Syntesen hos ny DNA med celledeling blokeres, og DNA- ophelingsmekanismen hæmmes, hvilket resulterer i en ophobning af DNA- strengebrud og et fald i NAD - (nikotinamid adenin dinukleotid) og ATP - koncentration, selv i hvilende celler.
The mechanism of action of cladribine is attributed to the incorporation of CdATP into DNA strands: the synthesis of new DNA in dividing cells is blocked and the DNA repair mechanism is inhibited resulting in an accumulation of DNA strand breaks and a decrease of NAD (nicotinamide adenine dinucleotide) and ATP concentration even in resting cells.