Interaction between clonidine and desipramine in man

Review of clinical pharmacokinetics and pharmacodynamics of clonidine as an adjunct to opioids in palliative care

Clonidine is an α-adrenoceptor agonist acting on receptors in the brain and peripheral tissues, leading to a reduction in sympathetic outflow and release of certain neurotransmitters. Clonidine has multiple uses across various medical conditions. One of its uses is as adjuvant to anaesthetic and analgesic agents specially opioids, mostly administered through intravenous and epidural routes. The opioids, effective in cancer pain management, are associated with various side effects such as sedation, pruritus, constipation, nausea, respiratory depression, tolerance and dependence. Combination of clonidine with opioids seems to help to achieve better pain management and less need of opioids. Use of clonidine in palliative care has been less common, but it is gradually gaining recognition for its potential benefits in managing symptoms like cancer pain and agitation. This combination approach has been explored in palliative care settings, including cancer pain and agitation, where patients experience complex and refractory symptoms. It seems to be well tolerated and gives better symptom relief. The available literature on clonidine's use in cancer pain and agitation management, especially in subcutaneous form, is limited and outdated. Therefore, the optimal dosing, safety profile and overall effectiveness of subcutaneous clonidine requires further exploration through prospective research studies.

Antidepressant Drugs Effects on Blood Pressure

Individuals suffering from depressive disorders display a greater incidence of hypertension compared with the general population, despite reports of the association between depression and hypotension. This phenomenon may depend, at least in part, on the use of antidepressant drugs, which may influence blood pressure through different effects on adrenergic and serotoninergic pathways, as well as on histaminergic, dopaminergic, and cholinergic systems. This review summarizes extant literature on the effect of antidepressant drugs on blood pressure. Selective serotonin reuptake inhibitors are characterized by limited effects on autonomic system activity and a lower impact on blood pressure. Thus, they represent the safest class-particularly among elderly and cardiovascular patients. Serotonin-norepinephrine reuptake inhibitors, particularly venlafaxine, carry a greater risk of hypertension, possibly related to greater effects on the sympathetic nervous system. The norepinephrine reuptake inhibitor reboxetine is considered a safe option because of its neutral effects on blood pressure in long-term studies, even if both hypotensive and hypertensive effects are reported. The dopamine-norepinephrine reuptake inhibitor bupropion can lead to blood pressure increases, usually at high doses, but may also cause orthostatic hypotension, especially in patients with cardiovascular diseases. The norepinephrine-serotonin modulators, mirtazapine and mianserin, have minimal effects on blood pressure but may rarely lead to orthostatic hypotension and falls. These adverse effects are also observed with the serotonin-reuptake modulators, nefazodone and trazodone, but seldomly with vortioxetine and vilazodone. Agomelatine, the only melatonergic antidepressant drug, may also have limited effects on blood pressure. Tricyclic antidepressants have been associated with increases in blood pressure, as well as orthostatic hypotension, particularly imipramine. Oral monoamine-oxidase inhibitors, less frequently skin patch formulations, have been associated with orthostatic hypotension or, conversely, with hypertensive crisis due to ingestion of tyramine-containing food (i.e., cheese reaction). Lastly, a hypertensive crisis may complicate antidepressant treatment as a part of the serotonin syndrome, also including neuromuscular, cognitive, and autonomic dysfunctions. Clinicians treating depressive patients should carefully consider their blood pressure status and cardiovascular comorbidities because of the effects of antidepressant drugs on blood pressure profiles and potential interactions with antihypertensive treatments.

Depressive und Angststörungen bei somatischen Krankheiten

Depressiv-ängstliche Störungen sind bei den unterschiedlichen somatischen Erkrankungen häufig. Sie sind nicht nur als Reaktion auf die Situation der Erkrankung zu verstehen, sondern in ein komplexes Bedingungsgefüge eingebettet. Sie sind besonders häufig bei Erkrankungen, die das Zentralnervensystem oder endokrine Regulationssysteme direkt betreffen. Es besteht ein enger Zusammenhang zur Chronizität, Schwere und Prognose der Erkrankung. Eigenständige Effekte von diversen pharmakologischen Substanzgruppen sind wahrscheinlich.

