Effects of membrane transport activity and cell metabolism on the unbound drug concentrations in the skeletal muscle and liver of drugs: A microdialysis study in rats.

The unbound concentrations of 14 commercial drugs, including five non-efflux/uptake transporter substrates-Class I, five efflux transporter substrates-class II and four influx transporter substrates-Class III, were simultaneously measured in rat liver, muscle, and blood via microanalysis. Kpuu,liver and Kpuu,muscle were calculated to evaluate the membrane transport activity and cell metabolism on the unbound drug concentrations in the skeletal muscle and liver. For Class I compounds, represented by antipyrine, unbound concentrations among liver, muscle and blood are symmetrically distributed when compound hepatic clearance is low. And when compound hepatic clearance is high, unbound concentrations among liver, muscle and blood are asymmetrically distributed, such as Propranolol. For Class II and III compounds, overall, the unbound concentrations among liver, muscle, and blood are asymmetrically distributed due to a combination of hepatic metabolism and efflux and/or influx transporter activity.

Diphenhydramine pharmacokinetics after oral and intravenous administration of diphenhydramine and oral administration of dimenhydrinate to healthy dogs, and pharmacodynamic effect on histamine-induced wheal formation: a pilot study.

BACKGROUND: Histamine type-1 (H1) receptor antagonists such as diphenhydramine are frequently used for treatment of pruritus in dogs, yet therapeutic efficacy for allergic disorders is reported to be highly variable. Dimenhydrinate is a salt of diphenhydramine and 8-chlorotheophylline, and has been reported to produce superior oral absorption of diphenhydramine. HYPOTHESIS/OBJECTIVE: To determine the pharmacokinetic and pharmacodynamic properties of diphenhydramine in dogs after intravenous (1 mg/kg) and oral (5 mg/kg) administration, and when given orally as dimenhydrinate at a dose of 10 mg/kg (≈5 mg/kg diphenhydramine). ANIMALS: Each drug was administered to six healthy, fasted mixed-breed dogs in a research facility, using a cross-over design. METHODS AND MATERIALS: Blood samples were collected for pharmacokinetic analysis of diphenhydramine and chlorotheophylline at defined intervals. Pharmacodynamic response was measured by histamine-mediated cutaneous wheal formation. RESULTS: There was great variability in the data and one dog was an extreme outlier. The mean systemic availabilities of diphenhydramine were 7.8% and 22.0% after oral administration of diphenhydramine and dimenhydrinate, respectively, whereas the mean maximum concentrations were 36 (± 20) and 124 (± 46) ng/mL. The terminal elimination half-lives of diphenhydramine and dimenhydrinate were 5.0 (± 7.1) and 11.6 (± 17.7) h, respectively. Plasma diphenhydramine concentrations did not correlate with the percentage reduction in histamine-induced wheal formation. Theophylline reached plasma concentrations considered to be therapeutic for dogs. CONCLUSION: Oral absorption of diphenhydramine was approximately three times greater with a longer half-life when it was administered as the combination product dimenhydrinate.

Determination of d-amphetamine and diphenhydramine in beagle dog plasma by a 96-well formatted liquid-liquid extraction and capillary zone electrophoresis with field-amplified sample stacking.

This paper describes a method for quantification of d-amphetamine and diphenhydramine in beagle dog plasma by organic solvent field-amplified sample stacking (FASS)-capillary zone electrophoresis (CZE), using amlodipine as the internal standard. The separation was carried out at 25 °C in a 40.2 cm × 75 µm fused-silica capillary with an applied voltage of 20 kV using 25 mM phosphate-18.75 mM borate (pH 3.5). The detection wavelength was 200 nm. Clean-up and preconcentration of plasma biosamples were developed by 96-well formatted liquid- liquid extraction (LLE). In this study, the peak areas of d-amphetamine, diphenhydramine and amlodipine in the plasma sample increased by the factor of 48, 67 and 43 compared to the CZE without sample stacking. The method was suitably validated with respect to stability, specificity, linearity, lower limit of quantitation, accuracy, precision and extraction recovery. The calibration graph was linear from 2 to 500 ng/ml for d-amphetamine and 2-5000 ng/ml for diphenhydramine. All the validation data were within the required limits. Compared with the LC/MS/MS method that we previously established, there was no significant difference between the two methods in validation characteristics, except the LLOQs. The developed method was successfully applied to the evaluation of pharmacokinetic study of the Quick-Acting Anti-Motion Capsules (QAAMC) in beagle dogs.

