Studies have shown that different percentages of body fat can alter the way drugs are distributed in the body. This study will use blood samples taken at different time points for patients taking Neupogen to determine if higher body weights affect drug exposure. The information gathered from this study will help understand if patients with higher body weights need a different dosing plan.

Patients in this study will have blood draws once before they take Neupogen and 6 times after they take the Neuopen (for a total of 24 hours). These patients will be in the hospital already and will not need to make additional trips back to have blood drawn. A total of about 5-6 tablespoons of blood will be drawn for this study. 15 obese patients and 15 matched, non-obese patients will be enrolled into this study.

Inclusion Criteria:

• Age greater than or equal to 18 years
• Receiving filgrastim at 5mcg/kg ± 10%
• Admitted as an inpatient with an expected stay of at least 24 hours
• Weight is > 190% of their ideal body weight (IBW) for "obese" patients or within 80 - 124% of IBW for matched control patients.
• Patient or their legally authorized representative understands and voluntarily signs the written informed consent prior to any study-specific procedures. A copy of the signed informed consent form will be retained by the treating institution.

Exclusion Criteria:

• Patients who have received filgrastim within 24 hours prior to enrollment
• Patients who have received pegfilgrastim within 14 days prior to enrollment
• Hypersensitivity reaction to filgrastim or any related product
• Patients who have taken lithium within 7 days of enrollment
• Serum Creatinine > 1.5 mg/dL
• Patients who are pregnant or breastfeeding
• Patients who are unable to understand and/or render informed consent

Obese and non-obese patients receiving filgrastim