For long-term treatments Dipyridamole 200 mg modified-release capsules, formulated as pellets have been developed. The pH dependent solubility of Dipyridamole 200 mg modified-release capsules which prevents dissolution in the lower parts of the gastrointestinal tract is overcome by means of a formula containing tartaric acid. Retardation of release is achieved by a diffusion membrane which is sprayed onto the pellets.
Absorption
Dipyridamole 200 mg modified-release capsules
Peak plasma concentrations are reached about 2 - 3 hours after administration. Mean peak concentrations at steady state conditions with 150 mg b.d. are 1.43 μg/mL (range 0.705 - 2.75 μg/mL), trough levels are 0.351 μg/mL (range 0.200 - 0.741 μg/mL). With a daily dose of 400 mg, the corresponding peak concentrations are 1.98 μg/mL (range 1.01 - 3.99 μg/mL), trough concentrations are 0.53 μg/mL (range 0.18 - l.01 μg/mL). There is no clinically relevant effect of food on the pharmacokinetics of Dipyridamole 200 mg modified-release capsules. The absolute bioavailability is about 70%. The dose linearity of dipyridamole after oral b.i.d. administration of the modified release capsules containing 150 and 200 mg was demonstrated.
As first pass removes approx. 1/3 of the dose administered, near to complete absorption of Dipyridamole 200 mg modified-release capsules can be assumed.
Dipyridamole 200 mg modified-release capsules given twice daily has been shown to be bioequivalent to the same total daily dose of Dipyridamole Tablets given in four divided doses.
Peak plasma concentrations are reached 2 - 3 hours after administration. Steady state conditions are reached within 3 days.
Distribution
Owing to its high lipophilicity, log P 3.92 (n-octanol/0.1 N, NaOH), dipyridamole distributes to many organs.
Non-clinical studies indicate that, dipyridamole is distributed preferentially to the liver, then to the lungs, kidneys, spleen and heart, it does not cross the blood-brain barrier to a significant extent and shows a very low placental transfer. Non-clinical data have also shown that dipyridamole can be excreted in breast milk.
-Protein binding of dipyridamole is about 97 - 99%, primarily it is bound to alpha 1-acid glycoprotein and albumin.
Metabolism
Metabolism of dipyridamole occurs in the liver. Dipyridamole is metabolized by conjugation with glucuronic acid to form mainly a monoglucuronide and only small amounts of diglucuronide. In plasma about 80% of the total amount is parent compound, 20% of the total amount is monoglucuronide with oral administration .
Elimination
Dominant half-lives ranging from 2.2 to 3 hours have been calculated after the administration of modified-release dipyridamole. A prolonged terminal elimination half-life of approximately 15 h is observed. This terminal elimination phase is of relatively minor importance in that it represents a small proportion of the total AUC, as evidenced by the fact that steady-state is achieved within 2 days with both t.d.s. and q.d.s., regimens. There is no significant accumulation of the drug with repeated dosing. Renal excretion of parent compound is negligible (< 0.5%). Urinary excretion of the glucuronide metabolite is low (5%), the metabolites are mostly (about 95%) excreted via the bile into the faeces, with some evidence of entero-hepatic recirculation. Total clearance is approx. 250 mL/min and mean residence time is approx. 8 h (resulting from an intrinsic MRT of approx. 6.4 h and a mean time of absorption of 1.4 h).
Elderly subjects
Plasma concentrations (determined as AUC) in elderly subjects (> 65 years) were about 50% higher for tablet treatment and about 30% higher with intake of Dipyridamole 200 mg modified release capsules than in young (<55 years) subjects. The difference is caused mainly by reduced clearance; absorption appears to be similar. A similar increase in plasma concentrations in elderly patients was observed in the ESPS2 study.
Hepatic impairment
Patients with hepatic insufficiency show no change in plasma concentrations of dipyridamole, but an increase of (pharmacodynamically inactive) glucuronides. It is suggested to dose dipyridamole without restriction as long as there is no clinical evidence of liver failure.
Renal impairment
Since renal excretion is very low (5%), no change in pharmacokinetics is to be expected in cases of renal insufficiency. In the ESPS2 trial, in patients with creatinine clearances ranging from about 15 mL/min to >100 mL/min, no changes were observed in the pharmacokinetics of dipyridamole or its glucuronide metabolite if data were corrected for differences in age.