Rectal apomorphine in Parkinson's disease

Intermittent Apomorphine Use for off Period Rescue in Parkinson's Disease: A Pragmatic Review of over Three Decades of Clinical Experience

Background

Although proven very efficacious as treatment for Parkinson's disease by Schwab as far back as the 1950s, and later confirmed by Cotzias and colleagues in the early 1970s, use of intermittent subcutaneous injections of the dopamine agonist apomorphine remains limited worldwide.

Objectives

To review evidence regarding use of intermittent, on-demand apomorphine as a treatment for off-period disability in Parkinson's disease.

Methods

A PRISMA-compliant structured literature search was carried out with a focus on clinical effect (motor improvement, daily off time decrease; latency, duration), antiemetic prophylaxis, and adverse events.

Results

Fifty-eight studies were evaluated. Apomorphine administration route was subcutaneous in 29 (50%), sublingual in 14 (24.1%), intranasal in 6 (10.3%), inhaled in 5 (8.6%), rectal in 3 (5.2%) and transdermal in 1 (1.7%). Irrespective of the route, motor disability improved 19% to 74% and daily off time decreased 3% to 68%, with subcutaneous having the fastest onset of action ranging from 6 to 24 minutes and lasting 28 to 96 minutes. Antiemetic prophylaxis was used in almost all studies. Systemic side effects like nausea and yawning were mild and well tolerated, but sedation led to discontinuation of subcutaneous apomorphine in 5.5%. Local side effects to subcutaneous administration did not result in discontinuation. Stomatitis with the early sublingual formulations led to discontinuation in nearly half of patients and was reduced to 16.7% with novel film strips.

Conclusions

Intermittent subcutaneous injections remain the most reliable and safest route of apomorphine administration, with an efficacy for off period treatment supported by nearly four decades of clinical experience.

On-Demand Therapy for OFF Episodes in Parkinson's Disease

Levodopa is the most effective therapy for Parkinson's disease; however, chronic treatment is associated with the development of OFF episodes, in which there is a return of parkinsonian features following a dose of levodopa and prior to the onset of benefit from the subsequent dose. OFF episodes can be a major source of disability for PD patients and frequently result in depression, apathy and an unwillingness to participate in social activities. Most currently available medical and surgical therapies are designed to reduce total daily OFF time but do not provide a rapid and reliable "on-demand" therapy for individual OFF episodes. Indeed, responses to individual doses of levodopa during an acute OFF episode are unreliable, frequently leading to partial-ON, delayed-ON, or no-ON responses even at different times in the same patient. There are now 3 therapies that are available for the on-demand treatment of OFF episodes; subcutaneous injection of apomorphine, sublingual apomorphine film, and inhaled levodopa. The first has not enjoyed widespread use in the PD community, whereas the latter 2 therapies have only recently been approved. This review will consider the currently available on-demand therapies and their potential advantages and disadvantages. © 2021 International Parkinson and Movement Disorder Society.

Apomorphine in the treatment of Parkinson's disease: a review

Optimizing idiopathic Parkinson's disease treatment is a challenging, multifaceted and continuous process with direct impact on patients' quality of life. The basic tenet of this task entails tailored therapy, allowing for optimal motor function with the fewest adverse effects. Apomorphine, a dopamine agonist used as rescue therapy for patients with motor fluctuations, with potential positive effects on nonmotor symptoms, is the only antiparkinsonian agent whose capacity to control motor symptoms is comparable to that of levodopa. Subcutaneous administration, either as an intermittent injection or as continuous infusion, appears to be the most effective and tolerable route. This review summarizes the historical background, structure, mechanism of action, indications, contraindications and side effects, compares apomorphine infusion therapy with other treatments, such as oral therapy, deep brain stimulation and continuous enteral infusion of levodopa/carbidopa gel, and gives practical instructions on how to initiate treatment.

Challenges and trends in apomorphine drug delivery systems for the treatment of Parkinson's disease

Parkinson's disease (PD) is a chronic debilitating disease affecting approximately 1% of the population over the age of 60. The severity of PD is correlated to the degree of dopaminergic neuronal loss. Apomorphine has a similar chemical structure as the neurotransmitter dopamine and has been used for the treatment of advanced PD patients. In PD patients, apomorphine is normally administered subcutaneously with frequent injections because of the compound's extensive hepatic first-pass metabolism. There is, hence, a large unmet need for alternative administrative routes for apomorphine to improve patient compliance. The present review focuses on the research and development of alternative delivery of apomorphine, aiming to highlight the potential of non-invasive apomorphine therapy in PD, such as sublingual delivery and transdermal delivery.

