L-Methadone and D,L-methadone in methadone maintenance treatment: a comparison of therapeutic effectiveness and plasma concentrations.

The clinical effectiveness of l-methadone maintenance treatment (LMMT) carried out using d,l-methadone or l-methadone have been compared with ambulatory heroin-dependent subjects. A total of 40 heroin-dependent subjects, previously maintained on l-methadone in Frankfurt am Main, were divided into two groups under randomised double-blind conditions and received either an equivalent dose of l-methadone as d,l-methadone or remained on the previous l-methadone treatment. Requests for a change in the dose of d,l-methadone and l-methadone were recorded, urine samples for determination of illicit drug use were collected and the individual level of opiate craving was determined over a 22-day observation period. There was no significant difference between the two groups in the number requests for a dose change (dose increase <10%). However, there was a significant increase in heroin use in the group which continued to receive l-methadone. Although there was less variability in opiate craving in the group receiving d,l-methadone, the mean intensity of opiate craving did not differ between the two groups. The mean l-methadone dose:l-methadone plasma concentration ratio, an index of the bioavailability of l-methadone in individual subjects, showed no significant change when the treatment was changed to d,l-methadone. The mean d-methadone:l-methadone plasma concentration ratio was 1.17. There was no significant difference between these ratios for day 15 and day 22. The mean l-methadone:EDDP plasma concentration ratio in the l-methadone group was 22.2 and the d,l-methadone:EDDP plasma concentration ratio was 18.4 . The plasma EDDP concentration in the d,l-methadone group increased 3-fold after starting treatment with d, l-methadone. These findings suggest that d,l-methadone can be used in methadone maintenance treatment of heroin-dependent subjects but that further studies are required to evaluate pharmacokinetic interactions between methadone enantiomers.

Cardiac effects of benzodiazepine receptor agonists and antagonists in the isolated rat heart: a comparative study.

Effects of PK 11195 and flumazenil on cardiac responses to diazepam, clonazepam and zolpidem were compared. Coronary flow rate was increased at relatively low doses of diazepam and decreased at higher doses. Clonazepam induced a dose-dependent increase, and zolpidem a decrease of coronary flow rate. PK 11195 reduced the diazepam-induced increase of coronary flow rate, and flumazenil was ineffective. Neither antagonist evoked substantial changes in the decrease of coronary flow rate. PK 11195, and less so flumazenil, antagonized the clonazepam-induced increase. PK 11195 and flumazenil only in their highest doses suppressed and respectively potentiated the zolpidem-induced decrease. Inotropy showed a biphasic response in the presence of diazepam, i.e. an initial transient decrease, followed by a dose-dependent increase in two steps. Clonazepam induced a similar response. Zolpidem increased the inotropy. The negative inotropic response induced by diazepam did not change significantly in the presence of PK 11195 or flumazenil. The positive inotropic response was suppressed by PK 11195, and less so by flumazenil. The negative response to clonazepam was antagonized by both PK 11195 and flumazenil; the positive response was not significantly changed. In the presence of lower doses of PK 11195, the zolpidem-induced response was potentiated, whereas higher doses produced reversal; flumazenil potentiated the response. In conclusion, the results support earlier suggestions, involving receptor mechanisms with cardiac effects of benzodiazepines. Both agonists and antagonists (inter)act in a different manner, suggesting that rather ambiguous receptor mechanisms are involved in benzodiazepine effects in the heart.

Modification of cardiac actions of RO 05-4864 by PK 11195 and flumazenil in the perfused rat heart.

The benzodiazepine analogue Ro 05-4864 [chlorodiazepam] (2.10[-5] to 4.10[-4] M) induced a concentration-dependent increase of coronary flow rate (Emax 82.4% [+/- 2.2 SEM]) and an increase of contraction force (Emax 68.3% [+/- 4.7 SEM]) of the retrograde perfused, isolated Langendorff rat heart. The influence of PK 11195, antagonist of the peripheral type benzodiazepine receptor, and flumazenil (Anexate), antagonist of the central type benzodiazepine receptor, on these responses to Ro 5-4864 was studied. In concentrations of 10(-7) to 5.10(-5) M, PK 11195 significantly reduced both the increase of coronary flow rate and of contraction force, without affecting these functions by itself; the positive inotropic response produced by Ro 05-4864 was even abolished in the presence of 5.10(-5) M PK 11195. The Emax values of Ro 05-4864 on both coronary flow and inotropy were reduced significantly by PK 11195. In the presence of flumazenil, 10(-7) to 10(-5) M, both the vasodilatory and the positive inotropic response induced by Ro 05-4864 were significantly counteracted as well. The Emax values of Ro 05-4864 were reduced significantly. In conclusion, the results support earlier suggestions that it is tempting to involve peripheral type benzodiazepine receptors in cardiac actions of benzodiazepines. The finding that the centrally acting benzodiazepine antagonist flumazenil reduced the cardiac actions of Ro 05-4864 is as yet difficult to explain. On the other hand concentrations of both agonist and antagonist employed are so-much high that interference of other receptors than benzodiazepine receptors must be considered as well.

