Cilostazol

Introduction Overview

Generic Name

cilostazol

Brand Name

Pletal

Dosage Form

oral tablet (100 mg; 50 mg)

Drug Class

Miscellaneous cardiovascular agents, Platelet aggregation inhibitors

Pharmacokinetics

Absorption:
Cilostazol is administered orally and exhibits good absorption from the gastrointestinal tract. Pharmacokinetic studies show that cilostazol reaches peak plasma concentrations within 2 to 4 hours post-administration. Bioavailability is moderate due to first-pass metabolism. Administration guidelines recommend taking cilostazol on an empty stomach, at least 30 minutes before or two hours after meals, to maximize absorption and clinical efficacy. Food intake can reduce the rate and extent of absorption, thereby potentially diminishing therapeutic outcomes. The influence of gastric pH and gastrointestinal motility on cilostazol absorption is considered clinically insignificant.

Distribution:
Cilostazol exhibits extensive plasma protein binding, primarily to albumin (approximately 95%). The volume of distribution is relatively high, indicating wide tissue distribution, including vasculature smooth muscle tissues. Its distribution to red blood cells is minimal. Cilostazol is lipophilic, facilitating penetration into various tissues but does not significantly accumulate in fatty tissues. The pharmacokinetic profile suggests that cilostazol readily reaches peripheral arteries, the site of action for the treatment of intermittent claudication. Distribution is not significantly affected by age, gender, or race.

Metabolism:
Cilostazol undergoes extensive hepatic metabolism primarily via cytochrome P450 enzymes CYP3A4 and CYP2C19 to produce two main active metabolites. These metabolites contribute significantly to the pharmacologic effects, sustaining the inhibition of platelet aggregation and vasodilation. The metabolic pathways involve oxidation, hydroxylation, and further conjugation. Drug-drug interactions affecting CYP3A4 and CYP2C19 can markedly alter cilostazol plasma levels, which may increase adverse effects or diminish therapeutic efficacy. Genetic polymorphisms in CYP2C19 can also affect metabolism and clinical response.

Elimination:
The elimination half-life of cilostazol is approximately 11 to 13 hours, supporting twice-daily dosing. Excretion occurs primarily via feces (about 60%), with the remainder eliminated in urine as metabolites; less than 5% of unchanged drug is detected in urine. Renal impairment has minimal effect on cilostazol clearance; however, hepatic dysfunction can prolong elimination half-life and increase plasma exposure, necessitating clinical caution. Cilostazol’s clearance is influenced by hepatic enzyme activity and concomitant medications that modify metabolic enzyme function.

Dosage Forms

Available Dosage Forms:
Cilostazol is commercially available as oral tablets in two strengths: 50 mg and 100 mg. These tablets are film-coated and designed for oral administration. The 100 mg tablet is the recommended dose for the majority of patients treating intermittent claudication.

Dosages for Adults and Adolescents:
The usual adult dose for intermittent claudication is 100 mg orally twice daily. Tablets should be taken at least 30 minutes before or two hours after breakfast and dinner to optimize absorption and efficacy. Treatment duration typically extends up to 12 weeks, with initial clinical improvement possibly observed as early as 2 to 4 weeks. If symptoms persist after 3 months of therapy without improvement, discontinuation is advised.

Specific Patient Populations:
Use in elderly patients does not require dosage adjustment, although clinical monitoring is recommended due to increased sensitivity to adverse effects. Patients with mild to moderate hepatic impairment should be monitored closely, as drug clearance may be reduced, increasing systemic exposure. Cilostazol is contraindicated in patients with any form of heart failure due to potential worsening of condition. Safety and efficacy in pediatric populations have not been established, and therefore, use in adolescents is not generally recommended.
Dosing adjustments are not typically required in mild to moderate renal impairment; however, caution is advised in severe renal impairment.

