Pharmacology. The use of co-beneldopa and selegiline in the treatment of Parkinsons disease

by zan74 (student)

University Degree Subjects allied to Medicine

Pharmacology – Principles and Practice

The use of co-beneldopa and selegiline in the treatment of Parkinson’s disease

Drugs as stated by Luty and Harrison (1997) are chemical compounds which produce a desirable physiological or psychological effect when administered. This essay will discuss two different drugs which are used in the treatment of Parkinson’s disease, co-beneldopa and selegiline hydrochloride. All drugs are absorbed, distributed and then excreted (Luty and Harrison, 1997), so this essay will discuss pharmacokinetics and look at what happens to the drug once it has been administered and what effects the drug has on the body (Neal, 1992), It will also look at pharmacodynamics, the way the body affects the drug (Neal, 1992).

Parkinson's disease is a neurodegenerative condition and second to Alzheimer's disease (Allcock, 2007). It is a and affects one person in every five hundred, which is about one hundred and twenty thousand people in the United Kingdom (Parkinson’s UK, 2011).

Most Parkinson's disease sufferers are aged fifty or over but younger people can get it too, one in twenty is under the age of forty (Parkinson UK, 2011). An earlier onset can be due to acute encephalitis, carbon monoxide poisoning or metallic poisoning (Beckford-Bell, 2006). The disease results in motor symptoms including tremor, rigidity, postural instability and bradykinesia a slow ability to move and continue movements.

Parkinson’s disease is the steady deterioration of dopamine releasing neurons in the substania nigra (Luty and Harrison, 1997). Without dopamine people can find that their movements become slower so it takes longer to do things (Parkinson’s UK, 2011).

Parkinson’s disease process develops as the cells in the Substantia nigra, the crescent shaped cell mass in the brain stem are destroyed (ADAM, 2011). Parkinson’s disease affects movement, muscle control, and balance. Nerve cells in the substantia nigra send out fibres to tissue located in both sides of the brain. There the cells release essential dopamine neurotransmitters that help control movement and coordination (ADAM, 2011).

Currently, there is no cure for Parkinson's disease and as yet no knowledge as to why people get the condition (Parkinson’s UK, 2011). Parkinson's doesn't directly cause people to die, but symptoms do get worse over time (Parkinson’s UK, 2011). Parkinson's doesn't directly cause people to die, but symptoms do worsen over time (Parkinson’s UK, 2011) which does have a contributory factor to mortality rates.

Pharmocokinetics is a branch of pharmacology that is concerned with both the rates at which the drug is absorbed and eliminated and what influences the time the drug moves between one biological compartment and another (Hollinger, 2003). Most drugs are given orally and enter the blood stream by passing through the gut wall (Neal, 1992). Most drugs are recognised by the liver as a toxin and are broken down into metabolites (Campbell, 2011). First pass metabolism is when the strength of a drug becomes reduced before they can be circulated throughout the entire system satisfactorily (Disease.com, 2010). The first pass refers to the first trip ingested drugs take through the liver, once it has passed through only a small amount of the drug is passed on to the rest of the system. First pass metabolism is usually only associated to drugs that are taken orally. After certain drugs are ingested by the body, they are absorbed by the digestive system after being metabolised through digestion (Disease.com, 2010). After the drugs have gone through first pass metabolism the absorbed drugs enter the hepatic portal system, where they are carried by the portal vein to the liver (Disease.com, 2010). If first pass metabolism occurs, it means that the liver will not allow enough of the drugs to pass into the blood stream to be effective at helping the condition they are being taken for (Disease.com, 2010). This is known as bioavailability, which is a term to describe the proportion of the drug administered reaching the systemic circulation. If a drug is taken by intravenous injection the bioavailability is one hundred percent as it is not metabolised through the liver. The bioavailability of a drug does vary with different drugs and from patient to patient (Neal, 1992). A standard reaction of the liver is first pass metabolism and it is a reaction to certain drugs, or a particular drug or a number of drugs (Neal, 1992). This may be caused by a deficiency of the drug or a patient may have a condition than can affect the drug (Neal, 1992). When it is the drug that is the problem, the pharmaceutical company have many options to resolve it. For example, keeping the drug in the same preparation, they can increase the concentration of the drug, or combining other compounds which are designed to facilitate the passage of the drug through the digestive system and the wall of the gut. Although, this can be risky as an excess amount of the drug can impair metabolic function and in turn lead to harmful quantities in the systemic system (Neal, 1992). However, if a drug is highly sensitive to first pass metabolism, then the pharmaceutical company will find another way to administer the drug which will bypass the digestive system and the liver, sending the drug directly into the systemic circulation. Administrating drugs this way, avoids the liver and is in the systemic circulation fully concentrated to be carried through the system, an example of this would be sublingual administration (Neal, 1992). The other factor that can affect first pass metabolism is the liver itself. Chronic liver disease can lead to an increase in bilirubin which may compete for binding sites on protein (Laurence, Bennett and Brown, 1997).

