Trihexyphenidyl, biperiden and procyclidine are anticholinergic drugs produced as racemates for the treatment of Parkinson's disease. This paper describes a simple and sensitive LC-MS method for the simultaneous determination of these compounds in human serum. An on-line sample clean-up procedure was used, where serum samples were directly injected into a "restricted-access media" pre-column. After the exclusion of the serum proteins, the drug molecules were eluted to a beta-cyclodextrin analytical column for chiral separation. The quantitation was done by electrospray ionization MS using diphenidol as an internal standard. The method developed has limits of detection of 1 ng/ml, at least two-orders-of-magnitude linear dynamic ranges (r>0.999), and RSDs of less than 10%. The system can be completely automated for increased sample throughput and unattended analyses.
In order to shorten the list of candidate drugs with anticonvulsant potential against nerve agents, critical subreceptors in seizure controlling brain regions should be specified. Epileptiform activity does not spread randomly throughout the brain, but appears to be generated and propagated by specific anatomical routes. Nerve agents evoke seizure activity in the forebrain that progresses to the hind brain resulting in tonic-clonic convulsions. In some recent studies, it was shown that lesion of the area tempestas (AT), medial septum (MS), perirhinal cortex (PRC), or posterior piriform cortex (PPC) produces anticonvulsant effects (prevention of convulsions or delayed onset of convulsions) in rats exposed to soman, whereas damage to nucleus accumbens, nucleus basalis magnocellularis, amygdala, hippocampus, or entorhinal cortex does not cause anticonvulsant impact. These results are in compliance with findings that seizures can be generated in AT, MS, PRC, and PPC by means of nerve agents, chemoconvulsants, or kindling. Results from microinfusion studies show that anticonvulsant efficacy is obtained by GABA(A) modulators or cholinergic antagonists (M1-M5) in AT, cholinergic antagonists (M1-M5) in MS, combined glutamatergic (NMDA) and cholinergic antagonist (M1-M4), AMPA antagonist, or modulators of metabotropic glutamate receptors (mGluR5, mGluR2/3) in PRC, and cholinergic antagonist (M1-M5) or GABA(A) agonist in PPC. Calculation of impact factors for the most potent drugs (percentage of positive effects in the seizure controlling sites) showed that scopolamine and procyclidine were ranking highest (75) followed by muscimol (50), NBQX (33), and caramiphen (33). Potential strategies for prophylactic and post-exposure treatments are discussed.
On the basis of the hypothesis that there is a common structural basis for central nervous system (CNS) drug action consisting primarily of an aromatic group and a nitrogen atom, a four-point model for a common pharmacophore is defined with use of five semirigid CNS-active drug molecules: morphine, strychnine, LSD, apomorphine, and mianserin. Two of the points of the model represent possible hydrophobic interactions between the aromatic group and the receptor, while the other two represent hydrogen bonding between the nitrogen atom and the receptor. The model is then extended by the inclusion of nine additional CNS-active drug molecules: phenobarbitone, clonidine, diazepam, bicuculline, diphenylhydantoin, amphetamine, imipramine, chlorpromazine, and procyclidine, each being chosen as a key representative of a different CNS-active drug class or neurotransmitter system. Consideration of all phenyl group and nitrogen atom combinations, as well as all feasible conformations, shows that all nine molecules closely fit the common model in low-energy conformations. It is proposed that the model may eventually be used to design CNS-active drugs by mapping the relative locations of secondary binding sites. It can also be used to predict whether a given structure is likely to show CNS activity: a search over 1000 entries in the Merck Index shows a high probability of CNS activity in compounds fitting the common structural model.
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Fluorescence imaging techniques are valuable tools for the pharmacological characterization of CNS drugs. Dissected cerebellar granule neurons (CGN) are an important model system in the study of mechanisms of excitotoxicity, glutamate receptors and transporters. Widely applied techniques use fluorescent probes loaded in neural cells cultured on glass supports. CGN, however, require at least 7 days for differentiation and over time cells tend to cluster and loose adherence to the glass substrate. This problem is accentuated in small wells (e.g. 96-well plates).