Additional Clinical Guidelines:
Patients should be advised to adhere strictly to dosing schedules due to cilostazol’s pharmacokinetic profile. Missed doses should be taken as soon as possible unless close to the next dose, to avoid doubled dosing. Grapefruit products should be avoided during therapy due to CYP3A4 inhibition increasing cilostazol levels and risk of toxicity.

Mechanism Of Action

Cilostazol exerts its pharmacological effects primarily through selective inhibition of phosphodiesterase type 3 (PDE3) enzyme found in vascular smooth muscle and platelets. PDE3 catalyzes the degradation of cyclic adenosine monophosphate (cAMP). By inhibiting PDE3, cilostazol increases intracellular cAMP levels. Elevated cAMP results in activation of protein kinase A, which subsequently leads to phosphorylation of various intracellular targets responsible for vasodilation and inhibition of platelet aggregation.

The vasodilatory effect arises from relaxation of vascular smooth muscle cells, particularly in the peripheral circulation arteries supplying the legs. This action leads to widening of blood vessels, decreased vascular resistance, and enhanced blood flow, which addresses the ischemic symptoms characteristic of intermittent claudication. The improved blood flow increases oxygen delivery to walking muscles, thereby reducing pain during ambulation.

In platelets, increased cAMP inhibits platelet activation and aggregation by reducing the release of pro-aggregatory substances such as thromboxane A2 and interfering with platelet shape change and granule release. This anti-platelet effect enhances blood fluidity and helps prevent thrombotic complications associated with atherosclerotic vascular disease.

Comparatively, cilostazol’s mechanism differs from traditional antiplatelet agents like aspirin which inhibit cyclooxygenase, and from direct vasodilators that do not have anti-platelet effects. Clinical studies demonstrate combined vascular and platelet benefits, contributing to improved walking distance and symptom reduction in patients with peripheral arterial disease. Research also suggests potential benefits in preventing restenosis post-angioplasty, though clinical use for this indication remains investigational.

Pharmacological Actions

Selective inhibition of phosphodiesterase type 3 (PDE3), leading to increased intracellular cAMP levels.
Vasodilation of peripheral arteries through relaxation of vascular smooth muscle cells.
Inhibition of platelet aggregation by increasing cAMP in platelets, thereby reducing thrombotic risk.
Improvement of red blood cell flexibility and reduction of blood viscosity, enhancing microcirculatory flow.
Enhancement of walking distance and reduction of intermittent claudication symptoms in peripheral arterial disease.
Mild inhibition of adenosine uptake, potentially contributing to vasodilatory effects.
Modulation of vascular endothelial function promoting anti-proliferative effects on vascular smooth muscle.
Potential reduction of inflammation in vascular tissues by decreasing leukocyte activity.
No significant direct effect on heart rate or cardiac contractility at therapeutic doses.
Dual action on both circulation and platelet function distinguishes it from pure antiplatelet or pure vasodilator agents.

Therapeutic Or Clinical Uses

Management of intermittent claudication symptoms associated with peripheral arterial disease (PAD).
Improvement of pain-free walking distance in patients with lower extremity arterial insufficiency.
Adjunctive therapy to lifestyle modifications such as exercise and smoking cessation in PAD patients.
Potential off-label use in prevention of restenosis after percutaneous coronary interventions (research ongoing).
Improvement of microvascular circulation in patients with diabetic vascular complications (investigational use).
Reduction of risk of thrombotic events through inhibition of platelet aggregation in peripheral vascular disease.
Alternative therapy for patients intolerant to other antiplatelet or vasodilatory treatments.
Used in patients who have contraindications to or have failed conservative PAD management.
Aid in symptomatic management to increase quality of life in chronic circulatory ischemic conditions.
Investigational use in cerebrovascular insufficiency and other conditions involving impaired blood flow.

