Ian R. Tebbett

Analgesic effects of codeine-6-glucuronide after intravenous administration

Centrally administered codeine glucuronide has been shown to exhibit antinociceptive properties with decreased immunosuppressive effects compared to codeine. In this study, codeine‐6‐glucuronide was administered to rats, and its analgesic effect was compared to that of codeine. The concentrations of codeine and its metabolites in plasma and brain were also determined at the peak response time after administration of each compound. Receptor‐binding studies with rat brain homogenates and affinity profiles were also determined. Intravenous administration of codeine‐6‐glucuronide resulted in approximately 60% of the analgesic response elicited by codeine itself. Analysis of plasma and brain showed that codeine‐6‐glucuronide is relatively stable in vivo, with only small amounts of morphine‐6‐glucuronide being detected in addition to unchanged codeine‐6‐glucuronide. The receptor affinity of codeine‐6‐glucuronide was similar to that of codeine. It is concluded that intravenously administered codeine‐6‐glucuronide possesses analgesic activity similar to that of codeine, and may have clinical benefit in the treatment of pain

Detection of Cocaine and Its Metabolites in Breast Milk

A method was developed for measuring cocaine and its metabolites, benzoylecgonine, ecgonine methyl ester, norcocaine, ecgonine ethyl ester, cocaethylene, and m-hydroxybenzoylecgonine, in breast milk by gas chromatography/mass spectrometry. Limits of detection for this method ranged from 2.5 to 10 ng/mL, and limits of quantitation ranged from 5 to 50 ng/mL. For each of the compounds measured by this method, linear response was demonstrated to 750 ng/mL. Breast milk was collected from 11 mothers who admitted to drug use during pregnancy and ten drug-free volunteers serving as control subjects. Cocaine was detected in six of the specimens obtained from drug-exposed subjects, and in none of the drug-free control subjects. In breast milk specimens where cocaine and one or more of its metabolites were detected, the concentration of parent compound was greater than any of the metabolites. The highest cocaine concentration found was over 12 microg/mL. Breast-fed infants of cocaine abusing mothers may be exposed to significant amounts of drug orally.

Analgesic and immunomodulatory effects of codeine and codeine 6-glucuronide

AbstractPurpose. The antinociceptive and immunosuppressive effects of codeine and codeine 6-glucuronide were determined in rats after intra-cerebroventricular administration. Methods. Codeine 6-glucuronide was synthesized using a modification of the Koenigs-Knorr reaction. A lipophilic intermediate formed during synthesis, methyl [codein-6-yl-2,3,4-tri-O-acetyl-β-D-glucopyranosid] uronate, was also tested. Morphine was used as a positive control to compare antinociceptive potencies of these compounds. Results. All compounds tested produced significant analgesic responses, as assessed by the tail flick model. Additionally, codeine 6-glucuronide showed significantly less immunosuppressive effects than codeine in vitro. Conclusions. We conclude that codeine 6-glucuronide and related compounds may have clinical benefit in the treatment of pain in immune compromised patients.

7-Alkylcarbonyloxymethyl prodrugs of theophylline: topical delivery of theophylline

Abstract Five members of an homologous series of 7-n-alkylcarbonyloxymethyl (ACOM) prodrugs (C1 to C5, acetyl- to hexanoyloxymethyl) of a potential topical antiproliferative drug, theophylline (Th, 1) have been synthesized, characterized and evaluated for their abilities to deliver Th into and through hairless mouse skin from suspensions in isopropyl myristate (IPM). The synthesis used a tertiary amine quaternary salt of the ACOM chlorides (2) as the alkylating agent to give about twice the percent yields as previously reported. Although all of the members of the 7-ACOM-Th prodrugs (C1 to C5, 3a to 3e) were more soluble in IPM than Th (10–200 times), the most water soluble members (C1 and C3, acetyl- and butyryloxymethyl) were only about 0.25 times as soluble as Th; C2 (propionyloxymethyl) was only about 0.1 times as soluble. In addition to being almost as water soluble as C1, C3 was almost 10 times more lipid soluble than C1 or C2. Thus, the C3 prodrug exhibited the best biphasic solubility properties in the series. In the diffusion cell experiments, the C3 prodrug was the only member that was significantly (2 times) more effective than Th at delivering total Th species (Ji). In addition, all of the prodrugs of the series delivered significant amounts of intact prodrug through the skin (Jp): Jp/Ji for C1=47%, C2=29%, C3=32%, C4=7% and C5=1%. None of the prodrugs delivered as much Th into the skin (Cs) as Th itself. Fluxes of Th from propylene glycol (Jj) subsequent to the initial application of prodrug or Th/IPM were all of a similar magnitude, so that the differences in Ji were not caused by differences in damage to the skins from the initial applications. 7-Hydroxymethyltheophylline (7-HOCH2-Th, 4) which was as lipid soluble as C1 and C2, but 10 times more water soluble than Th gave a Ji which was 2 times that of Th and a Cs value that was 2 times that of Th. 7-HOCH2-Th was the best prodrug studied for increasing the delivery of Th.

