Answer:
Injectable bovine collagen (Zyderm) was approved by the Food and Drug Administration (FDA) in 1981. There are currently three forms of injectable Zyderm collagen. Zyderm I is 3.5% bovine collagen (95% type 1 and 5% type 3) mixed with normal saline and 0.3% lidocaine. Zyderm II is 6.5% collagen. Zyplast, approved by the FDA in 1985, is 3.5% bovine collagen, which is cross-linked with glutaraldehyde to form a network that is thicker with increased longevity. Each material has its advantages and disadvantages. The selection of each agent correlates with the defect being corrected.
Before treatment, skin testing is mandatory. When collagen was first introduced, single skin testing was the standard of care. The site was then observed at 48 hours and at 4 weeks. If no adverse reactions were noted, it was presumed to be a negative skin test and the patient could be treated. A large percentage of physicians have switched to double skin testing. The basic premise is that exposing the individual twice to the antigenic stimulus increases the chance of a positive allergic reaction. Since no form of skin testing can eliminate the risk of an allergic reaction, this is at least believed to reduce it significantly. In most cases an initial skin test is performed and observed at 48 hours. A second skin test is performed 2 weeks later. If this second test is negative for at least 2 weeks, collagen can then be injected into the patient. Patients should be advised that a negative skin test does not guarantee that they will not react to the material when it is injected into them the third time. However, the significantly reduced number of allergic reactions to the material following double skin testing is well worth the added effort.
It is important for the physician as well as the patient to understand the role of injectable collagen in facial rejuvenation. Realistic expectations must be conveyed to the patient so there is no disappointment. Collagen works best on fine to medium lines and soft untethered scars. Although deep furrows and grooves can be corrected, it requires a large amount of material, and the correction is short-lived. The type of skin, skin thickness, and type of defect will indicate which material should be used and the appropriate depth of injection.