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Once administered and the drug has gone through first pass metabolism, the drug attaches to plasma proteins which are formed in the liver (Campbell, 2011). The main binding protein is albumin (Laurence, Bennett, Brown, 1997). It has a complex structure which binds drugs but is also readily releases them (Laurence, Bennett, Brown, 1997). Protein binding reduces the availability of a drug for diffusion or transport into the target organ because only the unbound form of the drug is capable of diffusion across membranes (Golan et al, 2008). Plasma bound drugs are confined to the vascular system and are not able to exert their pharmacological actions (Neal, 1992). There are many factors that can effect drug distribution with regards to plasma protein binding. One is the administration of two drugs both of which are highly bound to plasma protein, which would result in higher than expected plasma concentration of the free form of one or both drugs (Golan et al, 2008). This increase of free drug has the potential to cause an increase in therapeutic and/or toxic effects of the drug (Golan et al, 2008). A decrease in plasma protein binding capacity in the elderly is another factor that affects drug distribution and it has been attributed to changes in renal failure and its decrease is fifteen to twenty five percent (Ginsberg et al, 2005). The reduced protein binding capacity can lead to a higher potential to drug-drug interactions (Ginsberg et al, 2005).

As an active drug decreases in its concentration in the blood, drug metabolism and excretion shorten the time during which a drug is capable of acting on the target organ (Golan et al, 2008). Half life of a drug is defined as “the amount of time over which the drug concentration in the plasma decrease to one-half of it original value” (Golan et al, 2008). Having the knowledge of a drugs half-life allows a clinician to estimate the frequency of dosing required to maintain plasma concentration of the drugs therapeutic range (Golan et al, 2008). When arranging a drug regime, careful consideration should be made as the effects from a drug with a long half life, as it may last for a number of days (Golan et al, 2008). Purse (2007) states that no matter what the half life of a drug, it will always take four half lives for the concentration of the drug in the system to reach a steady rate. For an example taking a medication with a half-life of twenty four hours, on the fifth day the rate of intake of the drug will approximately equal the rate of elimination. If the half-life is twelve hours, it will reach that state at the beginning of the third day (Purse, 2007).

As mentioned earlier two drugs used in the treatment of Parkinson’s disease are selegiline hydrochloride and co-beneldopa. Selegiline is a selective monoamine oxidase B inhibitor, however in larger doses it loses its specificity and will also inhibit monoamine oxidase A (Drugsupdate.com 2011). A monoamine oxidase B inhibitor prevents the breakdown of dopamine in the brain by blocking the enzyme monamine oxidase type B, Ahlskog, (2009 and Grosset et al, (2009) cited by Lindahl and MacMahon, (2011)). In the early progression of Parkinson’s disease, selegiline can be used as a monotherapy or later on in the progression of the disease with levodopa (Chan et al, 2004). The use of selegiline can delay the need for treatment with levodopa. Neal (1992) states that there is evidence to show the progression of the disease may slow with the use of selegiline. Although Chan et al (2004) states that any claims of treatment with any Parkinson’s disease drugs slow down the disease progression or repair neuronal degeneration should be viewed with scepticism. A study was undertaken in Sweden to study the effects of selegiline in monotherapy and in combination with levodopa in the early phase of Parkinson disease. One hundred fifty-seven Parkinson’s disease patients were randomly chosen in a controlled study for a duration of 7 years, to look at the long term effects of the drugs. The results for selegiline as a monotherapy showed that it significantly delayed the initiation of levodopa therapy vs placebo. The study concluded by confirming earliy findings indicated that selegiline delays the progression of the signs and symptoms of Parkinson disease (Neurology, 2006)

In practice Parkinson’s disease it treated using monamine oxidase type B inhibitors as first-line therapy in young patients who cannot tolerate dopamine agonists but who wish to delay treatment with levodopa (Allcock, 2007). By inhibiting the enzyme monamine oxidase type B, selegiline increases the dopamine levels in the substantia nigra. Dopamine concentration is increased in the brain as selegiline also blocks dopamine re-uptake from the synaptic cleft (Allcock, 2007).

