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PubMed2006

Levodopa availability improves with progression of Parkinson's disease.

BACKGROUND: Previous pharmacokinetic trials with standard levodopa formulations showed a different behaviour of levodopa degradation in plasma of patients with Parkinson's disease (PD) in various stages. OBJECTIVES: To investigate associations between levodopa plasma levels in relation to the scored intensity of PD. SUBJECTS AND METHODS: We administered water soluble 100 mg levodopa and 25 mg benserazide to 50 PD patients, taken off medication for at least 12 hours, and assessed the levodopa plasma concentrations during an 180 minutes period under standardised conditions. RESULTS: The computed area under the curve (AUC) values of levodopa plasma levels were significant higher in advanced PD patients. PD rating scores significantly correlated to the AUC outcomes and the maximum levodopa plasma concentration. CONCLUSIONS: Levodopa availability improves with progression of PD. This may result from deteriorated peripheral activity of levodopa metabolising enzymes or an increasing enteric dysfunction with subsequent better duodenal levodopa absorption or both.

Adult↗

PubMed1999

Narrow beneficial effect of dextromethorphan on levodopa-induced motor response alterations in an experimental model of parkinsonism.

The effects of acute and chronic dextromethorphan on levodopa-induced motor response alterations have been studied in rats with unilateral lesion of nigrostriatal pathway induced by 6-hydroxydopamine (6-OHDA). Male Sprague-Dawley rats received a 6-OHDA injection (8 microg) into the left medial forebrain bundle. To validate the effect of acute dextromethorphan administration, groups of rats were treated with levodopa (25 mg/kg, twice daily) for 22 days. On day 23, animals received dextromethorphan (20, 30 or 40 mg/kg) immediately before levodopa. In a second set of experiments, lesioned rats were concomitantly treated with levodopa plus dextromethorphan (20, 30 or 40 mg/kg, twice at day) for 22 consecutive days in order to investigate the potential effect of chronic dextromethorphan administration in preventing the decrease in the duration of motor response. As expected, the duration of the motor response to levodopa had significantly decreased by the 22nd day of levodopa in each group of treatment. Acute administration of dextromethorphan on day 23 reversed the reduction in the duration of the levodopa response only when administered at the lowest dose used in the present study (20 mg/kg) (p<0.05). Chronic administration of dextromethorphan concomitant to levodopa did not prevent levodopa effect showing a significant decrease on motor response duration (124+/-4 on day 1 vs. 88+/-16 on day 22, p<0.05, 30 mg/kg, twice a day). Our results indicate that in parkinsonian rats dextromethorphan is not a useful drug to prevent levodopa-induced motor alterations, however, low doses of dextromethorphan may be beneficial to reverse these alterations in motor response.

Animals↗

PubMed1975

Urinary excretion of monoamines and their metabolites in patients with Parkinson's disease. Response to long-term treatment with levodopa alone or in combination with a dopa decarboxylase inhibitor and clinical correlations.

Urinary excretion of DA, DOPAC, 3-MT, HVA, NMA, MA, VMA and 5-HIAA were studied in 33 parkinsonian patients treated with 1.5-7.5 g of levodopa daily for up to six months and in 30 patients receiving levodopa (800-1,000 mg) combined with a dopa decarboxylase inhibitor, benserazide (200-250 mg). Basal urinary excretions were within normal limits except for that of 3-MT which was significantly lower in parkinsonian patients as compared to controls. Levodopa induced an increase of about 400 fold in urinary DA; DOPAC was increased about 300 fold, 3-MT only about 70 fold, but HVA about 300 fold. Urinary NMA and MA did not change but VMA was increased significantly. On the other hand, urinary 5-HIAA was significantly decreased. The amounts of excreted DA and its subsequent metabolities were increased with the continuation of treatment, suggesting inductive phenomena in enzyme systems. During combined treatment with levodopa and benserazide urinary DA was increased, but only to about one tenth the extent seen with levodopa alone. The excretion of DOPAC was about one 20th, of 3-MT about one fourth and of HVA one 25th that seen during levodopa treatment. No signs of enzyme induction were seen. NMA was lowered significantly but MA remained unchanged. VMA was increased and significantly more than during therapy with levodopa alone. 5-HIAA was again significantly decreased and the decrease was significantly greater than that seen with levodopa alone. Some statistically significant correlations were seen between the excretions of NMA, MA and VMA and cardiovascular side effects, indicating an affection on the NA-ergic system by levodopa treatment. Significant correlation between 5-HIAA excretion and clinical improvement of tremor during levodopa treatment may suggest that participation of 5-HT in the mechanism of tremor.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1996

The effects of co-administration of benzhexol on the peripheral pharmacokinetics of oral levodopa in young volunteers.

