Monoamine oxidase inhibitors and L-dopa

Optimizing levodopa therapy, when and how? Perspectives on the importance of delivery and the potential for an early combination approach

INTRODUCTION

There is currently a resurgence of levodopa as the initial treatment of choice for most patients with Parkinson's disease, albeit at lower doses than previously used. The addition of adjuvant treatments (including MAO-B inhibitors, COMT inhibitors and dopamine agonists) is an established strategy to reduce motor complications that develop with sustained levodopa therapy.

AREAS COVERED

In this narrative review, the authors discuss the evidence underpinning current levodopa optimization strategies, during early disease and once motor complications occur. To support the discussion, the authors performed a broad PubMed search with the terms 'levodopa/L-dopa/L-Dopa, and Parkinson's disease,' restricted to clinical trials. There is now a wealth of evidence that improving levodopa delivery to the brain improves outcomes and we discuss how agents can be combined earlier in the course of disease to leverage the full potential of this strategy.

EXPERT OPINION

Levodopa remains the cornerstone of antiparkinsonian therapy. Several promising advances in formulation have been made and include novel extended-release oral drugs as well as non-oral delivery systems. However, evidence has long suggested that anti-parkinsonian medications may be better used in combination earlier in the disease, and consequently patients will benefit from low doses of several agents rather than ever larger levodopa doses.

Monoamino oxidase alleles correlate with the presence of essential hypertension among hypogonadic patients

Background

Monoamine oxidase (MAO) activity has been traditionally implicated in blood pressure through its effects on biogenic amine levels such as catecholamines, serotonin, and dopamine. Nowadays, this role is considered relegated to side‐effects such as orthostatic hypotension and/or hypertensive crisis derived from MAO‐inhibitory treatments in patients with psychiatric disease.

Methods

In the present work we have found an association between a polymorphic variant of MAOB gene and arterial hypertension in obese hypogonadic patients. The study cases comprised a series of 219 nondiabetic males with a body mass index ≥30 kg/m² and aged <45 years. Hypogonadism was defined as subnormal testosterone concentrations, when free testosterone values ranged <65 pg/ml.

Results

MAOB rs3027452‐A allele carriers were significantly over‐represented among hypertensive (HT) patients (25.49%) in comparison to either the non‐HT patients (10%, OR = 3.079 CI₉₅ [1.364–6.952], p = .005, Chi‐square test) and the control population series of nonobese nor hypogonadic males (also 10%, p = .003 Chi‐square test). Upon adjusted, an independent association was shown with the hypogonadic group with hypertension when compared with nonhypertensive hypogonadics (Beta = 3.653, p = .005). When quantitative analysis was performed, hypertensive patients harboring rs3027452‐A allele showed higher systolic blood pressure values (p = .038, Mann–Whitney U‐test) as well as an increased Systolic‐Diastolic range despite following HT treatment (∆mmHg 54 vs. 48 for rs3027452‐A and rs3027452‐G respectively, p‐value .019, Mann–Whitney U‐test). Previous studies on MAOB revealed that rs3027452‐A allele has been correlated to a lower activity of the enzyme, what gives a functional evidence over our observation.

Conclusion

If this result could be extrapolated to other hypertensive patient groups, it would implicate a review of the markers and therapeutic targets on human hypertension.

90 years of monoamine oxidase: some progress and some confusion

It would not be practical to attempt to deal with all the advances that have informed our understanding of the behavior and functions of this enzyme over the past 90 years. This account concentrates key advances that explain why the monoamine oxidases remain of pharmacological and biochemical interest and on some areas of continuing uncertainty. Some issues that remain to be understood or are in need of further clarification are highlighted.

Banisteriopsis caapi, a Forgotten Potential Therapy for Parkinson's Disease?

