Unique treatment potential of cannabidiol for the prevention of relapse to drug use: preclinical proof of principle.

Cannabidiol (CBD), the major non-psychoactive constituent of Cannabis sativa, has received attention for therapeutic potential in treating neurologic and psychiatric disorders. Recently, CBD has also been explored for potential in treating drug addiction. Substance use disorders are chronically relapsing conditions and relapse risk persists for multiple reasons including craving induced by drug contexts, susceptibility to stress, elevated anxiety, and impaired impulse control. Here, we evaluated the "anti-relapse" potential of a transdermal CBD preparation in animal models of drug seeking, anxiety and impulsivity. Rats with alcohol or cocaine self-administration histories received transdermal CBD at 24 h intervals for 7 days and were tested for context and stress-induced reinstatement, as well as experimental anxiety on the elevated plus maze. Effects on impulsive behavior were established using a delay-discounting task following recovery from a 7-day dependence-inducing alcohol intoxication regimen. CBD attenuated context-induced and stress-induced drug seeking without tolerance, sedative effects, or interference with normal motivated behavior. Following treatment termination, reinstatement remained attenuated up to ≈5 months although plasma and brain CBD levels remained detectable only for 3 days. CBD also reduced experimental anxiety and prevented the development of high impulsivity in rats with an alcohol dependence history. The results provide proof of principle supporting potential of CBD in relapse prevention along two dimensions: beneficial actions across several vulnerability states and long-lasting effects with only brief treatment. The findings also inform the ongoing medical marijuana debate concerning medical benefits of non-psychoactive cannabinoids and their promise for development and use as therapeutics.

Conversion of Cannabidiol Following Oral Administration: Authors' Response to Grotenhermen et al. DOI: 10.1089/can.2016.0036.

In a commentary, Grotenhermen, Russo, and Zuardi questioned not only the clinical relevance but also the conclusions of a recently published study by Merrick et al. on the conversion of cannabidiol (CBD) to delta-8 and delta-9-tetrahydrocannabinol (THC) in simulated gastric fluid. In response, this article aims to provide a thorough review of the in vitro and in vivo studies of gastric CBD conversion as well as potential consequences resulting from such conversion. Findings highlight (1) consistent evidence over the past half century of gastric conversion of CBD, (2) evidence from human studies, indicating the importance of testing for THC metabolites as well as a number of other cannabinoids in the detection of such conversion, and (3) THC-like effects after administration of oral CBD in humans that may not only stem from CBD's conversion to THC, but also its conversion to 9α-hydroxy-hexahydrocannabinol and 8α-hydroxy-iso-hexahydrocannabinol. These findings, coupled with a number of limitations in the existing literature, point to the need for large-scale human studies, specifically designed to explore gastric conversion and potential THC-like side effects after oral administration of CBD.

Identification of Psychoactive Degradants of Cannabidiol in Simulated Gastric and Physiological Fluid.

Introduction: In recent research, orally administered cannabidiol (CBD) showed a relatively high incidence of somnolence in a pediatric population. Previous work has suggested that when CBD is exposed to an acidic environment, it degrades to Δ9-tetrahydrocannabinol (THC) and other psychoactive cannabinoids. To gain a better understanding of quantitative exposure, we completed an in vitro study by evaluating the formation of psychoactive cannabinoids when CBD is exposed to simulated gastric fluid (SGF). Methods: Materials included synthetic CBD, Δ8-THC, and Δ9-THC. Linearity was demonstrated for each component over the concentration range used in this study. CBD was spiked into media containing 1% sodium dodecyl sulfate (SDS). Samples were analyzed using chromatography with UV and mass spectrometry detection. An assessment time of 3 h was chosen as representative of the maximal duration of exposure to gastric fluid. Results: CBD in SGF with 1% SDS was degraded about 85% after 60 min and more than 98% at 120 min. The degradation followed first-order kinetics at a rate constant of -0.031 min-1 (R2=0.9933). The major products formed were Δ9-THC and Δ8-THC with less significant levels of other related cannabinoids. CBD in physiological buffer performed as a control did not convert to THC. Confirmation of THC formation was demonstrated by comparison of mass spectral analysis, mass identification, and retention time of Δ9-THC and Δ8-THC in the SGF samples against authentic reference standards. Conclusions: SGF converts CBD into the psychoactive components Δ9-THC and Δ8-THC. The first-order kinetics observed in this study allowed estimated levels to be calculated and indicated that the acidic environment during normal gastrointestinal transit can expose orally CBD-treated patients to levels of THC and other psychoactive cannabinoids that may exceed the threshold for a physiological response. Delivery methods that decrease the potential for formation of psychoactive cannabinoids should be explored.