1. The effects of benzhexol on the absorption and pharmacokinetics of an oral dose of levodopa have been studied in 10 young healthy volunteers. Subjects were given a suspension of levodopa (250 mg) 90 min after either benzhexol (5 mg) or placebo in a randomized cross over design with doses separated by at least 1 week; on each occasion carbidopa was given 1 h before and 5 h after the dose of levodopa. Soluble paracetamol and radiolabelled DTPA were given with the levodopa as markers of gastric emptying. 2. Most subjects showed two peaks in the levodopa plasma concentration-time curve on the placebo day, with the second minor peak occurring 1-2 h after the dose. After benzhexol administration all subjects showed two or more peak levodopa concentrations in plasma. Benzhexol administration caused a significant decrease in the maximum concentration (43%; P < 0.05) of the initial peak and an increase (22%; P < 0.1) in the maximum concentration of the second peak. This change in absorption profile caused by benzhexol significantly altered the ratios of the second peak compared with the initial peak for both the maximum concentrations (P < 0.02) and for the AUC values (P < 0.05). Benzhexol administration did not affect the total AUC of levodopa (7.30 +/- 1.09 vs 7.19 +/- 1.26 micrograms ml-1 h; means +/- s.d.). 3. The plasma concentration-time curves for paracetamol showed similar profiles to those for levodopa and the ratios of the peak concentrations and AUC values for the second peak compared with the initial peak were increased significantly by benzhexol administration (P < 0.05). The total AUC of paracetamol was not affected by benzhexol administration (39.4 +/- 8.2 vs 40.0 +/- 8.9 micrograms ml-1 h; mean +/- s.d.) 4. Benzhexol altered the gastric emptying profile, shown by gamma-scintigraphy, with a reduced extent of initial emptying prior to the establishment of the plateau which is characteristic of levodopa administration in the fasting state. In consequence the ratio of the second to the initial phase of emptying was significantly higher (P < 0.01) following benzhexol treatment. 5. Benzhexol reduces the initial phase of gastric emptying after a dose of levodopa so that there is a decrease in the initial peak and a greater proportion of the dose is absorbed subsequently following the second phase of gastric emptying which occurs approximately 1 h later. Theoretically, this altered concentration-time profile could be an advantage for some patients with Parkinson's disease.

Acetaminophen↗

PubMed2002

The effect of stage of Parkinson's disease at the onset of levodopa therapy on development of motor complications.

The aim of this study was to ascertain whether the stage of Parkinson's disease (PD) (according to the Hoehn and Yahr staging system) would affect the length of time between the introduction of levodopa therapy and appearance of levodopa-associated motor complications. Forty patients with clinically definite PD were studied. In all, clinical and therapeutic data were collected from the time of diagnosis to the time of levodopa-associated motor complications (i.e. dyskinesia, motor fluctuations). In 17 patients, levodopa could be started in Hoehn and Yahr stage I (H & Y-I; 16.2 months after the onset of PD), whilst in 13 patients levodopa could be started in H & Y-II (19.6 months after the onset of the disease) and in 10 in H & Y-III (45.1 months after the onset of PD). Cox proportional hazard regression model shows that the PD patients in whom the initial levodopa treatment was introduced at stage III develop both dyskinesias and motor fluctuations significantly earlier than the patients whose levodopa started in stage I and II of PD. The median interval to develop dyskinesias was 66, 72 and 24 months for patients in whom levodopa was introduced in stage I, II and III, respectively. These values were 64, 55 and 14 months for motor fluctuations. These findings add to the clinical arguments that favour an essential role of severity of PD at levodopa initiation as a risk factor for the development of levodopa-associated motor complications.

Age of Onset↗

PubMed1987

Influence of meal ingestion time on pharmacokinetics of orally administered levodopa in parkinsonian patients.

