Freeze drying--principles and practice for successful scale-up to manufacturing.

Freeze Drying involves transfer of heat and mass to and from the product under preparation, respectively, thus it is necessary to scale these transport phenomena appropriately from pilot plant to manufacturing-scale units to maintain product quality attributes. In this manuscript we describe the principal approach and tools utilized to successfully transfer the lyophilization process of a labile pharmaceutical product from pilot plant to manufacturing. Based on pilot plant data, the lyophilization cycle was tested during limited scale-up trials in manufacturing to identify parameter set-point values and test process parameter ranges. The limited data from manufacturing were then used in a single-vial mathematical model to determine manufacturing lyophilizer heat transfer coefficients, and subsequently evaluate the cycle robustness at scale-up operating conditions. The lyophilization cycle was then successfully demonstrated at target parameter set-point values.

Free radicals in rabbit spinal cord ischemia: electron spin resonance spectroscopy and correlation with SOD activity.

1. In nonanesthetized rabbits temporal occlusion of the abdominal aorta was used to induce oxidative stress in the lower part of the body including distal segments of the spinal cord. 2. Spinal cord samples were taken from the animals exposed to 25-min aortic occlusion (AO) or to occlusion followed by 1- or 2-hr reperfusion (AO/R1 or AO/R2, respectively) or from sham-operated animals (C). The presence of free radicals (FR) in the spinal cord samples frozen in liquid N2 was assessed by ESR spectroscopy without spin trapping. Moreover, superoxide dismutase (SOD) activity and conjugated diene (CD) levels were measured in the samples. 3. In the AO group FR were detected in the spinal cord regions close to the occlusion (lower thoracic and distal segments) along with a decrease in SOD activity. The calculated g value (g = 2.0291) indicated that the paramagnetic signal recorded might be attributed to superoxide radicals. FR were absent in the AO/R1 group. Concurrently, the SOD activity revealed a significant tendency to return to the control level. FR appeared again in the AO/R2 group, mostly in the upper and middle lumbar regions, along with a decrease in SOD activity. No sample from the C group revealed FR. A significant increase in CD levels was observed in the thoracolumbar region only in the AO/R2 group. The temporary absence of FR in the AO/R1 group suggests activation of defense antioxidant mechanisms (e.g., specific enzymatic systems such as SOD), which might have been exhausted later. 4. Changes in SOD activity similar to those observed in the thoracolumbar region, though less noticeable, occurred in the obviously noncompromised tissue (upper cervical region). This points to a kind of generalized response of the animal to aortic occlusion. 5. Direct ESR spectroscopy revealed the presence of FR as well as their time course in the spinal cord during the early phase of ischemia/reperfusion injury and the inverse relationship between FR and SOD activity.