Biliary excretion of amphetamine and methamphetamine in the rat

Radiation Effects on Methamphetamine Pharmacokinetics and Pharmacodynamics in Rats

BACKGROUND AND OBJECTIVES

Whole-body radiation exposure has been shown to alter the pharmacokinetics of certain drugs in both animal models and humans, but little is known about the effect of radiation on psychoactive medications. These drugs may have altered pharmacokinetics when administered during or after space travel or therapeutic or accidental radiation exposure, resulting in reduced efficacy or increased toxicity.

METHODS

Methamphetamine was used to determine the effects of acutely administered 1, 3, and 6 Gy radiation on drug pharmacokinetics and pharmacodynamics. Male Wistar rats were exposed to 0, 1, 3, or 6 Gy X-ray radiation on day 0. The serum pharmacokinetics of subcutaneously administered 1 mg/kg methamphetamine was determined on day 3. Methamphetamine-induced (1 mg/kg) locomotor activity was measured on day 5. Brain methamphetamine concentrations were determined 2 h after methamphetamine administration (1 mg/kg) on day 6. Renal and hepatic serum biomarkers were assessed on days 3 and 6, with liver histology performed on day 6.

RESULTS

While serum half-life and unchanged methamphetamine urine clearance were unaffected by any radiation dose, maximum methamphetamine concentrations and methamphetamine and amphetamine metabolite area under the serum concentration-time curve values from 0 to 300 min were significantly reduced after 6 Gy radiation exposure. Additionally, methamphetamine-induced locomotor activity and the brain to serum methamphetamine concentration ratio were significantly elevated after 6 Gy radiation.

CONCLUSIONS

While 1-6 Gy radiation exposure did not affect methamphetamine elimination, 6 Gy exposure had effects on both subcutaneous absorption and brain distribution. These effects should be considered when administering drugs during or after radiation exposure.

Teratogen update: Amphetamines

Amphetamines are synthetic noncatecholamine sympathomimetic amines that act as psychostimulants. They have been prescribed for the treatment of attention-deficit/hyperactivity disorder (ADHD), narcolepsy, and additional health conditions. Amphetamines are also drugs of abuse. Some experimental animal studies suggested adverse developmental effects of amphetamines, including structural malformations. These effects were most often observed in experimental animals at higher dose levels than those used for treatment or abuse and at dose levels that produce maternal toxicity. Controlled studies of amphetamine use for the treatment of ADHD and other indications did not suggest that amphetamines are likely to cause structural malformations, although there are three studies associating medication for ADHD or methamphetamine abuse with gastroschisis. We did not locate studies on the neurobehavioral effects of prenatal exposures to therapeutic amphetamine use. Amphetamine abuse was associated with offspring neurobehavioral abnormalities, but lack of adequate adjustment for confounding interferes with interpretation of the associations. Adverse effects of methamphetamine abuse during pregnancy may be due to factors associated with drug abuse rather than methamphetamine itself. The adverse effects observed in methamphetamine abuse studies may not be extrapolatable to amphetamine medication use.

Distribution and pharmacokinetics of methamphetamine in the human body: clinical implications

Background

Methamphetamine is one of the most toxic of the drugs of abuse, which may reflect its distribution and accumulation in the body. However no studies have measured methamphetamine's organ distribution in the human body.

Methods

Positron Emission Tomography (PET) was used in conjunction with [¹¹C]d-methamphetamine to measure its whole-body distribution and bioavailability as assessed by peak uptake (% Dose/cc), rate of clearance (time to reach 50% peak-clearance) and accumulation (area under the curve) in healthy participants (9 Caucasians and 10 African Americans).

Results

Methamphetamine distributed through most organs. Highest uptake (whole organ) occurred in lungs (22% Dose; weight ∼1246 g), liver (23%; weight ∼1677 g) and intermediate in brain (10%; weight ∼1600 g). Kidneys also showed high uptake (per/cc basis) (7%; weight 305 g). Methamphetamine's clearance was fastest in heart and lungs (7–16 minutes), slowest in brain, liver and stomach (>75 minutes), and intermediate in kidneys, spleen and pancreas (22–50 minutes). Lung accumulation of [¹¹C]d-methamphetamine was 30% higher for African Americans than Caucasians (p<0.05) but did not differ in other organs.