Quantitative prediction of histamine H1 receptor occupancy by the sedative and non-sedative antagonists in the human central nervous system based on systemic exposure and preclinical data.

Significant histamine H1 receptor occupation in the central nervous system (CNS) is associated with sedation. Here we examined the time profiles of the H1 receptor occupancy (RO) in the CNS using sedative (diphenhydramine and ketotifen) and non-sedative (bepotastine and olopatadine) antagonists at their therapeutic doses by integrating in vitro and animal data. A pharmacokinetic model was constructed to associate plasma concentrations and receptor binding in the brain. Dissociation and association rate constants with the H1 receptor and plasma and brain unbound fractions were determined in vitro. Passive and active clearances across the blood-brain barrier (BBB) were estimated based on physicochemical properties and microdialysis studies in mice and monkeys. The estimated RO values were comparable with the reported values determined at time to maximum concentration (Tmax) of plasma by positron-emission tomography in humans. The simulation suggested that the predicted maximum ROs by bepotastine and olopatadine were greater than the reported values. Sensitivity analysis showed that active transport across BBB had a significant impact on the RO duration of the H1 antagonists examined. The present study demonstrated that modeling and simulation permits a reasonable RO estimation in the human CNS. Our findings will facilitate the development of CNS-acting drugs.

Diphenhydramine as a selective probe to study H+-antiporter function at the blood-brain barrier: Application to [11C]diphenhydramine positron emission tomography imaging.

Diphenhydramine, a sedative histamine H1-receptor (H1R) antagonist, was evaluated as a probe to measure drug/H+-antiporter function at the blood-brain barrier. In situ brain perfusion experiments in mice and rats showed that diphenhydramine transport at the blood-brain barrier was saturable, following Michaelis-Menten kinetics with a Km = 2.99 mM and Vmax = 179.5 nmol s-1 g-1. In the pharmacological plasma concentration range the carrier-mediated component accounted for 77% of diphenhydramine influx while passive diffusion accounted for only 23%. [14C]Diphenhydramine blood-brain barrier transport was proton and clonidine sensitive but was influenced by neither tetraethylammonium, a MATE1 (SLC47A1), and OCT/OCTN (SLC22A1-5) modulator, nor P-gp/Bcrp (ABCB1a/1b/ABCG2) deficiency. Brain and plasma kinetics of [11C]diphenhydramine were measured by positron emission tomography imaging in rats. [11C]Diphenhydramine kinetics in different brain regions were not influenced by displacement with 1 mg kg-1 unlabeled diphenhydramine, indicating the specificity of the brain positron emission tomography signal for blood-brain barrier transport activity over binding to any central nervous system target in vivo. [11C]Diphenhydramine radiometabolites were not detected in the brain 15 min after injection, allowing for the reliable calculation of [11C]diphenhydramine brain uptake clearance (Clup = 0.99 ± 0.18 mL min-1 cm-3). Diphenhydramine is a selective and specific H+-antiporter substrate. [11C]Diphenhydramine positron emission tomography imaging offers a reliable and noninvasive method to evaluate H+-antiporter function at the blood-brain barrier.

Limitations of the Anticholinergic Activity Assay and Assay-Based Anticholinergic Drug Scales.