The effects of acute and repeated pyridostigmine bromide administration on response acquisition with immediate and delayed reinforcement

This experiment was designed to assess the effects of acute and repeated administration of pyridostigmine bromide (a carbamate with prophylactic and therapeutic uses) on response acquisition. Experimentally naïve, male Sprague-Dawley rats were exposed to a situation in which lever presses were either immediately followed by food-pellet presentation or after a 16-s resetting delay. Different groups of rats received either one acute administration of pyridostigmine bromide (10 mg/kg, by gavage) or repeated pyridostigmine administration for 7 days (1.5 mg/kg/day, by gavage). Other groups were treated with distilled water for the same period of time. Both acute and repeated pyridostigmine bromide administration decreased serum cholinesterase levels by approximately 50%, but neither treatment affected brain cholinesterase levels in our assay. Acute and repeated drug administration produced the same behavioral effects. Subjects exposed to the 0-s delay conditions obtained many more food pellets than those exposed to the 16-s delay conditions. Administration of pyridostigmine bromide delayed the onset of responding in some, but not all, of the subjects in the treated groups, independent of the delay condition to which they were exposed. Many more responses were observed on an inoperative lever during the 16-s delay conditions than during the 0-s delay conditions, especially during the 16-s delay condition in which subjects had received acute vehicle administration. Whether or not these effects of small doses of pyridostigmine bromide on response acquisition are of central or peripheral origin will need to be determined in future studies, as response acquisition in the present experiment may have been affected by pyridostigmines effects on gastrointestinal functioning and/or motor activity.

In vitro-in vivo myotoxicity of intramuscular liposomal formulations

AbstractPurpose. The first objective was to study the in vitro myotoxicity of empty liposomes and to examine whether liposome size, charge and fluidity affect liposome myotoxicity. The second objective was to investigate the effect of liposomal encapsulation on the in vitro and in vivo myotoxicity of loxapine compared to the loxapine commercial preparation (Loxitane®). Methods. The in vitro myotoxicity of empty liposomes and loxapine liposomes was evaluated by the cumulative efflux of the cytosolic enzyme creatine kinase (CK) from the isolated rat extensor digitorum longus (EDL) muscle over a 2 hour period. In the in vivo studies, the area under plasma CK curve over 12 hours was used to evaluate muscle damage. Results. The in vitro myotoxicity for all empty liposomal formulations was not statistically different from negative controls (untreated control muscles and normal saline injected muscles). However, these empty liposomal formulations were significantly less myotoxic than the positive controls (muscles injected with phenytoin and muscle sliced in half). In vitro-in vivo studies showed that the liposomal encapsulation of loxapine resulted in significant (P < 0.05) reduction in myotoxicity (80% in vitro and 60% in vivo) compared to the commercially available formulation which contains propylene glycol (70% V/V) and polysor-bate 80 (5% W/V) prepared at equal concentration. Conclusions. Results indicate that empty liposomes do not induce myotoxicity. Furthermore, liposomal size, charge and fluidity do not affect myotoxicity. In addition, in vitro and in vivo studies have demonstrated that liposomal encapsulation of loxapine can reduce myotoxicity compared to a formulation containing organic cosolvents.

Cocaine Suppresses Fetal Immune System

The effects of cocaine are well documented in the CNS; however, recent evidence suggests that cocaine may suppress the immune system. Maternal cocaine use essentially exposes the fetus to a continuous exposure of cocaine. The objective of this study was to investigate the immunomodulatory effects of cocaine and its metabolites on maternal and fetal immune systems. Subjects were recruited from an Investigational Review Board approved protocol, and biologic specimens were collected. For each subject peripheral blood mononuclear cells (PBMCs) were isolated by density gradient. Each PBMC sample was stimulated in separate wells with phytohemagglutinin and phrobol 12-myristate 13-acetate. Samples were radiolabeled and stimulation was measured. Cytokine measurements were made on the serum via ELISA assay techniques. In both the phorbol 12-myrisate 13-acetate and the phytohemagglutinin group, the PBMCs isolated from fetal cord blood in the cocaine-using group had significantly (p < 0.05) decreased responses compared with control subjects. IL 1 and IL 2 concentrations were suppressed in the cocaine-exposed fetal serum compared with controls(p < 0.005 and p < 0.05, respectively). We have shown that in utero cocaine exposure results in a nonspecific suppression of fetal T lymphocyte response. The clinical consequences of prenatal cocaine-induced immunosuppression need to be further explored.

