A Mechanistic Investigation of the TTP-like State Associated with Intravenous Abuse of Opana® ER

Background: Since 2012, a growing list of case reports has emerged describing the occurrence of a TTP-like state following intravenous (i.v.) abuse of extended release oxymorphone (Opana® ER). The pathophysiology resulting from intravenous exposure to Opana® ER has demonstrated a spectrum of severity with unclear etiology, and approaches to treatment/management have ranged from early plasma exchange to supportive care alone. As a result these cases have spurred a collaborative investigation to better understand mechanisms of toxicity. Given the temporal relation between the reformulation of the drug product to achieve extended release and the onset of reported cases, we investigated the inert ingredient mixture as a possible causal factor. Methods : Guinea pigs were used as an animal model to understand the hematopathologic and nephrotoxic potential of the inert ingredient mixture of Opana® ER, which was provided by Endo Pharmaceuticals under a research collaborative agreement. Animal studies were approved by Institutional Animal Care and Use Committees and conducted in adherence with NIH guidelines. Animals were studied over various i.v. dosing schemes (single injections of 0.1, 0.3, or repeated dosing of 0.3mg/kg (5 doses at 1.5hr intervals)) with either the entire inert ingredient mixture ("PEO+") or high molecular weight polyethylene oxide alone ("PEO")-the major constituent of the inert ingredient mixture. The dose range was based on estimates of the inert ingredient mass introduced during the adulteration and injection of the drug product. Additional in vitro and cell-based assessments of coagulation (thromboelastography, thrombin generation) and ADAMTS13 function were carried out to better understand in vivo observations. Results: Intravenous administration of the solubilized inert ingredient mixture in guinea pigs resulted in dose-dependent pathologic changes in blood parameters and kidney function. Hematological changes included a dose dependent increase in free plasma hemoglobin (Hb), decreased hematocrit and platelet count. Acute kidney injury was characterized by dose-dependent renal cortical iron deposition, plasma creatinine increase, distal convoluted tubular injury (NGAL mRNA induction), and glomerular damage (hemoglobinuria) (Table 1). At high doses, red blood cell aggregation and renal hypoxia (HIF-1 accumulation) was observed. These observations were similar following the administration of PEO alone, and occurred independent of changes to ADAMTS13 and its cleavage of Von Willebrand Factor. PEO, when spiked into blood in vitro, does not directly modulate coagulability as indicated by global assays of coagulation. Conclusions: The present animal study suggests that i.v. exposure to the inert ingredients included in Opana® ER can trigger hematologic responses resembling elements of TTP, namely intravascular hemolysis and acute renal injury/failure. However, the renal injury observed in the guinea pig model is distinct from classic TTP, which involves spontaneous platelet clumping and subsequent microvascular thrombosis; instead, the nephrotoxicity likely arises from a multifactorial process encompassing renal tubular injury and glomerular damage, arising secondary to hemolysis, extracellular Hb/heme/iron mediated oxidative tissue damage and compromised tissue oxygenation. Table 1. Guinea pig dose group(mg of PEO+/kg) Cmax of plasma free Hb [mg/ml] AUC0-24h of plasma free Hb [mg/ml x h] hematocrit at 24h [%] platelet count at 24h [K/µl] NGAL induction** (renal cortex) plasma creatinine at 24h [µmol/L] hemoglobinuria at end of study [mg/ml] iron deposition (renal cortex)[µg/g tissue] Control 0.8 ±0.1 (n=4) 16.2 ±4.8 (n=4) 36 ±1.7 (n=5) 205 ±11.6 (n=5) 1 ±0.3 (n=3) 87.0 ±9.3 (n=4) 0.1 (n=1) 33 ±3.5 (n=3) 0.1 single dose 1.4 ±0.6 (n=11) 20.5 ±5.75 (n=11) 35 ±3.1 (n=5) 157 ±20.5 (n=5) 1 ±0.5 (n=3) 104 ±41.3 (n=4) 0.6 (n=2) 49 ±7.3 (n=3) 0.3 single dose 2 ±0.3 (n=13) 36.5 ±5.1 (n=13) 31 ±1.1 (n=6) 135 ±11.2 (n=6) 1.6 ±0.4 (n=3) 145 ±36.7 (n=4) 1.2 (n=2) 153 ±2.5 (n=3) 0.3 multi dose (5 injections at 1.5h intervals)* 5.1 ±1.3 (n=5) 87.8 ±15.8 (n=4) 28 ±0.8 (n=4) 62 ±12.4 (n=4) 24 ±0.8 (n=4) 421.1 ±33.8 (n=4) 9.8 ±5 (n=3) 139 ±9.5 (n=4) data represented as mean ±SEM, n = number of animals *endpoint 24h, all other groups 48h **Fold induction over baseline Disclosures Wong: Haemonetics Corporation: Research Funding.

THE EFFECT OF SODIUM BENTONITE ADMINISTRATION ON VITAMIN A METABOLISM IN THE RAT

The inclusion of sodium bentonite in the diet severely limited the ability of vitamin A deficient rats to store the vitamin in the liver. This effect was observed both with vitamin A and with the provitamin β-carotene. Moreover, the liver weight per 100 gm. body weight was found to be less in most of the groups receiving sodium bentonite than in control groups. The results may be interpreted in terms of a physical adsorption of vitamin A or β-carotene on sodium bentonite present in the small intestine. Sodium bentonite cannot be regarded as an inert ingredient of the diet of rats and its prolonged administration might be expected to have deleterious effects.

THE EFFECT OF SODIUM BENTONITE ADMINISTRATION ON VITAMIN A METABOLISM IN THE RAT

The inclusion of sodium bentonite in the diet severely limited the ability of vitamin A deficient rats to store the vitamin in the liver. This effect was observed both with vitamin A and with the provitamin β-carotene. Moreover, the liver weight per 100 gm. body weight was found to be less in most of the groups receiving sodium bentonite than in control groups. The results may be interpreted in terms of a physical adsorption of vitamin A or β-carotene on sodium bentonite present in the small intestine. Sodium bentonite cannot be regarded as an inert ingredient of the diet of rats and its prolonged administration might be expected to have deleterious effects.

Studies on aqueous Suspensions of Insecticides

Mosquitos were exposed for short contact periods to deposits on plaster blocks from aqueous suspensions of insecticides.There is an inverse relation between the size of ground DDT crystals fractionated into size ranges by sedimentation and their effectiveness. Smaller particles are more effective than larger ones even when equivalent numbers are compared. Differences in effectiveness are attributed to differences in the amounts of insecticide picked up and retained by the insect.There is no significant increase in kills of mosquitos exposed for the same contact period to dosages of 10–20 micron DDT crystals above 3 mg. per sq. ft. “Persistence” of deposits of these crystals, however, increases as the dosage increases.Crystal length alone is not critical, for fine 60 micron DDT needles are slightly more effective than ground crystals in the 10–20 micron range. The shape and mass of crystals together influence pick-up and determine their effectiveness.There is also an inverse relation between crystal size and effectiveness of methoxychlor and DDD. The effectiveness of Compound 497 and of the gamma isomer of benzene hexachloride is influenced much less by particle size than is that of DDT.The inert ingredient of a wettable powder has a masking effect on the insecticide, and this is intensified as the proportion of diluent to insecticide increases.The availability of the deposit from an aqueous suspension of DDT crystals depends largely on the nature of the surface to which it is applied.