[Apomorphine in advanced Parkinson disease]

Apomorphine is the most potent dopamine receptor agonist and its symptomatic effectiveness is comparable to levodopa. Subcutaneous apomorphine is rapidly and completely absorbed. Plasma peak concentrations are achieved after 5-15 minutes and onset of clinical effect is within 20 minutes. Apomorphine intermittent subcutaneous injections are effective as rescue therapy for unpredictable off periods in advanced Parkinson disease (PD). More often apomorphine is administered as a subcutaneous infusion which secures the continuous dopaminergic stimulation. The benefit on 'off' periods is consistent across all studies, but dyskinesia improvement is not so obvious. Two infusion therapies (apomorphine and intraduodenal levodopa) and deep brain stimulation (DBS) are effective in advanced PD patients with untreatable motor complications. Apomorphine infusions should be considered in patients unable to undergo DBS because of cognitive impairment and neurosurgical contraindications.

Phase IIa randomized double-blind, placebo-controlled study of inhaled apomorphine as acute challenge for rescuing 'off' periods in patients with established Parkinson's disease

BACKGROUND AND PURPOSE

In this first study of inhaled apomorphine (VR040) in patients with Parkinson's disease, the primary objective was to find the minimum efficacious dose of apomorphine that was useful in rescuing patients during 'off' periods. Safety, tolerability and pharmacokinetics of inhaled apomorphine were assessed during the study.

METHODS

A double-blind, placebo-controlled, randomized trial of three escalating single doses of inhaled apomorphine (0.2, 0.5 and 0.8 mg fine particle dose) versus placebo (3 : 1 active:placebo) was performed. Parkinson's motor severity assessments by a clinician, and disease state assessment by the patient, were performed at baseline during an 'off' state, and at specified times after test drug administration. Safety assessments (including vital signs, electrocardiogram and forced expiratory volume) were performed, and plasma apomorphine levels measured.

RESULTS

All 24 patients completed the study, and considering the three dose levels together, inhaled apomorphine did not significantly increase the proportion of patients switching from 'off' to 'on' (0/6 at 0.2 mg, 3/6 at 0.5 mg and 2/6 at 0.8 mg vs. 1/6 for placebo), or decrease the time from 'off' to 'on' post-treatment (10 min for 0.5 mg, 40 min for 0.8 mg, vs. 20 min for placebo). However, there was a suggestion of benefit at the higher doses (5/12 switched 'on' at the 0.5 or 0.8 mg doses, vs. 1/6 for placebo). There were no serious adverse events and treatment was well tolerated. Peak plasma concentration was 1-3 min post-dose, and plasma level dose proportionality was observed.

CONCLUSIONS

Inhaled apomorphine was safe and well tolerated at the doses tested for an acute challenge to rescue 'off' periods, but efficacy at these doses was limited. A follow-up study at higher doses is appropriate given these initial findings.

Apomorphine in the treatment of Parkinson's disease

Motor fluctuations, refractory to conventional medical management, are one of the most troubling aspects of Parkinson's disease. Apomorphine is a dopaminergic agent that has been known to the medical community for more than a century, but has only recently been developed to treat such motor fluctuations. In this article, the authors review the historical background, structure, mechanism of action, pharmacologic properties, clinical trials, indications and side effects, as well as avenues of further research, of apomorphine.

Advances in the treatment of Parkinson's disease

Parkinson's disease (PD) affects one in every 100 persons above the age of 65 years, making it the second most common neurodegenerative disease after Alzheimer's disease. PD is a disease of the central nervous system that leads to severe difficulties with body motions. The currently available therapies aim to improve the functional capacity of the patient for as long as possible; however they do not modify the progression of the neurodegenerative process. The need for newer and more effective agents is consequently receiving a great deal of attention and consequently being subjected to extensive research. This review concisely compiles the limitations of currently available therapies and the most recent research regarding neuroprotective agents, antioxidants, stem cell research, vaccines and various surgical techniques available and being developed for the management of PD.

