• Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune neuromuscular disorder, which can be treated symptomatically with 3,4-diaminopyridine (amifampridine).

• The authors of a Cochrane review concluded that limited evidence from two randomised controlled trials (RCTs) showed that 3,4-diaminopyridine improved muscle strength scores and compound muscle action potential amplitudes in patients with LEMS. However, there are insufficient data at present to quantify this treatment effect.

• Until recently, oral 3,4-diaminopyridine was only available as an unlicensed formulation as 3,4-diaminopyridine base, which was used in the RCTs. A phosphate salt formulation of oral 3,4-diaminopyridine (amifampridine) has now been licensed in the UK for the symptomatic treatment of LEMS in adults.

 
• No information on dose conversion from the base to the phosphate salt preparation of 3,4-diaminopyridine is stated in the Summary of Product Characteristics, although it would be prudent to monitor patients and titrate the dose if necessary when patients swap between formulations.

 
• To date, there is no published evidence that the licensed product has improved clinical effectiveness over 3,4-diaminopyridine base.