Banisteriopsis caapi, a liana indigenous to the Amazon basin with metagnomigenic properties and possible anti-depressant effects is one of the natural sources of harmala alkaloids. A summary of early trials with extracts of Banisteriopsis caapi and Peganum harmala (from which harmine was first isolated) in the 1920s and 1930s on various forms of parkinsonism is given as well as a brief overview of the known pharmacological properties of harmine. Despite its earlier abandonment because of perceived weaker efficacy than solanaceous alkaloids like scopolamine and hyoscine we propose that harmine should be reconsidered as a potential rapidly acting anti-Parkinsonian agent.

L-DOPA inhibits nitric oxide-dependent vasorelaxation via production of reactive oxygen species in rat aorta

OBJECTIVES

To clarify the underlying mechanisms of L-DOPA induced vasoconstriction in rat aorta.

METHODS

The effect of L-DOPA on phenylephrine-induced contractile force of blood vessels was examined in vitro using rat aortic ring preparations by isometric tension experiment. Involvement of nitric oxide (NO) in the effect of L-DOPA on vascular smooth muscle was studied by using N(omega)-Nitro-L-arginine (L-NNA), Sodium nitroprusside (SNP) in endothelium-intact and endothelium-denuded aortic rings.

RESULTS

L-DOPA potentiated alpha-adrenergic receptor- and depolarization-induced vascular contraction and inhibited acetylcholine-induced vasorelaxation. This effect was diminished by pretreatment of the aortic rings with L-NNA, an inhibitor of NO synthesis, or by removing the endothelium from the ring preparations. In endothelium-denuded rings, L-DOPA inhibited exogenous NO-dependent but not cGMP-mediated vasorelaxation. Increases in cGMP levels in response to an NO donor were attenuated by L-DOPA in cultured rat aortic smooth muscle cells. L-DOPA could not contract rings (without endothelium) pretreated with 3-(5'-hydroxymethyl- 2'-furyl)-1-benzyl indazole (YC-1), an activator of guanylyl cyclase, but SOD (150 U/ml) pretreatment of rings with endothelium inhibited contraction by L-DOPA.

CONCLUSIONS

These results suggest that L-DOPA inhibits nitric-dependent vasorelaxation on vascular smooth muscle cells via production of reactive oxygen species.

Cardiovascular responses to combined treatment with selective monoamine oxidase type B inhibitors and L-DOPA in the rat

BACKGROUND AND PURPOSE

Postural hypotension is a common side-effect of L-DOPA treatment of Parkinson's disease, and may be potentiated when L-DOPA is combined with selegiline, a selective inhibitor of monoamine oxidase B (MAO-B). Rasagiline is a new, potent and selective MAO-B inhibitor, which does not possess the sympathomimetic effects of selegiline. We have studied the effects of these selective MAO inhibitors, L-DOPA and dopamine on the cardiovascular system of the rat.

EXPERIMENTAL APPROACH

Blood pressure and heart rate was measured in conscious rats following acute or chronic administration of rasagiline, selegiline and L-DOPA, by comparison with the selective MAO-A inhibitor clorgyline, or the MAO-A/B inhibitor tranylcypromine. Cardiovascular responses, catecholamine release, and modification of pressor response to dopamine were studied in pithed rats.

KEY RESULTS

In conscious rats neither rasagiline nor selegiline caused significant potentiation of the effects of L-DOPA (50, 100, 150 mg.kg(-1)) on blood pressure or heart rate at doses which selectively inhibited MAO-B, but L-DOPA responses were potentiated by clorgyline and tranylcypromine. In rats treated twice daily for 8 days with L-DOPA and carbidopa, selegiline (5 mg.kg(-1)) but not rasagiline (0.2 mg.kg(-1)) caused a significant hypotensive response to L-DOPA and carbidopa, although both drugs caused similar inhibition of MAO-A and MAO-B. In pithed rats, selegiline but not rasagiline increased catecholamine release and heart rate, and potentiated dopamine pressor response at MAO-B selective dose.

CONCLUSIONS AND IMPLICATIONS

The different responses to the two MAO-B inhibitors may be explained by the amine releasing effect of amphetamine metabolites formed from selegiline.