The influence of meal ingestion time on rate and extent of oral levodopa absorption was evaluated in a group of 17 patients, after administration of their usual second daily dose of levodopa plus carbidopa (Sinemet 10:1) or benserazide (Madopar 4:1). Standard meals were consumed by the patients after they had fasted 15-17 h, on one occasion 30 min before ingestion of the levodopa "study dose" and, at another time, 2 h after ingestion of the same dose. This study dose, ranging from 50 to 250 mg levodopa, was given to the patients at 11 a.m., 4 h after their first morning dose. Time to peak plasma levodopa concentration increased threefold (from 45 +/- 23 to 134 +/- 76 min, p less than 0.001), when levodopa was administered after meals. Area under the 6-h plasma concentration-time curve for levodopa was decreased in 10 subjects, unchanged in three and higher in four after ingestion of meals, the latter finding probably resulting from an erratic absorption even at fasting. On the whole, levodopa absorption proved significantly lower (p less than 0.01), on the average 15%. Similarly, peak plasma levodopa concentrations were lower in 12 patients, unchanged in two, and higher in three, with an overall significant decrease (p less than 0.001) of 30% on the average. The data confirm the importance of meal ingestion time in relation to levodopa dose as a determinant of drug absorption.

Aged↗

PubMed1989

Levodopa and 3-O-methyldopa plasma levels in parkinsonian patients with stable and fluctuating motor response.

Many parkinsonian patients with motor fluctuations in response to levodopa show a good response to initial morning doses but fail to respond in the afternoon and evening. We have studied levodopa and 3-O-methyldopa (3-OM-dopa) plasma profiles in 21 patients with fluctuations and eight patients with stable motor function throughout the day. Levodopa plasma peaks and valleys were similar for both group of patients. No significant difference for levodopa absorption index [defined as levodopa plasma levels after each dose divided by the quantity (mg) of ingested levodopa] was found between the first and the second levodopa-carbidopa dose in either group of patients. Even in patients who failed to improve after the second levodopa-carbidopa tablet (p.o.) on the day of the study, no significant variation in levodopa absorption index was observed. 3-OM-dopa values depended mainly upon levodopa consumption and were not different for patients with fluctuating or stable motor response. These findings provide further evidence of the prime role of central pharmacokinetic and pharmacodynamic factors in the pathogenesis of motor fluctuations in Parkinson's disease.

Aged↗

PubMedDate not supplied

Diurnal motor variations to repeated doses of levodopa in Parkinson's disease.

Patients with Parkinson's disease (PD) in long-term levodopa therapy often complain of worsening of motor symptoms in the afternoon and evening. The pathophysiology of this phenomenon is not known. We evaluated the motor response to repeated doses of levodopa during a 12-hour period in 52 parkinsonian patients (19 de novo, 20 stable, and 13 wearing-off). On the day of the study, all patients received standard doses of levodopa/carbidopa at 8:00 a.m., 12:00 noon, and 4:00 p.m. Motor measurements such as tapping test, walking time, and tremor score, and blood samples for levodopa and 3-O-methyldopa (3OMD) plasma analysis, were performed hourly. Mean motor scores and pharmacokinetic data, evaluated for a period of 3 hours after each levodopa dose, were compared. In de novo patients, we did not observe diurnal changes in motor score, whereas a progressive daytime worsening was visible in stable and wearing-off patients. No significant difference in levodopa pharmacokinetics after each levodopa dose was observed within each patient group, whereas 3OMD plasma levels significant increased with repeated levodopa administrations. However, no significant correlation between motor scores and 3OMD plasma levels was observed, suggesting that the diminishing motor response to afternoon and evening doses of levodopa in patients in long-term levodopa therapy does not relate to the pharmacokinetics of the drug. It is possible that this phenomenon may be an expression of the occurrence of tolerance to repeated doses of levodopa.

Administration, Oral↗

PubMed2005

Unilateral pallidotomy in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated common marmosets exhibiting levodopa-induced dyskinesia.

