Impact of soaking gentamicin-containing collagen implants on potential antimicrobial efficacy

The purpose of this study is to evaluate how wetting of Collatamp (a gentamicin-containing collagen implant [GCCI]) impacts on the gentamicin content of the implant and whether this affects its potential antibacterial efficacy.

GCCI (Collatamp(®), EUSA Pharma [Europe], Oxford, United Kingdom) containing 130 mg gentamicin and 280 mg collagen (10 cm × 10 cm) were immersed in 300 mL normal saline for up to 6h. At set times after immersion the GCCI were removed, the saline diluted in normal human serum and the gentamicin content assayed by a validated immunoassay (Cedia, Microgenics Ltd, UK) to provide an estimate of the loss from each implant. The mean concentration data were then fitted to an exponential decay model (WinNonLin, Pharsight, US).

After a very short immersion period there was significant loss of gentamicin from the implants with a mean loss of 6.7% at 2 s, increasing to 40.5% at 1 min and essentially total loss by 6 h of immersion. Loss of gentamicin followed a complex elution profile, with elution half-lives ranging from 50 s on initial immersion to 99 min late in the elution period.

This study provides clear evidence that even a short period of dipping of Collatamp implants, and probably other GCCI, before insertion into the patient results in a significant loss of gentamicin which may be of clinical significance unless the period of soaking is very short. We therefore recommend that wetting of these implants before insertion is not undertaken.