Systematic overview of drug interactions with antidepressant medications

OBJECTIVE

Antidepressants are commonly used drugs with potential for numerous drug interactions. This study aims to systematically review the literature on drug interactions with antidepressants.

METHODS

We searched MEDLINE (1966 to November 2003) and EMBASE (1980 to 2003), using the heading drug interactions combined with individual antidepressant names. We restricted searches to English-language articles and human studies. We screened drug interaction texts and review articles for relevant studies. We included articles reporting original human data on drug interactions with antidepressants commonly used in North America. Articles were independently evaluated by 2 reviewers on clinical effect, clinical significance, and quality of evidence. Discrepancies were resolved by consensus.

RESULTS

There were 904 eligible interactions, involving 9509 patients, for a total of 598 summary interactions. Of these, 439 (73%) demonstrated an interaction, 148 (25%) had no effect, and 11 (2%) had conflicting evidence. For 510 interactions (85%), the quality of evidence was poor. It was fair for 67 (11%) interactions and good for 10 (2%) interactions. There were no interactions with excellent quality of evidence. There were 145 (24%) interactions of major clinical significance. These were predominantly hypertensive emergencies and serotonin syndrome. Most interacting drugs had central nervous system (CNS) activity. As expected, monoamine oxidase inhibitors (MAOIs) appear to be the most problematic family in terms of potential for serious drug interactions.

CONCLUSIONS

Drug interactions with antidepressants are an important cause for concern, but this concern is based primarily on poor evidence. We recommend caution when combining antidepressants with other CNS drugs, particularly when coadministering MAOIs with other substances.

Safety of selegiline (deprenyl) in the treatment of Parkinson's disease

Selegiline (deprenyl), a selective, irreversible inhibitor of monoamine oxidase type B (MAO-B) is widely used in the treatment of Parkinson's disease. As the first MAO-B inhibitor approved for the treatment of Parkinson's disease, concerns were raised about the safety of the drug based on the adverse effect profiles of older, nonselective MAO inhibitors. Unlike the nonselective MAO inhibitors, selegiline does not significantly potentiate tyramine-induced hypertension (the 'cheese effect') at the dosages (5 to 10 mg daily) used for the treatment of Parkinson's disease. Selegiline has been well tolerated when given alone. The most frequent adverse events seen during monotherapy have been insomnia, nausea, benign cardiac arrhythmias, dizziness and headache. When combined with levodopa, selegiline can potentiate the typical adverse effects of levodopa, if the dose of levodopa is not reduced sufficiently. Thus, the most common adverse effects associated with this combination are nausea, dizziness, fatigue, constipation and insomnia. At the later stages of Parkinson's disease when fluctuations in disability occur, peak dose dyskinesias, psychiatric complications like hallucinations and insomnia, and orthostatic hypotension are further potentiated by selegiline. Mortality was recently reported to be increased when selegiline and levodopa were given together in comparison with treatment with levodopa alone, but a large meta-analysis of 5 long term studies and 4 separate studies did not support this conclusion. Selegiline seems to be generally well tolerated in combination with other drugs. However, when pethidine (meperidine) has been given to patients who are receiving selegiline therapy, severe adverse effects have been reported. Thus, the concomitant use of these drugs is not recommended. A low tyramine diet is recommended if selegiline is used together with nonselective MAO inhibitors or the selective, reversible MAO-A inhibitor, moclobemide. Several adverse effects have been reported when fluoxetine and selegiline have been used together. A recent survey revealed that the incidence of a true serotonin syndrome is, however, very low with this combination. Concomitant use of selegiline and other selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors (SSRIs) like citalopram, which have generally less interactions than fluoxetine, seems to be well tolerated. Nevertheless, caution is advised when combining a SSRI or a tricyclic antidepressant and selegiline.

