Pharmacokinetics, bio-distribution and dosmimetry of some widely used radiopharmaceuticals in nuclear medicine under Bangladesh condition

Abstract

The present study was carried out with forty patients, twenty each, for kidney and liver and were categorized in three different age groups of21-30 years, 31-40 years and 41-50 years. The radiopharmaceuticals, 99mTc_DTPAfor target organ kidney and 99mTc_Tin Colloid for target organ liver were used as the injected radiopharmaceuticals. Besides the target organs kidney and liver, other surrounding organs' distribution was also measured. 99mTc_DTPA (Diethylene-Triamine-Pentaacetic Acid) was introduced in individual human bodies to study the renal function and 99mTc_TinColloid was introduced to study the liver function in-terms ofbiodistribution and also in-terms of measuring the cumulative activity, the dose absorbed by different organs of the body and also by the radiation absorbed dose in the whole body. For interpretation of the clinical findings pharmacokinetic studies were also performed in kidneys of twenty patients of different age group. Data of pharmacokinetic distribution of radiation dose from Tc-99m DTPA were measured in twenty individuals who had undergone diagnostic process. The biodistribution of Tc-99m DTPAwas found highest in lungs followed by kidneys. In lungs it varied from 9.31% to 13.26% and in kidney biodistribution ranged from 5.68% to 10.28. The lowest biodistribution was recorded in bones of the body which indicated that the radiopharmaceutical did not move sufficiently through the more solid part of the body. The biodistribution of 99mTc_Tin Colloid was highest in liver which ranged between 46.06% and 70.22%, the average value being 62.58%. It is observed that, most of the radiopharmaceutical remained concentrated in the liver, which indicates the high affinity of the radiopharmaceutical to the organ. The lowest biodistribution was recorded in the vi small intestine (SI) which shows a lower affinity of the radiopharmaceutical to the small intestine. In case of kidney, the highest amount of 99mTc -DTPA was absorbed in the target organ kidney which ranged from 0.132 to 0.293rads, the average value being 0.182 rad. Lowest absorption was recorded in thyroid. This indicated that, the movement of the radiopharmaceutical varied according to the position of the organ from the source organ. In case of liver, The highest amount of radiopharmaceutical was absorbed in the target organ liver, the average value was' 1.2445 rads. Lowest absorption was recorded in bladder. The radiation absorbed dose in the kidney ranged from 0.0383 to 0.06952 rad per mCi. The mean value was 0.048 rad/mCi. Some variations were observed in radiation absorbed dose of twenty patients but these variation is not very significant .The variation may be due to the difference in age group of patients. The 20 patients were grouped into three categories, 5 being in the 21-30 years age group, 8 in the 31-40 years age group and 7 in the 41-50 years age group. The radiation absorbed dose is higher in patients of lower age group of 21-30 years, followed by middle age group of 31-40 years. The lowest absorbed dose was observed in older age group of 41-50 years. The radiation absorbed dose in the liver of the twenty patients ranged between 0.1909 rads/ mCi to 0.2816 rads/mCi, the mean value being 0.2482 rads/mCi. A little variations were observed in radiation absorbed dose in twenty patients due to the difference in age group of patients. Among all of them, 37% of patients showed highest radiation absorption who are in the younger group. This was followed by middle aged patient group which is 33% and the older group include only 30%. This study indicates that the radiation absorption was higher in young age patients who are normally much healthier and stronger. The radiation absorbed dose in adults for Tc-99m DTPA and also for Tc-99m Tin Colloid was very much within the limit as reported in world vii literature. Dose estimates for the patients, studied at different times included in this study are in reasonable accord for individual organ doses between different patients. The biodistribution of 99mTc_DTPAand dose absorbed in kidney alone/5mci of the injected dose was also compared. It is obtained that there is similarity in the trend of biodistribution and dose absorbed by kidney. The patient who showed higher biodistribution, had higher dose absorption in kidney and vice-versa. This was same for the comparison between biodistribution of the radiopharmaceutical and the dose absorption in liver alone due to the injected dose of 5mCi. A study was undertaken to observe the radioactivity remaining in the body and its clearance with time. It is found that the three half-lives of the radiopharmaceutical was observed at 9,90 and 600 min in case of all the samples taken after 3,5,7 and 11th min of infusion. This indicates that the remaining activity of the radiopharmaceutical becomes negligible after 10 hrs of infusion and thereafter the activity becomes gradually cle¥ed. So the patients are free of any hazardous effect of the radiopharmaceuticals. The obtained result for both the readiopparmaceutical was very much within the limit as reported before. They are obviously in agreement with the result obtained by other investigators.