Transdermal treatment options for neurological disorders: impact on the elderly

As people grow old, their need for medications increases dramatically because of the higher incidence of chronic pain, diabetes mellitus, cardiovascular and neurological diseases in the elderly population. Furthermore, the elderly require special consideration with respect to drug delivery, drug interactions and adherence. In particular, patients with chronic neurological diseases often require multiple administration of drugs during the day to maintain constant plasma medication levels, which in turn increases the likelihood of poor adherence. Consequently, several attempts have been made to develop pharmacological preparations that can achieve a constant rate of drug delivery. For example, transdermal lisuride and apomorphine have been shown to reduce motor fluctuations and duration of 'off' periods in advanced Parkinson's disease, while rotigotine allows significant down-titration of levodopa without severe adverse effects. Thus, parkinsonian patients with long-term levodopa syndrome or motor disorders during sleep could benefit from use of transdermal lisuride and apomorphine. Moreover, transdermal dopaminergic drugs, particularly rotigotine, seem the ideal treatment for patients experiencing restless legs syndrome or periodic limb movement disorder during sleep, disorders that are quite common in elderly people or in association with neurodegenerative diseases. Unlike dopaminergic drugs, transdermal treatments for the management of cognitive and behavioural dysfunction in patients with Parkinson's disease and Alzheimer's disease have inconsistent effects and no clearly established role. Nevertheless, because of their favourable pharmacological profile and bioavailability, the cholinesterase inhibitors tacrine and rivastigmine are expected to show at least the same benefits as oral formulations of these drugs, but with fewer severe adverse effects. Transdermal delivery systems play an important role in the management of neuropathic pain. The transdermal lidocaine (lignocaine) patch is recommended as first-line therapy for the treatment of postherpetic neuralgia. Furthermore, in patients with severe persistent pain, transdermal delivery systems using the opioids fentanyl and buprenorphine are able to achieve satisfactory analgesia with good tolerability, comparable to the benefits seen with oral formulations. Transdermal administration is the ideal therapeutic approach for chronic neurological disorders in elderly people because it provides sustained therapeutic plasma levels of drugs, is simple to use, and may reduce systemic adverse effects. Several transdermal delivery systems are currently under investigation for the treatment of Parkinson's disease, Alzheimer's disease and neuropathic pain. Although most transdermal delivery systems treatments cannot be considered as first-line therapy at present, some of them provide clear advantages compared with other routes of administration and may become the preferred treatment in selected patients. In general, however, most transdermal treatments still require long-term evaluation in large patient groups in order to optimise dosages and evaluate the actual incidence of local and systemic adverse effects.

Advances in the delivery of treatments for Parkinson's disease

Innovative drug delivery in Parkinson's disease (PD) has the potential to reduce or avoid many side effects of current treatment, such as wearing-off type fluctuations, dyskinesia, on-off phenomena or bouts of motor freezing. The traditional orally administered formulations of l-dihydroxyphenylalanine combined with a peripheral aromatic acid decarboxylase inhibitor remain the mainstay of treatments for PD. However, such combination therapies have been further formulated to extend their duration of action by including a catechol-O-methyltransferase inhibitor. Preventing the breakdown of dopamine has also been achieved by monoamine oxidase-B inhibition; this approach now having been formulated for sublingual use (Zelapar, Valeant Pharmaceuticals). An alternative approach bypasses the oral route of administration and instead relies on continuous duodenal infusion (Duodopa, Solvay, NeoPharma AB) for better therapeutic effect. The clinical use of dopamine agonists as antiparkinsonian drugs now incorporates a variety of delivery techniques. For example, apomorphine, which relies on parenteral administration for maximum bioavailability, may be delivered via rectal, intranasal, sublingual and subcutaneous (e.g., Apokyn, Mylan Bertek) routes. Meanwhile, rotigotine and lisuride have both been formulated for delivery via skin patches. Finally, the authors examine more experimental delivery techniques, including the delivery of genes via viral vectors or liposomes, intracranial transplant of a variety of cells and of L-dihydroxyphenylalanine by prodrug-dispensing liposomes or pulmonary delivery (AIR, Alkermes). The advent and application of these varied technologies will help encourage patient-specific means of treatment for PD.

