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McKeown L, Taylor RW, Day E, Shah R, Marwood L, Tee H, Kerr-Gaffney J, Oprea E, Geddes JR, McAllister-Williams RH, Young AH, Cleare AJ. Patient perspectives of lithium and quetiapine augmentation treatment in treatment-resistant depression: A qualitative assessment. J Psychopharmacol 2022; 36:557-565. [PMID: 35475375 PMCID: PMC9112618 DOI: 10.1177/02698811221089042] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
BACKGROUND Treatment-resistant depression (TRD) has a profound cost to patients and healthcare services worldwide. Pharmacological augmentation is one therapeutic option for TRD, with lithium and quetiapine currently recommended as first-line agents. Patient opinions about pharmacological augmentation may affect treatment outcomes, yet these have not been systematically explored. AIMS This study aimed to qualitatively assess patient experiences of lithium and quetiapine augmentation. METHODS Semi-structured interviews were conducted with 32 patients from the ongoing lithium versus quetiapine open-label trial comparing these augmentation agents in patients with TRD. Interviews were audio recorded, transcribed and a thematic analysis was used to assess patient opinions of each agent. RESULTS Four main themes were generated from the thematic analysis: 'Initial concerns', 'Experience of side effects', 'Perception of treatment efficacy' and 'Positive perception of treatment monitoring'. Patient accounts indicated a predominantly positive experience of lithium and quetiapine augmentation. Greater apprehension about side effects was reported for lithium prior to treatment initiation, but greater experience of negative side effects was reported for quetiapine. Clinical monitoring was perceived positively. CONCLUSION Patient accounts suggested treatment augmentation with lithium or quetiapine was acceptable and helpful for most patients. However, anticipation and experiences of adverse side effects may prevent some patients from benefitting from these treatments.
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Affiliation(s)
- Lucas McKeown
- Centre for Affective Disorders, Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK
| | - Rachael W Taylor
- Centre for Affective Disorders, Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK
| | - Elana Day
- Centre for Affective Disorders, Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK
| | - Rupal Shah
- Centre for Affective Disorders, Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK
| | - Lindsey Marwood
- Centre for Affective Disorders, Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK
| | - Helena Tee
- Centre for Affective Disorders, Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK
| | - Jess Kerr-Gaffney
- Centre for Affective Disorders, Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK,Jess Kerr-Gaffney, Centre for Affective Disorders, Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London WC2R 2LS, UK.
| | - Emanuella Oprea
- Centre for Affective Disorders, Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK
| | - John R Geddes
- Department of Psychiatry, Warneford Hospital, University of Oxford, Oxford, UK,Warneford Hospital, Oxford Health NHS Foundation Trust, Oxford, UK
| | - R Hamish McAllister-Williams
- Cumbria, Northumberland, Tyne and Wear NHS Foundation Trust, Newcastle upon Tyne, UK,Northern Centre for Mood Disorders, Newcastle University Translational and Clinical Research Institute, Newcastle upon Tyne, UK
| | - Allan H Young
- Centre for Affective Disorders, Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK,South London and Maudsley NHS Foundation Trust, London, UK
| | - Anthony J Cleare
- Centre for Affective Disorders, Department of Psychological Medicine, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, London, UK,South London and Maudsley NHS Foundation Trust, London, UK
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Abstract
The pharmacological treatment of the elderly differs from that of younger patients, mainly because of altered pharmacokinetics and the higher proportion of patients with organic disorders. We deal here with dementia, delirium, affective disorder, late-life schizophrenia, sleep disturbance, and rapid tranquillisation.
