Nimodipine

BRAND NAMES

Nimodipine is marketed under several brand names worldwide, including:

• Nimotop (most widely recognized brand)

• Nimotop S (modified formulation in some regions)

• Brainal

• Dilceren (in certain countries)

MECHANISM OF ACTION

Nimodipine works by blocking L-type calcium channels in vascular smooth muscle, with a strong preference for cerebral blood vessels. This reduces calcium entry into smooth muscle cells, causing relaxation and vasodilation of cerebral arteries.

PHARMACOKINETICS

Absorption

Nimodipine is well absorbed after oral administration, but undergoes extensive first-pass metabolism in the liver, which significantly reduces its systemic bioavailability. Food, especially high-fat meals, can increase its absorption and bioavailability, so dosing is often recommended at consistent times relative to meals to maintain steady drug levels.

Distribution

Nimodipine is widely distributed in the body after absorption due to its high lipid solubility. It shows strong binding to plasma proteins (mainly albumin), and it readily crosses the blood–brain barrier, allowing it to concentrate in cerebral tissues where it exerts its primary vasodilatory effect on brain blood vessels.

Metabolism

Nimodipine is extensively metabolized in the liver, mainly by the cytochrome P450 enzyme system, especially CYP3A4. It undergoes oxidative metabolism to inactive metabolites, and very little unchanged drug remains in circulation. Because of this first-pass metabolism, its oral bioavailability is low and can be significantly affected by CYP3A4 inhibitors or inducers.

Elimination

Nimodipine is eliminated primarily through hepatic metabolism, with inactive metabolites excreted mainly in the urine and a smaller portion in feces via bile. The parent drug is present in only minimal amounts in excreta. It has a relatively short elimination half-life, but continuous dosing is required to maintain therapeutic effects, especially in preventing cerebral vasospasm.

PHARMACODYNAMICS

Nimodipine produces its pharmacodynamic effects by blocking L-type calcium channels in vascular smooth muscle, with a strong selectivity for cerebral arteries. This inhibition reduces calcium influx, leading to relaxation and dilation of cerebral blood vessels, which increases cerebral blood flow. Its primary clinical effect is the prevention of cerebral vasospasm and reduction of ischemic neurological damage, especially after subarachnoid hemorrhage. It has minimal direct effect on cardiac contractility, with its action mainly focused on cerebral vasculature.

ADMINISTRATION

Nimodipine is given orally, usually every 4 hours for about 21 days in conditions like subarachnoid hemorrhage. It should be taken regularly at fixed times, preferably on an empty stomach or as directed. If the patient cannot swallow, it may be given through a nasogastric tube under supervision.

DOSAGE AND STRENGTH

Nimodipine is commonly available in 30 mg oral tablets or capsules. The usual adult dosage for subarachnoid hemorrhage is 60 mg every 4 hours for 21 days, started within 96 hours of bleeding. Dose adjustments may be required based on blood pressure response, but IV use is generally avoided due to risk of severe hypotension.

DRUG INTERACTIONS

Nimodipine is extensively metabolized by CYP3A4, so it has important drug interactions:

• CYP3A4 inhibitors (e.g., ketoconazole, itraconazole, erythromycin, ritonavir) → increase drug levels, risk of severe hypotension

• CYP3A4 inducers (e.g., rifampin, phenytoin, carbamazepine) → reduce effectiveness

• Other antihypertensives → additive hypotensive effect

FOOD INTERACTIONS

Nimodipine has important food interactions. Taking it with food, especially high-fat meals, can increase its absorption and blood levels, which may enhance its effects. Grapefruit or grapefruit juice should be avoided because it inhibits CYP3A4 and can significantly increase drug concentration, raising the risk of hypotension and side effects.

CONTRAINDICATIONS

Nimodipine is contraindicated in patients with hypersensitivity to the drug or other dihydropyridine calcium channel blockers. It should not be used in severe hypotension or conditions where blood pressure is already dangerously low, as it may worsen hemodynamic instability. Concomitant use with strong CYP3A4 inhibitors (e.g., certain antifungals or macrolide antibiotics) is also contraindicated due to the risk of excessive drug levels and severe hypotension.

SIDE EFFECTS

• Hypotension 

• Headache 

• Flushing 

• Dizziness 

• Nausea 

OVER DOSAGE

• Severe hypotension 

• Dizziness 

• Tachycardia (reflex) 

• Flushing 

• Headache

TOXICITY

Nimodipine toxicity occurs due to excessive calcium channel blockade, leading to severe hypotension, reflex tachycardia, dizziness, flushing, and syncope. In severe cases, it may cause shock or circulatory collapse due to marked vasodilation. Management is supportive with drug discontinuation, IV fluids, and vasopressor support if needed.