It is important that prophylactics used to protect military and emergency personnel against lethal doses of nerve agents do not by themselves produce impairment of cognitive capability. The purpose of the present study was to examine whether physostigmine, scopolamine, and various doses of procyclidine might reduce rats' innate preference for novelty. When these drugs were tested separately, the results showed that physostigmine (0.1 mg/kg) and procyclidine (3 mg/kg) did not affect preference for novelty, whereas scopolamine (0.15 mg/kg) and procyclidine in a higher dose (6 mg/kg) resulted in a preference deficit (Experiment 1). In Experiment 2, the combination of physostigmine and scopolamine or physostigmine and procyclidine (6 mg/kg) caused a marked deficit in preference for novelty. A much milder deficit was observed when physostigmine was combined with lower doses (1 or 3 mg/kg) of procyclidine. The latter combinations also had milder adverse impact on the animals' interest in the test environment and activity measures than the former combinations. By combining physostigmine with anticholinergics, a potentiation of adverse effects on behavior was seen. It is concluded that a slight cognitive impairment might be unavoidable with effective prophylactics.
A case of procyclidine abuse is described in which the clinical presentation was indistinguishable from mania. The patient was a long-standing poly-drug abuser and was obtaining the drugs from medical sources. Controlled exposure on the ward to drugs of abuse, including a double-blind comparison with placebo, confirmed that procyclidine caused a manic response in this patient.
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The authors administered haloperidol 4.5 mg t.i.d. to 33 drug-free schizophrenic patients. Ten patients did not receive anything else (group HPL), while ten patients received procyclidine 5 mg t.i.d., and 13 patients were given promethazine 25 mg t.i.d. (groups HPRC and HPRM respectively) in addition. Seven patients dropped out of the HPL group and three out of the HPRM group, but none out of the HPRC group. These drop outs were due to the development of early extrapyramidal side effects, which were absent in the HPRC group. The findings suggest that antiparkinson prophylaxis is useful during commencement of therapy with high-potency neuroleptic agents.
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A 51-year-old gentleman was admitted with a history of severe depression with marked agitation in the background of cocaine abuse. He had multiple medical problems like deep vein thrombosis, hepatitis C and tardive dyskinesia. Besides him being on antidepressant medication, risperidone was prescribed by his previous physician for a period of 2 years. Since commencement on this medication, he developed tardive dyskinesia that was never recognised and managed. This side effect caused additional anxiety to the patient and affected his social life. Upon admission, his medications were reviewed, risperidone was gradually withdrawn and procyclidine 2 mg twice daily was added. After being discharged from hospital, he was regularly seen in the out patient clinic. Within 3 months, his tardive dyskinesia improved tremendously, his quality of social life got better and by virtue of this, there was a faster remission in his depression and anxiety symptoms.
The nature of the antagonism by anticholinergic compounds of nicotine-induced convulsion in mice has not been defined clearly. Although, because they do not compete effectively for agonist binding to brain tissue in-vitro, these compounds are thought to be non-competitive antagonists in the brain, pharmacological evidence is lacking. This study describes the anti-nicotinic properties of the clinically used anticholinergic antiparkinson drugs, benztropine, biperiden, caramiphen, ethopropazine, procyclidine and trihexyphenidyl. Nicotine-induced convulsion and arecoline-induced tremor in mice were effectively prevented by these drugs. The concentrations of benztropine, biperiden, caramiphen, ethopropazine, procyclidine and trihexyphenidyl affording 50% prevention of nicotine-induced convulsion (ED50 values) were 7.4, 4.6, 7.8, 4.9, 3.1 and 3.3 mg kg(-1), respectively. The classical muscarinic receptor antagonist atropine had potent anti-muscarinic effects but very weak anti-nicotinic activity. The classical nicotinic receptor antagonist mecamylamine had potent anti-nicotinic activity but no anti-muscarinic effects. The pattern of shift of the dose-response curve for nicotine-induced convulsion in mice was determined in the presence of increasing concentrations of the anticholinergic antiparkinson drugs. These drugs were found to increase the ED50 (0.49 mg kg(-1)) of nicotine-induced convulsion in a dose-related manner. The maximum effect of nicotine and the slope of nicotine dose-response curve were not significantly influenced by either low or high doses of benztropine, procyclidine or trihexylphenidyl, which suggests competitive action. Biperiden, caramiphen and ethopropazine, at low doses which significantly increased the ED50 of nicotine, did not affect the maximum effect of nicotine or the slope of the nicotine dose-response curve; at higher doses, however, they reduced the maximum effect and the slope, which suggests that these drugs have both competitive and non-competitive properties in antagonizing nicotine-induced convulsion in mice. The experiments demonstrate that the anticholinergic antiparkinson drugs and mecamylamine effectively antagonize nicotine-induced convulsion, but atropine does not; some of these drugs have competitive properties whereas others seem to have both competitive and non-competitive properties in antagonizing nicotine-induced convulsion in mice.
