Urinary tract infection is a very common side effect and since infections have a potential to trigger acute porphyric attacks vigilance is motivated regarding signs or symptoms of infection and/or possible symptoms of a porphyric attack.

Urinary tract infection is a very common side effect and since infections might trigger an acute porphyric attack, vigilance regarding signs and symptoms of an infection and/ or a porphyric attack is recommended. Common adverse reactions of fampridine that can be confused with an acute porphyric attack are nausea, vomiting, constipation and dyspepsia. These side effects may potentially be porphyrinogenic if leading to a decrease in carbohydrate intake.

Fampridine is not an inducer or a mechanism-based inhibitor of CYP-enzymes, and is not observed to alter the metabolism of other CYP metabolizing drugs. No pharmacokinetic porphyrinogenic effects are suspected.

Aminopyridine

Fampridine is a potassium channel blocker indicated for the improvements of walking in patients with multiple sclerosis. It is administered orally.

Fampridine is excreted mainly in the urine as unchanged drug (90 %) and less than 10 % of the drug is metabolized by CYP2E1. Fampridine is found to inhibit CYP2E1, however this is at concentrations well above the average plasma concentration of fampridine and is therefore insignificant. Fampridine is not found to induce CYP1A2, 2B6, 2C9, 2C19, 2E1 or 3A4/5, and is not a substrate for P-glycoprotein (SPC, Weir 2013).