Safinamide

Medical uses

Safinamide has been approved by the European Medicines Agency for the treatment of adult patients with idiopathic Parkinson’s disease as add-on therapy to a stable dose of levodopa (L-dopa) alone or in combination with other Parkinson drugs in patients with mid-to-late-stage fluctuating disease.

Contraindications

Safinamide is contraindicated in patients with severe liver impairment, with albinism, retinitis pigmentosa, severe diabetic neuropathy, uveitis and other disorders of the retina. Combination with other monoamine oxidase (MAO) inhibitors and pethidine is also contraindicated.

Adverse effects

Common adverse events in clinical trials (in more than 1% of patients) included nausea, dizziness, tiredness, sleeplessness, orthostatic hypotension (low blood pressure), and headache. There was no significant difference in the occurrence of these effects between safinamide and placebo treated patients.

In experiments with rats (but not in those with monkeys), retinopathies have been observed.

Overdose

Expected overdose effects are hypertension (high blood pressure), orthostatic hypotension, hallucinations, psychomotor agitation, nausea, vomiting, and dyskinesia. In studies, a singe patient was suspected to have overdosed for a month; symptoms were confusion, drowsiness and mydriasis (dilation of the pupils) and subsided completely after the drug was discontinued. No specific antidote is available.

Interactions

As a MAO inhibitor, safinamide can theoretically cause hypertensive crises, serotonin syndrome and other severe side effects when combined with other MAO inhibitors or with drugs that are known to interact with MAO inhibitors, such as pethidine, dextromethorphan, selective serotonin reuptake inhibitors (SSRIs), serotonin–noradrenaline reuptake inhibitors (SNRIs), tricyclic and tetracyclic antidepressants. An interaction with tyramine, a substance found in various foods, could be expected by the same reasoning but has been excluded in studies.

Another theoretical interaction is with drugs with affinity to the transporter protein ABCG2 (also known as BCRP), such as pitavastatin, pravastatin, ciprofloxacin, methotrexat, and diclofenac; a study with the latter has shown no clinical relevance. A study testing possible interactions with amidase inhibitors is part of the post-authorisation development plan. There are no relevant interactions related to cytochrome P450 (CYP) liver enzymes, although one inactivation pathway of safinamide seems to be mediated by CYP3A4.

Mechanisms of action

Like the older antiparkinson drugs selegiline and rasagiline, safinamide is a selective monoamine oxidase B inhibitor, reducing degradation of dopamine; in contrast to the other two, its action is reversible. Safinamide also inhibits glutamate release and dopamine reuptake. Additionally, it blocks sodium and calcium channels, the relevance of which for its antiparkinson action is however unknown.

Pharmacokinetics

Safinamide is absorbed quickly and nearly completely from the gut and reaches highest blood plasma concentrations after 1.8 to 2.8 hours. There is no relevant first-pass metabolism; total bioavailability is 95%. The substance is bound to plasma proteins to 88–90%.

The metabolism is not well understood. The principal step is mediated by amidases which have not been identified, and produces safinamide acid (NW-1153). Other relevant metabolites are O-debenzylated safinamide (NW-1199), the N-dealkylated amine which is then oxidized to a carboxylic acid (NW-1689), and the glucuronide of the latter. In tests with liver microsomes, dealkylation seemed to be mediated by CYP3A4, but other CYP enzymes appear to be involved as well. Safinamide acid binds to the organic anion transporter 3 (OAT3), but this has probably no clinical relevance. Safinamide itself transiently binds to ABCG2. No other transporter affinities have been found in preliminary studies.

Safinamide is eliminated, mainly (>90%) in form of its metabolites, via the kidney, with an elimination half-life of 20 to 30 hours. Only 1.5% are found in the stool.

History

The compound was originally discovered at Farmitalia-Carlo Erba, which was acquired by Pharmacia in 1993. In 1995, Pharmacia merged with Upjohn. Safinamide was first disclosed in 1998. In the course of a major restructuring in the same year, all rights for safinamide were transferred to the newly formed company Newron Pharmaceuticals, which developed the drug until it was sold to Merck KGaA in 2006.

In 2007, a Phase III clinical trial was started, scheduled to run until 2011. In October 2011 Merck, now Merck-Serono, announced that they would give all rights to develop the compound back to Newron because they wanted to prioritise other projects and had corrected their estimates for safinamide's market potential downwards.

The US Food and Drug Administration (FDA) refused to file Newron's application in 2014 on formal grounds. Newron re-applied in December 2014. In spring 2015, the European Medicines Agency (EMA) approved the drug. Safinamide is the first antiparkinson medication to be approved for ten years.

Research

Potential additional uses might be restless legs syndrome (RLS) and epilepsy. They were being tested in Phase II trials in 2008, but no results are available.