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Knöchel C, Alves G, Friedrichs B, Schneider B, Schmidt-Rechau A, Wenzlera S, Schneider A, Prvulovic D, Carvalho AF, Oertel-Knöchel V. Treatment-resistant Late-life Depression: Challenges and Perspectives. Curr Neuropharmacol 2015; 13:577-91. [PMID: 26467408 PMCID: PMC4761630 DOI: 10.2174/1570159x1305151013200032] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2015] [Revised: 02/25/2015] [Accepted: 02/27/2015] [Indexed: 12/28/2022] Open
Abstract
The current Review article provides a narrative review about the neurobiological underpinnings and treatment of treatment resistant late-life depression (TRLLD). The manuscript focuses on therapeutic targets of late-life depression, which include pharmacological, psychological, biophysical and exercise treatment approaches. Therefore, we summarize available evidences on that kind of therapies for patients suffering from late-life depression. The search for evidences of therapeutic options of late-life depression were done using searching websites as "pubmed", and using the searching terms "depression", "late-life depression", "treatment", "biophysical therapy", "exercise therapy", "pharmacological therapy" and "psychological therapy". To the end, we summarize and discuss current data, providing some directions for further research. Treatment recommendations for elderly depressive patients favour a multimodal approach, containing psychological, pharmacological and secondary biophysical therapeutic options. Particularly, a combination of psychotherapy and antidepressant medication reflects the best therapeutic option. However, mostly accepted and used is the pharmacological treatment although evidence suggests that the drug therapy is not as effective as it is in younger depressive patients. Further studies employing larger samples and longer follow-up periods are necessary and may focus on comparability of study designs and involve novel approaches to establish the validity and reliability of multimodal treatment programs.
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Affiliation(s)
- Christian Knöchel
- Laboratory for Neuroimaging, Dept. of Psychiatry, Psychosomatic Medicine and Psychotherapy, Goethe Univ., Frankfurt/Main, Germany
| | - Gilberto Alves
- Center for Alzheimer’s Disease and Related Disorders, Universidade Federal, do Rio de Janeiro, Brazil
| | - Benedikt Friedrichs
- Laboratory for Neuroimaging, Dept. of Psychiatry, Psychosomatic Medicine and Psychotherapy, Goethe Univ., Frankfurt/Main, Germany
| | | | - Anna Schmidt-Rechau
- Laboratory for Neuroimaging, Dept. of Psychiatry, Psychosomatic Medicine and Psychotherapy, Goethe Univ., Frankfurt/Main, Germany
| | - Sofia Wenzlera
- Laboratory for Neuroimaging, Dept. of Psychiatry, Psychosomatic Medicine and Psychotherapy, Goethe Univ., Frankfurt/Main, Germany
| | - Angelina Schneider
- Laboratory for Neuroimaging, Dept. of Psychiatry, Psychosomatic Medicine and Psychotherapy, Goethe Univ., Frankfurt/Main, Germany
| | - David Prvulovic
- Laboratory for Neuroimaging, Dept. of Psychiatry, Psychosomatic Medicine and Psychotherapy, Goethe Univ., Frankfurt/Main, Germany
| | - André F. Carvalho
- Center for Alzheimer’s Disease and Related Disorders, Universidade Federal, do Rio de Janeiro, Brazil
| | - Viola Oertel-Knöchel
- Laboratory for Neuroimaging, Dept. of Psychiatry, Psychosomatic Medicine and Psychotherapy, Goethe Univ., Frankfurt/Main, Germany
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4
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Going beyond antidepressant monotherapy for incomplete response in nonpsychotic late-life depression: a critical review. Am J Geriatr Psychiatry 2013; 21:973-86. [PMID: 23567381 PMCID: PMC3543487 DOI: 10.1097/jgp.0b013e31826576cf] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2011] [Revised: 03/06/2012] [Accepted: 04/23/2012] [Indexed: 10/27/2022]
Abstract
Many older adults with major depressive disorder (MDD) do not respond to antidepressant monotherapy. Although there are evidence-based treatment options to support treatment beyond monotherapy for adults, the evidence for such strategies, specifically in late-life MDD, is relatively scarce. This review examines the published data describing strategies for antidepressant augmentation or acceleration studied specifically in older adults, including lithium, stimulants, and second-generation antipsychotics. In addition, the authors suggest strategies for future research, such as study of specific agents, refining understanding of the impact of medical or cognitive comorbidity in late-life depression, and comparative effectiveness to examine methods already used in clinical practice.