Apomorphine in Dopaminergic Therapy

Apomorphine is a potent molecule for the treatment of Parkinson's disease (PD). It can be obtained in both the R and S forms, and it is the former that is the therapeutically active form. Due to its structural similarity with 3,4-dihydroxyphenethylamine, dopamine, apomorphine can function as an agonist in the treatment of PD as it can stimulate both the D1 and D2 receptors of the striatum. The clinical efficacy of apomorphine is similar to that of 3,4-dihydroxyphenylalanine, levodopa (L-dopa), the cornerstone drug in dopaminergic therapy. (R)-Apomorphine is efficacious for one of the most challenging aspects in the management of PD, namely, managing the unpredictable "on-off" period as a rescue medication after oral administration of a therapeutic drug such as L-dopa. The effectiveness is due to its rapid control of the wearing-off period of the orally administered medicine. This short review will trace the progress of apomorphine use starting with its initial discovery and the first indications for which it was used, discovery of its "cure" for PD, and the studies that led to demonstrating its therapeutic efficacy. The key structural features of apomorphine responsible for its activity are illustrated along with major issues of chemical stability. From a drug delivery point of view, the current form of administration of apomorphine and some of the potential alternate methods of delivery are reviewed.

Transdermal apomorphine permeation from microemulsions: a new treatment in Parkinson's disease

We studied absorption, efficacy, and tolerability in Parkinson's disease (PD) of a new preparation of apomorphine included in a microemulsion and administered by transdermal route (Apo-MTD). Twenty-one PD patients were treated with levodopa plus oral dopamine-agonists (T0), with levodopa alone (T1), finally with levodopa plus Apo-MTD (T2). Apo-MTD provided therapeutic plasma levels for many hours, improved Unified Parkinson's Disease Rating Scale III scores, and reduced total duration of off periods compared to T0 and T1. We concluded that Apo-MTD is absorbed and demonstrates clinical efficacy and long action. Therefore, it seems a promising add-on treatment for uncontrolled prolonged off phases in PD patients, but chronic tolerability needs further study.

The effect of apomorphine administration on smooth pursuit ocular movements in early Parkinsonian patients

Electrooculography (EOG) recordings in 21 L-DOPA-naive patients suffering from Parkinson's disease (PD) were made before and after apomorphine subcutaneous administration (ASA). The effect of apomorphine on smooth pursuit eye movements (SPEM) was studied. Age-matched healthy subjects, who underwent SPEM recordings without the ASA procedure, were examined in order to compare baseline SPEM. EOG recordings were used to compare the patient group and the control group, and to compare the SPEM before and after ASA within the patient group. Significant differences in SPEM were found between both groups, as well as in the SPEM before and after ASA. The theory that SPEM is disturbed in early PD patients was confirmed. The dopaminergic control of horizontal SPEM is supposed.

Iontophoretic delivery of apomorphine: from in-vitro modelling to the Parkinson patient

Apomorphine is a mixed dopamine D1/D2 receptor agonist which is potentially useful in the treatment of Parkinson's disease. The delivery of apomorphine is however complicated because it is not absorbed orally and other delivery routes with the exception of the intravenous route seem to fail. The most interesting route for controlled delivery of apomorphine is transdermal iontophoresis because this could enable the Parkinson patient to directly control the needed amount of apomorphine by increasing or decreasing the drug input in order to achieve optimal drug therapy ('on-demand') with a minimum of toxic side effects. The typical features of Parkinson's disease could be used to monitor the needed drug input and even more elegantly by means of suitable chip sensors which are able to directly measure bradykinesia, akinesia and/or tremor and to regulate in such a way the drug input. Such a chip-controlled iontophoretic system would be the first closed-loop system monitoring not pharmacokinetic data (blood levels) but more importantly externally measurable pharmacodynamic effects of Parkinson's disease. This scenario is more feasible as skin irritation and toxicity studies have proven that iontophoresis is a safe route of treatment. This review describes the basics of iontophoresis and the development of a transdermal iontophoretic delivery system on the basis of integrated pharmacokinetic/pharmacodynamic (PK/PD) investigations in patients with idiopathic Parkinson's disease. Transdermal iontophoretic transport of apomorphine was studied both in vitro with human stratum corneum using a newly developed iontophoretic continuous flow-through transport cell and in vivo in a first exploratory study in patients with Parkinson's disease. These studies showed that the delivery of apomorphine is feasible and furthermore the rate of delivery can be controlled by variation of the current densities. Additionally the pretreatment of the skin either with a mono-surfactant or a vesicular suspension of elastic liquid-state vesicles may be useful to further increase the apomorphine flux across the skin in combination with iontophoresis.