Pallidotomy paradoxically reduces the intensity of levodopa-induced dyskinesia without worsening motor symptoms. The reasons for this are not clear and no experimental study has investigated this phenomenon. The objective of this investigation was to evaluate the effects of unilateral pallidotomy on locomotor activity, motor disability and levodopa-induced dyskinesia in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated levodopa-primed common marmosets. Animals were primed to exhibit dyskinesia by daily administration of levodopa until stable dyskinesia was evoked by each dose. Locomotor activity, motor disability and dyskinesia were assessed weekly at baseline and following an acute levodopa challenge. Prior to pallidotomies, two distinct groups of animals emerged: poor responders to levodopa with mild dyskinesia (Group 1) and those exhibiting a marked increase in motor activity and pronounced dyskinesia (Group 2). Electrolytic lesions were placed in the left internal segment of the globus pallidus. Pallidotomy had no effect on basal or levodopa-induced motor activity in either group but significantly improved basal motor disability in Group 2. Following pallidotomy, the ability of levodopa to reduce motor disability was significantly increased in both groups. Pallidotomy improved dyskinesia in both Groups 1 and 2 but it was more effective in reducing dystonia compared with chorea. The effect of pallidotomy on dyskinesia in Group 2 was transient, with the intensity of involuntary movements reverting to presurgery levels 4 weeks later. This study shows that in levodopa-primed, parkinsonian marmosets, placement of discrete globus pallidus lesions can ameliorate levodopa-induced dyskinesia but not akinesia. This model allows the evaluation of pallidotomy-induced biochemical changes in dyskinetic primates.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed2003

Levodopa is toxic to dopamine neurons in an in vitro but not an in vivo model of oxidative stress.

Levodopa is the "gold standard" for the symptomatic treatment of Parkinson's disease (PD). There is a theoretical concern, however, that levodopa might accelerate the rate of nigral degeneration, because it undergoes oxidative metabolism and is toxic to cultured dopaminergic neurons. Most in vivo studies do not show evidence of levodopa toxicity; levodopa is not toxic to normal rodents, nonhuman primates, or humans and is not toxic to dopamine neurons in dopamine-lesioned rodents or nonhuman primates in most studies. However, the potential for levodopa to be toxic in vivo has not been tested under conditions of oxidative stress such as exist in PD. To assess whether levodopa is toxic under these circumstances, we have examined the effects of levodopa on dopamine neurons in mesencephalic cultures and rat pups in which glutathione synthesis has been inhibited by L-buthionine sulfoximine. Levodopa toxicity to cultured dopaminergic neurons was enhanced by glutathione depletion and diminished by antioxidants. In contrast, treatment of neonatal rats with levodopa, administered either alone or in combination with glutathione depletion, did not cause damage to the dopamine neurons of the substantia nigra or changes in striatal levels of dopamine and its metabolites. This study provides further evidence to support the notion that although levodopa can be toxic to dopamine neurons in vitro, it is not likely to be toxic to dopamine neurons in vivo and specifically in conditions such as PD.

Animals↗

PubMed1997

Catechol-O-methyltransferase inhibition with tolcapone reduces the "wearing off" phenomenon and levodopa requirements in fluctuating parkinsonian patients.

BACKGROUND: More than 50% of patients with Parkinson's disease develop motor response fluctuations (the "wearing off" phenomenon) after more than five years of levodopa therapy. Inhibition of catechol-O-methyltransferase by tolcapone has been shown to increase levodopa bioavailability and plasma elimination half life, thereby prolonging the efficacy of levodopa. OBJECTIVES: The primary objective was to evaluate the efficacy of tolcapone in reducing "wearing off" in levodopa treated, fluctuating parkinsonian patients. Secondary objectives included assessment of reduction in levodopa requirements, improvement in patients' clinical status, duration of improvements, and tolerability of tolcapone. METHODS: In this multicentre, randomised, double blind, placebo controlled trial, 58 patients received placebo, 60 received 100 mg tolcapone three times daily (tid), and 59 received 200 mg tolcapone tid, in addition to levodopa/benserazide. RESULTS: After three months with 200 mg tolcapone tid, "off" time decreased by 26.2% of the baseline value, "on" time increased by 20.6% (P<O.01 v placebo), and the mean total daily levodopa dose decreased by 122 mg from the baseline dose of 676 mg (P<0.01). These responses were maintained up to nine months. With 100 mg tolcapone tid, "off" time decreased by 31.5% (P<0.05), "on" time increased by 21.3% (P<0.01), and the mean total daily levodopa dose decreased by 109 mg from the baseline dose of 668 mg (P<0.05). With 200 mg tolcapone tid, unified Parkinson's disease rating scale motor and total scores were significantly reduced, and quality of life (sickness impact profile) scores were significantly improved. Both dosages were well tolerated. Dyskinesia was the most often reported levodopa induced adverse event. Diarrhea was the most often reported non-dopaminergic adverse event and the most frequent reason for withdrawal from the study: four patients in the 100 mg tolcapone tid group and six in the 200 mg tid group withdrew because of diarrhea. CONCLUSION: Tolcapone prolongs "on" time in fluctuating parkinsonian patients while allowing a reduction in daily levodopa dosage, thereby improving the efficacy of long term levodopa therapy.