Flunarizine but not theophylline modulates inotropic responses of the isolated rat heart to diazepam.

Diazepam (2 x 10(-5)-6 x 10(-4) M) induced a concentration-dependent positive inotropic effect on the perfused rat heart which was preceded by a transient concentration-dependent negative inotropic response. The influence of the Ca(2+)-entry blocking drug, flunarizine, and the adenosine receptor blocking drug, theophylline on these inotropic responses was studied. Flunarizine in concentrations of 10(-9)-10(-6) M antagonized the positive inotropic response to diazepam significantly; the negative inotropic response was reduced as well. At the lower concentrations of diazepam the negative inotropic response was completely abolished in the presence of flunarizine. The actions of the Ca(2+)-entry blocker were related to the concentrations used. Theophylline in concentrations up to 5 x 10(-5) M did not interfere with either inotropic response to diazepam. The results suggest that Ca2+ currents in the myocardium are involved with the response of the isolated heart to diazepam. It is concluded that the finding that the negative inotropic effect of diazepam was almost abolished by flunarizine suggests that the site of this response most be associated with Ca(2+)-current mechanisms.

PK 11195 antagonizes the positive inotropic response of the isolated rat heart to diazepam but not the negative inotropic response.

The influence of the ligand PK 11195 (1-(2-chlorophenyl)-N-methyl-N-(1- methylpropyl)-3-isoquinolinecarboxamide), antagonist of the peripheral-type benzodiazepine receptor, on the inotropic response of the perfused rat heart to diazepam (7-chloro-5-phenyl-methyl- 1,3-dihydro-2H-1,4-benzodiazepin-2-one) was studied. Diazepam induced a positive inotropic response which was preceded by a transient negative inotropic response. Concentrations of 10(-7) M PK 11195 were ineffective, whereas concentrations of 10(-6) and 10(-5) M PK 11195 reduced the positive inotropic response significantly. At 5 x 10(-5) M PK 11195 the response was completely abolished. The negative inotropic response was not changed by either concentration of PK 11195 used. It is concluded that the positive inotropic response of the isolated rat heart to diazepam may well be mediated through peripheral-type benzodiazepine receptors; the negative inotropic response must be related to other (more complex) mechanisms.

Ivermectin detection in serum of onchocerciasis patients: relationship to adverse reactions.

Ivermectin treatment of onchocerciasis patients can be accompanied by adverse reactions. Not much is known concerning the pathogenesis of these reactions. Previous studies have demonstrated that the occurrence and extent of adverse reactions are related to infection intensity. However, some severely infected patients experience relatively few adverse effects. The aim of the present study was to investigate whether this seeming discrepancy could be due to diminished ivermectin absorption. Ivermectin concentrations one and two days after treatment were measured by high-performance liquid chromatography in sera of 71 skin snip-positive onchocerciasis patients (21 without reactions, 25 with mild reactions, 14 with moderate reactions, and 11 with severe reactions). The overall mean +/- SD ivermectin concentrations one and two days after a single oral dose (150 micrograms/kg) were 16.4 +/- 6.4 and 6.6 +/- 3.1 ng/ml, respectively. The overall mean +/- SD half-life was estimated to be 19.9 +/- 8.6 hr. The data presented did not show a relationship between ivermectin concentrations and the grade of adverse reactions.

Pharmacokinetics of methadone and its primary metabolite in 20 opiate addicts.

In a closed metabolic ward the pharmacokinetics of methadone and its primary metabolite (EDDP) were studied in 20 long-term opiate addicts. After administration of the daily oral dose of methadone HCl (mean 60 mg, range 10-225 mg) blood samples were taken and analysed, using a newly developed high-performance liquid chromatography (HPLC) method. The steady-state plasma concentrations of the 20 subjects varied from 65-630 ng x ml(-1) and from 5 to 55 ng x ml(-1), whereas the peak concentrations were 124-1255 ng x ml(-1) and 10-301 ng x ml(-1) for methadone and the AUC(0-24 h) for EDDP varied from 5.9 to 44.6, indicating interindividual differences in metabolic activity. In 19 out of 20 subjects the pharmacokinetics of methadone are best described using a two-compartment model. The mean body clearance was 1.64 ml x min(-1) x kg(-1), whereas the mean elimination rate constant (beta) and plasma half-life (t1/2beta) were 0.026 x h(-1) (range 0.013-0.053 x h(-1)) and 31.2 h (range 13-53 h), respectively. Differences of gender were also found. A poor correlation was found between the methadone dose and the steady-state level. A much better correlation was found between the normalized steady-state level and the body clearance.