Antiparkinsonian agents. Drug interactions of clinical significance

Within the past 3 decades revolutionary changes have taken place in the pharmacological management of Parkinson's disease. Used alone, or often in combination, antiparkinsonian agents can dramatically and meaningfully ameliorate the symptoms of Parkinson's disease. However, with the development of effective therapeutic agents has come the potential for drug interactions; these interactions can produce consequences that range from the inconsequential to incapacitating and even life-threatening. Drug-drug interactions are not a major problem with either the anticholinergic medications or amantadine. However, cumulative anticholinergic toxicity may occur when multiple drugs with anticholinergic properties are utilised concomitantly, and amantadine toxicity can be triggered by drugs that impair its renal clearance. Gastric emptying and levodopa absorption can be significantly altered by medications and dietary contents. A rather extensive array of medications can interfere with dopaminergic function and thus produce clinical parkinsonism or impair the effectiveness of levodopa. The effectiveness of direct dopamine agonists can also be affected by a small group of agents. As a selective monoamine oxidase type B (MAO-B) inhibitor, selegiline (deprenyl) is free of the 'cheese-effect' when employed in recommended dosages. However, potentially life-threatening drug interactions, with both pethidine (meperidine) and with fluoxetine and other antidepressant medications, have been described, presumably occurring via serotonergic mechanisms. Awareness of the potential for drug interactions with antiparkinsonian agents, and prompt recognition of them when they do occur, is vital for the optimum clinical management of Parkinson's disease.

Clinical pharmacokinetics of the monoamine oxidase-A inhibitor moclobemide

There has been a resurgence of interest in the use of monoamine oxidase (MAO) enzyme inhibitors for the treatment of depression. Unlike the first-generation MAO inhibitors, the current drugs are readily reversible in their action, resulting in far less concern about interactions with certain foods and drugs which could lead to serious pressor effects. Furthermore, the current drugs are far more selective in their actions as a result of the ability to affect either the MAO-A or the MAO-B isoenzyme. Moclobemide is an example of a reversible MAO-A inhibitor which has been extensively studied and whose pharmacokinetic, clinical pharmacological and toxicological profiles have been thoroughly defined. Moclobemide has a short disposition half-life and intermediate values for systemic clearance and volume of distribution; half-life increases somewhat with dose. The drug is completely metabolised by the liver. Moclobemide is rapidly and completely absorbed following oral administration in a variety of dosages and forms. The drug has a high intrinsic (apparent oral) clearance which results in a substantial hepatic first-pass effect and, while there is marked interindividual variation, differences within an individual are small. A time- and dose-dependence is observed with multiple oral administration: clearance decreases with administration during the first week and thereafter remains constant. The exact mechanism of this effect is not known, but it may reflect inhibition of elimination by metabolites (the kinetics may always be described as being first-order). Moclobemide disposition is not affected by renal disease, nor is there substantial alteration with advanced age. Liver disease causes a dramatic reduction in clearance; dosage must be adjusted for patients with liver disease. There is minimal transfer of the drug into breast milk, such that breast-feeding neonates are exposed to only a very small dose of the drug. Moclobemide administration results in a minimal interaction with exogenous amines (e.g. tyramine and pressor amine drugs); the so-called 'cheese effect' is therefore of little concern. As a result, the drug has an excellent tolerability profile both within the therapeutic dose range and in overdose (no deaths have been attributed to moclobemide intoxication per se). Cimetidine inhibits the elimination of moclobemide. Moclobemide appears to affect several isoenzymes of the cytochrome P450 (CYP) system (CYP2C19, CYP2D6 and CYP1A2). The adverse events profile of moclobemide indicates only mild and transient effects at a relatively low rate of occurrence.

Lifestyle advice in general practice: rates recalled by patients

OBJECTIVE

To document how often patients with varying cardiovascular risk levels reported receiving lifestyle advice from general practice.

DESIGN

Cross sectional descriptive survey by postal questionnaire.

SETTING

5 general practices in Bedfordshire.

SUBJECTS

4941 people aged 35-64 years who had consulted a general practitioner at least once during the 12 months before completing the questionnaire and who subsequently attended for a health check as part of the OXCHECK trial.

