Cilostazol

The effect of CYP3A4 and CYP2C19 inducers (such as carbamazepine, phenytoin, rifampicin and St. John’s wort) on cilostazol pharmacokinetics has not been evaluated. The antiplatelet effect may theoretically be altered and should be carefully monitored when cilostazol is co-administered with CYP3A4 and CYP2C19 inducers.

Cilostazol has been shown to increase the AUC of lovastatin (sensitive substrate for CYP3A4) and its β-hydroxy acid by 70%.

Caution is advised when cilostazol is co-administered with CYP3A4 substrates with a narrow therapeutic index (e.g. cisapride, halofantrine, pimozide, ergot derivates). Caution is advised in case of co-administration with statins metabolised by CYP3A4, for example simvastatin, atorvastatin and lovastatin.

Administration of a single dose of 100 mg cilostazol with 240 ml grapefruit juice (an inhibitor of intestinal CYP3A4) did not have a notable effect on the pharmacokinetics of cilostazol. Based on these data, no dose adjustment is necessary. A clinically relevant effect on cilostazol is still possible at higher quantities of grapefruit juice.

Cilostazol is extensively metabolised by CYP enzymes, particularly CYP3A4 and CYP2C19 and to a lesser extent CYP1A2. The dehydro metabolite, which has 4-7 times the potency of cilostazol in inhibiting platelet aggregation, appears to be formed primarily via CYP3A4. The 4'-trans-hydroxy metabolite, with potency one-fifth that of cilostazol, appears to be formed primarily via CYP2C19. Therefore, drugs inhibiting CYP3A4 (e.g. some macrolides, azole antifungals, protease inhibitors) or CYP2C19 (like proton pump inhibitors, PPIs) increase the total pharmacological activity and could have the potential to enhance the undesirable effects of cilostazol. Consequently, for patients concomitantly taking strong CYP3A4 or CYP2C19 inhibitors the recommended dose is 50 mg twice daily.

In a single-dose clinical study, no inhibition of the metabolism of warfarin or an effect on the coagulation parameters (PT, aPTT, bleeding time) was observed. However, caution is advised in patients receiving both cilostazol and any anticoagulant agent, and frequent monitoring is required to reduce the possibility of bleeding.

Cilostazol treatment is contraindicated in patients receiving two or more additional antiplatelet/anticoagulant agents.

Concomitant administration of cilostazol and clopidogrel did not have any effect on platelet count, prothrombin time (PT) or activated partial thromboplastin time (aPTT). All healthy subjects in the study had a prolongation of bleeding time on clopidogrel alone and concomitant administration with cilostazol did not result in a significant additional effect on bleeding time. Caution is advised when co-administering cilostazol with any drug that inhibits platelet aggregation. Consideration should be given to monitoring the bleeding time at intervals. Cilostazol treatment is contraindicated in patients receiving two or more additional antiplatelet/anticoagulant agents.

A higher rate of haemorrhage was observed with the concomitant use of clopidogrel, ASA and cilostazol in the CASTLE trial.

Caution is needed when co-administering cilostazol with any other agent which has the potential to reduce blood pressure due to the possibility that there may be an additive hypotensive effect with a reflex tachycardia.

Cilostazol reversibly impaired fertility of female mice but not in other animal species. The clinical significance is unknown.

Short term (≤4 days) co-administration of ASA with cilostazol suggested a 23-25% increase in inhibition of ADP-induced ex vivo platelet aggregation when compared to ASA alone.

There were no apparent trends toward a greater frequency of haemorrhagic adverse effects in patients taking cilostazol and ASA compared to patients taking placebo and equivalent doses of ASA.

Administration of cilostazol with diltiazem (a weak inhibitor of CYP3A4) resulted in an increase in the AUC of cilostazol of 44% accompanied by a 4% increase in AUC of the dehydro metabolite and a 43% increase in the AUC of the 4'-trans-hydroxy metabolite. Based on AUC, overall pharmacological activity of cilostazol increases 19 % when co-administered with diltiazem. Based on these data, no dose adjustment is necessary.

Administration of cilostazol with erythromycin (an inhibitor of CYP3A4) resulted in an increase in the AUC of cilostazol by 72%, accompanied by a 6% increase in AUC of the dehydro metabolite and a 119% increase in AUC of the 4'-trans-hydroxy metabolite.

Based on AUC, the overall pharmacological activity of cilostazol increases 34% when co-administered with erythromycin. Based on these data, the recommended dose of cilostazol is 50 mg bid in the presence of erythromycin and similar agents (e.g. clarithromycin).

Co-administration of ketoconazole (an inhibitor of CYP3A4) with cilostazol resulted in a 117% increase in the AUC of cilostazol, accompanied by a 15% decrease in the AUC of the dehydro metabolite and a 87% increase in the AUC of the 4'-trans-hydroxymetabolite.Based on AUC, the overall pharmacological activity of cilostazol increases 35% when co-administered with ketoconazole. Based on these data, the recommended dose of cilostazol is 50 mg bid in the presence of ketoconazole and similar agents (e.g. itraconazole).

Administration of cilostazol with omeprazole (an inhibitor of CYP2C19) increased the AUC of cilostazol by 22%, accompanied by a 68% increase in the AUC of the dehydro metabolite and a decrease of 36% in the AUC of the 4'-trans hydroxy metabolite. Based on AUC, the overall pharmacological activity increases by 47% when co-administered with omeprazole. Based on these data, the recommended dose of cilostazol is 50 mg bid in the presence of omeprazole.

There have been rare or very rare reports of haematological abnormalities including thrombocytopenia, leucopenia, agranulocytosis, pancytopenia and aplastic anaemia.

Most patients recovered on discontinuation of cilostazol. However, some cases of pancytopenia and aplastic anaemia had a fatal outcome.

Caution should be exercised when prescribing cilostazol for patients with atrial or ventricular ectopy and patients with atrial fibrillation or flutter.

Due to cilostazol’s platelet aggregation inhibitory effect it is possible that an increased bleeding risk occurs in combination with surgery (including minor invasive measurements like tooth extraction). If a patient is to undergo elective surgery and anti-platelet effect is not necessary, cilostazol should be stopped 5 days prior to surgery.

Patients who may be at increased risk for serious cardiac adverse events as a result of increased heart rate, e.g. patients with stable coronary disease, should be closely monitored during treatment with cilostazol.

In clinical trials, smoking (which induces CYP1A2) decreased cilostazol plasma concentrations by 18%.

There are no adequate data in the use of cilostazol in pregnant women. Studies in animals have s hown reproductive toxicity. The potential risk for humans is unknown. Cilostazol must not be used during pregnancy.

The transfer of cilostazol to breast milk has been reported in animal studies. The excretion of cilostazol in human milk is unknown. Due to the potential harmful effect in the newborn child breast fed by a treated mother, the use of Cilostazol is not recommended during breast feeding.

Fertility

Cilostazol reversibly impaired fertility of female mice but not in other animal species.

The clinical significance is unknown.

Cilostazol may cause dizziness and patients should be warned to exercise caution before they drive or operate machinery.