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5
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Hegerl U, Holtzheimer P, Mergl R, McDonald W. The neurobiology and treatment of late-life depression. HANDBOOK OF CLINICAL NEUROLOGY 2012; 106:265-278. [PMID: 22608627 DOI: 10.1016/b978-0-444-52002-9.00016-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Affiliation(s)
- Ulrich Hegerl
- Department of Psychiatry, University of Leipzig, Leipzig, Germany.
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7
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Abstract
There seems reasonable, if depressing, agreement from studies of mixed aged subjects and elderly subjects in psychiatric settings that nonresponse or poor response to a course of an antidepressant occurs in at least one-third of depressed patients. The figure may be higher in elderly patients in general and those with poor physical health. The human cost of chronic depression is highlighted in the Medical Outcomes Study. The level of functional impairment and intereference with quality of life associated with depression was comparable with or worse than that of eight major chronic medical conditions, including diabetes, arthritis and severe coronary artery disease. The final tragedy for unremitting depression may of course be suicide.
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Abstract
In spite of its origins deeply rooted in the discipline, pharmaco-EEG applications in psychiatry remain limited to its achievements in the field of psychotropic drugs classification and, in few instances, discovery. In the present paper two attempts to transfer pharmaco-EEG methods to psychiatric clinical routine will be described: 1) monitoring of psychotropic drug toxicity at the central nervous system level, and 2) prediction of clinical response to treatment with psychotropic drugs. Both applications have been the object of several investigations providing promising and sometimes consistent findings which, however, had no impact on clinical practice. For the first topic, the review is limited to antipsychotics, lithium and recreational drugs, as for other psychotropic drugs mostly case studies are available, while for the response prediction it will include antipsychotics, antidepressants, anxiolytics, psychostimulants and nootropics. In spite of several methodological limitations, pharmaco-EEG studies dealing with monitoring of antipsychotic- and lithium-induced EEG abnormalities went close to, but never became, a clinical routine. EEG studies of recreational drugs are flawed by several limitations, and failed, so far, to identify reliable indices of CNS toxicity to be used in clinical settings. Several QEEG studies on early predictors of treatment response to first generation antipsychotics have produced consistent findings, but had no clinical impact. For other psychotropic drug classes few and inconsistent reports have appeared. Pharmaco-EEG had the potential for important clinical applications, but so far none of them entered clinical routine. The ability to upgrade theories and methods and promote large scale studies represent the future challenge.
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Affiliation(s)
- Armida Mucci
- Department of Psychiatry, University of Naples SUN, Naples, Italy.
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9
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Abstract
The pharmacotherapeutic use of lithium in the elderly as acute and maintenance therapy in bipolar disorder and augmentation therapy for major depression is well documented. Differences in the response to lithium are explained, in part, by the effect of age-related physiological changes, comorbid conditions, and concurrent medications on the pharmacokinetics of lithium in the elderly. The pharmacokinetic profile of lithium has been studied for many years, primarily in younger adult populations. Lithium pharmacokinetics may be influenced by a number of factors including age. It was first noted several years ago that elderly individuals required lower doses of lithium to achieve serum concentrations similar to those observed in younger adults. This is due to the combination of a reduced volume of distribution and reduced renal clearance. The composition of the human body changes with aging producing an increase in body fat, a decrease in fat-free mass and a decrease in total body water. Lithium clearance decreases as the glomerular filtration rate decreases with increasing age. The effects of other medical conditions in the elderly on the pharmacokinetics of lithium are less well delineated. Reduced lithium clearance is expected in patients with hypertension, congestive heart failure or renal dysfunction. Larger lithium maintenance doses are required in obese compared with non-obese patients. The most clinically significant pharmacokinetic drug interactions associated with lithium involve drugs which are commonly used in the elderly. Thiazide diuretics, ACE inhibitors, and nonsteroidal anti-inflammatory drugs can increase serum lithium concentrations. The tolerability of lithium is lower in the elderly. Neurotoxicity clearly occurs in the elderly at concentrations considered 'therapeutic' in general adult populations. There are no placebo-controlled randomised trials of lithium in old age and recommendations for clinical use are based on extrapolations from pharmacokinetic studies, anecdotal reports from mixed age populations and clinical experience in old age psychiatry. Serum concentrations of lithium need to be markedly reduced in the elderly population and particularly so in the very old and frail elderly.