Side Or Adverse Effects

Headache, often mild to moderate in intensity, commonly reported during initial therapy.
Diarrhea and other abnormal bowel movements such as dyspepsia or nausea.
Palpitations, including sensations of fast or pounding heartbeats (tachycardia).
Dizziness or light-headedness, particularly upon standing, related to vasodilation.
Peripheral edema due to vascular effects in some patients.
Easy bruising or unusual bleeding, reflecting antiplatelet activity and increased bleeding risk.
Rare allergic reactions including hives, angioedema, and anaphylaxis.
Mouth sores and sore throat indicating possible hypersensitivity.
Fever and chills, potentially indicating systemic reactions or infections.
Purple or red spots under the skin suggesting petechiae or purpura due to platelet inhibition.
Rare chest pain or palpitations necessitating prompt medical evaluation.
Potential interactions causing exacerbation of cardiovascular adverse effects with concurrent PDE inhibitors.
Possible liver enzyme elevations necessitating hepatic function monitoring in predisposed patients.
Fatigue and malaise reported less frequently but contributing to overall tolerability profile.
Very rare reports of arrhythmias or worsening heart failure symptoms in susceptible individuals.

Precautions

Contraindicated in patients with any form of heart failure due to risk of exacerbation.
Use with caution in patients with history of bleeding disorders or hemorrhagic stroke.
Monitor liver function in patients with hepatic impairment, as metabolism and elimination may be affected.
Avoid use in patients with severe renal impairment until safety is established.
Caution advised in elderly patients due to increased sensitivity to cardiovascular adverse effects.
Avoid concomitant use with strong CYP3A4 or CYP2C19 inhibitors to prevent elevated cilostazol levels.
Advise patients against consuming grapefruit or grapefruit juice during therapy due to interaction risks.
Pregnancy and lactation: safety not established, avoid use unless benefits outweigh risks and discontinue breastfeeding.
Monitor for signs of bleeding or bruising during therapy and adjust or discontinue treatment if necessary.
Careful dose titration and monitoring recommended in patients with history of cardiovascular events.
Advise patients to adhere to dosing schedule strictly and not to double doses if missed.
Evaluate potential drug interactions, including over-the-counter and herbal products, before starting therapy.
Educate patients about symptoms of allergic reactions and cardiovascular adverse events.
Periodic assessment of therapeutic response and adverse effects is essential during prolonged therapy.
Withdrawal recommended if no clinical improvement is observed after 12 weeks of treatment.

Warnings

Do not use cilostazol in patients with any form of heart failure; cilostazol may worsen cardiac function.
Potential for serious cardiovascular side effects including chest pain and arrhythmias; urgent evaluation required if they occur.
Increased risk of bleeding due to platelet aggregation inhibition; use with caution in patients with bleeding tendencies.
Avoid use with strong CYP3A4 inhibitors and inducers to prevent altered drug levels and toxicity or loss of efficacy.
Use with caution in patients with recent myocardial infarction or stroke; clinical judgement needed.
Avoid grapefruit and grapefruit juice intake to prevent increased plasma concentrations and adverse effects.
Not recommended during pregnancy and breastfeeding due to insufficient safety data and potential risks.
Patients should be informed about possible signs of allergic reactions requiring immediate medical attention.
Discontinue treatment if no improvement in symptoms is seen after three months to avoid unnecessary exposure.
Monitor closely for side effects such as palpitations and hypotension, especially in elderly or comorbid patients.
Use caution when co-administered with other antiplatelet or anticoagulant therapies due to additive bleeding risk.
Avoid abrupt discontinuation without consulting healthcare provider as symptoms may worsen.
Pregnant women or women planning pregnancy should discuss alternative therapies with their healthcare provider.
Patients with hepatic impairment require careful evaluation before initiation due to altered drug metabolism.
Educate patients on avoiding self-medication or combining with other cardiovascular agents without medical advice.