Conclusions

The high accumulation of methamphetamine, a potent stimulant drug, in most body organs is likely to contribute to the medical complications associated with methamphetamine abuse. In particular, we speculate that methamphetamine's high pulmonary uptake could render this organ vulnerable to infections (tuberculosis) and pathology (pulmonary hypertension). Our preliminary findings of a higher lung accumulation of methamphetamine in African Americans than Caucasians merits further investigation and questions whether it could contribute to the infrequent use of methamphetamine among African Americans.

Novel biomarkers of prenatal methamphetamine exposure in human meconium

Meconium analysis can detect fetal exposure to drugs taken by the mother during pregnancy. Methamphetamine (MAMP) and amphetamine (AMP) have previously been observed in meconium of MAMP-exposed neonates; the presence of other metabolites has not been investigated. Detection of such analytes may lead to more sensitive identification and thus improved medical treatment of affected infants. Forty-three MAMP-positive meconium specimens were analyzed for newly identified MAMP biomarkers, p-hydroxymethamphetamine, p-hydroxyamphetamine, and norephedrine. Due to MAMP adulteration in illicit ecstasy and to simultaneously monitor 3,4-methylenedioxymethamphetamine and MAMP prenatal exposure, 3,4-methylenedioxymethamphetamine, its metabolites, and related sympathomimetic amines were assayed. MAMP, AMP, and unconjugated p-hydroxymethamphetamine were the most prevalent and abundant analytes present in meconium; however, unconjugated p-hydroxyamphetamine and norephedrine also were identified. It is possible that one of these additional analytes could be important for predicting toxicity or maternal or neonatal outcome measures in fetuses exposed to MAMP at specific gestational ages or with different metabolic capabilities. Although these new biomarkers were present in lower concentrations than MAMP and AMP in the meconium of previously confirmed specimens, additional research will determine if inclusion of these analytes can increase identification of MAMP-exposed neonates. Novel methamphetamine biomarker concentrations were characterized in meconium of infants exposed in utero to MAMP.

Postmortem distribution of 3,4-methylenedioxy-N,N-dimethyl-amphetamine (MDDM or MDDA) in a fatal MDMA overdose

In this manuscript, a newly identified compound, 3,4-methylenedioxy-N,N-dimethylamphetamine (MDDM or also called MDDA), was quantified. The substance was identified in the biological specimens of a 31-year-old man who died following a massive 3,4-methylenedioxymethamphetamine (MDMA) overdose. In addition, the postmortem distribution of the identified substance in various body fluids and tissues was evaluated. For MDDM quantitation, a formerly reported and validated liquid chromatography tandem mass spectrometry (LC-MS/MS) method was adapted. The following quantitative results of the MDDM quantitation were obtained: Femoral blood, aorta ascendens, and right atrial blood contained 2.5, 21.7, and 11.6 ng MDDM/ml, respectively. In left and right pleural fluid and pericardial fluid, concentrations of 47.0, 21.7, and 31.9 ng/ml, respectively, were found. MDDM levels in urine, bile, and stomach contents were 42.4, 1,101, and 1,113 ng/ml, respectively. MDDM concentrations in lungs, liver, kidney, and left cardiac muscle ranged from 12.8 to 39.8 ng/g, whereas these levels were below the limit of quantitation (< LOQ) in right cardiac and iliopsoas muscle. In conclusion, for the first time, MDDM was unambiguously identified in a fatal MDMA overdose. MDDM was probably present as a synthesis by-product or impurity in the MDMA tablets, which were taken in a huge amount by the victim, or MDDM was ingested separately and prior to the MDMA overdose. A third option, i.e., the eventual formation of MDDM as a result of postmortem methylation of MDMA by formaldehyde, produced by putrefaction processes or during storage under frozen conditions, is also discussed. The MDDM levels, substantiated in various body fluids and tissues, are in line with the distribution established for other amphetamine derivatives and confirm that peripheral blood sampling, such as that of femoral blood, remains the "golden standard".