Actions of benzodiazepines on the inotropy of the perfused rat heart.

The inotropic responses of four benzodiazepines (diazepam, midazolam and the more recently developed adinazolam and alprazolam) have been studied in a Langendorff heart preparation of the rat. Added to the perfusate in increasing concentrations (2 x 10(-5) to 6 x 10(-4) M), diazepam induced a concentration-dependent biphasic effect on the contractile force (n = 12), and, in low concentrations (2 x 10(-5) to 1 x 10(-4) M), a significant enhancement which diminished after concentrations higher than 1 x 10(-4) M were applied. The increase in contractile force was preceded by a transient short-lasting concentration-dependent inhibition. Midazolam (2 x 10(-5) to 6 x 10(-4) M) produced a significant concentration-dependent increase in heart contractile force which diminished at the highest concentrations. The maximum increase was only half that caused by diazepam (60 and 140%, respectively). Adinazolam and alprazolam, in the range of 2 x 10(-8) to 2 x 10(-7) M and 6 x 10(-7) to 1 x 10(-5) M, respectively, produced a marked concentration-dependent and short-lasting increase in inotropy (maximum response = 290 and 180%, respectively). Propranolol (10(-7) M) antagonized the inotropic effects of both diazepam and midazolam, whereas the positive inotropic response to alprazolam remained unchanged. This study shows that benzodiazepines may elicit both positive and negative concentration-dependent inotropic responses in the isolated rat heart. Differences between the drugs tested are both qualitative and quantitative. The newer benzodiazepines adinazolam and alprazolam are more powerful in increasing contractile force, as judged from the maximum response, even at relatively low concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of pentobarbital and benzodiazepines on GABA-responses in the periphery and spinal cord in vitro.

Pentobarbital and benzodiazepines were compared in their interaction with the gamma-aminobutyric acid (GABA) antagonists picrotoxin and bicuculline on GABAA receptor-mediated events. On excised vagal nerves and dorsal roots pentobarbital, in contrast to the benzodiazepines diazepam, lorazepam and flurazepam, was able to enhance GABA-induced depolarizations recorded in the presence of picrotoxin or bicuculline. On hemicord preparations picrotoxin simultaneously depressed the electrically evoked dorsal root-dorsal root potential and enhanced the dorsal root-ventral root potential. Pentobarbital overcame the effects of picrotoxin, whereas diazepam and midazolam were without effect. These results may be explained by the suggestion that the GABA receptors in these test systems are not tightly associated with the benzodiazepine receptor activated by diazepam, lorazepam, midazolam and flurazepam, and correspond to the recently described GABAA2 subdivision of GABA receptors.

Changes induced by diazepam in the synaptic vesicle size of rat phrenic nerve terminals.

The effect of diazepam (Valium), administered by i.p. injection on the cross-sectional area of synaptic vesicle profiles of the endplate-rich area of the rate diaphragm was studied by electron microscopy at 15-180 min after treatment. In the dose range of 0.25-10 mg/kg, diazepam induced a significant increase of the size of the synaptic vesicles. This increase was dose-related within a certain margin, dependent on the treatment time, while the effect of each dose increased significantly with the period after treatment. At 2.5-10 mg/kg a maximum seemed to be reached at 90 min.

Presynaptic, facilitatory effects of the corticosteroid dexamethasone in rat diaphragm: modulation by beta-bungarotoxin.

Low concentrations of dexamethasone (up to 200 nM) increase the accumulation of choline (Ch) and its incorporation into acetylcholine (ACh) in the endplate rich area (EPA) of stimulated and unstimulated diaphragms in the presence of 10 microM Ch. Tissue ACh is not significantly altered, even after 140 min incubation. The specific radioactivity of the ACh in the EPA is thus increased by dexamethasone (Dex). The corticosteroid has no effects on acetylcholinesterase or choline acetyltransferase in diaphragm extracts. In the same medium, the amplitudes of the MEPPs, MEPCs and EPCs are also increased by Dex. Neither the quantal content of the EPCs nor the MEPP frequency, nor the half decay time of the MEPCs are altered. Therefore Dex (200 nM) increases both the resting and evoked output, and turnover of ACh in rat diaphragm. Beta-bungarotoxin (beta-BuTx) antagonizes the Dex-induced increase in Ch accumulation and its incorporation into ACh, and abolishes the increases in MEPC- and EPC-amplitudes, providing further argument for a presynaptic effect of Dex. In continuously-stimulated diaphragms, beta-BuTx causes an accumulation of ACh which is much greater than in unstimulated tissue. This accumulation of ACh is less in the presence of Dex, provided that Dex is added before beta-BuTx. The interaction of Dex and beta-BuTx is discussed in terms of their possible presynaptic sites of action.

