Makindo Medical Notes.com

Levodopa is not given alone but always with a peripheral decarboxylase inhibitor.

About: Always check the BNF link here

• Introduced in the late 1960's and made a huge change in the management of patients with PD.
• Therapy becomes less effective with time with side effects.
• In Parkinson's disease there is a deficiency of dopamine in the corpus striatum.

Mode of action

• L-Dopa crosses the Blood-Brain barrier whereas dopamine doesn't. There is a deficiency of dopamine
• L-Dopa is metabolised centrally into the neurotransmitter dopamine by the enzyme decarboxylase.
• L-tyrosine → L-dopa → dopamine → dopamine receptors (D2, D3, D4) → G proteins
• It is given with a peripheral decarboxylase inhibitor which prevents peripheral conversion to dopamine and therefore side effects such as nausea

Indications

• Idiopathic Parkinson's disease
• post-encephalitic parkinsonism - Oliver Sacks book/film Awakenings
• Symptomatic parkinsonism which may follow injury to the nervous system by carbon monoxide intoxication and/or manganese intoxication

Dose

• Co-beneldopa Madopar 25/100 = 100 Levodopa + 25 Benserazide
• Co-careldopa Sinemet 25/100 = 100 Levodopa + 25 Carbidopa. Start Madopar/ Sinemet 62.5 (50/12.5) mg BD or TDS.
• Aim 400-800 mg Levodopa per day with decarboxylase inhibitor in split doses

Contraindications

• Drug induced Parkinsonism

Side effects

• Nausea, Hypotension, Confusion/Delirium
• Dopamine induced dyskinesias
• Visual and possibly auditory hallucinations
• Sudden withdrawal can cause the neuroleptic malignant syndrome

Interactions

• Levodopa is transported as are some other proteins across the gut wall. A protein meal can reduce absorption

References

• CO-BENELDOPA