Pharmacokinetic and pharmacodynamic drug interactions in the treatment of attention-deficit hyperactivity disorder

The psychostimulants methylphenidate, amphetamine and pemoline are among the most common medications used today in child and adolescent psychiatry for the treatment of patients with attention-deficit hyperactivity disorder. Frequently, these medications are used in combination with other medications on a short or long term basis. The present review examines psychostimulant pharmacology, summarises reported drug-drug interactions and explores underlying pharmacokinetic and pharmacodynamic considerations for interactions. A computerised search was undertaken using Medline (1966 to 2000) and Current Contents to provide the literature base for reports of drug-drug interactions involving psychostimulants. These leads were further cross-referenced for completeness of the survey. Methylphenidate appears to be more often implicated in pharmacokinetic interactions suggestive of possible metabolic inhibition, although the mechanisms still remain unclear. Amphetamine was more often involved in apparent pharmacodynamic interactions and could potentially be influenced by medications affecting cytochrome P450 (CYP) 2D6. No published reports of drug interactions involving pemoline were found. The alpha2-adrenergic agonists clonidine and guanfacine have been implicated in several interactions. Perhaps best documented is their antagonism by tricyclic antidepressants and phenothiazines. In additional, concurrent beta-blocker use, or abrupt discontinuation, can lead to hypertensive response. Although there are few published well-controlled interaction studies with psychostimulants and alpha2-adrenergic agonists, it appears that these agents may be safely coadministered. The interactions of monoamine oxidase inhibitors with psychostimulants represent one of the few strict contraindications.

Cardiovascular drug-drug interactions

The drug-drug interactions discussed in this article have either documented or suspected clinical relevance for patients with cardiovascular disease and the clinician involved in the care of these patients. Oftentimes, drug-drug interactions are difficult, if not impossible, to predict because of the high degree of interpatient variability in drug disposition. Certain drug-drug interactions, however, may be avoided through knowledge and sound clinical judgment. Every clinician should maintain a working knowledge of reported drug-drug interactions and an understanding of basic pharmacokinetic and pharmacodynamic principles to help predict and minimize the incidence and severity of drug-drug interactions.

Antidepressant drug administration modifies the interactive relationship between alpha(2)-adrenergic sensitivity and levels of TNF in the rat brain

A reciprocally permissive interaction occurs between cellular responses elicited by the pleiotropic cytokine tumor necrosis factor-alpha (TNF) and alpha(2)-adrenergic receptor activation, such that each may adapt in response to modifications in the other's effects. Changes in presynaptic adrenergic sensitivity as well as neuronal sensitivity to TNF have been implicated in the mechanism of action of antidepressant drugs. The present study examines the influence of alpha(2)-adrenergic receptor activation on levels of TNF in regions of the brain associated with adrenergic function and the expression of mood. Additionally, the role of TNF as a neuromodulator is demonstrated by in vivo microinfusion of rrTNF proximal to the hippocampus. Administration to rats of an alpha(2)-adrenergic receptor agonist (clonidine) decreases levels of TNF in homogenates of rat locus coeruleus and hippocampus within 7.5 min. Chronic (14 days) administration of the antidepressant drugs desipramine or zimelidine transforms alpha(2)-adrenergic receptor-dependent decreases in TNF levels to increases in levels of TNF in the locus coeruleus. This transformation to an increase in total levels of TNF also occurs, although transiently, in the hippocampus following acute (1 day) antidepressant drug administration. The effect of TNF on presynaptic alpha(2)-adrenergic sensitivity was also investigated. Field stimulation of hippocampal slices from rats microinfused with rrTNF proximal to the hippocampus for 14 days demonstrates a decrease in fractional release of [3H]NE and an increase in alpha(2)-adrenergic autoreceptor sensitivity. These data demonstrate a mutual dependence between alpha(2)-adrenergic receptor activation and levels of TNF in the central nervous system that would culminate in an increase in neurotransmitter release following antidepressant drug administration.

