Lithium and calcium channel blockers: possible neurotoxicity

Behavioural and biochemical responses of the sea snail Tritia reticulata to lithium concentration gradient

Lithium (Li) is present in many modern technologies, most notably in rechargeable batteries. Inefficient recycling strategies for electronic waste containing this element may result in its release into aquatic systems, which may induce harmful effects on wildlife. The present study evaluated the effect of Li contamination on the gastropod Tritia reticulata exposed to different concentrations of Li (100, 200, 500 and 1000 µg L-1) for 21 days. Biochemical analyses showed that this species was not significantly affected by this contaminant at the cellular level, as no significant differences were observed in terms of metabolism, oxidative stress, and neurotoxicity. Results further revealed that snails attempted to avoid Li accumulation by burying in the sediment at a faster rate when exposed to the highest concentrations (500 and 1000 µg L-1). More research is needed to fully assess the response of T. reticulata to Li contamination, such as investigating longer exposure periods or other endpoints.

How safe are the new green energy resources for marine wildlife? The case of lithium

Considering the increasing use of Lithium (Li) and the necessity to fulfil this demand, labile Li occurrence in the environment will be enhanced. Thus, additional research is needed regarding the presence of this element in marine environment and its potential toxic impacts towards inhabiting wildlife. The aim of the present study was to evaluate Li toxicity based on the exposure of Mytilus galloprovincialis to this metal, assessing the biochemical changes related with mussels' metabolism, oxidative stress and neurotoxicity. For this, organisms were exposed to different Li concentrations (100, 250, 750 μg/L) for 28 days. The results obtained clearly demonstrated that Li lead to mussels' metabolism depression. The present study also revealed that, especially at the highest concentrations, antioxidant and biotransformation enzymes were not activated, leading to the occurrence of lipid peroxidation and loss of redox homeostasis, with increased content in oxidized glutathione in comparison to the reduced form. Furthermore, after 28 days, higher Li exposure concentrations induced neurotoxic effects in mussels, with a decrease in acetylcholinesterase enzyme activity. The responses observed were closely related with Li concentrations in mussels' tissues, which were more pronounced at higher exposure concentrations. Such results highlight the potential toxic effects of Li to marine species, which may even be higher under predicted climate changes and/or in the presence of other pollutants.

Lithium therapy

Since the introduction of lithium therapy 30 years ago it has become a major weapon in psychiatrists' armamentarium. It is the drug of first choice for the prevention of recurrent mood disorders, and it is estimated that about one person in every thousand people in Britain receives lithium at any one time. It therefore behoves doctors to be familiar with its use. This article is not a comprehensive account of the pharmacology of lithium (for this the reader is referred to Johnson (1987) and Peet & Pratt (1993)) but concentrates on its clinical use in practice and some less well known, but important, phenomena.

Lithium Poisoning

Lithium is a commonly prescribed treatment for bipolar affective disorder. However, treatment is complicated by lithium’s narrow therapeutic index and the influence of kidney function, both of which increase the risk of toxicity. Therefore, careful attention to dosing, monitoring, and titration is required. The cause of lithium poisoning influences treatment and 3 patterns are described: acute, acute-on-chronic, and chronic. Chronic poisoning is the most common etiology, is usually unintentional, and results from lithium intake exceeding elimination. This is most commonly due to impaired kidney function caused by volume depletion from lithium-induced nephrogenic diabetes insipidus or intercurrent illnesses and is also drug-induced. Lithium poisoning can affect multiple organs; however, the primary site of toxicity is the central nervous system and clinical manifestations vary from asymptomatic supratherapeutic drug concentrations to clinical toxicity such as confusion, ataxia, or seizures. Lithium poisoning has a low mortality rate; however, chronic lithium poisoning can require a prolonged hospital length of stay from impaired mobility and cognition and associated nosocomial complications. Persistent neurological deficits, in particular cerebellar, are described and the incidence and risk factors for its development are poorly understood, but it appears to be uncommon in uncomplicated acute poisoning. Lithium is readily dialyzable, and rationale support extracorporeal treatments to reduce the risk or the duration of toxicity in high-risk exposures. There is disagreement in the literature regarding factors that define patients most likely to benefit from treatments that enhance lithium elimination, including specific plasma lithium concentration thresholds. In the case of extracorporeal treatments, there are observational data in its favor, without evidence from randomized controlled trials (none have been performed), which may lead to conservative practices and potentially unnecessary interventions in some circumstances. More data are required to define the risk–benefit of extracorporeal treatments and their use (modality, duration) in the management of lithium poisoning.

