Effect of chronic γ-hydroxybutyrate (GHB) administration on GHB toxicokinetics and GHB-induced respiratory depression.

BACKGROUND: γ-hydroxybutyrate (GHB) has a high potential for illicit use; overdose of this compound results in sedation, respiratory depression and death. Tolerance to the hypnotic/sedative and electroencephalogram effects of GHB occurs with chronic GHB administration; however, tolerance to respiratory depression has not been evaluated. GHB toxicodynamic effects are mediated predominantly by GABAB receptors. Chronic treatment may affect monocarboxylate transporters (MCTs) and alter the absorption, renal clearance and brain uptake of GHB. OBJECTIVES: To determine effects of chronic GHB dosing on GHB toxicokinetics, GHB-induced respiratory depression, and MCT expression. METHODS: Rats were administered GHB 600 mg/kg intravenously daily for 5 days. Plasma, urine and tissue samples and respiratory measurements were obtained on days 1 and 5. Plasma and urine were analyzed for GHB by LC/MS/MS and tissue samples for expression of MCT1, 2 and 4 and their accessory proteins by QRT-PCR. RESULTS: No differences in GHB pharmacokinetics or respiratory depression were observed between days 1 and 5. Opposing changes in MCT1 and MCT4 mRNA expression were observed in kidney samples on day 5 compared to GHB-naïve animals, and MCT4 expression was increased in the intestine. CONCLUSIONS: The lack of tolerance observed with GHB-induced respiratory depression, in contrast to the tolerance reported for the sedative/hypnotic and electroencephalogram effects, suggests that different GABAB receptor subtypes may be involved in different GABAB-mediated toxicodynamic effects of GHB. Chronic or binge users of GHB may be at no less risk for fatality from respiratory arrest with a GHB overdose than with a single dose of GHB.

An Extended Minimal Physiologically Based Pharmacokinetic Model: Evaluation of Type II Diabetes Mellitus and Diabetic Nephropathy on Human IgG Pharmacokinetics in Rats.

Although many studies have evaluated the effects of type 2 diabetes mellitus (T2DM) on the pharmacokinetics (PK) of low molecular weight molecules, there is limited information regarding effects on monoclonal antibodies. Our previous studies have reported significant increases in total (2-4 fold) and renal (100-300 fold) clearance of human IgG, an antibody isotype, in Zucker diabetic fatty (ZDF) rats. Pioglitazone treatment incompletely reversed the disease-related PK changes. The objective of this study was to construct a mechanistic model for simultaneous fitting plasma and urine data, to yield physiologically relevant PK parameters. We propose an extended minimal physiologically based PK (mPBPK) model specifically for IgG by classifying organs as either leaky or tight vascular tissues, and adding a kidney compartment. The model incorporates convection as the primary mechanism of IgG movement from plasma into tissues, interstitial fluid (ISF) in extravascular distribution space, and glomerular filtration rate (GFR), sieving coefficient and fraction reabsorbed in the kidney. The model captured the plasma and urine PK profiles well, and simulated concentrations in ISF. The model estimated a 2-4 fold increase in nonrenal clearance from plasma and 30-120 fold increase in renal clearance with T2DM, consistent with the experimental findings, and these differences in renal clearance were related to changes in GFR, sieving coefficient, and proximal tubular reabsorption. In conclusion, the mPBPK model offers a more relevant approach for analyzing plasma and urine IgG concentration-time data than conventional models and provides insight regarding alterations in distributional and elimination parameters occurring with T2DM.

Effect of Type 2 Diabetes Mellitus and Diabetic Nephropathy on IgG Pharmacokinetics and Subcutaneous Bioavailability in the Rat.

The objective of this research was to assess the effects of type 2 diabetes mellitus (T2DM) and diabetic nephropathy (DN) on the pharmacokinetics of human IgG (hIgG), an antibody isotype, in Zucker diabetic fatty (ZDF) rats. Furthermore, the specific role of T2DM in the altered disposition of hIgG was evaluated by treating diabetic rats with pioglitazone, while the role of chronic kidney disease (CKD) was assessed using 5/6 nephrectomized Sprague Dawley rats. ZDF male (lean non-diabetic control and obese diabetic) and pioglitazone-treated ZDF rats were studied at ages 12-13 weeks (only DM was present), and at ages 29-30 weeks (progression to DN). All animals were dosed with 1 mg/kg of hIgG intravenously (IV) or subcutaneously (SC). ZDF rats had significantly higher blood glucose concentrations and urinary albumin excretion compared to control rats. Significant increases in total clearance (2.5-fold) and renal clearance (100-fold) of hIgG were observed; however the major increase in total clearance was due to increased non-renal clearance. Greater changes in urinary albumin excretion and total and renal clearances of IgG (3.5-fold and 300-fold, respectively) were observed with progression to DN. SC bioavailability of hIgG in all animal groups was similar (>84%). With pioglitazone-treatment, diabetic animals remained euglycemic and treatment was able to reverse the clearance changes, although incompletely. In the CKD group, no difference in hIgG clearance was observed when compared with controls. In conclusion, the increased clearance of hIgG in ZDF diabetic animals, reversal by pioglitazone treatment and lack of effect of CKD, demonstrate the influence of T2DM on hIgG pharmacokinetics.