The present invention relates to an oral modified release pharmaceutical composition for the administration of a therapeutically and/or prophylactically effective amount of an active substance (a drug substance), to obtain a relatively fast or quick onset of the therapeutic and/or prophylactic effect. The drug substances contained in a modified release pharmaceutical composition according to the invention are suitably a drug substance which has a pKa value below about 5, such as in a range of from about 4 to about 5. The composition is based on a powder comprising a therapeutically and/or prophylactically active substance and has such a particle size that: when the powder is subjected to a sieve analysis, then at least about 90% w/w of the particles pass through a 180 micron sieve, and when the powder is contacted with an aqueous medium to form a particulate composition, which as such a particle size that when the particulate composition is subjected to a sieve analysis, then at least about 50% w/w of the particles passes through a 180 micron sieve. Further more, the composition, when tested in accordance with the dissolution method (I) defines herein, employing 0.07 HCl as dissolution medium, release at least about 50% w/w of the active substance within the first 20 minutes of the test.