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Affiliation(s)
- B A Sproule
- Psychopharmacology Research Program, Sunnybrook and Women's College Health Sciences Centre, University of Toronto, Ontario, Canada.
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10
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Bauer M, Zaninelli R, Müller-Oerlinghausen B, Meister W. Paroxetine and amitriptyline augmentation of lithium in the treatment of major depression: a double-blind study. J Clin Psychopharmacol 1999; 19:164-71. [PMID: 10211918 DOI: 10.1097/00004714-199904000-00012] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
To study the efficacy and safety of antidepressant augmentation of ongoing lithium therapy, lithium-maintained patients suffering from an breakthrough episode of major depression were randomly assigned under double-blind conditions to receive paroxetine 20 mg/day (N = 19) or amitriptyline 75 mg/day (N = 23). The initial dosages could be increased after 2 weeks to 40 mg/day and 150 mg/day, respectively, and the patients were treated for a total of 6 weeks. Efficacy was assessed weekly with the 21-item Hamilton Rating Scale for Depression (HAM-D) and the Clinical Global Impression Scale (CGI), and safety was assessed with the Dosage Record and Treatment Emergent Symptom Scale. After 4 weeks, a significantly greater proportion of patients in the paroxetine group had achieved a 50% reduction in baseline HAM-D scores, and the mean improvement in CGI severity of illness was significantly greater in the paroxetine group at weeks 3 and 5. The type and number of emergent events occurring during study treatment corresponded to the known side effect profiles of paroxetine and amitriptyline. Serum lithium levels were not affected by either antidepressant. The authors proposed that the more rapid improvement demonstrated by the group receiving the combination of lithium and paroxetine may be due to the synergistic serotonergic effects of these two medications.
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Affiliation(s)
- M Bauer
- Department of Psychiatry, Berlin Lithium Clinic, Freie Universität Berlin, Germany
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11
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Schweitzer I, Tuckwell V. Risk of adverse events with the use of augmentation therapy for the treatment of resistant depression. Drug Saf 1998; 19:455-64. [PMID: 9880089 DOI: 10.2165/00002018-199819060-00003] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Augmentation therapy is used for those situations where a patient's depression is either treatment-resistant, or partially and/or insufficiently responsive to treatment. It also may be used to attempt to induce a more rapid treatment response. Using drugs together may increase the risk of adverse effects, through potentiation of existing adverse effects or alterations in plasma concentrations of the drug. It is important that clinicians are aware of potential risks of augmentation therapy. Lithium augmentation of a tricyclic antidepressant is relatively well tolerated and the dangers are no greater than using these medications on their own. There are also no reports of serious adverse events when lithium is added to a monoamine oxidase inhibitor. With lithium augmentation of selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitor (SSRI) therapy there have been case reports of the development of a central serotonin syndrome, and thus caution must exercised. A serious concern when using a tricyclic antidepressant to augment an SSRI is the effect of the SSRI on the cytochrome P450 system and the resulting significant increase in tricyclic antidepressant blood concentrations. Augmentation with thyroid hormones appears to be well tolerated and effective. Case reports and open studies indicate that augmentation with buspirone and the psychostimulants, carbamazepine and valproic acid (valproate sodium) is effective and results in minimal adverse effects. However, there is no empirical evidence supporting these results. Recent work supports the tolerability and efficacy of pindolol augmentation. Considerable caution should be exercised when combining psychotropic drugs. The practitioner should only do so with a full knowledge of the compounds involved and their pharmacological properties.
