Ropinirole

Ropinirole (INN; trade names Requip, Ropark, Adartrel) is a non-ergoline dopamine agonist. It is manufactured by GlaxoSmithKline (GSK), Cipla and Sun Pharmaceutical. It is used in the treatment of Parkinson's disease. Ropinerole is one of three medications approved by the FDA to treat Restless Legs Syndrome, the other two being pramipexole (Mirapex) and gabapentin encarbil (Horizant). The discovery of the drug's utility in RLS has been used as a successful example of drug repurposing.

Ropinirole's patent expired in May 2008, and the drug is now available in generic form.

Dosage
Ropinirole in the Requip form is available in various preparations, ranging from a 0.25 mg tablet to a 5 mg tablet. The primary reason for such is dose titration. This implies that the person taking Requip has to closely interact and communicate with the primary care physician with regard to how much should actually be taken by the patient.

For restless legs syndrome (RLS), the maximum recommended dose is 4 mg per day, taken 1 to 3 hours before bedtime. A 52-week open label study had a mean dosage of 1.90 mg, once daily 1 to 3 hours before bedtime.

For Parkinson's disease (PD), the maximum recommended dose is 24 mg per day, taken in three separate doses spread throughout the day. The maximum dose recommendations of ropinirole for subjects with ESRD should be reduced by 25% compared with those recommended for subjects with normal renal function. A 25% dose reduction represents a more straightforward dosage regimen in terms of available tablet strength, compared with a 30% dose reduction.

Pharmacology
Ropinirole acts as a D2, D3, and D4 dopamine receptor agonist with highest affinity for D3. It is weakly active at the 5-HT2, and α2 receptors and is said to have virtually no affinity for the 5-HT1, benzodiazepine, GABA, muscarinic, α1, and β-adrenoreceptors.

Ropinirole is metabolized primarily by cytochrome P450 CYP1A2 to form two metabolites; SK&F-104557 and SK&F-89124, both of which are renally excreted, and at doses higher than clinical, is also metabolized by CYP3A4. At doses greater than 24 mg, CYP2D6 may be inhibited, although this has only been tested in vitro.

Side effects
Ropinirole can cause nausea, dizziness, hallucinations, orthostatic hypotension, and sudden sleep attacks during the daytime. Rarer and more unusual side effects specific to D3-preferring agonists such as ropinirole and pramipexole can include hypersexuality and compulsive gambling, even in patients without a prior history of these behaviours.