Pharmacokinetics of recombinant human interleukin 3 administered subcutaneously and by continuous intravenous infusion in patients after chemotherapy for ovarian cancer.

Twenty chemotherapy-naive patients with ovarian carcinoma received 1, 5, 10, or 15 micrograms/kg/day (five patients per dose step) of recombinant human interleukin 3 (rhIL-3) over 7 days after carboplatin/cyclophosphamide in Cycles 1 and 3. Patients received rhIL-3 by continuous i.v. infusion or once daily s.c. injection in Cycle 1 and the alternate route in Cycle 3. Plasma rhIL-3 samples were obtained once daily on Days 1 to 6 and serially over a 24-h period on Day 7 for pharmacokinetic assessment of s.c. and i.v. administered rhIL-3 in 16 and 17 patients, respectively. Concentrations were assayed by a time-resolved fluorescence sandwich immunoassay. Pharmacokinetic parameters were derived by noncompartmental methods. Mean steady-state concentrations during continuous i.v. infusion ranged from 117 pg/ml (1 microgram/kg/day) to 2217 pg/ml (15 micrograms/kg/day) and were linearly related to dose (r = 0.87, P < 0.001). When dose normalized, the mean steady-state concentrations were comparable at all doses. The total-body clearance was approximately 4 to 5 ml/min/kg. Elimination half-life (t1/2 i.v.) could be assessed for the 5- to 15-micrograms/kg/day dose levels and was 53, 41, and 26 min for the 5-, 10-, and 15-micrograms dose levels, respectively (not significant between dose levels). Following s.c. injection, the maximum rhIL-3 plasma concentration ranged from 206 pg/ml (1 microgram/kg/day) to 6930 pg/ml (15 micrograms/kg/day). Both the maximum measured plasma concentration (r = 0.89, P < 0.0001) and the area under the plasma concentration/time curve (r = 0.93, P < 0.0001) were related to dose. Dose-normalized values were comparable over the entire dose range. Elimination t1/2s.c. was 4.8 h at the 1-microgram dose level and roughly half this time for the 5- to 15-micrograms/kg/day dose levels. The systemic clearance of approximately 5 to 6 ml/min/kg was comparable at all dose levels. Based on trough levels of the 7-day s.c. course, no rhIL-3 accumulation occurred. Bioavailability of s.c. administered rhIL-3 was nearly 100%. No correlation between creatinine clearance and pharmacokinetic parameters of rhIL-3 could be demonstrated. Since there was also no difference in hematological efficacy between the two routes of rhIL-3 administration, we conclude that the s.c. route of administration appears to have no disadvantages over the i.v. route and may facilitate its clinical application.

How large a hormone can be measured by microencapsulated antibody?

The size of molecules able to be measured in immunoassays where antibody is encapsulated within semipermeable microcapsules is restricted by the pore size of the membrane. This study was performed to determine the approximate molecular weight cut-off of this membrane. Permeability was assessed by measuring which labelled hormones were able to enter and bind their respective microencapsulated antibody. Hormones with molecular weights of less than 4000 (angiotensin II, thyroxine, 17-hydroxyprogesterone, progesterone, testosterone and androstenedione) passed freely through the pores but larger molecules, with molecular weights in excess of 10,000 (parathyroid hormone, human GH, TSH) could not. Insulin, with a molecular weight of 6000 (approximate minimum diameter 3.5 nm), had restricted entry while the next smallest hormone tested, the 1-34 amino acid portion of parathyroid hormone (molecular weight 4000; diameter 1.8 nm), was able to bind encapsulated antibody, suggesting that the pore diameter is between 1.8 and 3.5 nm. It can now be predicted that the method is able to measure compounds with a diameter within this range and with a molecular weight below 6000. Microcapsules may be useful for improving specificity of assays where a cross-reactant is too large to penetrate the membrane.

A study of immune responses to Tamm-Horsfall glycoprotein in the sera of patients with renal tubular acidosis.

Antibody to Tamm-Horsfall glycoprotein in the sera of patients with distal renal tubular acidosis (dRTA) was measured by radioimmunoassay, as well as in samples of normal human serum. Normal human serum contains small amounts of IgG capable of interacting with Tamm-Horsfall glycoprotein. Appropriate assays were carried out on antiserum raised in rabbits against human Tamm-Horsfall glycoprotein serially diluted with normal human serum. Corrections were applied for the presence of interfering substances in serum. The amounts of antibody found in samples of normal and patient sera were not significantly different, although some of the patients were diagnosed as having immune as opposed to familial dRTA. Studies of cell-mediated immunity to Tamm-Horsfall glycoprotein was found not to differentiate between the normal and patient samples. dRTA does not appear to be associated with immune responses to Tamm-Horsfall glycoprotein.

Measuring free thyroxin by using magnetic antibody-containing microcapsules.

We describe a novel magnetic-separation microencapsulated antibody displacement assay for free thyroxin. The method is rapid (results available in just over an hour), with a detection limit of 3 pmol/L, and an interassay precision of less than 10% over the range 8-75 pmol/L. Results are not influenced by changes in the concentration of thyroxin-binding globulin or albumin, nor by the presence of circulating anti-thyroxin antibodies or physiological concentrations of nonesterified (free) fatty acids. A reference interval of 8.4-18.4 pmol/L was established for a large euthyroid adult population. Patients with various nonthyroidal illnesses exhibited a similar reference interval (6.2-17.4 pmol/L). Results from pregnant women, at all stages of gestation, were within the nonpregnant euthyroid reference interval. Complete discrimination was obtained between the euthyroid reference interval and values from patients with untreated thyrotoxicosis (24-75 pmol/L). Excellent, though incomplete, discrimination was obtained for patients with untreated hypothyroidism (less than 3.0-9.0 pmol/L). Results for a group of patients defined as having compensated euthyroidism (5.0-15 pmol/L) showed considerable overlap with the euthyroid reference interval. Patients taking thyroxin, who were clinically euthyroid and whose serum concentration of thyrotropin was within its euthyroid reference interval, had free thyroxin concentrations in the range 13.4-24.2 pmol/L. We discuss the validity of this assay in clinical practice.