OBJECTIVE: The anticholinergic activity (AA) assay is a common method to determine a patient's anticholinergic load. Several limitations, however, are expected when applying the AA assay to patients or using drug scales to estimate anticholinergic burden based on AA levels. This study aims to demonstrate common pitfalls in an experimental setting and outline their clinical consequences. METHODS: The AA was analyzed for five drugs with reported interaction with muscarinic receptors. Concentration-response curves were constructed for furosemide (weak anticholinergic), diphenhydramine (moderate anticholinergic), the strong anticholinergic amitriptyline and its metabolite nortriptyline, and the cholinergic pilocarpine. The Combination Index (CI) was used to assess the interaction of three drug combinations with amitriptyline. RESULTS: All compounds displaced the radioactive tracer from its receptor binding site in a concentration-dependent manner, and full displacement was reached for all compounds except furosemide (Emax 16%). The CI indicated that amitriptyline and thioridazine have antagonistic effects (CI = 1.46) at low and synergistic effects (CI = 0.88) at higher concentrations (p < 0.0001), whereas synergistic effects (CI = 0.47-0.48) were observed for amitriptyline in any concentration combined with pilocarpine (p < 0.001). CONCLUSION: When the patient's anticholinergic load is estimated using AA levels, the actual exposure, combination of anticholinergic drugs, their active metabolites, and also drugs with an opposite pharmacologic action will contribute to AA levels, whereas weak anticholinergic drugs in therapeutic concentrations are rather negligible.

Prevalence of alcohol and drug use in injured British Columbia drivers.

OBJECTIVES: Determine the prevalence of drug use in injured drivers and identify associated demographic factors and crash characteristics. DESIGN: Prospective cross-sectional study. SETTING: Seven trauma centres in British Columbia, Canada (2010-2012). PARTICIPANTS: Automobile drivers who had blood obtained within 6 h of a crash. MAIN OUTCOME MEASURES: We analysed blood for cannabis, alcohol and other impairing drugs using liquid chromatography/mass spectrometry (LCMS). RESULTS: 1097 drivers met inclusion criteria. 60% were aged 20-50 years, 63.2% were male and 29.0% were admitted to hospital. We found alcohol in 17.8% (15.6% to 20.1%) of drivers. Cannabis was the second most common recreational drug: cannabis metabolites were present in 12.6% (10.7% to 14.7%) of drivers and we detected Δ-9-tetrahydrocannabinol (Δ-9-THC) in 7.3% (5.9% to 9.0%), indicating recent use. Males and drivers aged under 30 years were most likely to use cannabis. We detected cocaine in 2.8% (2.0% to 4.0%) of drivers and amphetamines in 1.2% (0.7% to 2.0%). We also found medications including benzodiazepines (4.0% (2.9% to 5.3%)), antidepressants (6.5% (5.2% to 8.1%)) and diphenhydramine (4.7% (3.5% to 6.2%)). Drivers aged over 50 years and those requiring hospital admission were most likely to have used medications. Overall, 40.1% (37.2% to 43.0%) of drivers tested positive for alcohol or at least one impairing drug and 12.7% (10.7% to 14.7%) tested positive for more than one substance. CONCLUSIONS: Alcohol, cannabis and a broad range of other impairing drugs are commonly detected in injured drivers. Alcohol is well known to cause crashes, but further research is needed to determine the impact of other drug use, including drug-alcohol and drug-drug combinations, on crash risk. In particular, more work is needed to understand the role of medications in causing crashes to guide driver education programmes and improve public safety.

The pharmacokinetics of DPH after the administration of a single intravenous or intramuscular dose in healthy dogs.

The objective of this study was to determine the pharmacokinetics of diphenhydramine (DPH) in healthy dogs following a single i.v. or i.m. dose. Dogs were randomly allocated in two treatment groups and received DPH at 1 mg/kg, i.v., or 2 mg/kg, i.m. Blood samples were collected serially over 24 h. Plasma concentrations of DPH were determined by high-performance liquid chromatography, and noncompartmental pharmacokinetic analysis was performed with the commercially available software. Cardio-respiratory parameters, rectal temperature and effects on behaviour, such as sedation or excitement, were recorded. Diphenhydramine Clarea , Vdarea and T1/2 were 20.7 ± 2.9 mL/kg/min, 7.6 ± 0.7 L/kg and 4.2 ± 0.5 h for the i.v. route, respectively, and Clarea /F, Vdarea /F and T1/2 20.8 ± 2.7 mL/kg/min, 12.3 ± 1.2 L/kg and 6.8 ± 0.7 h for the i.m. route, respectively. Bioavailability was 88% after i.m. administration. No significant differences were found in physiological parameters between groups or within dogs of the same group, and values remained within normal limits. No adverse effects or changes in mental status were observed after the administration of DPH. Both routes of administration resulted in DPH plasma concentrations which exceeded levels considered therapeutic in humans.

