Pharmacokinetics of heroin and its metabolites in vitreous humor and blood in a living pig model

Evaluating the Reliability of Dipstick Drug Screens on Vitreous and Postmortem Blood as a Triage Modality in Forensic Pathology

Dipstick drug screens are cheap, easy to use, and quick presumptive tests to detect common drugs of abuse. Dipsticks are designed for drug detection in urine. There is no literature regarding their potential use on fluids different from urine. The study aimed to determine the performance of dipstick screening tests on postmortem vitreous and blood specimens compared to urine dipsticks and final confirmatory toxicology analyses on blood. The study population included cases in which a complete toxicology analysis was performed. Each subject was screened for three substances: cocaine, fentanyl, and opiates. Dipstick results were checked by visual inspection. Results were compared with urine screening tests and quantitative, confirmatory toxicological analyses by gas chromatography/mass spectrometry on postmortem blood samples as the gold standards for screening and confirmatory analysis, respectively. There was a high number of false-negative results for opiates. Cocaine dipsticks in blood showed the highest reliability. Fentanyl dipsticks in vitreous showed a high number of false-negative results. Both vitreous and blood dipstick screening tests for all substances performed well on negative cases. When both blood and vitreous screening tests are negative, the chance that the confirmatory toxicology analysis will be positive is very low.

Drug Permeability: From the Blood-Brain Barrier to the Peripheral Nerve Barriers

Drug delivery into the peripheral nerves and nerve roots has important implications for effective local anesthesia and treatment of peripheral neuropathies and chronic neuropathic pain. Similar to drugs that need to cross the blood-brain barrier (BBB) and blood-spinal cord barrier (BSCB) to gain access to the central nervous system (CNS), drugs must cross the peripheral nerve barriers (PNB), formed by the perineurium and blood-nerve barrier (BNB) to modulate peripheral axons. Despite significant progress made to develop effective strategies to enhance BBB permeability in therapeutic drug design, efforts to enhance drug permeability and retention in peripheral nerves and nerve roots are relatively understudied. Guided by knowledge describing structural, molecular and functional similarities between restrictive neural barriers in the CNS and peripheral nervous system (PNS), we hypothesize that certain CNS drug delivery strategies are adaptable for peripheral nerve drug delivery. In this review, we describe the molecular, structural and functional similarities and differences between the BBB and PNB, summarize and compare existing CNS and peripheral nerve drug delivery strategies, and discuss the potential application of selected CNS delivery strategies to improve efficacious drug entry for peripheral nerve disorders.

A retinal contribution to opioid-induced sleep disorders?

Chronic opioid use is linked to persistent and severe sleep/wake disturbances in patients. These opioid-related sleep problems increase risk for developing opioid dependence, mood disorders and in turn overdose in chronic pain patients receiving opioid therapy. Despite the well-established link between long-term opioid use and sleep disorders, the mechanism by which opioids perturb sleep remains unclear. Interestingly, animal studies indicate that opioids disrupt sleep/wake behaviors by altering an animal’s ability to synchronize their circadian rhythms to environmental light cycles (i.e., photoentrainment). A specific subset of retinal cells known as intrinsically photosensitive retinal ganglion cells (ipRGCs) that express μ-opioid receptors are exclusively responsible for transmitting environmental light information to sleep/circadian centers in the brain. Thus, this review will focus on the effect of opioids on ipRGCs and their projection regions that are involved in the photoentrainment of sleep/wake behaviors. Lastly, we discuss the viability of ipRGCs as a potential therapeutic target for treating opioid-related sleep/wake problems.

Morphine Accumulates in the Retina Following Chronic Systemic Administration

Opioid transport into the central nervous system is crucial for the analgesic efficacy of opioid drugs. Thus, the pharmacokinetics of opioid analgesics such as morphine have been extensively studied in systemic circulation and the brain. While opioid metabolites are routinely detected in the vitreous fluid of the eye during postmortem toxicological analyses, the pharmacokinetics of morphine within the retina of the eye remains largely unexplored. In this study, we measured morphine in mouse retina following systemic exposure. We showed that morphine deposits and persists in the retina long after levels have dropped in the serum. Moreover, we found that morphine concentrations (ng/mg tissue) in the retina exceeded brain morphine concentrations at all time points tested. Perhaps most intriguingly, these data indicate that following chronic systemic exposure, morphine accumulates in the retina, but not in the brain or serum. These results suggest that morphine can accumulate in the retina following chronic use, which could contribute to the deleterious effects of chronic opioid use on both image-forming and non-image-forming visual functions.

Analysis of rumen contents and ocular fluid for toxic alkaloids from goats and cows dosed larkspur (Delphinium barbeyi), lupine (Lupinus leucophyllus), and death camas (Zigadenus paniculatus)

Larkspurs, lupines, and death camas can be acutely toxic to livestock and are serious poisonous plant problems in western North America. The toxicity of these plants depends on the composition and concentrations of the toxic alkaloids in the plants. In this study, goats and cows were dosed sub-lethal doses of larkspur, lupine, and death camas. Rumen contents and ocular fluid samples were collected, and simple extraction, sample preparation, and analytical methods were developed for the detection of toxic alkaloids in the rumen contents and ocular fluid samples. Toxic alkaloids were detected in the rumen contents and ocular fluid samples from the goats and cows dosed larkspur, lupine, and death camas. In addition, results from a case report where rumen contents were analyzed from a steer that was suspected to have died due to larkspur are reported. This demonstrates the utility of the methods described for the diagnosis of acute plant poisonings.

Urinary Kinetics of Heroin Metabolites in Pigs Shortly After Intake

In previous experimental studies on heroin metabolites excretion in urine, the first sample was often collected a few hours after intake. In forensic cases, it is sometimes questioned if a positive urine result is expected e.g., 30 min after intake. The aim of this study was to investigate urinary excretion of heroin metabolites (morphine, 6-monoacetylmorphine (6-MAM) and morphine-3-glucuronide (M3G)) every 30 min until 330 min after injection of a 20 mg heroin dose in six pigs. Samples were analyzed using a previously published, fully validated liquid chromatography-tandem mass spectrometry method. All metabolites were detected after 30 min in all pigs. The time to maximum concentration (Tmax) median (range) for 6-MAM and morphine was 30 min (first sample) (30-120), and 90 min (30-330) for M3G. In four of the six pigs, the Tmax of 6-MAM and morphine was reached within 30 min. All analytes were still detectable at the end of study. This study showed that positive results in urine are expected to be seen shortly after use of heroin in pigs. Detection times were longer than previously indicated, especially for 6-MAM, but previous studies used lower doses. As the physiology of these animals resembles that of the humans, transferability to man is expected.