Question

1. The usual adult dose of levofloxacin is a 500-mg initial dose followed by subsequent doses of 250 mg every 24 hours for 10 days. For patients with a CrCl of less than 19 mL/min, doses following the initial dose are administered every 48 hours. How many 250-mg levofloxacin tablets should be dispensed to a 75-year-old, 160-lb female patient with a serum creatinine of 1.32 mg/dL? (Use the Cockcroft-Gault equation to determine creatinine clearance.)

2. An order is written for 2g of vancomycin to be given IV every 12 hours for an adult. Calculate

the volume in milliliters needed for a single dose if vancomycin is available in a 50mg/ml

concentration.

3. A neonate born at 32 weeks' gestation weighs 2005 g and is transferred to the hospital's neonate intensive care unit with a diagnosis of sepsis. Among the physician's orders are aminophylline 5 mg/kg IV q6h, cefotaxime 50 mg/kg q12h, and vancomycin 10 mg/kg q12h. Calculate the initial dose of vancomycin, in milligrams.

Answer 1

1) Calculation number of tbalets dispensed for this patient.

Creatinine clearance (Female) formula

CrCl = ([140-age] * Weight in kg)/(Serum creatinine) * 72) * 0.85

Here

Serum creatinine = 1.32 mg/dl.

Weight = 160 lb.

Convert lb to kg for calculation

1 lb = 0.454 kg.

So

Weight in kg = 72.6 kg.

As per above formula

CrCl = ([140 - 75 * 72.6)/ 1.32 * 72 ) 0.85

= (65 * 72.6)/95.04) 0.85

= (4719/95.04) * 0.85

= 49.65 * 0.85

= 42.2 ml/min.

So

Number of tablets required = Ordered dose/Available dose

Ordered dose =500 mg + 250 mg every 24 hr for 10 days.

Available dose = 250 mg/tablet.

Number of tablets dispensed = 500/250 + 250/250 * 10

= 2 + 1 * 10

= 2 + 10

= 12 tablets for 10 days.

2) Calculation of volume(ml) for single dose.

Volume(ml) = Desire ddose/Dose in hand * Quantity.

Here

Desired dose = 2000 mg (2 g).

Dose in hand = 50 mg.

Quantity = 1 ml.

As per above formula

Volume(ml) = 2000/50 * 1

= 40 * 1

= 40 ml per dose.

3) Calculation of initial dose of vancomycin.

Ordered dose = 10 mg/kg/q12h.

Weight of the patient = 2005 gm.

Convert gm to kg for calculation

1 gm = 0.001 kg.

So

Weight of th epatient = 2005 * 0.001

= 2 kg.

Initial dose of vancomycin required = 10 * 2

= 20 mg q12h.