In vitro microdialysis of hydrophilic and lipophilic compounds

The feasibility of microdialysis to study both hydrophilic and lipophilic compounds was investigated. In vitro microdialysis was performed with glucose, sodium fusidate, betamethasone dipropionate and calcipotriol. For all the tested drugs, recovery was dependent on the dialysed compound, the perfusion rate, the length of the membrane, the temperature and the stirring rate in the surrounding medium. Recovery was independent of concentration for glucose, betamethasone dipropionate and calcipotriol, but was dependent on the concentration of sodium fusidate. Loss (delivery) of betamethasone dipropionate was independent of concentration, whereas loss of sodium fusidate was not. The more lipophilic the compound, the lower the recovery; 74.6%, 41.0%, 36.4% and 31.1% for glucose, sodium fusidate, betamethasone dipropionate and calcipotriol, respectively. A difference in recovery and loss was found for sodium fusidate, betamethasone dipropionate and calcipotriol, whereas glucose had the same recovery and loss. In vitro calibration was performed with glucose and sodium fusidate. The estimated glucose concentration was equal to the true concentration in the surrounding medium. A modification of the point of no-net-flux method was necessary to estimate the true concentration of sodium fusidate. Special tubing was needed for the highly lipophilic compounds betamethasone dipropionate and calcipotriol. It may be more critical and problematic to use microdialysis for lipophilic compound and the method might be limited to the study for hydrophilic compounds in vivo.