Influence of activated charcoal on the disposition kinetics of methamphetamine enantiomers in the rat following intravenous dosing

Methamphetamine (MAP) is a central nervous system stimulant that is widely abused by populations of several countries. There is no specific antidote for the treatment of an overdose. Activated charcoal administered orally has been used to enhance the systemic elimination of certain toxic substances via "gastrointestinal dialysis". The results of in vitro studies have shown that MAP can be rapidly adsorbed from solution by activated charcoal. We have evaluated the effect of a single oral dose of activated charcoal on the disposition kinetics of MAP following a short iv infusion. Male Sprague-Dawley rats were given an oral dose of activated charcoal (Actidose-aqua, 1 g/kg) 10 min before a short iv infusion of racemic MAP; whereas the control group was given an equivalent volume of water. Enantiomers of MAP and metabolites in serum and urine were analyzed by an enantiomer-specific method which employed HPLC and detection of a fluorescent derivative. There were no differences in any of the disposition parameters between the two groups. Within each group, the clearance (CLs) of l-MAP was greater than that of d-MAP. However, there were no differences in the steady-state volume of distribution (Vss). The CLs (mL/(min kg)) and Vss (L/kg) values for l- and d-MAP in the control group were (mean +/- SD): 55.8 +/- 20.4, 48.7 +/- 17.9, 2.64 +/- 1.16, and 2.90 +/- 1.36, respectively. The corresponding values in the charcoal-pretreated group were (mean +/- SD): 57.4 +/- 23.4, 51.1 +/- 20.7, 2.79 +/- 1.32, and 2.98 +/- 1.47. These results suggest that oral activated charcoal does not enhance the elimination of MAP from the body.

Screening for drugs of abuse. I: Opiates, amphetamines and cocaine

(1) In order to provide an efficient and reliable service for drugs of abuse screening in urine, the laboratory should analyse 20-30 samples per week, and the staff should include a scientist with special expertise in the subject. (2) Turnaround times should be between 2-3 days of sample collection. To achieve this aim it may be necessary to make special arrangements for the delivery of samples to the laboratory. Results should preferably be transmitted by electronic mail or facsimile with the necessary precautions for security and confidentiality: hardcopy reports may also be required. (3) Good communications between the requesting clinician and the laboratory are essential. An advisory service should be provided by the laboratory and clinicians should be encouraged to discuss requests and results with laboratory staff. It is important that the laboratory inform doctors of the range of substances detected and the sensitivity and specificity of laboratory assays. (4) Assays should be performed according to the manufacturer's protocols, or by modified methods that have been rigorously validated. Quality control samples should be included in each analytical run and participation in an external quality assessment scheme, e.g. UKNEQAS, is essential to provide independent confirmation and confidence that results compare with those from other laboratories. Other requirements include adequate training and supervision of staff, and careful recording of samples and results. (5) Drugs to be tested will depend on the drug 'scene' in the area but should include those drugs regularly prescribed for maintenance therapy (e.g. methadone, dihydrocodeine, benzodiazepines), and drugs frequently misused (e.g. heroin, buprenorphine, amphetamines, cocaine). (6) Positive results obtained by preliminary screening methods e.g. EMIT, should be confirmed by another analytical technique, e.g. TLC, GC or GC-MS. If there are potentially serious or legal implications, and in employment and preemployment testing, confirmation of positive results is mandatory. In some cases, e.g. checking for methadone or benzodiazepine compliance, it may be considered unnecessary to confirm positive results although possible spiking of samples cannot be excluded without checking for the presence of metabolites by a chromatographic procedure.

Identification of the biliary metabolites of (+/-)-3-dimethylamino-1,1-diphenylbutane HCl (recipavrin) in rats

1. The in vivo biliary metabolites of (+/-)-3-dimethylamino-1,1-diphenylbutane hydrochloride (recipavrin) isolated from Wistar rats have been characterized by g.l.c.-mass spectrometry. 2. Non-conjugated metabolites include recipavrin (1), norrecipavrin (2), diphenylbutanone (3), diphenylbutanone oxime (4), diphenylbutanone phenol (12), diphenylbutanone oxime phenol (14), recipavrin phenol (19), diphenylbutanone O-methylcatechol (16) and diphenylbutanone oxime O-methylcatechol (18). 3. Following beta-glucuronidase hydrolysis and extraction from pH 10 solution, diphenylbutanone (3), diphenylbutanone oxime (4), an unidentified compound (6), primary amine (8), norrecipavrin (2), recipavrin (1), phenols (12, 14, 15), norrecipavrin phenol (13), O-methylcatechols (16, 18), diphenylbutanol O-methylcatechol (17), recipavrin O-methylcatechol (19) and a secondary formamide (5) were identified by g.l.c.-mass spectrometry. 4. Various extraction solvents were employed in sample workup. The formamide (5) was present regardless of solvent used, while the trace presence of secondary acetamide (7) may be associated with the use of ethyl acetate. 5. Metabolites isolated after beta-glucuronidase hydrolysis were characterized by g.l.c.-mass spectrometry of the underivatized form, and as the trimethylsilyl (TMS) derivatives, or following methylation with diazomethane or trimethylanilinium hydroxide (TMAH).