Motor fluctuations in Parkinson's disease: pathophysiology and treatment

At the initial stages of Parkinson's disease (PD), levodopa (LD) is able to reduce most motor symptoms and to significantly improve the patient's quality of life. However, in the vast majority of patients with prolonged LD usage, some decline in efficacy occurs and motor complications eventually begin to appear. These complications consist not only of daily fluctuations in the voluntary motor performance often accompanied by involuntary movements, but also of fluctuations in cognitive, autonomic, and sensory functions. Several recent studies on LD complications in PD have led to a better understanding of their pathophysiology and of the possible therapeutic interventions, and a summary of these findings is presented in this review. Different observations now suggest that postsynaptic pharmacodynamic factors play a major role in determining fluctuations in PD. Two explanations are given: chronic intermittent dopaminergic therapy may lead to postsynaptic receptor downregulation in PD; or, receptor changes in the striatum may occur independently of treatment as a result of structural adaptation of the postsynaptic dopaminergic system to the progressive decline of the nigrostriatal pathway. The hypothesis of reversible postsynaptic changes as the main mechanism underlying a fluctuating response to LD lends itself to a possible pharmacological manipulation of the dopaminergic response to reverse, or even avoid, motor fluctuations (initial monotherapy with dopamine agonists and early combination LD/dopamine agonists). The role of peripheral pharmacokinetics factors is also critical and the use of controlled release LD formulations, of monoamine oxidase (MAO)-B and of catechol-O-methyltransferase (COMT) inhibitors may all, to a different degree, improve such phenomena. In the last decade, there has been a resurgence in surgical therapies in advanced PD, due to higher levels of accuracy and safety provided by the new surgical devices, and to a more precise localization of the target areas allowed by the neurophysiological mapping techniques. The surgical procedures currently used in advanced PD are stereotactic brain lesions (internal globus pallidus and subthalamic nucleus), chronic brain stimulation (of the same nuclei) and striatal grafting of dopamine-producing cells. All these procedures have already shown their efficacy in the management of severe fluctuations in PD, but their indications, and relative advantages and disadvantages, are still the subject of considerable debate and controversy.

Subcutaneous apomorphine in late stage Parkinson's disease: a long term follow up

OBJECTIVES

Despite the recent introduction of new peroral drugs as well as neurosurgical methods for Parkinson's disease, treatment of late stage parkinsonian patients remains difficult and many patients become severely handicapped because of fluctuations in their motor status. Injections and infusions of apomorphine has been suggested as an alternative in the treatment of these patients, but the number of studies describing the effects of such a treatment over longer time periods is still limited. The objective was to investigate the therapeutic response and range of side effects during long term treatment with apomorphine in advanced Parkinson's disease.

METHODS

Forty nine patients (30 men, 19 women; age range 42-80 years) with Parkinson's disease were treated for 3 to 66 months with intermittent subcutaneous injections or continuous infusions of apomorphine.

RESULTS

Most of the patients experienced a long term symptomatic improvement. The time spent in "off" was significantly reduced from 50 to 29.5% with injections and from 50 to 25% with infusions of apomorphine. The quality of the remaining "off" periods was improved with infusion treatment, but was relatively unaffected by apomorphine injections. The overall frequency and intensity of dyskinesias did not change. The therapeutic effects of apomorphine were stable over time. The most common side effect was local inflammation at the subcutaneous infusion site, whereas the most severe were psychiatric side effects occurring in 44% of the infusion and 12% of the injection treated patients.

CONCLUSION

Subcutaneous apomorphine is a highly effective treatment which can substantially improve the symptomatology in patients with advanced stage Parkinson's disease over a prolonged period of time.

Clinical pharmacology of dopamine agonists in Parkinson's disease

Oral levodopa is the most effective symptomatic treatment for Parkinson's disease. Dopamine agonists are useful adjuvants to levodopa in the pharmacotherapy of parkinsonian patients. Monotherapy with dopamine agonists in early Parkinson's disease has been advocated in order to delay the occurrence of complications associated with long term administration of levodopa. The use of dopamine agonists alone provides an adequate antiparkinsonian effect in only a minority of patients. In early stages of Parkinson's disease, dopamine agonists can produce a clinical response comparable with levodopa but, thereafter, their efficacy wanes. Early initiation of combination therapy with levodopa and dopamine agonists appears to reduce the severity and delay the appearance of the complications associated with long term administration of levodopa. Currently, dopamine agonists are most commonly used in combination with levodopa in patients in advanced stages of the disease who experience fluctuations of their motor symptoms. Despite their different pharmacodynamic and pharmacokinetic profiles, the ergot derivatives bromocriptine, lisuride and pergolide appear to be very similar in terms of their clinical efficacy. Continuous dopaminergic stimulation by parenteral infusion of water-soluble dopamine agonists such as apomorphine and lisuride can overcome motor fluctuations in advanced Parkinson's disease. Other dopamine agonists such as cabergoline, pramipexole and ropinirole are currently being studied. Further studies with these compounds will be required to determine their efficacy and adverse effects in comparison with the currently available orally active ergot agonists. It has been suggested that oxidative stress resulting from dopamine metabolism may be reduced by the administration of dopamine agonists. These drugs may therefore slow the rate of progression of Parkinson's disease. At present, however, there is no convincing clinical data to support a neuroprotective effect of dopamine agonists.