Microneedle-assisted percutaneous delivery of naltrexone hydrochloride in yucatan minipig: in vitro-in vivo correlation.

Although microneedle-assisted transdermal drug delivery has been the subject of multiple scientific investigations, very few attempts have been made to quantitatively relate in vitro and in vivo permeation. The case of naltrexone hydrochloride is not an exception. In the present study, a pharmacokinetic profile obtained following a "poke and patch" microneedle application method in the Yucatan minipig is reported. The profile demonstrates a rapid achievement of maximum naltrexone hydrochloride plasma concentration followed by a relatively abrupt concentration decline. No steady state was achieved in vivo. In an attempt to correlate the present in vivo findings with formerly published in vitro steady-state permeation data, a diffusion-compartmental mathematical model was developed. The model incorporates two parallel permeation pathways, barrier-thickness-dependent diffusional resistance, microchannel closure kinetics, and a pharmacokinetic module. The regression analysis of the pharmacokinetic data demonstrated good agreement with an independently calculated microchannel closure rate and in vitro permeation data. Interestingly, full-thickness rather than split-thickness skin employed in in vitro diffusion experiments provided the best correlation with the in vivo data. Data analysis carried out with the model presented herein provides new mechanistic insight and permits predictions with respect to pharmacokinetics coupled with altered microchannel closure rates.

Diclofenac enables unprecedented week-long microneedle-enhanced delivery of a skin impermeable medication in humans.

PURPOSE: Microneedles applied to the skin create micropores, allowing transdermal drug delivery of skin-impermeable compounds. The first human study with this technique demonstrated delivery of naltrexone (an opioid antagonist) for two to three days. Rapid micropore closure, however, blunts the delivery window. Application of diclofenac (an anti-inflammatory) allows seven days of naltrexone delivery in animals. The purpose of the current work was to demonstrate delivery of naltrexone for seven days following one microneedle treatment in humans. METHODS: Human subjects were treated with microneedles, diclofenac (or placebo), and naltrexone. Impedance measurements were used as a surrogate marker to measure micropore formation, and plasma naltrexone concentrations were measured for seven days post-microneedle application. RESULTS: Impedance dropped significantly from baseline to post-microneedle treatment, confirming micropore formation. Naltrexone was detected for seven days in Group 1 (diclofenac + naltrexone, n = 6), vs. 72 h in Group 2 (placebo + naltrexone, n = 2). At study completion, a significant difference in impedance was observed between intact and microneedle-treated skin in Group 1 (confirming the presence of micropores). CONCLUSION: This is the first study demonstrating week-long drug delivery after one microneedle application, which would increase patient compliance and allow delivery of therapies for chronic diseases.

Diclofenac enables prolonged delivery of naltrexone through microneedle-treated skin.