Aged↗

PubMed2004

Levodopa with carbidopa diminishes glycogen concentration, glycogen synthase activity, and insulin-stimulated glucose transport in rat skeletal muscle.

We hypothesized that levodopa with carbidopa, a common therapy for patients with Parkinson's disease, might contribute to the high prevalence of insulin resistance reported in patients with Parkinson's disease. We examined the effects of levodopa-carbidopa on glycogen concentration, glycogen synthase activity, and insulin-stimulated glucose transport in skeletal muscle, the predominant insulin-responsive tissue. In isolated muscle, levodopa-carbidopa completely prevented insulin-stimulated glycogen accumulation and glucose transport. The levodopa-carbidopa effects were blocked by propranolol, a beta-adrenergic antagonist. Levodopa-carbidopa also inhibited the insulin-stimulated increase in glycogen synthase activity, whereas propranolol attenuated this effect. Insulin-stimulated tyrosine phosphorylation of insulin receptor substrate (IRS)-1 was reduced by levodopa-carbidopa, although Akt phosphorylation was unaffected by levodopa-carbidopa. A single in vivo dose of levodopa-carbidopa increased skeletal muscle cAMP concentrations, diminished glycogen synthase activity, and reduced tyrosine phosphorylation of IRS-1. A separate set of rats was treated intragastrically twice daily for 4 wk with levodopa-carbidopa. After 4 wk of treatment, oral glucose tolerance was reduced in rats treated with drugs compared with control animals. Muscles from drug-treated rats contained at least 15% less glycogen and approximately 50% lower glycogen synthase activity compared with muscles from control rats. The data demonstrate beta-adrenergic-dependent inhibition of insulin action by levodopa-carbidopa and suggest that unrecognized insulin resistance may exist in chronically treated patients with Parkinson's disease.

Animals↗

PubMed1994

Levodopa and dopamine agonists in the treatment of Parkinson's disease: advantages and disadvantages.

Recent studies have suggested that free radicals play a key role in the progression of Parkinson's disease (PD). Although levodopa is the most effective therapeutic agent in the treatment of PD and has improved the quality of life and increased life expectancy, its beneficial effects are not permanent. Long-term treatment with levodopa produces a variety of side effects in patients with PD. We have previously reported that levodopa may accelerate the progression of PD in certain patients. To determine whether neuronal damage can be caused by levodopa overdoses, we estimated the effects of levodopa on free radical formation. Electron spin resonance spectrometry showed that levodopa oxidation produced levodopa radicals. Furthermore, chronic administration of levodopa increased thiobarbituric acid-reacting substances (TBARS) in various brain regions of 6-hydroxydopamine (6-OHDA; i.c.v.)-pretreated mice, although levodopa administration in control mice had no effect on TBARS. These results indicate that high dose levodopa accelerates neuronal degeneration in some parkinsonian brains. We then evaluated the protective effects of bromocriptine on striatal dopaminergic neurons, with determination of dopamine (DA) and its metabolites as markers. Pretreatment of bromocriptine completely protected mice against the decreases in striatal DA and its metabolites induced by intracerebroventricular injection of 6-OHDA, while levodopa/carbidopa had no protective effects. Furthermore, in an in vitro system that generated .OH from FeSO4-H2O2, bromocriptine dose-dependently scavenged .OH. These findings clearly indicate that bromocriptine has neuroprotective effects against neurotoxins such as 6-OHDA, probably due in part to its free redical scavenging activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Effect of peripheral catechol-O-methyltransferase inhibition on the pharmacokinetics and pharmacodynamics of levodopa in parkinsonian patients.