MAIN OUTCOME MEASURES

Report of having received advice from a general practitioner or practice nurse about smoking, alcohol consumption, exercise, or diet during the 12 months before completing the questionnaire. Cardiovascular risk assessed by a nurse during structured health check.

RESULTS

The overall reported rate of advice was 27% for smoking, 4.5% for exercise, 12% for diet, and 3% for alcohol consumption. Those with unhealthy behaviour profile or at increased cardiovascular risk received more advice--for example, 47% of smokers with a history of cardiovascular disease received advice on smoking. Among those at increased risk, men were more likely than women to receive advice about exercise (11% v 4%, p = 0.04) and alcohol consumption (10% v 4%, p = 0.007), while women received more advice about weight (17% v 23%, p < 0.001). The rate of receiving advice was unaffected by age, marital status, or social class.

CONCLUSION

The low rate of lifestyle advice reported by patients implies that more preventive advice could be provided in primary care.

A review of the pharmacology of selegiline

Selegiline (1-deprenyl) is an irreversible inhibitor of monoamine oxidase (MAO) type B. Because in the human brain, dopamine is metabolised mainly by MAO-B, selegiline increases dopamine content in the central nervous system. Besides the inhibition of MAO-B, selegiline also inhibits the uptake of dopamine and noradrenaline into presynaptic nerve and increases the turnover of dopamine. Thanks to these properties, selegiline significantly potentiates the pharmacological effects of levodopa. These favourable characteristics have been applied in the treatment of Parkinson's disease using selegiline both with levodopa and alone. Unlike earlier MAO-inhibitors, selegiline does not potentiate the hypertensive effects of tyramine. This is due to the selectivity to MAO-B, leaving intestinal MAO-A intact, and also due to the fact that selegiline inhibits the uptake of tyramine into neurons. Selegiline can prevent the parkinsonism caused by MPTP in animals; similar findings have been reported with other toxins like 6-OHDA and DSP-4, that destroys noradrenergic nuclei. Furthermore, selegiline reduces oxidative stress caused by degradation of dopamine and increases free radical elimination by enhancing superoxide dismutase and catalase activity. These findings may be important when considering the possible neuroprotective effects of selegiline. Besides the basic pharmacology also the interactions and pharmacokinetics of selegiline are reviewed in this article.

The current status of monoamine oxidase and its inhibitors

The enzyme monoamine oxidase (MAO) plays an important role in the inactivation of both dietary amines and also of neurotransmitter amines. A study of the properties of irreversible inhibitors of this enzyme suggests that the enzyme exists in two broad types--MAO-A and MAO-B. Although irreversible inhibitors of MAO were once widely used as antidepressant agents, they fell from favour because of adverse reactions after the ingestion of amine-containing foodstuffs ("the cheese reaction"). However, these inhibitors (phenelzine and tranylcypromine) are probably best for the treatment of atypical depression providing the patient is aware of dietary reactions. A new series of reversible, MAO-A selective inhibitors are being developed which do not exhibit serious dietary interactions. These reversible inhibitors show promise as rapidly acting antidepressant agents. An atypical irreversible MAO-B selective inhibitor, selegiline (deprenyl) does not exhibit an adverse reaction on the ingestion of amine-containing foods. This drug has been used as an adjuvant in the treatment of Parkinson's disease since it allows the dose of L-dopa to be reduced by approximately 25%. More important, selegiline may slow the degeneration of dopaminergic neurons that is characteristic of Parkinson's disease.

Parkinson's disease in 1984: an update

This update reviews several important topics in the field of Parkinson's disease, including etiologic studies, the types and mechanisms of drug complications and their treatment, when and how to begin treatment, the association of dementia with Parkinson's disease, and the development of the newer research tools. The recent discovery of a highly selective neurotoxin (MPTP) that causes parkinsonism in humans and other primates and the use of positron emission tomography in living patients should improve our understanding of the cause of cell death in Parkinson's disease and assist in the development of more definitive treatment for this common, disabling neurologic condition.