Hypertensive urgency induced by an interaction of mirtazapine and clonidine

Mirtazapine is a new antidepressant with a tetracyclic chemical structure that is not related to selective serotonin reuptake inhibitors, tricyclic antidepressants, or monoamine oxidase inhibitors. The antidepressant effect results from stimulation of the noradrenergic system through antagonism at central (alpha2-inhibitory receptors. Clonidine exerts its antihypertensive effect by stimulating these receptors to cause a reduction in endogenous release of norepinephrine. Therefore, the two agents have mechanisms of action that potentially oppose one another. We report a case of hypertensive urgency that ensued after a patient stabilized on clonidine began taking mirtazapine.

Drug-drug interactions in pediatric psychopharmacology

Serious consequences caused by drug-drug interactions continue to plague contemporary pharmacotherapy. The possibility of a drug-drug interaction should be suspected anytime a new or unexpected effect occurs that complicates the clinical management of a patient in the setting where the patient is receiving more than one drug. In this article, the authors address the mechanisms of pharmacokinetic-based drug-drug interactions focusing on important interactions that may occur with the common medications a pediatrician may prescribe to the child receiving psychoactive medication(s) prescribed by a child psychiatrist.

Drug interactions in hypertensive patients. Pharmacokinetic, pharmacodynamic and genetic considerations

Antihypertensive treatment has proven benefits, and the number of patients being treated with these drugs is significant. Hypertensive patients may have other medical illnesses for which they receive medications, and interactions between antihypertensive agents and other drugs is likely. Some of these interactions may lead to undesirable effects or even loss of blood pressure control. However, drug interactions can also be beneficial when 2 antihypertensive drugs with different pharmacological actions are prescribed in combination and with a clear therapeutic objective in mind. Clinicians should be aware of the mechanisms and the consequences of the different types of interaction in hypertensive patients, so that a desired pharmacological response can be achieved with the fewest side effects in the patients.

Reflex changes induced by clonidine in spinal cord injured patients

In a single blind study of 6 spinal cord injured (SCI) men, the effects of clonidine, a selective alpha-2 adrenergic agonist, on spasticity were compared to diazepam and placebo. Since a potential side-effect of clonidine is postural hypotension, a combination of clonidine and desipramine was also tested. Vibration of the leg will inhibit the H reflex in a normal subject; whereas, this inhibition is markedly reduced in SCI patients with spasticity. A vibratory inhibition index (VII) was derived for each treatment. The pre-treatment VII was 92.08 +/- 3.15%; for SCI subjects, compared to 46.5 +/- 7.7% for 6 normal subjects. Clonidine significantly reduced the mean index of SCI patients to 59.42 +/- 3.91% (p less than 0.001). The VII for placebo, diazepam and the clonidine-desipramine combination were not statistically different than the pre-treatment values in SCI patients. In conclusion, clonidine has an anti-spasticity effect in SCI patients, both subjectively, and objectively, in terms of vibratory inhibition of the H reflex.

The cardiovascular effects of antidepressants

This monograph comprises a review of the cardiovascular effects of the various types of antidepressant drugs in clinical use. The frequency, severity and clinical importance of these effects are placed in perspective. Most antidepressants can cause changes in blood pressure. Both the tricyclic type (TCA) and the monoamine oxidase inhibitors (MAOIs) can produce postural hypotension which may be dose-limiting. In addition, the MAOIs may be associated with severe hypertension when amine-containing foods or medicines are ingested. It is unlikely that therapeutic doses of any available antidepressant drug could impair cardiac contractility. Typical TCAs can cause abnormalities of cardiac conduction and arrhythmias, but this affects less than 5% of patients, mostly to a clinically insignificant extent. Newer compounds such as lofepramine, mianserin, trazodone and viloxazine seem safer in this respect. Reports of an association between therapeutic use of TCAs and sudden death are far from convincing. Overdosage with the MAOIs, lithium and carbamazepine is dangerous but not common; overdose with a TCA is a major source of morbidity and mortality. Lofepramine, mianserin and trazodone are relatively safe in overdose. The use of various antidepressants in patients with hypertension, cardiac failure, angina pectoris, myocardial infarction, or cardiac arrhythmias is discussed and guidelines suggested for the selection and use of antidepressant medication.

