Isradipine
- Generic name
- isradipine
- Brand names
- DynaCirc / DynaCirc CR (US, brand discontinued, generics remain)
- Drug class
- Calcium Channel Blocker (Dihydropyridine)
- Form
- Capsule (2.5 mg, 5 mg)
- Route
- Oral
- Legal status
- Prescription only in the US. Confirmed Never Authorised in Canada. Previously Authorised in New Zealand (historical evidence, not reconfirmed current). UK and Australia status could not be independently verified.
Supply Rules Vary
Trade names by country: United States
Australia: · Full directory
What isradipine is and how it works
Isradipine is a dihydropyridine calcium channel blocker FDA-approved for hypertension, alone or with a thiazide-type diuretic. (1) (3)
Isradipine has also been studied in a large clinical trial as a possible treatment to slow the progression of early Parkinson's disease. That trial's main result was negative — isradipine did not slow disease progression — so it should not be understood as a Parkinson's treatment.
Mechanism of action: how isradipine works
Isradipine is a dihydropyridine calcium channel blocker with 15-24% absolute bioavailability (extensive first-pass metabolism despite 90-95% absorption), 95% protein binding, and a biphasic elimination (early phase 1.5-2h, terminal phase ~8h). Completely metabolized to six identified metabolites; no unchanged drug in urine. (1)
What isradipine is used for
Hypertension
Isradipine capsules are FDA-approved to treat hypertension, alone or with a thiazide-type diuretic. (1)
Before taking isradipine
Do not take / not appropriate for
- Do not use isradipine if you have a known hypersensitivity to it or any formulation ingredient. (hypersensitivity) (1)
Tell your clinician about
- Every prescription medicine, nonprescription medicine, vitamin, and supplement you currently use — especially rifampicin or cimetidine.
- Any liver or kidney disease.
- If you are pregnant, planning pregnancy, or breastfeeding.
How to take isradipine
- The FDA label describes an initial dose of 2.5 mg twice daily, increased by 5 mg/day at intervals of 2-4 weeks if needed, up to a maximum of 20 mg/day (most people get no extra benefit above 10 mg/day).
- It may take 2-4 weeks to see the full blood-pressure-lowering effect, though some effect is usually seen within 2-3 hours of a dose.
- Do not stop taking isradipine suddenly without consulting your doctor.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6) (7) (8)
Missed dose
Contact your prescriber or pharmacist for guidance on a missed dose rather than doubling your next dose.
Overdose
Seek emergency care immediately for a suspected overdose. Reported cases (20-100 mg) caused lethargy, fast heart rate, and transient low blood pressure; treatment is supportive (activated charcoal, gastric lavage, IV fluids, vasoconstrictors like epinephrine/norepinephrine, or IV calcium/glucagon for refractory low blood pressure). Cimetidine should be withheld since it raises isradipine levels further. Isradipine is not removed by hemodialysis. (1)
Side effects
Headache, dizziness, and swelling are the most common side effects.
Headache
What to notice: Occurred in 13.7% of people on isradipine.
What to do: Mention persistent or severe headache to your clinician. (1)
Dizziness and swelling (edema)
What to notice: Dizziness in 7.3%, edema in 7.2%; edema, palpitations, fatigue, and flushing all increase at higher doses (15-20mg/day).
What to do: Mention persistent or bothersome symptoms to your clinician. (1)
Rare serious cardiovascular or neurological events
What to notice: Fainting, irregular heartbeat, chest pain, or stroke-like symptoms have been rarely reported.
What to do: Seek emergency care for these symptoms. (1)
Serious warnings
Rifampicin interaction — serious
Symptoms: Rifampicin has been shown to reduce isradipine to undetectable blood levels, meaning it may stop working.
Action: This combination should be avoided; your prescriber may choose an alternative. (1)
Excessive hypotension on initiation — serious
Symptoms: Marked blood pressure drop, especially when starting or increasing the dose.
Action: Contact your clinician for severe dizziness or fainting. (1)
Overdose — emergency
Symptoms: Lethargy, fast heart rate, low blood pressure.
Action: Seek emergency care immediately. (1)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Rifampicin | Reduces isradipine to undetectable blood levels via increased metabolism. | Avoid this combination; your prescriber may choose an alternative. (1) |
| Cimetidine | Increases isradipine peak levels by about 36% and total exposure by about 50%. | Your clinician may monitor more closely or reduce the dose if these are combined. (1) |
| Propranolol | A single-dose study showed a 27% increase in isradipine exposure and 58% increase in peak level; steady-state changes were smaller (<20%). | Your clinician will weigh this when combining the two. (1) |
| Digoxin, warfarin, nitroglycerin, hydrochlorothiazide | No clinically significant interaction found in the label reviewed. | Still disclose these to your clinician as part of a complete medicine review. (1) |
| Fentanyl anesthesia with a beta-blocker | Severe hypotension possible. | Anesthesia teams may need to maintain fluid volume; a clinical-setting consideration. (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Hepatic impairment
Impaired liver function raises isradipine's peak level by about 32% and total exposure by about 52%. Start at the standard 2.5 mg twice daily with closer monitoring. (1)
Renal impairment — a real, counterintuitive finding
Mild kidney impairment raises isradipine exposure by about 45%. But in people with severe kidney impairment on hemodialysis, isradipine exposure was actually 20-50% LOWER than in people with normal kidney function — the opposite direction from mild impairment. Your prescriber will take this into account when dosing. (1)
Older adults
Peak levels are about 13% higher and total exposure about 40% higher in people over 65; start at the standard 2.5 mg twice daily. (1)
Pregnancy
Isradipine is FDA-labeled under the older Pregnancy Category C system: animal studies showed reduced maternal weight gain and more fetal resorption at higher doses, without birth defects. There are no adequate, well-controlled human studies. Use only if the potential benefit justifies the potential risk — a decision for your obstetric care team. (1)
Breastfeeding — a real, disclosed evidence gap
No information at all is available on isradipine's use during breastfeeding, according to the NIH's LactMed database, which suggests an alternate drug may be preferred. This is a genuine gap, not a reassurance — discuss it directly with your prescriber and your baby's healthcare provider. (2)
Parkinson's disease research — real history, not a treatment
A large clinical trial (STEADY-PD), following promising laboratory studies, tested whether isradipine could slow the early progression of Parkinson's disease in 300 people over 36 months. The main result was negative: isradipine did not slow disease progression compared with placebo. This is real research history worth knowing about, but isradipine is not an approved or effective Parkinson's treatment. (3)
Monitoring
Before starting
- Review liver and kidney function.