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Current treatment of nerve agent poisoning with ionotropic drugs proves inadequate, and alternative treatment strategies are searched for. Based on positive findings with metabotropic glutamate modulators in microinfusion studies, the present study was initiated to examine anticonvulsant effects of MPEP (2-Methyl-6-(phenylethynyl)pyridine hydrochloride), a metabotropic glutamate receptor 5 antagonist, and DCG-IV ((2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine), a metabotropic glutamate receptor 2/3 agonist, when administered systemically in combinations with HI-6 (1-[([4-(aminocarbonyl)pyridino]methoxy)methyl]-2-[(hydroxyimino)methyl]pyridinium) and procyclidine or HI-6 and levetiracetam relative to the combination of HI-6, procyclidine, and levetiracetam. The results showed that MPEP or DCG-IV combined with HI-6 and procyclidine resulted in substantial antidotal efficacy when administered 20 min after onset of seizures elicited by soman. MPEP or DCG-IV combined with HI-6 and levetiracetam did not terminate seizures and preserve lives. When given 20 min before challenge with soman, DCG-IV in combination with HI-6 and procyclidine provided protection, whereas MPEP combined with HI-6 and procyclidine did not. Combinations with metabotropic glutamate receptor modulators did not achieve the same high level of antidotal efficacy as the combination of HI-6, procyclidine, and levetiracetam. MPEP alone inhibited pseudocholinesterase activity in the brain markedly. A positive correlation was found between latency to seizure onset or full protection and level of pseudocholinesterase activity in brain. MPEP and DCG-IV can serve as effective anticonvulsants against nerve agent poisoning when combined with HI-6 and procyclidine. Metabotropic glutamate receptor modulators may represent an alternative or supplement to treatment with ionotropic drugs.
The goals of the present study were: (1) to investigate the binding properties of (R)- and (S)-procyclidine and two achiral derivatives of muscarinic M1, M2 and M4 receptor subtypes and (2) to identify the interactions which allow these receptors to discriminate between the two stereoisomers. (R)-Procyclidine showed a higher affinity for human neuroblastoma NB-OK 1 muscarinic M1 and rat striatum muscarinic M4 receptors, as compared to rat cardiac M2 receptors. (S)-Procyclidine had a 130-fold lower affinity than (R)-procyclidine for M1 and M4 receptors, and a 40-fold lower affinity for M2 receptors. Pyrrinol, the achiral diphenyl derivative with the cyclohexyl group of (S)-procyclidine replaced by a phenyl group, has an eight-fold lower affinity for M1 and M4 receptors, as compared to (R)-procyclidine, and a three-fold lower affinity for M2 receptors. Hexahydro-procyclidine, the corresponding achiral dicyclohexyl compound, had a 10- to 20-fold lower affinity than (R)-procyclidine for the three receptors. The increase in binding free energy, which is observed when the phenyl and cyclohexyl groups of procyclidine are separately replaced by cyclohexyl and phenyl groups, respectively, was additive in the case of M1, M2 and M4 receptors. This indicates that the muscarinic receptor stereoselectivity was based on the coexistence of two binding sites, one preferring a phenyl rather than cyclohexyl group and the second preferring a cyclohexyl rather than a phenyl group. In addition, there were also binding sites for the hydroxy moiety and the protonated amino group of the ligands. The greater affinity and stereoselectivity of M1 and M4 muscarinic receptors for (R)-procyclidine reflected the better fit of the cyclohexyl group of (R)-procyclidine to the subsite of M1 and M4 as compared to M2 receptors.
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The tolerance of five central muscarinic receptor antagonists has been studied in experimental animals. According to the effect on orientation-exploratory reaction, drugs were arranged in the following order of increasing toxicity: procyclidine < trihexiphenidyl < benactizine < atropine < scopolamine. For the same therapeutic index, trihexiphenidyl and benactizine were characterized by the maximum tolerance (TD50/ED50 > 10) in mice. Scopolamine and atropine exhibited anticonvulsant activity at doses exceeding the threshold values by a factor of 6.3 and 3.9, respectively. For procyclidine, the average anticonvulsant dose was threefold lower than the threshold value. Benactizine and procyclidine had maximum tolerance levels in rats. The TD50/ED50 ratio for these drugs was greater than 3 (against 0.5 - 0.7 in groups treated with trihexiphenidyl, atropine and scopolamine).