Drug interactions that matter. A critical reappraisal

Drug interactions are ubiquitous but those with proven clinical relevance are much less common. Only when the combined effects of the interacting drugs are greater or less than the arithmetic sum of their individual actions can the event be considered a true interaction. This eliminates many candidate 'interactions' which in reality merely describe the summation of similar or opposing, but independent, drug effects. An appreciation of those drug interactions that really do matter can be best achieved by combining a practical knowledge of the pharmacological mechanisms involved with awareness of the most vulnerable patients (those with little reserve capacity) and the drugs associated with the greatest risk (those with a narrow therapeutic index). This review follows these guidelines and provides an account of well documented drug interactions categorised according to mechanism.

Factors that contribute to resistant forms of hypertension. Pharmacological considerations

Treatment failure may be caused by induction of compensatory mechanisms that compromise effectiveness of the antihypertensive regimen. Antihypertensive agents have been classified according to mechanism of action, and compensatory mechanisms usually evoked by each class of drugs have been reviewed. Host factors may be responsible for the inability to control blood pressure or may predict special sensitivity or contraindication to a particular class of antihypertensive agents. Recommendations have been made for modification of stepped-care regimens and selection of initial antihypertensive agents based on host factors. Experimental evidence suggests the ability to target antihypertensive therapy in a manner that will prevent or reverse specific end-organ damage. Clinical studies are needed to define the long-term benefit derived from aggressive target organ protection.

An algorithm for the management of resistant hypertension

Before hypertension can be considered resistant to a rational triple drug regimen in maximal doses, the physician should rule out poor adherence to the regimen (including diet), adverse drug interactions, pseudotolerance (due to fluid retention), office hypertension, pseudohypertension, and an unrecognized secondary cause (e.g., renovascular disease, primary aldosteronism, and pheochromocytoma). When these have been excluded, hemodynamic measurements are indicated to identify the mechanism(s) at fault so that the therapeutic regimen can be modified appropriately.

Clonidine interaction in amitriptyline poisoning

The effect of clonidine on amitriptyline-induced cardiotoxicity was investigated in an experimental rat mode. A continuous infusion of amitriptyline (30 mg/kg/h) was given until the animal died, usually within 2 hours. Fifteen minutes after starting the amitriptyline infusion, 50 micrograms/kg of clonidine was given intravenously over five minutes. This led to an increase in blood pressure and left ventricular end-diastolic pressure. There was no significant change in cardiac contractility. Heart rate decreased. These changes can be explained by an increase in afterload due to peripheral vasoconstriction. No signs of reduced sympathetic outflow were seen on the ECG. The peripheral effects of clonidine dominated over the central effects, which may be due to a competitive inhibition of amitriptyline at central noradrenergic sites. An increased afterload pushes the heart towards failure and increases mortality. In this model, clonidine did not reverse amitriptyline-induced cardiovascular toxicity. It may even be potentially harmful if used to treat tricyclic antidepressant poisoning.

Do antidepressants cause postural hypotension by blocking cardiovascular reflexes?

Postural changes in blood pressure, respiratory sinus arrhythmia, the heart rate response to Valsalva's manoeuvre and to standing, and the blood pressure and heart rate responses to isometric exercise have been measured in seven young women taking antidepressant medication and compared with seven controls. Among the patients there was a significant rank order correlation between the degree of postural hypotension and the daily dose of antidepressant medication. There was a significant impairment among the patients of all cardiovascular reflex responses measured, suggesting both cholinergic and adrenergic blockade. These results suggest that postural hypotension associated with antidepressant medication is caused in large part by a failure of reflex peripheral vasoconstriction.