Iontophoretic delivery of apomorphine. II: An in vivo study in patients with Parkinson's disease

PURPOSE

Transdermal transport rates of the dopamine agonist R-apomorphine were determined in patients with idiopathic Parkinson's disease (IPD). Apomorphine was applied by iontophoresis at two current densities.

METHODS

In ten patients apomorphine was applied passively for one hour. Thereafter, in the first five patients, a current density of 250 microA.cm-2 was applied for one hour and a current density of 375 microA.cm-2 in the second group. The individual pharmacokinetic parameters were obtained separately following a 15-minute zero-order intravenous infusion of 30 micrograms.kg-1. Skin resistance was measured during current delivery. Current-induced irritation was measured by Laser Doppler Flowmetry (LDF). The pharmacodynamics were quantified by a unilateral tapping score. Qualitative clinical improvements (decreased tremor, rigidity or cramp) were also recorded.

RESULTS

In all patients increasing plasma concentrations of R-apomorphine were found during the interval of current application. The maximum concentrations that were attained were related to the applied current density: 1.3 +/- 0.6 ng.ml-1 at 250 microA.cm-2 and 2.5 +/- 0.7 ng.ml-1 at 375 microA.cm-2. When the current was switched off all concentrations returned to baseline values in about 90 minutes. By mathematical deconvolution of the profiles it was shown that steady-state fluxes were reached within the one-hour interval of current driven transport Steady-state fluxes were calculated to be 69 +/- 30 nmol.cm-2.h-1 at 250 microA.cm-2 and 114 +/- 34 nmol.cm-2.h-1 at 375 microA.cm-2. Individual drug input rates were inversely related to the overall resistance. Significantly elevated LDF values were found after patch removal, indicating mild current induced erythema. Only subtherapeutic plasma concentrations were obtained in all patients except for one.

CONCLUSIONS

The results show that current-dependent delivery of apomorphine is possible in vivo at acceptable levels of skin irritation. Excellent correlation was found between the calculated in vivo transport rates and the rates that were previously obtained in vitro.

Pen injected apomorphine against off phenomena in late Parkinson's disease: a double blind, placebo controlled study

The effect, therapeutic dose range, and pharmacokinetics of apomorphine, given as subcutaneous injections by a single use pen, were evaluated in the treatment of off phenomena in 22 patients with idiopathic Parkinson's disease. At study entry a placebo controlled apomorphine test was performed, and apomorphine doses were then individually titrated (mean 3.4 (range 0.8-6.0) mg) and compared with placebo in a double blind cross over phase. With apomorphine compared with placebo the mean daily duration of off periods was reduced by 51% as assessed by the patients and by 58% as assessed by the staff. The severity of off periods was also significantly reduced. The effect was unchanged after a maintenance phase of eight weeks. At study termination 13 of 14 patients were able to inject themselves and 11 of 14 patients found that their feeling of freedom had increased. The most common adverse events were nausea, subcutaneous nodules, and increased frequency of involuntary movements. Pharmacokinetics were linear and did not change with repeat dosing. The tmax ranged from five to 45 minutes (16 patients). It is concluded that pen injected apomorphine is a valuable treatment for patients with advanced Parkinson's disease with on-off phenomena.

Apomorphine for motor fluctuations and freezing in Parkinson's disease

OBJECTIVE

To review the pharmacokinetics and use of apomorphine in patients with Parkinson's disease; to report a case of beneficial outcome with apomorphine in a patient with Parkinson's disease with severe levodopa "on-off" fluctuations and freezing; and to outline the types of patients or situations where apomorphine may be useful.

DATA SOURCES

Case reports, review articles, and relevant clinical studies identified by a MEDLINE search of the English-language literature published between 1975 and October 1994.