Ion channel block in rat diaphragm by the venom of the digger wasp Philanthus triangulum.

In the rat phrenic nerve-diaphragm preparation the twitch tension and tetanic contractions, already reduced by d-tubocurarine, succinylchloride or neostigmine, are further reduced by the venom of the digger wasp Philanthus triangulum F. The venom reduces the temperature- and voltage-sensitivity of the acetylcholine-receptor-activated ion channels, at the motor end-plate, and shortens the decay time of the miniature end-plate currents, analogous to a block described for the purified toxin, delta-PTX, on insect glutamate-activated channels. Preliminary results show that delta-PTX has an effect similar to that of the total venom on the decay phase of miniature end-plate currents.

Effects of corticosteroids on the myoneural junction. A morphometric and electrophysiological study.

The mean size of the synaptic vesicles in the nerve endings of the isolated rat diaphragm was significantly increased after incubation with the glucocorticoids prednisolone (10(-5) mol/l) and dexamethasone (2 X 10(-7) mol/l). The shape of the vesicles was also changed, i.e. they became rounder. Similar increases in the mean size of the diaphragm synaptic vesicles were seen when the rats were injected with prednisolone (i.p., 2 mg/kg) and dexamethasone (i.p., 50 micrograms/kg) 2-4 h previously. The amplitude of the miniature endplate potentials was also significantly increased in diaphragms isolated from rats which had been injected with prednisolone or with dexamethasone. Changes in frequency of the MEPPs were less marked after injection of prednisolone, but a significant increase was seen after injection of dexamethasone. It is concluded that relatively low concentrations of glucocorticoids have direct effects on the motor endplate in rat diaphragm both in vitro and in vivo. We tentatively suggest that presynaptic effects may contribute to the beneficial effect of corticosteroids in deficient neuromuscular transmission, e.g. in myasthenia gravis.

Effects of corticosteroids on neuromuscular blocking actions of d-tubocurarine.

Dexamethasone (50 microgram/kg) significantly increased the LD50 of d-tubocurarine (d-TC) when administered i.p. simultaneously with d-TC. Choline (50 and 100 mg/kg) gave some protection against the lethal effects of d-TC and the cholinesterase inhibitors neostigmine (250 microgram/kg) and physostigmine (1000 microgram/kg) provided full protection against doses of d-TC twice the LD50. The blocking effect of d-TC (75 microgram/kg) on the sciatic nerve-tibialis anterior muscle preparation was antagonized by dexamethasone. Prednisolone delayed the occurrence of a complete neuromuscular block caused by d-TC in the phrenic nerve-diaphragm preparation, and antagonized the effect of d-TC on short tetanic contractions. d-TC (5 mumol/l) inhibited the [14C]choline uptake in the endplate-rich region of the rat diaphragm during stimulation. This inhibition was antagonized by dexamethasone as well as by physostigmine. The incorporation of radioactive choline into acetylcholine was inhibited in the presence of d-TC (15 mumol/l), and both dexamethasone and physostigmine counteracted this inhibition. It is concluded from these experiments that d-TC very probably has an effect on the choline carrier system. These experimental results support the hypothesis that glucocorticoids may improve reduced muscle performance by direct presynaptic effects at the neuromuscular junction.

The effect of prednisolone on neuromuscular transmission in the rat diaphragm.

Prednisolone, in concentrations of 0.004--0.032 mmol/l, increased the amplitude of the miniature end-plate potentials (MEPPs). A maximum increase to 134% of the control values was seen at 0.016 mmol/l. At higher prednisolone concentrations the MEPP amplitude gradually decreased to reach 77% of the control value at 0.62 mmol/l. The MEPP frequency was increased to twice the control value at 0.62 mmol/l. The quantal content of the end-plate potential (EPP), however, was not influenced by prednisolone. The response to iontophoretically applied acetylcholine was diminished, especially at 0.62 mmol/l prednisolone. Prednisolone, therefore, caused presynaptic effects as was shown by an increase in unitary MEPP amplitude and by a considerable number of giant MEPPs, which at increasing prednisolone concentrations was antagonized increasingly by a postsynaptic depressant effect. These results also provide an explanation for the adverse effects of prednisolone on the end-plate potential and on neuromuscular transmission.