However, due to by-products of selegiline metabolism, neuropsychiatric side-effects can occur (Allcock, 2007). However it may be difficult to decide if these side affects are due to the drugs or the progression of the disease (Laurance, Bennett and Brown, 1997). It is not yet known “if the lack of amphetamine metabolites with rasagiline confers any clinical benefit over selegiline. These agents are effective for reducing motor symptoms in Parkinson’s disease, and can delay the need for treatment with levodopa” (Allcock, 2007).

The pharmacokinetics of selegiline are highly variable. After the administration of an oral dose of selegiline, it is rapidly absorbed and metabolised to desmethylselegiline, levoamphetamine and levomethamphetamine (Selegiline data sheet, 2011). This metabolism is mainly in the liver (Delue et al, 2002). It is distributed into tissues including the brain. The drug is highly lipid-soluble, which is why it rapidly penetrates the central nervous system (Delue et al, 2002). Plasma protein binding is ninety nine point five percent (Drug bank, 2011). The absolute bioavailability of selegiline is approximately 10% (Medafe, 2000). Which means a lot of the drug is wasted before it reaches the systemic circulation. Selegiline bioavailability can be substantially increased however by up to threefold if it is administered with food high in fat (Medsafe, 2000 and Drugs.com, 2011). Selegiline is mainly excreted as metabolites in the urine, about fifteen percent is excreted in the faeces. The half life of selegiline is between one to two hours (Drug bank, 2011) or about ten hours (Medsafe, 2000).

Selegiline’s benefits in Parkinson's disease has only been recorded as an addition to levodopa. Drug.com (2011) documented selegiline’s effectiveness as a monotherapy was unknown, but past attempts to treat Parkinson's disease with non-selective monamine oxidase inhibitors as a sole treatment are reported to have been unsuccessful. However, Heinonen and Myllyla (1998) stated in all studies where selegiline has been used as monotherapy in the treatment of Parkinson’s disease the drug has been well tolerated if it is compared with, for example, dopamine agonists. Attempts to treat Parkinson’s disease with combinations of levodopa and currently marketed non-selective monamine oxidase inhibitors were stopped because of multiple side effects including hypertension, increase in involuntary movement, and toxic delirium (Drugs.com, 2011).

Serious drug interactions can occur with monamine oxidase type B inhibitors. An interaction of monamine oxidase type B inhibitors with antidepressants such as tricyclics and selective serotonin reuptake inhibitors is particularly important as this can result in a fatal serotonin syndrome (Allcock, 2007). A daily dose of selegiline is ten milligrams either as one dose or five milligrams twice daily (BNF, 2007). As selegiline is a irreversible monoamine oxidase B inhibition, the duration of clinical effect does not depend on the elimination time, and therefore once daily dosing can be applied (Medsafe, 2000). Selegiline can also be used in conjunction with levodopa in the later stages of the diseases (Craig and Stitzel 2004). The main adverse reactions caused by selegiline is due to the increased levels of dopamine (Craig and Stitzel, 2004).

A new preparation for selegiline has recently been tested. Zydis selegiline is a tablet that dissolves on the tounge and undergoes pregastric absorption. This provides high plasma concentrations of selegiline missing the first-pass metabolism. In this study, Zydis selegiline was assessed in patients who were experiencing motor fluctuations with levodopa for safety and its effects. “Zydis selegiline safely reduces daily offtime when used as adjunctive therapy with levodopa in patients with Parkinson’s disease” (Movement Disorder Society 2004).

Co-beneldopa is a mixture of benserazide and levodopa (BNF, 2007). Levodopa is the metabolic precursor of dopamine (Roche products, 2010). It is considered that giving levodopa raises the level of available dopamine (Roche products, 2010). Most of the levodopa dose is decarboxlated in the tissues outside the brain and as a result of this the full therapeutic effect of the drug may not be obtained which could lead to adverse reactions (Roche products, 2010). A prodrug is a drug which is inactive until metabolised in the body to the active drug. Dopamine is supplied as the pro-drug levodopa to dopamine in the brain, where it relieves the symptoms of Parkinson’s disease in the early stages. The amino acid levodopa is used to substitute the dopamine deficiency in Parkinson’s disease (TEVA UK Ltd, 2009). This is due to the fact that at least ninety five percent of orally administered levodopa is decarboxylated in extracerebral organs such as the intestines, liver, kidneys, heart and stomach. Only small amounts reach the central nervous system after administration of levodopa monotherapy. Many gastrointestinal and cardiovascular adverse reactions can occur with a build up of dopamine with levodopa monotherapy (TEVA UK Ltd, 2009). There are two problems with levodopa (McGovock, 2005). Firstly, less then ten percent of an oral dose reaches the brain the reminder is metabolised in many body tissues giving many intolerable adverse effects such as insomnia, nausea and vomiting and anorexia. The second is that levodopa does not replace lost nerve cells or stop the progression of the disease. So to overcome this problem drug companies combined levodopa with one of two drugs, one of which is benserazide, which inhibits the peripheral breakdown of dopamine and ensures that sufficient reaches the central nervous system (McGavock, 2005). Benserazide is a decarboxylase inhibitor and at the therapeutic dose it does not cross the blood-brain barrier however at a higher dose it may entre the central nervous system (Roche products, 2010).