Catechol-O-methyltransferase (COMT) metabolizes a portion of administered levodopa and thus makes it unavailable for conversion to dopamine in the brain. In an open-label trail, we examined the effects of entacapone, a peripheral inhibitor of COMT, administered acutely or for 8 weeks, on the pharmacokinetics and pharmacodynamics of levodopa in 15 parkinsonian subjects with a fluctuating response to levodopa. Acutely and chronically administered entacapone similarly decreased the plasma elimination of orally and intravenously administered levodopa. Absorption of levodopa was minimally affected. During chronic entacapone treatment, daily levodopa dosages were reduced by 27% yet mean plasma levodopa concentrations were increased by 23%. Plasma 3-O-methyldopa concentrations were decreased by 60%. Entacapone increased the duration of action of single doses of levodopa by a mean of 56%. The percent of the day "on" after 8 weeks of entacapone treatment was 77%; it dropped to 44% upon withdrawal of entacapone. We conclude that inhibition of COMT by entacapone increases the plasma half-life of levodopa and augments the antiparkinsonian effects of single and repeated doses of levodopa.

Aged↗

PubMed1998

Catechol-O-methyltransferase inhibition with tolcapone reduces the "wearing off" phenomenon and levodopa requirements in fluctuating parkinsonian patients.

BACKGROUND: More than 50% of patients with Parkinson's disease develop motor response fluctuations (the 'wearing off" phenomenon) after more than five years of levodopa therapy. Inhibition of catechol-O-methyltransferase by tolcapone has been shown to increase levodopa bioavailability and plasma elimination half life, thereby prolonging the efficacy of levodopa. OBJECTIVES: The primary objective was to evaluate the efficacy of tolcapone in reducing "wearing off" in levodopa treated, fluctuating parkinsonian patients. Secondary objectives included assessment of reduction in levodopa requirements, improvement in patients' clinical status, duration of improvements, and tolerability of tolcapone. METHODS: In this multicentre, randomised, double blind, placebo controlled trial, 58 patients received placebo, 60 received 100 mg tolcapone three times daily (tid), and 59 received 200 mg tolcapone tid, in addition to levodopa/benserazide. RESULTS: After three months with 200 mg tolcapone tid, "off" time decreased by 26.2% of the baseline value, "on" time increased by 20.6% (p < 0.01 vs. placebo), and the mean total daily levodopa dose decreased by 122 mg from the baseline dose of 676 mg (p < 0.01). These responses were maintained up to nine months. With 100 mg tolcapone tid, "off" time decreased by 31.5% (p < 0.05), "on" time increased by 21.3% (p < 0.01), and the mean total daily levodopa dose decreased by 109 mg from the baseline dose of 668 mg (p < 0.05). With 200 mg tolcapone tid, unified Parkinson's disease rating scale motor and total scores were significantly reduced, and quality of life (sickness impact profile) scores were significantly improved. Both dosages were well tolerated. Dyskinesia was the most often reported levodopa induced adverse event. Diarrhoea was the most often reported non-dopaminergic adverse event and the most frequent reason for withdrawal from the study: four patients in the 100 mg tolcapone tid group and six in the 200 mg tid group withdrew because of diarrhoea. CONCLUSION: Tolcapone prolongs "on" time in fluctuating parkinsonian patients while allowing a reduction in daily levodopa dosage, thereby improving the efficacy of long term levodopa therapy.

Aged↗

PubMed1998

History of levodopa and dopamine agonists in Parkinson's disease treatment.

Striatal dopamine deficiency in Parkinson's disease (PD), first described in 1960, was a key event that led to the era of levodopa therapy. In 1961, levodopa was first tried in PD patients, but throughout most of the 1960s the results were inconsistent. In 1967, questions about the effectiveness of levodopa in PD were finally set aside when Cotzias and colleagues reported dramatic improvement in PD patients with oral administration of levodopa in increasing amounts over long periods. The major side effects of levodopa administration, i.e., dyskinesias and motor fluctuations, also became apparent at this time. In the early 1970s, the advantages of adding a dopa decarboxylase inhibitor to treatment were discovered--reducing side effects and gaining better symptom control--and the first levodopa combination, carbidopa/levodopa, became commercially available in 1975. Since then, PD researchers have attempted to overcome complications with such techniques as continuous levodopa infusion and, most recently, long-acting levodopa combinations. A dopamine agonist, apomorphine, was used in 1970 as a means to overcome side effects and loss of levodopa efficacy. However, side effects and difficulty of administration limited its use. Dopamine agonists began to find a place in routine treatment of PD after the discovery of bromocriptine's benefits in PD in 1974. Since then, new approaches have been tried, such as dopamine agonist monotherapy and early therapy in combination with levodopa. The development of new dopamine agonists has led to characterization of dopamine receptor subtypes and agonists targeted to stimulation of specific receptors.