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Affiliation(s)
- I Schweitzer
- University of Melbourne and Professional Unit, The Melbourne Clinic, Richmond, Victoria, Australia.
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12
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Baldwin RC, Simpson S. Treatment resistant depression in the elderly: a review of its conceptualisation, management and relationship to organic brain disease. J Affect Disord 1997; 46:163-73. [PMID: 9547114 DOI: 10.1016/s0165-0327(97)00143-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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13
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Hardy BG, Shulman KI, Zucchero C. Gradual discontinuation of lithium augmentation in elderly patients with unipolar depression. J Clin Psychopharmacol 1997; 17:22-6. [PMID: 9004053 DOI: 10.1097/00004714-199702000-00005] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Recently, the therapeutic benefit of lithium augmentation in old age has come into question. These data, in light of the documented high incidence of side effects after lithium use in elderly patients, resulted in the design of a prospective, placebo-controlled lithium augmentation withdrawal study in elderly patients with unipolar depression. Twelve eligible geriatric patients (10 women and 2 men; mean [+/-SD] age, 76.2 +/- 5.7 years) with DSM-III-R unipolar depression receiving adjunct lithium therapy were randomized to receive continued lithium augmentation or matching placebo (withdrawal rate 150 mg/day/wk). At each clinic visit, patients were assessed for depression (Montgomery-Asberg Depression Rating Scale and Geriatric Depression Rating Scale) and lithium-induced toxicities (a 21-item side-effect checklist, renal and thyroid biochemistry). Over the 2-year observation period, the placebo group reported a decrease in composite 21-item side-effect score and specific lithium toxicities (e.g., urinary urgency, hand tremor, and renal/thyroid abnormalities). Two patients in the lithium maintenance group had a recurrence of depression at 61 and 96 weeks, respectively, immediately after a stressful life event (cerebrovascular accident [CVA] or death of spouse), and two patients had a recurrence in the placebo group at 7 and 92 weeks, respectively, without any apparent changes in life stresses. No other prognostic risk factors for recurrence were identified. Depression that recurred in patients who were receiving placebo was relatively resistant to reinstitution of lithium augmentation therapy. In otherwise stable geriatric patients with unipolar depression, the documented benefits of reduced side effects should be weighed against the risk of recurrence and subsequent lithium resistance before withdrawal of lithium augmentation.
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Affiliation(s)
- B G Hardy
- Department of Pharmacy, Sunnybrook Health Science Centre, Toronto, Ontario, Canada
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14
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Abstract
The treatment of depression in geriatric patients is challenging on all levels. Recognition, compliance, medical comorbidity, tolerance of drug regimens, and accessibility of the patient to therapy all represent major clinical problems. Treating depression in elderly, disabled patients requires patience, keen observation skills, and much flexibility. It is critical that these patients trust their physicians and have ready access if problematic side effects develop. In general, when treating patients with a history of failure to respond, the clinician should choose a medication with a tolerable side-effect profile, and persist with it as long as steady, slow gains are being made. Dosages should be maximized to clinical tolerance prior to considering switching agents or augmentation strategies. It is probably wiser to augment than switch if a partial response has been obtained. Particularly among the medically ill elderly, any "lost ground" may be very difficult to replace. All available psychosocial resources should be assessed and brought to bear productively in the treatment context. We are quite far from a full clinical understanding of "treatment resistance" in elderly depressive patients, but the eminent treatability of depression in elderly patients encourages creative exploration of treatment regimens. Rigorous, placebo-controlled studies of representative samples of elderly patients are needed to clarify the diverse interactions among the many pharmacologic agents available to treat resistant/refractory depression in the elderly.