Multidrug-related leukocytoclastic vasculitis raising suspicion of sexual homicide-things are not always what they seem.

Ambiguous findings during external examination of a deceased in combination with dubious autopsy findings can raise doubts concerning the manner and cause of death. We report the case of a 35-year-old female deceased who had suffered from a borderline personality and depressive disorder with suicidal ideation. At the death scene, the body showed massive facial swelling accompanied by complete reddening of the skin of the face, with patchy skin abrasions on the forehead and neck, and purple bruise-like discolorations distributed symmetrically over both shoulders, elbows, hands, hips, knees, lower legs, and feet, raising the suspicion of underlying massive external blunt force injury. Police investigators strongly suspected sexual homicide. At autopsy, dissection in layers revealed massive subcutaneous hemorrhages as the cause of the reddish skin discolorations. Toxicological analyses showed fatal levels of lamotrigine with additional proof of zopiclone, zolpidem, diphenhydramine, O-desmethylvenlafaxine, pregabalin, tramadol, and modafinil in venous blood. Histologically, both the macroscopically impressive purple skin changes with underlying bleeding into the subcutaneous tissue and the skin abrasions were due to leukocytoclastic vasculitis, a form of acute hypersensitivity vasculitis that was a reaction to the multiple therapeutic drugs that the woman had taken shortly before death. The manner of death was classified as suicide, and sexual homicide was ruled out.

Observed and modeled effects of pH on bioconcentration of diphenhydramine, a weakly basic pharmaceutical, in fathead minnows.

A need exists to better understand the influence of pH on the uptake and accumulation of ionizable pharmaceuticals in fish. In the present study, fathead minnows were exposed to diphenhydramine (DPH; disassociation constant = 9.1) in water for up to 96 h at 3 nominal pH levels: 6.7, 7.7, and 8.7. In each case, an apparent steady state was reached by 24 h, allowing for direct determination of the bioconcentration factor (BCF), blood-water partitioning (PBW,TOT), and apparent volume of distribution (approximated from the whole-body-plasma concentration ratio). The BCFs and measured PBW,TOT values increased in a nonlinear manner with pH, whereas the volume of distribution remained constant, averaging 3.0 L/kg. The data were then simulated using a model that accounts for acidification of the gill surface caused by elimination of metabolically produced acid. Good agreement between model simulations and measured data was obtained for all tests by assuming that plasma binding of ionized DPH is 16% that of the neutral form. A simpler model, which ignores elimination of metabolically produced acid, performed less well. These findings suggest that pH effects on accumulation of ionizable compounds in fish are best described using a model that accounts for acidification of the gill surface. Moreover, measured plasma binding and volume of distribution data for humans, determined during drug development, may have considerable value for predicting chemical binding behavior in fish.

Multi-drug and metabolite quantification in postmortem blood by liquid chromatography-high-resolution mass spectrometry: comparison with nominal mass technology.

High-resolution mass spectrometry (HRMS) is being applied in postmortem drug screening as an alternative to nominal mass spectrometry, and additional evaluation in quantitative casework is needed. We report quantitative analysis of benzoylecgonine, citalopram, cocaethylene, cocaine, codeine, dextromethorphan, dihydrocodeine, diphenhydramine, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine, hydrocodone, hydromorphone, meperidine, methadone, morphine, oxycodone and oxymorphone in postmortem blood by ultra-performance liquid chromatography (UPLC)-MS(E)/time-of-flight (TOF). The method employs analyte-matched deuterated internal standardization and MS(E) acquisition of precursor and product ions at low (6 eV) and ramped (10-40 eV) collision energies, respectively. Quantification was performed using precursor ion data obtained with a mass extraction window of ± 5 ppm. Fragment and residual precursor ion acquisitions at ramped collision energies were evaluated as additional analyte identifiers. Extraction recovery of >60% and matrix effect of <20% were determined for all analytes and internal standards. Defined limits of detection (10 ng/mL) and quantification (25 ng/mL) were validated along with a linearity analytical range of 25-3,000 ng/mL (R(2) > 0.99) for all analytes. Parallel UPLC-MS(E)/TOF and UPLC-MS/MS analysis showed comparable precision and bias along with concordance of 253 positive (y = 1.002x + 1.523; R(2) = 0.993) and 2,269 negative analyte findings in 159 postmortem cases. Analytical performance and correlation studies demonstrate accurate quantification by UPLC-MS(E)/TOF and extended application of HRMS in postmortem casework.

