Absorption
Isosorbide mononitrate is completely absorbed and is not subject to first pass metabolism by the liver. This reduces the intra- and inter-individual variations in plasma levels and leads to predictable and reproducible clinical effects.
The elimination half-life of isosorbide mononitrate is about 5 hours. The plasma protein binding is less than 5%. The volume of distribution for isosorbide mononitrate is about 0.6 l/kg and the total clearance around 115 ml/minute. Elimination is primarily by denitration and conjugation in the liver. The metabolites are excreted mainly via the kidneys. Only about 2% of the dose given is excreted intact via the kidneys.
Impaired liver or kidney function has no major influence on the pharmacokinetic properties.
Monomil XL/Carmil XL Tablets are prolonged release formulations. The active substance is released independently of pH, over a 10-hour period. Compared to ordinary tablets the absorption phase is prolonged and the duration of effect is extended.
The extent of bioavailability of isosorbide mononitrate in extended release tablets is about 90% compared to immediate release tablets. Absorption is not significantly affected by food intake and there is no accumulation during steady state. Isosorbide mononitrate exhibits dose proportional kinetics up to 120mg. After repeated peroral administration with 60mg once daily, maximal plasma concentration (around 3000 nmol/l) is achieved after around 4 hours. The plasma concentration then gradually falls to under 500 nmol/l at the end of the dosage interval (24 hours after dose intake). The tablets are divisible.
In placebo-controlled studies, Monomil XL/Carmil XL Tablets once daily has been shown to effectively control angina pectoris both in terms of exercise capacity and symptoms, and also in reducing signs of myocardial ischaemia. The duration of the effect is at least 12 h; at this point the plasma concentration is at the same level as at around 1 hour after dose intake (around 1300 nmol/l).
Monomil XL/Carmil XL Tablets are effective as monotherapy as well as in combination with chronic β -blocker therapy.
The clinical effects of nitrates may be attenuated during repeated administration owing to high and/or even plasma levels. This can be avoided by allowing low plasma levels for a certain period of the dosage interval. Monomil XL/Carmil XL Tablets, when administered once daily in the morning, produce a plasma profile of high levels during the day and low levels during the night. With the 60mg or 120mg once daily, no development of tolerance with respect to antianginal effect has been observed. Rebound phenomenon between doses as described with intermittent nitrate patch therapy has not been seen with this formulation.