Different pharmacological interaction of clonidine and guanabenz with antidepressive drugs

A study was made of the effect of several antidepressive drugs with different mechanisms of action on cardiovascular response induced by clonidine (CLO) or guanabenz (GUA) in anaesthetized normotensive rats. The acute pretreatment (1 mg.kg-1) with desipramine (DMI), maprotiline (MAP) and mianserin (MIA) reduced the hypotensive and bradycardiac responses induced by CLO (10 micrograms.kg-1), while only MIA prevented these central actions when elicited by GUA (30 micrograms.kg-1). Only chronic treatment with DMI reduced the hypotensive effect of CLO, but none of long-term antidepressant administrations decreased the fall in blood pressure induced by GUA. The long-term administration of DMI, MAP and MIA abolished the bradycardia from both agonists, CLO and GUA. The different pharmacological interaction of CLO and GUA with (acute or chronic) antidepressive treatments could be explained by a structural difference between the two agonists, and also by differences in localization and/or subtype of the alpha-adrenoceptors involved in their central cardiovascular effects.

Rat brain alpha 2-pre- and postsynaptic receptors are different or differently modulated?

In order to get better characterization of alpha 2-pre- and postsynaptic noradrenergic receptors in the rat brain, we investigated the alpha 2-receptor changes which take place during a 12-day treatment with the alpha 2-antagonists yohimbine (4 mg/kg) and mianserin (10 mg/kg). These treatments caused a significant increase in the sensitivity of hypothalamic synaptosomes to the inhibitory action of the noradrenergic agonist clonidine on the 3H-noradrenaline release elicited by K depolarization. Frontal cortex alpha 2-autoreceptors were not affected by drug treatments. However, the 3H-p-aminoclonidine (3H-PAC) binding to membranes from hypothalamus or frontal cortex from treated animals was the same as in controls. Changes in neural firing, elicited by the alpha 2-antagonists on noradrenergic neurons, could explain our results. The presynaptic autoreceptors may thus become hypersensitive to counteract the enhanced neurotransmitter release in the hypothalamus, where the noradrenaline is accumulated at the synaptic cleft. In the frontal cortex, where it seems that only 5% of the noradrenergic terminals make synaptic contacts with postsynaptic elements, the alpha 2-autoreceptors are less sensitive to an enhanced neurotransmitter release. Alternatively, they have scarce functional importance because the noradrenaline release is effectively modulated by the inhibitory recurrent locus coeruleus collaterals. At the postsynaptic level, the receptor down-regulation might be prevented by chronic presence of the antagonist drug. Thus the different behavior between pre- and postysynaptic alpha 2-receptors and between alpha 2-receptors of different brain areas may be ascribed to a different modulation rather than to different molecular arrangements.

Absence of an effect of mianserin on the actions of clonidine or methyldopa in hypertensive patients

The concurrent administration of tricyclic antidepressants has been shown in man to result in a clinically significant impairment of the antihypertensive effect of clonidine. This interaction is thought to be related to competition for central alpha 2 receptors where clonidine acts as an agonist and the tricyclics act as antagonists. Although it seems to cause less cardiovascular effects than tricyclic antidepressants, the tetracyclic antidepressant, mianserin also has been reported to be an alpha receptor antagonist and may, therefore, also interfere with the antihypertensive activity of centrally-acting drugs. This study investigates the effects of acute and chronic mianserin administration in patients with essential hypertension established on long term treatment with either clonidine or methyldopa. The first dose of mianserin was not associated with an increase in blood pressure and during a further two weeks of mianserin therapy there were no significant alterations in blood pressure, supine or erect. Similarly, mianserin did not alter heart rate either after acute or after chronic administration. Mianserin itself had a sedative effect but there was no interference with the sedation attributable to clonidine or methyldopa. Mianserin caused no reduction salivary flow and did not influence the reduced saliva production caused by clonidine. Both clonidine and methyldopa are associated with a reduction in sympathetic outflow but there was no evidence in this study of any further change in plasma noradrenaline or 24 h urinary catecholamine excretion. This study demonstrates that if mianserin is given acutely or chronically, it does not interfere with the effects of the centrally acting anti-hypertensive drugs, clonidine and methyldopa. Mianserin may therefore be a suitable antidepressant for patients receiving these antihypertensive agents if drug treatment for depression is indicated.