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Affiliation(s)
- B A Kamholz
- Department of Psychiatry, University of Michigan, Ann Arbor, USA
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A Retrospective Chart Review of Lithium Side Effects in a Geriatric Outpatient Population. Am J Geriatr Psychiatry 1994; 2:346-351. [PMID: 28530985 DOI: 10.1097/00019442-199402040-00010] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/1993] [Revised: 06/03/1994] [Accepted: 06/10/1994] [Indexed: 11/26/2022]
Abstract
The charts of 114 elderly outpatients with mood disorders treated with lithium were reviewed to determine the incidence of side effects. Patients had been treated with lithium for an average of 7.5 years, with an average serum lithium level of 0.5. Overall, 61.4% of patients experienced side effects from lithium at some point in their treatment, but only 0.11 side effects occurred per patient per year. Two (1.8%) patients had to discontinue lithium because of side effects and four (3-5%) required hospitalization. Delirium was the most common side effect noted (19.3%). Side effects occurred both at low ("subtherapeutic") and higher serum lithium levels. Variables significantly associated with experiencing side effects included male sex and higher serum lithium level. Hypothyroidism was significantly associated with longer length of time in years treated with lithium.
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Mørk A. Actions of lithium on the cyclic AMP signalling system in various regions of the brain--possible relations to its psychotropic actions. A study on the adenylate cyclase in rat cerebral cortex, corpus striatum and hippocampus. PHARMACOLOGY & TOXICOLOGY 1993; 73 Suppl 3:1-47. [PMID: 8146086 DOI: 10.1111/j.1600-0773.1993.tb01704.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
It has been estimated that in most industrialized countries 1 person out of every 1000 in the population is undergoing lithium treatment to stabilize their episodic mood disturbances due to manic-depressive illness. Lithium may stabilize mood swings by altering the action of certain neurotransmitters at the synaptic level in the brain. Recent research suggests that lithium alters neurotransmission by affecting neurotransmitter-coupled second messenger systems. A major second messenger system is the adenylate cyclase, which generates intracellular cAMP from ATP. The adenylate cyclases (type I-IV) are regulated by stimulatory and inhibitory receptors, which either stimulate or inhibit the adenylate cyclase activity. The stimulatory and inhibitory neurotransmitter-receptor signals are transferred to the catalytic unit of the adenylate cyclase by Gs and Gi, respectively. The activated receptor induces GTP stimulation of the heterotrimeric G protein, leading to a dissociation of the protein into the active alpha*GTP and the beta gamma complex. The former stimulates the catalytic unit of adenylate cyclase. The stimulation is terminated by a GTPase located on the alpha subunit that converts GTP to inactive GDP. At present, G proteins are known to play a central role in coupling receptors to effector proteins. In addition to extracellular regulation due to neurotransmitters, some adenylate cyclases (type I, III) are regulated by CaM as a consequence of enhanced intracellular concentrations of free Ca2+. The Ca(2+)-dependent stimulation of adenylate cyclase by CaM is assumed to occur by a direct effect on the catalytic unit. The catalytic units sensitive to Ca(2+)-CaM are also subjected to regulation by stimulatory and inhibitory neurotransmitter stimuli. Magnesium is essential for adenylate cyclase activity, since MgATP2- is the enzyme substrate. Furthermore, one Mg2+ site located on the G protein regulates both the receptor agonist affinity and the dissociation of the G protein during the activation cycle. A second Mg2+ site on the catalytic unit is responsible for Mg2+ regulation of the catalytic activity. The present work aimed at investigating the mechanisms by which lithium in vitro and after chronic treatment (ex vivo) affects adenylate cyclase activities in various regions of the rat brain. Lithium in vitro and ex vivo inhibited the selective stimulation of adenylate cyclase by Ca(2+)-CaM in the cerebral cortex. Furthermore, lithium in vitro interacted directly with the catalytic unit of adenylate cyclase.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- A Mørk
- Department of Pharmacology, University of Copenhagen
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