Verapamil augmentation of lithium treatment improves outcome in mania unresponsive to lithium alone: preliminary findings and a discussion of therapeutic mechanisms

OBJECTIVES

Attenuation of protein kinase C (PKC) is a mechanism common to both established (lithium, valproate) and some novel (tamoxifen) antimanic agents. Verapamil, although primarily known as a calcium channel blocker, also has PKC inhibitory activity. Verapamil has shown antimanic activity in some but not all studies. Therefore, we investigated verapamil, used alone or as an adjunctive treatment, in manic patients who did not respond to an initial adequate trial of lithium.

METHODS

Each study phase lasted three weeks. Subjects were treated openly with lithium in Phase 1 (n = 45). Those who failed to respond were randomly assigned to double-blind treatment in Phase 2 with either verapamil (n = 10) or continued-lithium (n = 8). Phase 2 nonresponders (n = 10) were assigned to combined verapamil/lithium in Phase 3.

RESULTS

Response in Phase 2 did not differ significantly between verapamil and continued-lithium. During Phase 3, response to combined treatment was significantly better than overall response to monotherapy in Phase 2 (Fisher's Exact test, p = 0.043). Mania ratings improved during combined treatment in Phase 3 by 88.2% (linear mixed model analysis, F = 4.34, p = 0.013), compared with 10.5% improvement during Phase 2.

CONCLUSIONS

In this preliminary investigation, verapamil monotherapy did not demonstrate antimanic efficacy. By contrast, the combination of verapamil plus lithium was highly efficacious. Our findings thus suggest that verapamil may have potential utility as an adjunct to lithium. This effect may be mediated by additive actions on PKC inhibition, which may be an important mechanism for antimanic agents in general.

A systematic review of existing data on long-term lithium therapy: neuroprotective or neurotoxic?

Lithium is an efficacious agent for the treatment of bipolar disorder, but it is unclear to what extent its long-term use may result in neuroprotective or toxic consequences. Medline was searched with the combination of the word 'Lithium' plus key words that referred to every possible effect on the central nervous system. The papers were further classified into those supporting a neuroprotective effect, those in favour of a neurotoxic effect and those that were neutral. The papers were classified into research in humans, animal and in-vitro research, case reports, and review/opinion articles. Finally, the Natural Standard evidence-based validated grading rationale was used to validate the data. The Medline search returned 970 papers up to February 2006. Inspection of the abstracts supplied 214 papers for further reviewing. Eighty-nine papers supported the neuroprotective effect (6 human research, 58 animal/in vitro, 0 case reports, 25 review/opinion articles). A total of 116 papers supported the neurotoxic effect (17 human research, 23 animal/in vitro, 60 case reports, 16 review/opinion articles). Nine papers supported no hypothesis (5 human research, 3 animal/in vitro, 0 case reports, 1 review/opinion articles). Overall, the grading suggests that the data concerning the effect of lithium therapy is that of level C, that is 'unclear or conflicting scientific evidence' since there is conflicting evidence from uncontrolled non-randomized studies accompanied by conflicting evidence from animal and basic science studies. Although more papers are in favour of the toxic effect, the great difference in the type of papers that support either hypothesis, along with publication bias and methodological issues make conclusions difficult. Lithium remains the 'gold standard' for the prophylaxis of bipolar illness, however, our review suggests that there is a rare possibility of a neurotoxic effect in real-life clinical practice even in closely monitored patients with 'therapeutic' lithium plasma levels. It is desirable to keep lithium blood levels as low as feasible with prophylaxis.