- Review all current medicines, especially rifampicin and cimetidine.
- Discuss pregnancy, pregnancy plans, and breastfeeding, including the real evidence gap on breastfeeding above.
During treatment
- Blood pressure monitoring at initiation and with any dose change.
- Watch for excessive dizziness or fainting, especially at initiation.
Storage
Store at controlled room temperature per the product's specific packaging instructions.
Professional information
Clinician-facing context only. Non-US product, brand, and supply information is limited to what is explicitly documented in country-brand-verification.json and country-supply-classification.json.
United States
Indication: Hypertension only
Dose summary: Initial 2.5mg PO BID; titrate by 5mg/day q2-4wk; max 20mg/day. Hepatic impairment/elderly: standard starting dose with closer monitoring (Cmax/AUC increased). Severe renal impairment/hemodialysis: exposure actually LOWER than normal — a real outlier.
Renal context: Mild impairment: AUC +45%. Severe impairment/hemodialysis: AUC 20-50% lower than healthy volunteers. (1)
United Kingdom
Indication: Unable to verify.
Dose summary: Not available.
Renal context: Not available. (6)
Australia
Indication: Unable to verify.
Dose summary: Not available.
Renal context: Not available. (7)
Canada
Indication: Never authorised — confirmed absent from the Health Canada Drug Product Database.
Dose summary: Not applicable.
Renal context: Not available. (4)
New Zealand
Indication: Previously authorised — a real 2014 DynaCirc SRO data sheet was found, current status not reconfirmed.
Dose summary: Not available.
Renal context: Not available. (5)
Hepatic guidance
Cmax +32%, AUC +52% in hepatic impairment; standard starting dose with closer monitoring.
Overdose note
Supportive care; not removed by hemodialysis; withhold cimetidine. (1)
Frequently asked questions
Does isradipine treat Parkinson's disease?
No. A large clinical trial tested whether isradipine could slow early Parkinson's disease progression, following promising lab studies, but the main result was negative. It is not an approved or effective Parkinson's treatment. (3)
Can I take isradipine with rifampicin?
This combination should be avoided — rifampicin has been shown to reduce isradipine to undetectable blood levels, meaning it may stop working. (1)
Is isradipine available outside the United States?
It is confirmed NOT authorised in Canada. A real, dated document shows it was authorised in New Zealand as of 2014, though this hasn't been reconfirmed as current. Its status in the UK and Australia could not be independently confirmed. (4) (5)
What is the mechanism of action of isradipine?
Isradipine is a dihydropyridine calcium channel blocker with 15-24% absolute bioavailability (extensive first-pass metabolism despite 90-95% absorption), 95% protein binding, and a biphasic elimination (early phase 1.5-2h, terminal phase ~8h). Completely metabolized to six identified metabolites; no unchanged drug in urine. (1)
What is the generic name of Isradipine?
The generic name is isradipine. It is sold under brand names including DynaCirc / DynaCirc CR (US, brand discontinued, generics remain). (1)
What class of drug is isradipine?
Isradipine is classed as: Calcium Channel Blocker (Dihydropyridine). (1)
References
- Isradipine Capsules — prescribing informationDailyMed / FDA · United States · accessed 2026-07-27 · source 1
- Isradipine (LactMed entry NBK500995)LactMed, NICHD / NCBI Bookshelf · United States · accessed 2026-07-27 · source 2
- STEADY-PD: Isradipine as a disease-modifying agent in early Parkinson's diseasePeer-reviewed clinical trial (STEADY-PD Phase 2 and Phase 3), secondary summaries from Neurology/AJMC/Cure Parkinson's · not country-specific — clinical research · accessed 2026-07-27 · source 3
- DPD active-ingredient API query for isradipine (zero results)Health Canada Drug Product Database, public API · Canada · accessed 2026-07-27 · source 4
- DYNACIRC SRO (isradipine) New Zealand Data Sheet, 2014New Zealand Data Sheet, Novartis (hosted via a third-party mirror, not confirmed on the current medsafe.govt.nz site) · New Zealand · accessed 2026-07-27 · source 5
- No indexed substance-file count found for ISRADIPINEMHRA Products (search-engine index) · United Kingdom · accessed 2026-07-27 · source 6
- No Healthdirect brand/medicine page found for isradipineHealthdirect Australia (absence check) · Australia · accessed 2026-07-27 · source 7
- Calcium Channel BlockersStatPearls, NCBI Bookshelf · class_level_not_country_specific · accessed 2026-07-27 · source 8
Brand names by country
Single-ingredient isradipine names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- Isradipine Capsules (generic) (1)FDA approved currently labeled brand discontinued · 2.5 mg, 5 mg · not specified in fetched source