Treatment of Parkinson's disease with agents other than levodopa and dopamine agonists: controversies and new approaches

Parkinson's disease is associated with a variety of neurotransmitter disturbances which may be further altered by its treatment with dopamine agonists. Based on this information a wide range of pharmacological approaches have been used in search of newer treatment alternatives and in hopes of reducing complications of long-term levodopa use. This paper reviews the various therapies which have had some success in the management of Parkinson's disease, other than levodopa and dopamine agonists. Special emphasis is placed on the many unresolved questions and controversies that exist in this area of neuropharmacology.

Clinical and pharmacological problems of deprenyl (selegiline) treatment in Parkinson's disease

The clinical pharmacology concerned in the evolution of deprenyl as an adjuvant in the treatment of Parkinson's disease is briefly reviewed, with an assessment of its therapeutic potential. Experiments to clarify its mode of action are described, indicating that its clinical effects do not depend upon its amphetamine metabolites.

The management of Parkinson's disease

It is useful to divide Parkinsonian patients into those whose signs are confined to tremor, rigidity and akinesia, and those with evidence of a more diffuse disturbance. The treatment of choice in the former is levodopa combined with a peripheral decarboxylase inhibitor. At the onset of the disease, when disability is minimal, amantadine or anticholinergic drugs may suffice. Bromocriptine is useful in some patients who derive only short-lived benefit from each dose of levodopa. The role of stereotactic surgery is now confined to patients with an incapacitating unilateral tremor which has not improved with drug therapy. In elderly patients with evidence of diffuse cerebral dysfunction such as dementia, grasp reflex, hyper-reflexia or severe postural hypotension, the beneficial effect of these drugs is often outweighed by the side effects. Small doses of levodopa alone may be tried. Anticholinergic drugs and amantadine should be avoided in such patients.

Deprenyl in the management of response fluctuations in patients with Parkinson's disease on levodopa

Fluctuations in response to levodopa are a common and serious complication of long-term levodopa therapy. It may be possible to prolong the effect of each dose of levodopa by retarding the breakdown of dopamine. The selective monoamine oxidase type B inhibitor deprenyl, which is extensively metabolised to amphetamine and methamphetamine, has this effect as well as possible actions on dopamine release and re-uptake. In a double-blind crossover trial against placebo, deprenyl prolonged the action of levodopa and produced an objective improvement in mobility in five of 10 patients with dose-related response swings, and a subjective improvement in a further four patients. In another group of seven patients with random fluctuations in symptoms, only two noted subjective improvement, and there was an apparent increase in the severity of response swings in five patients. Deprenyl exacerbated dyskinesias, but had no serious side-effects. We conclude that deprenyl is unlikely to benefit patients with random response swings, and may cause deterioration in such cases. However, it may be a useful adjuvant in the management of dose-related response fluctuations in patients already on optional levodopa therapy.

Gastric emptying effect of d,1-tranylcypromine and its stereoisomers

The effect of d,1-, d- and 1-tranylcypromine (Tc) on gastric emptying of rats trained to eat once a day during a 2-h period under conditions of normal or depleted catecholamine stores was studied. d,1-Tc and d-Tc reduced gastric emptying intensely and almost similarly whereas 1-Tc produced a qualitatively less intense effect. Reserpine did not modify this effect of d,1-Tc. It is concluded that d,1-Tc is the most effective form for delaying gastric emptying, this effect being mainly due to the d-isomer. Catecholamines are not involved in the gastric inhibiting effect of these drugs.

Drug interactions with antihypertensive drugs

Drug interactions with antihypertensive drugs can be either beneficial or hazardous. The hazardous interactions are relatively infrequent but must be shown so they can be avoided. Those of most importance involve interaction with guanethidine-type agents and tricyclic antidepressants, amphetamine-type anorexiants or phenolpropanolamine-type common cold remedies; combined use of potassium retaining diuretics with potassium supplements; and incautious use of diuretics with cardiac glycosides. The beneficial interactions are the basis for modern antihypertensive therapy and can be of major help if logically applied to therapeutic problems.