Levodopa is readily absorbed from the upper small intestine by active amino acid and has a half life of one and a half hours (Laurance, Bennett and Brown, 1997). Levodopa crosses the blood-brain barrier by means of a saturable transport mechanism. It is not bound to plasma protein. Half life in increased in the elderly by twenty five percent (TEVA UK Ltd, 2009). Co-beneldopa has a bioavailability of sixty percent, this is not reduced by food but can be reduced by antacids (Roche products, 2010). Ten to thirty percent of the drug binds to plasma protein (Drugsupdate, 2011). Co-beneldopa is said to be the best treatment for patients over the age of seventy five, or for younger patients with evidence of neuropsychiatric involvement cognitive impairment or hallucinations. For night-time hours the slow release preparation can be used, but it has reduced and more unpredictable bioavailability than standard-release preparations and so is recommended not to be used through the day time (Allcock, 2007). Benserazide is almost entirely eliminated by metabolism. Sixty four percent of metabolites are excreted in the urine and twenty four percent is in faeces (Roche products, 2010). Problems with long term treatment can begin after five years, some patients will have a gradual reoccurrence of parkinsonian akinesia (Neal, 1992). Various kinsesias may appear and in time many patients start to get increasingly severe and rapid oscillations in mobility and dyskinesias (Neal, 1992)

Selegiline and co-beneldopa have some of the same adverse reactions; the main ones are hypotension, nausea and sleep disorders (BNF, 2007). Nausea is caused by the stimulation of the chemoreceptor trigger zone which lies behind the blood brain barrier (Neal, 1992). Sleep disorder is due to stimulation of mesolimbic dopamine receptors and hypotension is common but often asymptomatic (Neal, 1992).

To maximise the effect in the early stages of the condition, some specialists advocate early treatment, whereas others who think delaying the treatment will lower the risk of long-term motor complications (Noble, 2006). Risks and benefits will need to be considered by the individual before a decision can be reached about their treatment.

Noble (2006) states research has suggested fifty percent of patients do not comply with their prescription, which resulting in high financial costs wasted medicines and serious health and lifestyle consequences for patients and their families.

It is important that the nurse is aware of their role when it comes to anti Parkinson medication. Sudden withdrawal of Parkinson’s disease medication should be avoided, as there can be serious adverse reactions or allowed to become ineffective due to problems with absorption. Sudden withdrawal can result in acute akinesia and neuroleptic malignant syndrome. Drug holidays should also be avoided (NICE, 2006).

Rigid medication rounds in hospital and nursing homes may not suit a person with Parkinson’s (NICE, 2006). Nurses should ensure that patients have their medication at the right time for them, which may require self-medication and that any changes in medication should be overseen by a Parkinson's disease specialist (Bedford-Bell, 2006). If drugs are not available or a patient is nil by mouth it is to remember as a nurse that an abrupt stop of this type of medication is potentially life threatening. If a person is due for surgery, they should take their medications as normally as possible and be nil by mouth for as little time as possible around the time of the operation. Occasionally people may need to be nil by mouth for some time in which case the advice of a Parkinson’s specialist nurse or doctor is crucial (Lindhal and MacMahon, 2011)

To manage Parkinson’s disease a nurse is required to assisting the patient with the symptoms as well as the adverse effects of the drug therapy can also help to improve motor function, prevent injury, and maintain autonomy. (Cranwell-Bruce, 2010).

“Despite the introduction of several new drugs to the antiparkinsonian armamentarium, no single best treatment exists for an individual patient with PD. Particularly in the advanced stage of the disease, treatment should be individually tailored”. (Deleu, Northway and Hanssens, 2002)

The most effective and common treatment for most people with Parkinson’s disease is with medication. However, it is important to remember that the medication is only a treat for the symptoms of the condition but may not slow down the progression of the disease. Each patient will have their own treatment and medication carefully balanced so that it suits them as an individual. As every person with Parkinson’s disease is different, it’s essential that the nurses takes a holistic approach to treatment, including therapies and consult patients’ Parkinson’s specialists before making any changes to their treatment programmes.