STUDY SELECTION

Because all but 2 reports were of open-label design with small sample sizes, all studies identified were evaluated.

DATA EXTRACTION

The following data were extracted from each study: apomorphine treatment duration, dosing, onset, duration, and adverse effects. The following efficacy variables were extracted: percent decrease in off periods, improvement in parkinsonian symptoms, and percent decrease in levodopa dosage.

DATA SYNTHESIS

Efficacy of apomorphine following subcutaneous, rectal, sublingual, and intranasal dosage forms are evaluated. We also describe the use of apomorphine in a patient with Parkinson's disease who experienced on-off fluctuations and freezing. Based on these reports, recommendations for patient selection, product selection, and apomorphine dosing guidelines are presented.

CONCLUSIONS

Apomorphine decreases off time, freezing, and levodopa requirements in patients with Parkinson's disease. It can be administered via a number of different nonoral routes; however, subcutaneous apomorphine is the most extensively studied. Rectal, sublingual, and intranasal routes also have been shown to provide benefit in motor fluctuations, but differ from the subcutaneous route in onset of action, duration of effect, and adverse effect profile.

Apomorphine in patients with Parkinson's disease

We present a review of the recent literature and personal experience with apomorphine in patients with Parkinson's disease. Apomorphine is a potent D1 and D2 dopaminergic agonist. It has a rapid and short duration effect after subcutaneous administration at doses ranging from 15 to 180 micrograms/kg. Plasma maximal concentration is reached in 8-16 minutes, with a plasma half life of 34-70 minutes. Bioavailability is close to 100%. Repeated injections in patients show post-stimulative hyposensitivity. Apomorphine test appears very useful for the differential diagnosis between idiopathic Parkinson's disease and other Parkinson plus syndromes, and as a predictive test for dopaminergic responsiveness. Appropriate doses are able to alleviate akinesia, rigidity and tremor. Recent therapeutic trials have demonstrated the high interest of intermittent multiple subcutaneous apomorphine injections to cut the "off" motor phases in fluctuating parkinsonian patients under chronic levodopa treatment. In some cases, continuous apomorphine subcutaneous infusion with a portable pump may be required, particularly when levodopa treatment is temporarily interrupted, as after abdominal surgery. During long-term treatment, the apomorphine dose able to relieve akinesia remains stable. Peripheral side effects such as nausea and hypotension may be prevented by the co-administration of domperidone, a peripheral dopaminergic antagonist. Cutaneous fibrous nodules and psychiatric symptoms may occur, but usually at high dosages with continuous infusion. Local allergic effects have limited the use of other routes of administration, such as intranasal, sublingual, and rectal routes. Apomorphine is also used as a pharmacological tool for clinical research with the aim of a better understanding of the pathophysiology of Parkinson's disease.

Comparison of two software programs to be used for the calculation of population pharmacokinetic parameters

The pharmacokinetic parameters of apomorphine, a potent dopamine agonist, were calculated after subcutaneous and intranasal administration. Two available software packages for TDM were used (USC*PACK and MW/PHARM). The findings for the calculated parameters Kel, Vslope, Ka and bioavailability were compared. Although small, sometimes significant differences were found, the NPEM program from the USC*PACK collection provides most information about the population under investigation. We found a median Vslope of 1.7408 +/- 0.8461 (S.D.) 1/kg, and a mean Kel of 1.5341 +/- 0.3748 h-1. The absorption after intranasal administration was extremely rapid: Ka = 20.5 +/- 1.96 h-1, comparable with that found with subcutaneous absorption: Ka = 23.04 +/- 2.20 h-1.

Subcutaneous apomorphine in Parkinson's disease: response to chronic administration for up to five years

Subcutaneous apomorphine, administered by continuous waking-day infusion with boluses, or by repeated intermittent injection, was given to 71 parkinsonian patients with severe refractory levodopa related on-off fluctuations for 1-5 years. A mean reduction in daily off period time of approximately 50% was maintained, and the incidence of neuropsychiatric toxicity remained low on long-term follow-up. No clinically significant tolerance or loss of therapeutic effect was seen, although increasingly severe on-phase dyskinesias and postural instability marred the long-term therapeutic response in many patients. Despite these drawbacks, apomorphine, when combined with the peripheral dopamine receptor agonist domperidone, represents a significant therapeutic advance in the management of late-stage Parkinson's disease and should certainly be considered before experimental implantation procedures.