The purpose of this clinical study (ChAMP - Comparability pharmacokinetics of Alpha-1 Modified Process) is to compare the pharmacokinetic, safety and tolerability of Alpha-1 Proteinase Inhibitor (Human), modified process (Alpha-1 MP) and Prolastin in adult Alpha1-antitrypsin deficient patients. Patients will be infused intravenously with study drug on a weekly schedule for 24 weeks.

The objective of this study is to demonstrate the pharmacokinetic comparability of Alpha-1 MP to Prolastin® in subjects with Alpha1-antitrypsin deficiency.

This study is divided into three 8-week treatment sequences including an initial 8-week double-blind treatment period (with one of the 2 study drugs), a second 8-week double-blind treatment period (with the other study drug), and a third 8-week open-label treatment period (with Alpha-1 MP).

• Experimental: Sequential, blinded treatment periods of Alpha-1 MP (experimental), then crossed-over to Prolastin (active comparitor), followed by open-label Alpha-1 MP
• Active Comparator: Sequential, blinded treatment periods of Prolastin (active comparitor), then crossed-over to Alpha-1 MP (experimental), followed by open-label Alpha-1 MP

Inclusion Criteria:

• Documented diagnosis of congenital Alpha1-antitrypsin deficiency
• Must be receiving augmentation therapy with plasma-derived (human) Alpha1-Proteinase Inhibitor (Prolastin®) for at least one month prior to study entry.
• Signed written informed consent prior to initiation of any study related procedures

Exclusion Criteria:

• Females who are pregnant, breast feeding, or if of child-bearing potential, unwilling to practice adequate contraception throughout the study
• Use of systemic steroids within the 2 weeks prior to receiving study treatment (this does not include the use of inhaled steroids used on a routine or as needed basis).
• Subjects who have had exacerbations of their disease within one month of trial entry.