Reference list:

ADAM (2011) Substantia nigra and Parkinson's disease. Available at: http://www.nlm.nih.gov/medlineplus/ency/imagepages/19515.htm (Accessed 1 December 2011).

Allcock, L. (2007) Managing patients with Parkinson's disease. Available at: http://www.pulsetoday.co.uk/article-content/-/article_display_list/10957176/may-2007-managing-patients-with-parkinson-s-disease (Accessed 2nd December 2011)

Beckford-Bell (2006) ‘Implications of the latest NICE Parkinson's disease guidance’, Nursing times, 102 (29) pg 26

British National Formulary (2007). London: RPS Publishing

Campbell, J. (2011) Campbell’s Physiology Notes. Glasgow: Bell and Bain Ltd

Chan, K., Jagait, P., Tugwell, C. (2004) Parkinsons disease current and future aspects of drug treatment PJ online 11 pp18-22

Craig, C. and Stitzel, R. (2004) Modern pharmacology with clinical applications. USA: Lippincott Williams and Wilkins USA 2004

Cranwell-Bruce, L. (2010) ‘Drugs for Parkinson’s Disease’, MEDSURG Nursing, 19 (November/December), pp 347-355

Dale, M., and Haylett, D. (2009) Pharmacology condensed. Churchill Livingstone: Elsevier

Deleu, D., Northway, M., and Hanssens, Y. (2002) Clinical Pharmacokinetic and Pharmacodynamic Properties of Drugs Used in the Treatment of

Parkinson’s Disease. Sultan Qaboos University: Adis International Limited

Disease.com (2011) Selegiline. available at http://disease.disease.com/Metabolism/First-Pass-Metabolism.html (Accessed 2 December 2011)

Drug Bank (2011) Selegiline. Available at: (Accessed 11 December 2011)

Drugs.com (2011) Selegiline. Available at: (Accessed 11 December 2011)

Drugsupdate.com (2011) Levodopa information from DrugsUpdate. Available at (Accessed 11 December 2011)

Ginsberg, G., Hattis, D., Russ, A., and Sonawane, B. (2004) Physiologic Changes That Can Affect Pharmacokinetic Function During Aging Available at: http://www.medscape.com/viewarticle/512459_3 (Accessed 5 December 2011)

Golan, D., Tashjian, A., Armstrong, E. and Armstrong, A. (2008) Principles of Pharmacology: The pathophysiologic basis of drug therapy. 2nd edn. USA: Lippincott Williams and Wilkins

Hollinger, M. (2003) Introduction to pharmacology. USA: CRC Press

Lindahl, A. and MacMahon, D. (2011) Parkinson’s: treating the symptoms British Journal of Nursing, 20 (14), pp. 852-857

Luty, J. and Harrison, P. (1997) Basic and clinical Pharmacology made memorable. USA: Churchill Livingston.

McGavock, H. (2005) How drugs work. Basic pharmacology for healthcare professionals. 2nd ed. Oxford. Radcliffe Publishing

Medsafe Data sheet (2000) Selgeline. Available at: (Accessed 11 December 2011)

NICE (2006) Parkinson’s Disease. Available at: (Accessed 5 December 2011)

Noble, C. (2006) ‘Modes of drug delivery used to manage Parkinson's disease’ Nursing.net 102(32) [online]. Available at: http://www.nursingtimes.net/nursing-practice-clinical-research/modes-of-drug-delivery-used-to-manage-parkinsons-disease/201110.article (Accessed 5 December 2011)

Palhagen, S., Heinonen, E., Hagglund, J., Kaugesaar, T., Maki-Ikola, O., Palm, R. and the Swedish Parkinson Study group (2006) Selegiline slows the progression of the symptoms of Parkinson disease. Available at: http://www.neurology.org (Accessed: 11 December 2011)

Parkinson’s UK (2011) available at http://www.parkinsons.org.uk (Accessed 1 December 2011)

Purse, M. (2007) Medication Half-life. Available at: http://bipolar.about.com/od/glossary/g/gl_medhalflife.htm (Accessed 11th December 2011)

Waters, C., Sethi, K., Hauser, R., Molho, E. and Bertoni, J. (2004)

Zydis selegiline reduces off time in Parkinson's disease patients with motor fluctuations: A 3-month, randomized, placebo-controlled study Movement Disorders. 19 (4) pp 426-432

TEVA UK Ltd (2009) SUMMARY OF PRODUCT CHARACTERISTICS version 3. Available at: http://www.tevauk.com/webroot/files/products/954/files/Co-benoldopaspc-50_12.5mgPL00289_0992v3.pdf (Accessed 11 December 2011)