Cardiac effects of antidepressant drugs. A comparison of the tricyclic antidepressants and fluvoxamine

1 The cardiovascular effects of the tricyclic antidepressants (TCAs) are reviewed and compared with those of fluvoxamine, a new 5-hydroxytryptamine (5-HT) re-uptake inhibitor. 2 The TCAs have important effects on the heart, related to their anticholinergic and quinidine-like properties. The major side effects in therapeutic dosage include heart rate increase, postural hypotension and slight prolongation of the intraventricular conduction time and QT interval. In toxic dosage (or normal dosage in patients with severe heart disease) both advanced heart block and ventricular arrhythmias can occur, together with clinically important loss of myocardial contractile force. 3 Fluvoxamine has no effects on the heart except for a statistically (but not clinically) significant slowing of the heart rate.

Assessment of the interaction between mianserin and centrally-acting antihypertensive drugs

1 The interaction between mianserin and centrally-acting antihypertensive drugs was evaluated in normal volunteers and in patients with essential hypertension receiving either clonidine or methyldopa. 2 The administration of the first dose of 20 mg mianserin to the normal volunteers was associated with a significant sedative effect and transient postural hypotension. 3 In the normal volunteers, the blood pressure responses to a single oral dose of 300 micrograms clonidine were not modified by pretreatment with mianserin. The bradycardia associated with clonidine alone, however, was significantly attenuated. 4 In the patient study, no significant changes in blood pressure control were observed, either after the first dose of 30 mg mianserin or after one and two weeks' continued treatment with mianserin. 5 There is no evidence from these studies that the addition of mianserin therapy results in a clinically significant impairment of the antihypertensive effects of clonidine or methyldopa.

Lack of interaction between the tetracyclic antidepressant maprotiline and the centrally acting antihypertensive drug clonidine

The well known interaction between tricyclic antidepressants and the centrally acting antihypertensive drug clonidine, namely impairment of the antihypertensive effect of clonidine, is thought to be related to blockade of noradrenaline uptake or competition at central alpha-receptors. The tetracyclic antidepressant maprotiline has been shown to be a potent inhibitor of noradrenaline uptake and it might, therefore, interfere with the antihypertensive action of clonidine. The possible interaction of clonidine and maprotiline was studied in 8 healthy subjects using doses in the therapeutic range. The study followed a double-blind, cross over design, in which clonidine alone (0.3 mg p.o.), clonidine (0.3 mg p.o.) plus maprotiline (100 mg in 4 divided doses over 22 h), maprotiline alone (100 mg in 4 divided doses over 22 h) and placebo were given by the double-dummy technique. Several pharmacodynamic parameters were measured for 12 h after administration of the drugs (supine and erect blood pressure, heart rate, saliva production and sedation). Concurrent administration of maprotiline did not alter the effect of clonidine and neither the size nor the time of the maximal response after clonidine were influenced by maprotiline. It is concluded that [1] blockade of noradrenaline uptake is not associated with the interaction of tricyclic antidepressants and clonidine, and [2] maprotiline should be preferred to tricyclic antidepressants in hypertensive patients on clonidine therapy if a concomitant depressive illness has to be treated.