Lithium neurotoxicity: the development of irreversible neurological impairment despite standard monitoring of serum lithium levels

We report the case of a 44 year old man who presented with a two-month history of dysarthria, ataxia and leg weakness whilst on maintenance lithium for bipolar disorder. Examination revealed significant cerebellar and pyramidal dysfunction. Serum lithium was 1.5 mmol/l, a moderate elevation above his usual stable levels of 0.4-0.8 mmol/l. The patient's past history included hypertension and chronic renal impairment and the development of neurological symptoms coincided with the recent onset of heart failure. On cessation of lithium he partially recovered, the main residuum being persistent cerebellar ataxia. The case is an example of lithium neurotoxicity developing insidiously in the absence of an overt acute phase syndrome, and highlights the need for keen observation of the patient in the hope of preventing permanent deficits.

Clinical pharmacokinetics of vasodilators. Part I

Understanding the mechanism of action and the pharmacokinetic properties of vasodilatory drugs facilitates optimal use in clinical practice. It should be kept in mind that a drug belongs to a class but is a distinct entity, sometimes derived from a prototype to achieve a specific effect. The most common pharmacokinetic drug improvement is the development of a drug with a half-life sufficiently long to allow an adequate once-daily dosage. Developing a controlled release preparation can increase the apparent half-life of a drug. Altering the molecular structure may also increase the half-life of a prototype drug. Another desirable improvement is increasing the specificity of a drug, which may result in fewer adverse effects, or more efficacy at the target site. This is especially important for vasodilatory drugs which may be administered over decades for the treatment of hypertension, which usually does not interfere with subjective well-being. Compliance is greatly increased with once-daily dosing. Vasodilatory agents cause relaxation by either a decrease in cytoplasmic calcium, an increase in nitric oxide (NO) or by inhibiting myosin light chain kinase. They are divided into 9 classes: calcium antagonists, potassium channel openers, ACE inhibitors, angiotensin-II receptor antagonists, alpha-adrenergic and imidazole receptor antagonists, beta 1-adrenergic agonist, phosphodiesterase inhibitors, eicosanoids and NO donors. Despite chemical differences, the pharmacokinetic properties of calcium antagonists are similar. Absorption from the gastrointestinal tract is high, with all substances undergoing considerable first-pass metabolism by the liver, resulting in low bioavailability and pronounced individual variation in pharmacokinetics. Renal impairment has little effect on pharmacokinetics since renal elimination of these agents is minimal. Except for the newer drugs of the dihydropyridine type, amlodipine, felodipine, isradipine, nilvadipine, nisoldipine and nitrendipine, the half-life of calcium antagonists is short. Maintaining an effective drug concentration for the remainder of these agents requires multiple daily dosing, in some cases even with controlled release formulations. However, a coat-core preparation of nifedipine has been developed to allow once-daily administration. Adverse effects are directly correlated to the potency of the individual calcium antagonists. Treatment with the potassium channel opener minoxidil is reserved for patients with moderately severe to severe hypertension which is refractory to other treatment. Diazoxide and hydralazine are chiefly used to treat severe hypertensive emergencies, primary pulmonary and malignant hypertension and in severe preeclampsia. ACE inhibitors prevent conversion of angiotensin-I to angiotensin-II and are most effective when renin production is increased. Since ACE is identical to kininase-II, which inactivates the potent endogenous vasodilator bradykinin, ACE inhibition causes a reduction in bradykinin degradation. ACE inhibitors exert cardioprotective and cardioreparative effects by preventing and reversing cardiac fibrosis and ventricular hypertrophy in animal models. The predominant elimination pathway of most ACE inhibitors is via renal excretion. Therefore, renal impairment is associated with reduced elimination and a dosage reduction of 25 to 50% is recommended in patients with moderate to severe renal impairment. Separating angiotensin-II inhibition from bradykinin potentiation has been the goal in developing angiotensin-II receptor antagonists. The incidence of adverse effects of such an agent, losartan, is comparable to that encountered with placebo treatment, and the troublesome cough associated with ACE inhibitors is absent.

