.}
3. _{Calculate total clearance of gentamicin.}

_{II. A 10 yr old, 25 kg patient suffering from Status Asthmaticus was given an iv bolus of aminophylline (500 mg). When theophylline serum concentrations were measured at 0 and 5 hours after injection, drug levels were found to be 35 and 14.4 m g/ml, respectively. Assume a therapeutic range of (10-20) m g/ml for theophylline, 1 mg aminophylline is equivalent to 0.8 mg theophylline, and elimination occurs by a first-order process.}

1. _{Calculate t1/2, ke, Vd and CL for theophylline in this patient.}
2. _{How long will it take before the patient is subtherapeutic ?}

_{III. A patient is admitted to the ER upon ingesting an overdose of theophylline. A serum drug level was measured at 53 m g/ml. Assuming an 8 hour t1/2 and and no further drug absorption, determine how long it would take for the serum level to drop to the upper limit of the therapeutic range (20 m g/ml).}

_{Answer provided by Jeffrey Stark, Graduate Student}