PURPOSE: The purpose of this study was to determine if non-specific COX inhibition could extend pore lifetime in hairless guinea pigs following microneedle treatment. METHODS: Hairless guinea pigs were treated with microneedle arrays ± daily application of Solaraze® gel (3% diclofenac sodium (non-specific COX inhibitor) and 2.5% hyaluronic acid); transepidermal water loss was utilized to evaluate pore lifetime. To examine the permeation of naltrexone, additional guinea pigs were treated with microneedles ± daily Solaraze® gel followed by application of a 16% transdermal naltrexone patch; pharmacokinetic analysis of plasma naltrexone levels was performed. Histological analysis was employed to visualize morphological changes following microneedle and Solaraze® treatment. RESULTS: Animals treated with microneedles + Solaraze® displayed extended pore lifetime (determined by transepidermal water loss measurements) for up to 7 days. Enhanced naltrexone permeation was also observed for an extended amount of time in animals treated with microneedles + Solaraze®. No morphological changes resulting from microneedle treatment or COX inhibition were noted. CONCLUSIONS: Non-specific COX inhibition is an effective means of extending pore lifetime following microneedle treatment in hairless guinea pigs. This may have clinical implications for extending transdermal patch wear time and therefore increasing patient compliance with therapy.

Transdermal delivery of naltrexol and skin permeability lifetime after microneedle treatment in hairless guinea pigs.

Controlled-release delivery of 6-beta-naltrexol (NTXOL), the major active metabolite of naltrexone, via a transdermal patch is desirable for treatment of alcoholism. Unfortunately, NTXOL does not diffuse across skin at a therapeutic rate. Therefore, the focus of this study was to evaluate microneedle (MN) skin permeation enhancement of NTXOL's hydrochloride salt in hairless guinea pigs. Specifically, these studies were designed to determine the lifetime of MN-created aqueous pore pathways. MN pore lifetime was estimated by pharmacokinetic evaluation, transepidermal water loss (TEWL) and visualization of MN-treated skin pore diameters using light microscopy. A 3.6-fold enhancement in steady-state plasma concentration was observed in vivo with MN treated skin with NTXOL.HCl, as compared to NTXOL base. TEWL measurements and microscopic evaluation of stained MN-treated guinea pig skin indicated the presence of pores, suggesting a feasible nonlipid bilayer pathway for enhanced transdermal delivery. Overall, MN-assisted transdermal delivery appears viable for at least 48 h after MN-application.

Human skin permeation of 3-O-alkyl carbamate prodrugs of naltrexone.

N-Monoalkyl and N,N-dialkyl carbamate prodrugs of naltrexone (NTX), an opioid antagonist, were synthesized and their in vitro permeation across human skin was determined. Relevant physicochemical properties were also determined. Most prodrugs exhibited lower melting points, lower aqueous solubilities, and higher oil solubilities than NTX. The flux values from N-monoalkyl carbamate prodrugs were significantly higher than those from NTX and N,N-dialkyl carbamates. The melting points of N-monoalkyl carbamate prodrugs were quite low compared to the N,N-dialkyl carbamate prodrugs and NTX. Heats of fusion for the N,N-dialkyl carbamate prodrugs were higher than that for NTX. N-Monoalkyl carbamate prodrugs had higher stratum corneum/vehicle partition coefficients than their N,N-dialkyl counterparts. Higher percent prodrug bioconversion to NTX in skin appeared to be related to increased skin flux. N,N-Dialkyl carbamate prodrugs were more stable in buffer and in plasma than N-monoalkyl carbamate prodrugs. In conclusion, N-monoalkyl carbamate prodrugs of NTX improved the systemic delivery of NTX across human skin in vitro. N,N-Dialkyl substitution in the prodrug moiety decreased skin permeation and plasma hydrolysis to the parent drug. The cross-sectional area of the carbamate head group was the major determinant of flux of the N-monoalkyl and N,N-dialkyl carbamate prodrugs of NTX.

Flux across [corrected] microneedle-treated skin is increased by increasing charge of naltrexone and naltrexol in vitro.