Chemistry, pharmacology, pharmacokinetics, adverse effects, and efficacy of the antidepressant maprotiline hydrochloride

Maprotiline, a tetracyclic antidepressant with sedative properties, exhibits strong inhibitory effects on norepinephrine uptake across nerve cell membranes but interferes relatively little with serotoninergic mechanisms. The biological half-life of unchanged maprotiline in blood averages 43 hours. Though several studies suggest a more rapid onset of antidepressant effects with maprotiline than with amitriptyline or imipramine, this issue remains unresolved. The adverse effect profile of maprotiline is similar to that of the tricyclic antidepressants, except that rashes are about twice as frequent with maprotiline as with amitriptyline or imipramine. The most frequent adverse reactions are anticholinergic effects and sedation. Data suggest less frequent and severe anticholinergic side effects with maprotiline than with amitriptyline. Maprotiline may be less likely to induce orthostatic hypotension and tachycardia than standard tricyclic antidepressants, but clinically important differences in cardiovascular effects remain to be conclusively demonstrated. Many patients benefit from the convenience of once daily dosing. Maprotiline is comparable in antidepressant efficacy to the tricyclic antidepressants.

Effects of antidepressants on cardiac function

Most antidepressants may affect the cardiovascular system adversely although their mode of action in causing these complications differs. They affect the cardiovascular system directly or through drug interactions. They may affect blood pressure, the inotropic state of the heart and cardiac conduction. The causes of these complications are discussed with relevance to the known action of these agents. Although serious cardiovascular complications do not occur frequently at therapeutic dosage, a knowledge of these abnormalities is essential for safe prescribing. After overdose many of these agents may prove lethal.

Pharmacodynamic studies on mianserin and its interaction with clonidine

There is evidence that clonidine's hypotensive effect is reduced by the concurrent administration of tricyclic antidepressants. It has been proposed that this results from an interaction at alpha 2-receptors in the brain stem where clonidine acts as a relatively selective agonist and the tricyclic antidepressants as antagonists. Mianserin is an antidepressant with a tetracyclic structure and, although it has been reported to cause less cardiovascular disturbance, there is evidence that it also has alpha-adrenoceptor blocking effects. This study in 6 normotensive healthy male volunteers was designed to investigate a possible interaction between clonidine and the antidepressant mianserin. Administration of the first dose of 20 mg mianserin was associated with acute cardiovascular effects, notably transient postural hypotension, but no significant disturbance of heart rate or blood pressure was detected after 3 days continuous treatment with mianserin 20 mg tid. Following pre-treatment with mianserin or placebo the responses to a single oral dose of 300 micrograms clonidine were then assessed. The combination of mianserin and clonidine was not associated with any attenuation of clonidine's hypotensive effect, erect or supine, but there was significant attenuation of clonidine's supine bradycardic effect. There was no evidence that mianserin interfered with the ability of clonidine to diminish salivary flow, cause sedation, and reduce catecholamine output, but it was noted that mianserin itself had a very pronounced sedative effect. Mianserin alone had no significant effect on salivary flow. This short term study demonstrates that mianserin does not significantly interfere with the responses to a single oral dose of clonidine.

Inhibition of neuronal uptake reduces the presynaptic effects of clonidine but not of alpha-methylnoradrenaline on the stimulation-evoked release of 3H-noradrenaline from rat occipital cortex slices