Antiparkinson Agents↗

PubMed2001

Effects of levodopa on pulmonary function in Parkinson's disease.

STUDY OBJECTIVES: Upper-airway obstruction (UAO) may be present in patients with Parkinson's disease (PD), and its reversibility after levodopa therapy has been suggested. To investigate the effects of oral intake of levodopa on pulmonary function and UAO criteria in patients with PD, we studied 22 patients with PD. DESIGN: Pulmonary function tests were performed after a 12-h withdrawal of levodopa therapy, and 1 h after oral intake of placebo or levodopa, according to a double-blind, placebo-controlled, crossover study. Six UAO criteria were recorded to detect UAO in patients. UAO was found in 5 of 21 patients on baseline conditions (1 patient could not perform all tests). RESULTS: Among the patients with UAO, after levodopa therapy three of five patients did not meet the four of six required criteria for defining UAO. Levodopa produced its effects on UAO criteria by means of a saw-tooth pattern improvement and/or a decrease below the defined thresholds of the peak inspiratory flow and the FEV(1)/peak expiratory flow (PEF) and FEV(1)/forced expiratory flow after 50% of the FVC (FEV(0.5)) ratios. Levodopa PEF increased by 0.85 L/s in patients with UAO and by 0.24 L/s in patients without UAO, while after placebo it increased by 0.03 L/s in patients with UAO and decreased by 0.16 L/s in patients without UAO (p = 0.02). Whereas in patients without UAO an increase of the FEV(1)/PEF and FEV(1)/FEV(0.5) ratios was observed after placebo and levodopa intake, these ratios decreased after levodopa and increased after placebo in patients with UAO. CONCLUSIONS: These results show that levodopa administration in patients with PD induces significant variations in PEF and UAO ratios (FEV(1)/PEF and FEV(1)/FEV(0.5)).

Aged↗

PubMed1996

Methods of managing levodopa-induced dyskinesias.

Levodopa-induced dyskinesias result in considerable functional impairment for patients and formidable therapeutic challenges for physicians. A practical method of treating such dyskinesias is first to classify the levodopa dyskinesias according to their temporal profile after drug administration, namely, into predictable (interdose, biphasic and 'off-period') and unpredictable ('on-off') dyskinesias. Treatment of each type of dyskinesia requires a different and relatively specific therapeutic strategy. With progression of Parkinson's disease, the threshold for interdose dyskinesia lowers, while the threshold for antiparkinsonian efficacy is unchanged; therefore, the strategy is to maintain levodopa concentrations between these 2 thresholds and avoid high concentrations. Frequent small doses of liquid levodopa preparations may be indicated. Clozapine appears to increase the threshold for dyskinesia. However, its usefulness is limited primarily by dose-related sedation and by dose-unrelated agranulocytosis. Buspirone and fluoxetine may have specific antidyskinetic benefit. Surgical treatment may aid selected patients, although criteria for selection are not fully established. The biphasic dyskinesias occur just before and just after an oral dose of levodopa. They result when levodopa concentrations fall below or rise above the threshold for therapeutic efficacy; therefore, the strategy is to maintain concentrations as nearly constant as possible above that threshold. Dopamine agonists such as subcutaneous apomorphine combined with domperidone may be particularly helpful. Thalamic stimulation can also benefit selected patients. 'Off-period' dyskinesias occur at times of predicted low concentrations of levodopa. The treatment strategy is to provide sufficient levodopa or dopaminergic stimulation during those intervals. Dopamine agonists (e.g. bromocriptine at night) may help the characteristic early foot dystonia. Anticholinergic agents may also help. The unpredictable ('on-off') dyskinesias are first analysed to establish a pattern of response. Then, on the basis of that pattern, they are treated by maintaining levodopa concentrations or dopaminergic tone during the periods that would ordinarily be 'off.' Administration of liquid levodopa preparations, addition of dopaminergic agents, restriction of treatment during the morning hours as well as restriction of the majority of dietary protein in the evening meal may provide a period of predictable good function early in the day. Clozapine, even early in treatment, appears to reduce the incidence of these dyskinesias. Rescue with apomorphine during a malignant prolonged 'off' phase is particularly valuable.

Antiparkinson Agents↗