Urinary and biliary metabolites of mephentermine in male Wistar rats

1. Excretion of urinary and biliary radioactivity, and metabolites of [3H]mephentermine (MP), after i.p. or subcutaneous administration of [3H]MP to male Wistar rats, were determined by preparative t.l.c.-liquid scintillation counting. 2. About 45% of the radioactivity administered i.p. was excreted in the 24 h urine. The major urinary metabolite was conjugated p-hydroxymephentermine (p-hydroxy-MP), which accounted for about 18% of the administered radioactivity in the 24 h urine. 3. About 4.2% of the radioactivity administered subcutaneously was excreted in bile during 24 h. The major biliary metabolite was conjugated p-hydroxy-MP, which accounted for about 39% of the radioactivity excreted in the bile in 24 h. 4. Urinary and biliary minor metabolites detected were phentermine (Ph), p-hydroxyphentermine (p-hydroxy-Ph), N-hydroxyphentermine (N-hydroxy-Ph), N-hydroxymephentermine (N-hydroxy-MP) and their conjugates, and conjugated MP. 5. The conjugates were considered to be glucuronides from the inhibitory effect of saccharic acid 1,4-lactone on their hydrolysis with beta-glucuronidase. 6. Biliary excretion rates of conjugated p-hydroxy-Ph and p-hydroxy-MP reached maxima at 3 to 4 h, and non-conjugated metabolites were maximal at 1 to 2 h, after administration. 50% of the biliary metabolites was excreted within 5 h.

Urinary excretion of p-hydroxylated methamphetamine metabolites in man. II. Effect of alcohol intake on methamphetamine metabolism

The effect of drinking alcoholic beverages on methamphetamine metabolism was investigated in man. The subjects, 97 males and 9 females, were divided into three groups by evaluation of their urinary pH; i.e., acidic, subacidic and neutral groups. The subjects in each group were further divided into ethanol-positive subjects and ethanol-negative subjects, depending on the presence or absence of ethanol in their urine. Gas chromatographic analysis showed the urinary concentrations of methamphetamine in the ethanol-positive subjects to be higher than those in the ethanol-negative subjects in both the acidic and subacidic urinary pH groups. Liquid chromatography, on the other hand, showed the urinary concentrations of p-hydroxymethamphetamine and p-hydroxyamphetamine for the ethanol-positive subjects to be lower than those for the ethanol-negative subjects in all three groups. The relative proportions of p-hydroxylated metabolites to unchanged methamphetamine in urine, therefore, were severely reduced in the ethanol-positive subjects. These results suggest that drinking alcoholic beverages probably results in a suppression of methamphetamine metabolism in man.

Distribution and excretion of methamphetamine and its metabolites in rats. III. Time-course of concentrations in blood and bile, and distribution after intravenous administration

The time-course of blood total radioactivity after i.v. administration of 3H-methamphetamine to rats showed a biphasic curve. The biological half-life of the alpha phase (t alpha 1/2) was 6.8 +/- 2.0 min, and that of the beta phase (t beta 1/2) was 11.3 +/- 0.8 h. The major metabolite in the blood was unconjugated p-hydroxymethamphetamine. The total radioactivity in bile peaked at 1.5 h after i.v. administration. The major metabolite in the bile was p-hydroxymethamphetamine glucuronide. The major compound excreted in urine was unchanged methamphetamine. Whole-body autoradiography was performed using 14C-methamphetamine, and tissue 3H concn. was determined after i.v. administration of 3H-methamphetamine to rats.

Distribution and excretion of methamphetamine and its metabolites in rats. I. Time-course of concentrations in blood and bile after oral administration

1. Concentration time-courses of methamphetamine and its metabolites in the blood after oral administration of [3H]methamphetamine to rats showed two distinct peaks at 2.5 and 8 h after dosing. The major metabolite present in the blood at all times was unconjugated p-hydroxymethamphetamine. 2. Biliary excretion of radioactivity after oral administration of [3H]methamphetamine to rats was about 30% dose in 24h. The major metabolite in the bile was p-hydroxymethamphetamine glucuronide. 3. Blood and bile were collected simultaneously from a rat fitted with a T-tube cannula in the common bile duct, and time-courses of blood and bile concn. of the drug and metabolites were investigated. The observation of two peaks in both blood and bile indicates enterohepatic circulation of the drug and metabolites.