Diphenhydramine's role in death investigations: an examination of diphenhydramine prevalence in 2 US geographical areas.

PURPOSE: Diphenhydramine (DPH), an over-the-counter first-generation H1 receptor antagonist, is not a common drug of abuse; however, it is encountered in cases of overdose both in the clinical setting and in death investigations. The toxicology laboratories in the Tarrant County Medical Examiner's Office and the District of Columbia Office of The Chief Medical Examiner analyze antemortem and postmortem specimens. Presented are the findings of this evaluation and detailed histories of cases involving DPH. METHODS: Toxicology reports, autopsy reports, and death investigator narratives were obtained in cases involving DPH at toxic and lethal levels in which this compound was the primary cause or a contributing factor in the death. RESULTS: Blood concentrations were quantified at a range of 2870 to 21,263 ng/mL. A rare occurrence of DPH abuse via documented intravenous administration leading to death is presented. The cases presented here generally involved much higher concentrations of DPH and an older population than those in previous published data regarding DPH's role in death investigation and abuse. CONCLUSIONS: As people seek legal alternative drugs to abuse and with the ease of obtaining information via online forums, there is a potential to see an increase in the number of cases involving excessive use of DPH.

A polydrug intoxication involving methoxetamine in a drugs and driving case.

Methoxetamine ((RS)2-(3-methoxyphenyl)-2-(ethylamino)cyclohexanone)) is becoming a drug of interest among practitioners of forensic toxicology. In this case report, we describe the case background, standard field sobriety tests, sampling, and analysis of this drug in a whole blood sample as well as screening methods and analysis from a driver operating under the influence of intoxicating substances. Methoxetamine was isolated from the blood sample using mixed mode solid phase extraction. After elution and evaporation, the residue was dissolved in mobile phase (consisting of acetonitrile and aqueous formic acid) for analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and gas chromatography-mass spectrometry (GC-MS). The case sample was found to contain clonazepam, 7-aminoclonazepam, carboxy-THC, Ddphenhydramine, and MDMA. The case sample was found to contain 10 ng/mL of the drug (methoxetamine) in whole blood. The results of this drug analysis and previous analyses are discussed in terms of this driver operating under the influence of drugs.

The role of hepatic transport and metabolism in the interactions between pravastatin or repaglinide and two rOatp inhibitors in rats.

A change in the function or expression of hepatic drug transporters may have significant effect on the efficacy or safety of orally administered drugs. Although a number of clinical drug-drug interactions associated with hepatic transport proteins have been reported, in practice it is not always straightforward to discriminate other pathways (e.g. drug metabolism) from being involved in these interactions. The present study was designed to assess the interactions between organic anion transporting polypeptide (Oatp) substrates (pravastatin or repaglinide) and inhibitors (spironolactone or diphenhydramine) in vivo in rats. The mechanisms behind the interactions were then investigated using in vitro tools (isolated hepatocytes and rat liver microsomes). The results showed a significant increase in the systemic exposures of pravastatin (2.5-fold increase in AUC) and repaglinide (1.8-fold increase in AUC) after co-administration of spironolactone to rats. Diphenhydramine increased the AUC of repaglinide by 1.4-fold. The in vivo interactions observed in rats between Oatp substrates and inhibitors may a priori be classified as transport-mediated drug-drug interactions. However, mechanistic studies performed in vitro using both isolated rat hepatocytes and rat liver microsomes showed that the interaction between pravastatin and spironolactone may be solely linked to the inhibition of pravastatin uptake in liver. On the contrary, the inhibition of cytochrome P450 seemed to be the reason for the interactions observed between repaglinide and spironolactone. Although the function and structure of transport proteins may vary between rats and humans, the approach used in the present study can be applied to humans and help to understand the role of drug transport and drug metabolism in a given drug-drug interaction. This is important to predict and mitigate the risk of drug-drug interactions for a candidate drug in pre-clinical development, it is also important for the optimal design of drug-drug interactions studies in the clinic.

