Nimodipine, a calcium channel blocker, directly targets vascular smooth muscle. It selectively inhibits the influx of calcium ions (Ca2+) into these cells, reducing their contraction. This vasodilation improves cerebral blood flow, mitigating the effects of vasospasm.
Pharmacokinetics
Oral nimodipine boasts high lipid solubility, facilitating rapid absorption. Peak plasma concentrations usually occur within 30-60 minutes of ingestion. Extensive first-pass metabolism in the liver significantly reduces its bioavailability to approximately 15-20%. Protein binding is extensive, about 98%. The elimination half-life is approximately 1.5-2.0 hours. This short half-life necessitates frequent dosing to maintain therapeutic levels.
Metabolism and Excretion
Nimodipine undergoes extensive hepatic metabolism, primarily via cytochrome P450 enzymes. Metabolites are predominantly excreted through the urine and feces. Impaired liver function can alter nimodipine pharmacokinetics, necessitating careful dose adjustments in patients with hepatic compromise. Renal elimination of unchanged drug is minimal.
Clinical Note: Consider the patient’s liver and kidney function when determining the appropriate dosage regimen. Regular monitoring of blood pressure and neurological status is advised during nimodipine therapy.
