Stability and pharmacokinetics of m-[131I]iodobenzylguanidine in patients

A pharmacokinetic study was done to elucidate the body distribution, elimination, and metabolism of m-[131I]iodobenzylguanidine (m-[131I]IBG). For this purpose, an analytical method using solid phase extraction columns was developed. m-[131I]IBG was administered as an i.v. infusion according to different schedules with doses of 7,055 to 13,580 MBq/m2. At the start of the infusion m-[131I]IBG accounted for 93.0 +/- 2.3% (SD; n = 10) of the total radioactivity. At the end of the infusion m-[131I]IBG accounted for 88.0 +/- 7.4%. The non-m-IBG-bound radioactivity was predominantly 131I. The pharmacokinetic parameters (n = 7) are adequately described by a three compartment model. The parameters for m-[131I]IBG were determined with a mean terminal half-life of 37.0 h, a volume of distribution of 307 liters/m2, and an area under the curve value of 1091 kBq x h/ml. The total body clearance was 189 ml/min/m2. The values for 131I showed a terminal half-life of 71.6 h, a volume of distribution of 190 liters/m2, and an area under the curve value of 1537 kBq x h/ml. The total body clearance was 70 ml/min/m2. The selectivity of the m-[131I]IBG treatment might be improved by a reduction of 131I in the infusion fluid and further investigations are warranted.