Acetaminophen/diphenhydramine overdose in profound hypothermia.

BACKGROUND: There are few reports of acetaminophen overdose in hypothermic patients and even fewer reports describing profound hypothermia. The kinetics, risk of hepatotoxicity, and the possible dose adjustments to N-acetylcysteine (NAC) therapy are not known in this setting. CASE REPORT: A 37-year-old female was found unconscious outside in December and was brought by ambulance to a tertiary care Emergency Department (ED) following a presumed overdose of acetaminophen and diphenhydramine. She later confirmed the ingestion and reported the ingestion had occurred approximately 18 hours prior to being found. On arrival, she was profoundly hypothermic, with a core rectal temperature of 17°C. Her initial serum acetaminophen concentration was 232 mcg/mL 19 hours post ingestion of a reported dose of approximately 50 grams of acetaminophen and 2.5 grams of diphenhydramine. Active rewarming was started immediately and IV NAC was initiated using the standard treatment protocol. The patient did not develop serious signs of hepatic injury or NAC toxicity. The patient's AST and ALT peaked 12 hours after admission at 84 IU/L (ref 10-37 U/L) and 104 IU/L (ref 12-78 U/L), respectively. Her INR peaked 2 hours after admission at 1.46 (ref < 1.2). DISCUSSION: Despite the significant ingestion of acetaminophen, delayed presentation, prolonged period of decreased responsiveness, and profound hypothermia, the patient did not develop any signs/symptoms of liver injury. NAC was administered in a standard dose during her rewarming period without apparent toxicity. The patient's absorption and/or metabolism of acetaminophen were likely slowed by her hypothermia and possibly by the anticholinergic coingestant. Initiation of IV NAC at a standard dose was apparently safe and effective in preventing hepatotoxicity as the patient was rewarmed. CONCLUSIONS: Profound hypothermia may be protective of hepatic injury in acetaminophen overdose. Delayed absorption from the coingestant, diphenhydramine, may also have played a role. IV NAC was given in a standard dose without apparent toxicity in the setting of profound hypothermia. Lastly, IV NAC, in standard dosing, appeared to be effective in preventing hepatotoxicity during rewarming in a patient with a potentially hepatotoxic concentration of acetaminophen with a coingestion of the anticholinergic agent, diphenhydramine.

Toxicological identification of diphenhydramine (DPH) in suicide.

Diphenhydramine (DPH), an H1-antihistamine, is identified during postmortem toxicological analyses on a relatively rare but still regular basis. This study examines suicidal intoxications with DPH by analyzing blood and gastric content concentration levels. Twenty cases of DPH intoxications within a 10-year period (2000-2010) were discovered by screening the autopsy records of the Institute of Legal Medicine and Forensic Sciences (ILMFS) in Berlin, Germany. In four cases, DPH levels were lower than 1 µg/mL and hence were not considered likely to be responsible for causing death. In 11 cases, DPH played a role in the fatal episode, and five of these cases were monointoxications. Considering that more than 8,000 autopsies were performed by the ILMFS within the time period under examination, there is only one monointoxication case every 2 years, which makes it a rare occurrence. In two of these intoxications, DPH was only measured in toxic but not "lethal" concentrations in blood, with a concentration of 5 µg/mL being generally used as the cut off between categories according to forensic literature. This raises the question as to whether a strict boundary for a "lethal" blood concentration, as suggested in some literature, can be set and applied in any of these cases. This study shows that an individual interpretation of each case is of utmost importance for correct classification. A thorough toxicological analysis of peripheral venous blood and gastric content, as well as a detailed work-up of the death circumstances, are the basis of an exact interpretation of intoxications with DPH.

Determination of tamsulosin in human plasma by liquid chromatography/tandem mass spectrometry and its application to a pharmacokinetic study.