The iminoimidazolidine clonidine reduced concentration-dependently the release of 3H-noradrenaline evoked by electrical stimulation from the rate cerebral cortex. Exposure to the neuronal uptake inhibitors cocaine (10 micro M), desipramine (0.1 to 1 micro M) and amphetamine (1 micro M) significantly increased the stimulation-evoked overflow of tritium. These uptake inhibitors antagonized the effects of clonidine on stimulation evoked 3H-noradrenaline release but failed to modify the inhibition induced by the catecholamine alpha-methylnoradrenaline. Inhibition of monoamine oxidase by preincubation of cerebral cortex slices with 0.5 mM pargyline significantly increased the stimulation-evoked overflow of tritium, but clonidine was as effective as in the controls in inhibiting 3H-noradrenaline overflow. The antagonism by desipramine of the clonidine-induced inhibition of neurotransmission could not be attributed to a blockade of presynaptic alpha-adrenoceptors because: (1) the facilitating effect of phentolamine on 3H-noradrenaline overflow was not modified in the presence of desipramine; (2) the magnitude of the inhibition of the stimulation-evoked 3H-noradrenaline release elicited by alpha-methylnoradrenaline was the same in the presence of cocaine or desipramine; (3) exposure to desipramine in the presence of cocaine did not further increase the stimulation-evoked release of 3H-transmitter. Since the catecholamine alpha-methylnoradrenaline inhibited neurotransmission in the presence of desipramine or cocaine, we can conclude that inhibition of neuronal uptake of noradrenaline antagonized selectively the presynaptic inhibitory effects of imidazolines on alpha 2-adrenoceptors. The influence of the inhibition of neuronal uptake on the presynaptic effects of imidazolines and catecholamines should be taken into account when the relative order of potencies of various alpha 2-adrenoceptors agonists is determined.

Antihypertensive pharmacology

Although drug treatment of hypertension is associated with improved survival and decreased vascular complications, drug compliance is a major problem in the control of hypertension. All antihypertensive medications are associated with side effects; thus, it is a physician's responsibility to explain to each patient the side effects of the drugs he prescribes to treat hypertension, and to instill in the patient a sense of necessity for the treatment of hypertension. The choice of antihypertensive drug should be made based on each patient's lifestyle, overall health and ability to tolerate the drug. Ideally, the antihypertensive regimen should be simple, effective, convenient to take and have very few side effects.

Clonidine: attenuation of sedative action by facilitated central noradrenergic neurotransmission

Administration of clonidine, 0.05 mg/kg i.p. to mice 30 min before trial significantly depressed the exploration of a Y-maze. This effect was completely antagonized by 1-amphetamine, 0.75 mg/kg i.p., given 10 min before trial, which by itself did not change the behaviour studied. The clonidine-induced behavioural depression also appeared reduced after pretreatment with desipramine (10 mg/kg i.p., 30 min before clonidine) which, like l-amphetamine, by itself was inactive. The above treatment with clonidine significantly reduced the accumulation of dopa after inhibition of central aromatic L-amino acid decarboxylase both in the noradrenaline (NA) rich neocortex and the dopamine-rich neocortex and the dopamine-rich corpus striatum, whereas the dopa accumulation in the limbic brain regions was not significantly affected. l-Amphetamine, 0.75 mg/kg i.p., did not by itself significantly affect the dopa accumulation, but reduced the clonidine-induced effects. The results are compatible with the notion that the depression of exploratory behaviour by clonidine is related to impaired central NA-neurotransmission and rule out the possibility that it is due to activation of central post-synaptic NA-(alpha-)-receptors.

The effects of desmethylimipramine on the pharmacological actions of alpha methyldopa in man

The effect of pretreatment with the tricyclic antidepressant desmethylimipramine (DMI) 75 mg daily for 3 days on the action of oral methyldopa 750 mg was investigated in a double blind crossover design in volunteers. DMI pretreatment caused a small but not significant increase in supine systolic and diastolic blood pressure and heart rate. However, the effects of methyldopa on lying and standing blood pressure and heart rate were not markedly altered by pretreatment. In particular, the fall in standing blood pressure after methyldopa was present with and without DMI and the sedative action of methyldopa was similar. DMI alone reduced saliva production. No evidence was found that tricyclic antidepressant drugs significantly modify the hypotensive effect of methyldopa in man.

Antidepressants in the general hospital

An approach to the use of antidepressant medication in the general hospital is presented. The type of depression most likely to respond to chemotherapy is described, categories of available antidepressant agents are discussed, and relevant pharmacologic aspects are outlined. This paper suggests clinical guidelines for the use of these drugs, particularly in medical and surgical patients.