Contraindication

Known hypersensitivity to cilostazol or any component of the formulation.
Patients with heart failure of any etiology, including congestive heart failure and left ventricular dysfunction.
Concomitant use with strong CYP3A4 inhibitors due to risk of increased plasma cilostazol levels.
History of significant bleeding disorders or hemorrhagic stroke without adequate risk-benefit assessment.
Pregnant women when safer alternative treatments are available due to unknown fetal risk.
Patients currently breastfeeding unless discontinuation of breastfeeding is acceptable.
Concurrent use with other PDE3 inhibitors or medications that may cause additive adverse cardiovascular effects.
Severe hepatic impairment due to potentially impaired metabolism and increased toxicity.
Known history of ventricular arrhythmia or tachyarrhythmia exacerbated by PDE3 inhibitors.
Use in pediatric populations is contraindicated due to lack of safety and efficacy data.
Concomitant use with strong CYP2C19 inhibitors or inducers without close monitoring.
Patients with unstable angina or recent acute coronary syndrome unless specifically advised by cardiologist.
Individuals with conditions predisposed to hypotension or syncope without adequate supervision.
Patients unable to comply with dosing instructions or monitoring requirements.
Patients with severe renal impairment until more data is available confirming safety.

Drug Interactions

Strong CYP3A4 inhibitors (e.g., ketoconazole, itraconazole, erythromycin) may increase cilostazol plasma concentrations, elevating adverse effect risk.
CYP2C19 inhibitors (e.g., omeprazole) can increase cilostazol exposure and require careful dose adjustment or avoidance.
CYP3A4 inducers (e.g., rifampin, carbamazepine, phenytoin) may decrease cilostazol efficacy by lowering plasma levels.
Antiplatelet agents (e.g., aspirin, clopidogrel) and anticoagulants (e.g., warfarin, heparin) may have additive bleeding risk when combined with cilostazol.
Grapefruit juice inhibits CYP3A4 and can significantly increase cilostazol plasma levels, leading to potential toxicity.
Drugs affecting heart rate or rhythm (e.g., beta-blockers, digoxin) require monitoring when co-administered due to potential for arrhythmogenic effects.
Other vasodilators may potentiate hypotensive effects when taken concomitantly with cilostazol.
Certain lipid-modifying agents (e.g., statins metabolized via CYP3A4) may have altered pharmacokinetics when combined with cilostazol.
Herbal supplements such as St. John's Wort may reduce cilostazol plasma concentration through CYP3A4 induction.
Use with medicine affecting renal or hepatic function can alter cilostazol metabolism and elimination.
Combination with other PDE inhibitors (e.g., dipyridamole) can enhance vasodilatory and antiplatelet effects, potentially increasing adverse reactions.
NSAIDs and corticosteroids may enhance bleeding risk in patients also receiving cilostazol.
Effectiveness of cilostazol may be reduced when co-administered with enzyme inducers increasing its metabolism.
Use caution with medications affecting cAMP pathways to avoid unexpected pharmacodynamic interactions.
Patients should disclose all supplements, over-the-counter medications, and herbal products to manage potential interactions.

Preparations Of The Drug

Oral film-coated tablets available in 50 mg strength for dose flexibility and titration.
Oral film-coated tablets available in 100 mg strength, the standard dose for intermittent claudication treatment.
Tablets designed for oral administration with specific instructions to be taken on an empty stomach.
Packaged in blister packs or bottles to maintain stability and protect from moisture and heat.
Manufactured following stringent quality control consistent with cardiovascular agent standards.
Formulated to ensure adequate bioavailability with consistent pharmacokinetic profiles.
Available under the brand name Pletal, distributed globally with regulatory approval.
Storage recommendation at room temperature away from moisture and direct heat sources to maintain drug integrity.
No currently available intravenous or alternative dosage forms; oral tablets are the sole preparation.
Tablet coatings minimize gastrointestinal irritation and improve patient compliance.
Packaging includes comprehensive patient information leaflets outlining dosing and precautions.
Supply forms allow for twice-daily dosing regimen adherence promoting therapeutic efficacy.
Formulations are free from common allergens such as gluten and lactose, enhancing tolerability.
Available through prescription only, ensuring medical supervision due to potential adverse effects.
Standard formulations compatible with generic production to promote accessibility and affordability.