Tamsulosin, a selective α1-adrenoceptor antagonist, is used for the treatment of benign prostatic hyperplasia (BPH). We developed and validated a rapid, sensitive, and simplified liquid chromatography analytical method utilizing tandem mass spectrometry (LC-MS/MS) for the determination of tamsulosin in human plasma. After liquid-liquid extraction with methyl t-butyl ether, chromatographic separation of tamsulosin was achieved using a reversed-phase Luna C18 column (2.0 mm × 50 mm, 5 µm particles) with a mobile phase of 10 mM ammonium formate buffer (pH 3.5)-methanol (25:75, v/v) and quantified by MS/MS detection in ESI positive ion mode. The flow rate of the mobile phase was 200 µL/min and the retention times of tamsulosin and the internal standard (IS, diphenhydramine) were 0.8 and 0.9 min, respectively. The calibration curves were linear over a range of 0.01-20 ng/mL (r>0.999). The lower limit of quantification using 500 µL of human plasma was 0.01 ng/mL. The mean accuracy and precision for intra- and inter-day validation of tamsulosin were both within acceptable limits. The present LC-MS/MS method showed improved sensitivity for quantification of tamsulosin in human plasma compared with previously described analytical methods. The validated method was successfully applied to a pharmacokinetic study in humans.

ABH gel is not absorbed from the skin of normal volunteers.

BACKGROUND: Lorazepam (Ativan(®)), diphenhydramine (Benadryl(®)), haloperidol (Haldol(®)) (ABH) topical gel is currently widely used for nausea in hospice because of perceived efficacy and low cost and has been suggested for cancer chemotherapy. However, there are no studies of absorption, a prerequisite for effectiveness. We completed this study to establish whether ABH gel drugs are absorbed, as a prerequisite to effectiveness. INTERVENTION: Ten healthy volunteers, aged 25 to 58 years (mean 37 years), two African Americans and eight Caucasian Americans, applied the standard 1.0 mL dose (2mg of lorazepam, 25mg of diphenhydramine, and 2mg of haloperidol in a pluronic lecithin organogel), rubbed on the volar surface of the wrists by the subject. MEASURES: Blood samples were obtained at 0, 30, 60, 90, 120, 180, and 240 minutes. Plasma concentrations were analyzed by liquid chromatography-tandem mass spectrometry using deuterated internal standards for each drug. OUTCOMES: No lorazepam or haloperidol was detected in any sample from any of the 10 volunteers down to a level of 0.05 ng/mL. Diphenhydramine was found in multiple plasma samples at concentrations >0.05 ng/mL in three patients, with the highest concentration of 0.30 ng/mL in one person at 240 minutes. Overall, five of 10 patients exhibited detectable diphenhydramine in one or more samples, supporting limited absorption. No subject noted any side effects. CONCLUSIONS/LESSONS LEARNED: As commonly used, none of the lorazepam, haloperidol, or diphenhydramine in ABH gel is absorbed in sufficient quantities to be effective in the treatment of nausea and vomiting. Diphenhydramine is erratically absorbed at subtherapeutic levels. The efficacy of ABH gel should be confirmed in randomized trials before its use is recommended.

Immunoassay screening of diphenhydramine (Benadryl®) in urine and blood using a newly developed assay.

Diphenhydramine (DPH) is a common over the counter antihistamine that produces drowsiness and has the potential to cause driving under the influence of drugs-related accidents. To date there are no commercially available immunoassay screening kits for its detection in biological fluids such as urine and/or blood. We describe a newly developed enzyme-linked immunosorbent assay (ELISA) screen and report on its utility in the analysis of authentic specimens taken from volunteers. The assay is specific for detection of DPH and does not detect closely related antihistamines like brompheniramine, chlorpheniramine, and doxylamine. There is a varying amount of cross-reactivity seen with certain tricyclic compounds, due to similarities in side chain structure with DPH. Intra- and interday precision of the assay were determined to be less than 10%. The assay is highly sensitive and has a working range from 1 to 500 ng/mL for urine and 1 to 250 ng/mL for blood. The assay was further validated with authentic urine and blood specimens obtained from volunteers and coroner's laboratories.