PURPOSE: The purpose of this investigation was to evaluate the in vitro microneedle (MN) enhanced percutaneous absorption of naltrexone hydrochloride salt (NTX x HCl) compared to naltrexone base (NTX) in hairless guinea pig skin (GP) and human abdominal skin. In a second set of experiments, permeability of the major active metabolite 6-beta-naltrexol base (NTXOL) in the primarily unionized (unprotonated) form at pH 8.5 was compared to the ionized form (pH 4.5). METHODS: In vitro fluxes of NTX, NTX.HCl and ionized and unionized NTXOL were measured through microneedle treated or intact full thickness human and GP skin using a flow through diffusion apparatus. Solubility and diffusion samples were analyzed by HPLC. RESULTS: Both GP and human skin show significant increases in flux when treated with 100 MN insertions as compared to intact full thickness skin when treated with NTX.HCl or ionized NTXOL (pH 4.5; p < 0.05). MN increased GP skin permeability for the hydrophilic HCL salt of NTX by tenfold and decreased lag time by tenfold too. Similar results were found using human skin, such that skin permeability to NTX.HCl was elevated to 7.0 x 10(-5) cm/h. Permeability of the primarily unionized (unprotonated) form of NTXOL at pH 8.5 was increased by MN only threefold and lag time was only modestly reduced. However, MN treatment with the primarily ionized (protonated) form of NTXOL at pH 4.5 increased skin permeability fivefold and decreased lag time fourfold. CONCLUSION: Enhancement was observed in vitro in both GP and human skin treated with MN compared to intact skin with the salt form of NTX and the ionized form of NTXOL. We conclude that transdermal flux can be optimized by using MN in combination with charged (protonated) drugs that have increased solubility in an aqueous patch reservoir and increased permeability through aqueous pathways created by MN in the skin.

Microneedles permit transdermal delivery of a skin-impermeant medication to humans.

Drugs with poor oral bioavailability usually are administered by hypodermic injection, which causes pain, poor patient compliance, the need for trained personnel, and risk of infectious disease transmission. Transdermal (TD) delivery provides an excellent alternative, but the barrier of skin's outer stratum corneum (SC) prevents delivery of most drugs. Micrometer-scale microneedles (MNs) have been used to pierce animal and human cadaver skin and thereby enable TD delivery of small molecules, proteins, DNA, and vaccines for systemic action. Here, we present a clinical study of MN-enhanced delivery of a medication to humans. Naltrexone (NTX) is a potent mu-opioid receptor antagonist used to treat opiate and alcohol dependence. This hydrophilic and skin-impermeant molecule was delivered from a TD patch to healthy human subjects with and without pretreatment of the skin with MNs. Whereas delivery from a standard NTX TD patch over a 72-h period yielded undetectable drug plasma levels, pretreatment of skin with MNs achieved steady-state plasma concentrations within 2 h of patch application and were maintained for at least 48 h. The MNs and NTX patch were well tolerated with mild systemic and application site side effects. The MN arrays were painless upon administration and not damaged during skin insertion, and no MNs were broken off into the skin. This human proof-of-concept study demonstrates systemic administration of a hydrophilic medication by MN-enhanced TD delivery. These findings set the stage for future human studies of skin-impermeant medications and biopharmaceuticals for clinical applications.

Human skin permeation of branched-chain 3-0-alkyl ester and carbonate prodrugs of naltrexone.

PURPOSE: Physicochemical characterization and in vitro human skin diffusion studies of branched-chain ester and carbonate prodrugs of naltrexone (NTX) were compared and contrasted with straight-chain ester and carbonate NTX prodrugs. METHODS: Human skin permeation rates, thermal parameters, solubilities in mineral oil and buffer, and stabilities in buffer and plasma were determined. Partition coefficients between stratum corneum and vehicle were determined for straight- and branched-chain esters with the same number of carbon atoms. RESULTS: Branched prodrugs had lower melting points, lower buffer solubilities, and higher mineral oil solubilities than NTX. The transdermal flux values from all of these branched prodrugs were significantly lower than flux values from the straight-chain ester and the methyl carbonate prodrugs. Straight-chain prodrugs had higher partition coefficient values and higher calculated thermodynamic activities than their branched-chain counterparts. The prodrug hydrolysis to NTX in buffer and plasma was slower for prodrugs with increased branching. CONCLUSIONS: Branched-chain prodrugs with bulky moieties had smaller stratum corneum-vehicle partition coefficients and lower thermodynamic activities that resulted in smaller transdermal flux values than straight-chain prodrugs.