Clinical relevance of drug interactions with lithium

Although lithium continues to be regarded as the treatment of choice for bipolar disorders, the clinical use of this mood stabiliser is associated with an extremely narrow therapeutic range. Relatively minor increases in serum concentrations may induce serious adverse sequelae, and concentrations within the therapeutic range may result in toxic reactions. The safety of combining lithium with other medications, therefore, is a major concern, and extensive clinical experience has served to identify several significant drug interactions. Lithium removal from the body is achieved almost exclusively via renal means. As a result, any medication that alters glomerular filtration rates or affects electrolyte exchange in the nephron may influence the pharmacokinetic disposition of lithium. Concomitant use of diuretics has long been associated with the development of lithium toxicity, but the risk of significant interactions varies with the site of pharmacological action of the diuretic in the renal tubule. Thiazide diuretics have demonstrated the greatest potential to increase lithium concentrations, with a 25 to 40% increase in concentrations often evident after initiation of therapy. Osmotic diuretics and methyl xanthines appear to have the opposite effect on lithium clearance and have been advocated historically as antidotes for lithium toxicity. Loop diuretics and potassium-sparing agents have minor variable effects. Nonsteroidal anti-inflammatory drugs (NSAIDs) have also been associated with lithium toxicity, although the relative interactive potential of specific NSAIDs is difficult to determine. Small prospective studies have demonstrated large interindividual differences in lithium clearance values associated with different NSAIDs. A growing body of evidence also suggests that ACE inhibitors may impair lithium elimination, but further investigations are needed to identify patients at risk. Anecdotal reports have linked numerous medications with the development of neurotoxicity without an apparent effect on the pharmacokinetic disposition of lithium. Antipsychotics, anticonvulsants and calcium antagonists have all be implicated in a sufficient number of case reports to warrant concern. As these medications have all been commonly coadministered with lithium, the relative risk of serious interactions appears to be quite low, but caution is advised.

Review of clinically important drug interactions with lithium

The therapeutic dosage of lithium is close to the toxic level, and drugs reducing the renal clearance of lithium can produce the most serious adverse effects. When used in combination with psychiatric drugs affecting mood, the therapeutic potential of lithium may be enhanced, and earlier concern regarding possible neurotoxic interactions with neuroleptics appear poorly substantiated. A number of specific interactions of low incidence have also been reported which should be borne in mind when new medications are introduced. The ready availability of lithium concentration monitoring in body fluids makes it possible to alter the effects of some potentially interactive drugs that may still need to be given in combination with lithium.

Preliminary controlled trial of nimodipine in ultra-rapid cycling affective dysregulation

We report the initial results of the first controlled double-blind trial of nimodipine, a calcium channel antagonist, in the acute and prophylactic treatment of patients with treatment-refractory affective dysregulation. Active drug nimodipine (A) was substituted for placebo (B) in 12 patients. Patients were studied in a B-A-B design, with 3 of the 12 patients rechallenged with active drug in a B-A-B-A design (patients 9, 10, and 11). Five of the nine patients who completed the drug trial responded. One of three patients suffering from ultra-ultra-rapid (ultradian) cycling bipolar II disorder (patient 6) showed an essentially complete response; the other two ultradian patients (patients 4 and 9) showed evidence of a partial response on manic and depressive oscillations, one of which was confirmed in a B-A-B-A design. Only one of five less rapidly, but continuously cycling patients showed an excellent response (patient 10), and this was confirmed in a B-A-B-A design. The one patient who had recurrent brief depression (patient 11) showed a complete resolution of severe depressive recurrences, with response re-confirmed in an extended prophylactic trial with a B-A-B-A design. In the eight patients who completed self-ratings, nimodipine was associated with a significant reduction in the magnitude of mood fluctuations compared with the baseline placebo condition. Further clinical study of nimodipine, a calcium channel blocker with a unique profile of behavioral and anticonvulsant properties, appears warranted in patients with treatment-refractory affective illness characterized by recurrent brief depression and ultradian cycling.