The effects of pyridostigmine bromide, permethrin, and DEET alone, or in combination, on fixed-ratio and fixed-interval behavior in male and female rats.

Concurrent exposure to pyridostigmine bromide (PB), permethrin (PERM) and/or N,N-diethyl-m-toluamide (DEET) may have contributed to the development of a syndrome that appears to have afflicted military personnel who served during the Gulf War. The present experiment sought to evaluate the behavioral effects of these compounds alone, or in various combinations, in male and female rats. Subjects were exposed to a multiple fixed-ratio (FR) 50, fixed-interval (FI) 2-min schedule of reinforcement. PB dose-dependently decreased FR and FI response rates. FR responding was disrupted by lower doses and there were no differences between the sexes. PERM vehicle administration decreased response rates maintained by both schedules of reinforcement; this was offset by an increase in response rate after the administration of the intermediate dose of PERM. The highest dose of PERM decreased both FR and FI response rates. FR rates in male rats were more disrupted than those in female rats. Only the highest dose of DEET decreased FR and FI response rates in male and female rats. FR rates were more disrupted in female rats than in male rats. Synergistic effects were only observed when FI response rates decreased in male rats upon exposure to half the low dose of PB with half the low dose of PERM or half the low dose of PB with half the low dose of DEET. The results of this experiment thus show that small doses of PB, PERM and DEET disrupt well-established, schedule-controlled behavior in male and female rats in a schedule- and gender-dependent manner; schedule-dependent and gender-dependent synergistic effects were also observed. The mechanism by which the compounds exert these behavioral effects remains to be determined.

The Effects of Pyridostigmine Bromide and Permethrin, Alone or in Combination, on Response Acquisition in Male and Female Rats

It has been hypothesized that concurrent exposure to pyridostigmine bromide and permethrin may have contributed to the development of neurocognitive symptoms in Gulf War veterans. The present experiment was designed to investigate the effects of pyridostigmine bromide and permethrin alone, or in combination, on the acquisition of a novel response, one measure of normal cognitive functioning. Male and female Sprague-Dawley rats were treated with pyridostigmine bromide (1.5 mg/kg/day, by gavage in a volume of 5 ml/kg) or its vehicle for 7 consecutive days. They then also received an intraperitoneal injection of permethrin (0, 15, or 60 mg/kg) before they were exposed to an experimental session during which they could earn food by pressing a lever in an operant chamber. Serum permethrin levels increased as a function of its dose, and were higher in rats treated with pyridostigmine bromide. Sex differences were observed as permethrin levels were higher in female rats than in male rats following the highest dose. Pyridostigmine bromide delayed response acquisition in male and female rats, and resulted in higher response rates on the inactive lever in female rats than in male rats. Although permethrin levels were higher in subjects treated with pyridostigmine bromide than in those treated with vehicle, there were no differences in the behavioral effects of permethrin. Whether or not these behavioral effects of pyridostigmine bromide are of central or peripheral origin will need to be determined in future studies, as its effects on motor activity and/or gastro-intestinal motility may have affected response acquisition.

Effect of chronic cocaine administration on amino acid uptake in rat placental membrane vesicles

This study evaluated the effects of chronic exposure to cocaine during pregnancy on amino acid uptake in placental membrane vesicles. Pregnant rats received 62 mg/kg of cocaine hydrochloride by intraperitoneal (IP) injection as a divided daily dose on gestation days 8-19 inclusive. Fetal body weights were significantly decreased by 19% in the cocaine group, while placental weights were unchanged. Placental apical membrane vesicles were prepared from control and cocaine-treated animals, and marker enzyme enrichments for alkaline phosphatase and [3H]-dihydroalprenolol binding did not differ between cocaine and control groups. Rates of uptake (10 sec) of selected radiolabeled amino acids were measured utilizing a rapid filtration technique. Na(+)-dependent apical membrane [3H]-glutamine transport (50 microM) was reduced by 95% (p < 0.05) in cocaine-treated compared to control placentas. Uptake of 50 microM [3H]-methyl aminoisobutyric acid (MeAIB) into apical membranes was also decreased by 43% (p < 0.05) in cocaine membranes. Na(+)-independent [3H]-arginine transport (10 microM), however, did not differ between control or cocaine-treated groups. In summary, chronic cocaine administration selectively inhibited the transport of glutamine and MeAIB into apical membrane vesicles, but had minimal effect on arginine transport. We postulate that this diminution in uptake may contribute to the fetal growth retardation noted in our model.