Deprenyl in Parkinson's disease

In a double-blind crossover trial, (-)-deprenyl, a fast-acting selective monoamine-oxidase-B inhibitor without a "cheese effect", was given to 41 patients with idiopathic Parkinson's disease who were receiving maximum tolerated doses of levodopa either alone or combined with carbidopa ("Sinemet"). In a dose of 10 mg, daily or on alternate days, (-)-deprenyl prolonged the therapeutic effect of levodopa and was effective in mild "on-off" disabilities with end-of-dose akinesia; the majority of patients with nocturnal and early-morning akinesia also improved. No statistically significant improvement occurred in diurnal akinesia, and there was no improvement in patients with severe on-off disabilities with freezing and rapid oscillations ("yo-yo" effect). Levodopa-induced dyskinesias were aggravated in 14 patients. In 5 previously untreated patients, (-)-deprenyl alone gave no benefit, but when it was used with levodopa and carbidopa a mean dosage reduction of 200 mg levodopa daily was possible. Depression, present in 15 patients, was unchanged. (-)-Deprenyl in combination with smaller total daily doses of levodopa and a peripheral decarboxylase inhibitor may prove useful in reducing the frequency and severity of some types of on-off effect with overall benefit comparable to that obtained with larger doses of levodopa.

Interactions between sympathomimetic amines and antidepressant agents in man

Intravenous infusions of phenylephrine, noradrenaline, adrenaline, and isoprenaline were given to healthy human volunteers after five to seven days on phenelzine, tranylcypromine, or imipramine, and cardiovascular responses were compared with those observed under control conditions. With monoamine oxidase inhibitors there was a 2-2(1/2) fold potentiation of the pressor effect of phenylephrine, but no clinically significant potentiation of cardiovascular effects of noradrenaline, adrenaline, or isoprenaline. With imipramine there was potentiation of the pressor effects of phenylephrine (2-3 fold), noradrenaline (4-8 fold), and adrenaline (2-4 fold); there were dysrhythmias during adrenaline infusions, but no noticeable or consistent changes in response to isoprenaline.Noradrenaline and adrenaline in amounts contained in local anaesthetics used in dentistry are not likely to be significantly potentiated in otherwise healthy patients receiving monoamine oxidase inhibitors. Hazardous potentiation of their cardiovascular effects might occur in patients receiving tricyclic antidepressants.Our observations do not indicate that the hazards associated with isoprenaline inhalation by bronchial asthmatics would be increased by coincident therapy with a monoamine oxidase inhibitor or tricyclic antidepressant.

Amyloidosis complicated by intractable postural hypotension

A patient is described in whom the nephrotic syndrome caused by amyloidosis was complicated by intractable postural hypotension. An account is given of his treatment with a combination of monoamine oxidase inhibitors and sympathomimetic pressor agents, after a failure of conventional therapy.

Augmenting the action of levodopa

Various pharmacological approaches to potentiate the therapeutic actions of levodopa and reduce side-effects are reviewed.

Of currently available drugs, anticholinergic agents and amantadine have been studied extensively. Inhibition of extracerebral decarboxylase appears to be the most promising new area of investigation, though experience is at present limited.

Other methods discussed include inhibition of enzymes catechol-O-methyl transferase, monoamine oxidase and dopamine beta hydroxylase. Conflicting evidence on 3-O-methyldopa is discussed.

Idiopathic orthostatic hypotension treated with levodopa and MAO inhibitor: a preliminary report

The clinical and pathophysiological features of a case of idiopathic orthostatic hypotension (Shy-Drager syndrome) are presented. Recent reports on the pathological findings in this condition indicate that there may be a defect in catecholamine synthesis in the pigmented brain stem nuclei and sympathetic ganglia similar to that in idiopathic parkinsonism. On this basis a new form of therapy using levodopa combined with MAO inhibition is derived. The results of a trial of this therapy, which produced improvements in both the hypotension and in the extrapyramidal features of the disease, are reported.