Pharmacotherapeutic group: Diltizem hydrochloride. Diltiazem hydrochloride is a benzothiazepine derivative, which acts as a calcium channel blocker.
ATCvet code: QC08DB01
Pharmacodynamic properties
This group of compounds exert their effect by interacting with the slow L-type calcium channels, thereby selectively inhibiting the inward movement of Ca ions across the cell membrane into vascular smooth muscle cells and myocardial cells.
With hypertrophic cardiomyopathy (HCM) the heart generally has a diminished capacity to restore low, resting levels of calcium during diastole. It appears that Diltiazem ameliorates HCM by decreasing calcium levels in the heart enabling proper relaxation of the muscle and halting or reversing the progression of the disease. It reduces cardiac work by moderating the heart rate and by reducing systemic vascular resistance thus reducing oxygen demand.
Pharmacokinetic properties
Diltiazem is rapidly absorbed following oral administration. Oral bioavailability in cats (71%) is higher than in other species and is most likely to be the result of a reduced first pass effect. Following administration of HyperCard 10 mg to cats, the average time to obtain maximum plasma concentration (Tmax) is approximately 90 minutes, with only low levels remaining after eight hours. No effect of feeding was observed on the absorption of Diltiazem from the gastrointestinal tract. There is no evidence of accumulation. In most species, Diltiazem is metabolised by the liver and little of the unchanged drug is excreted in the urine.
Plasma protein binding in cats is 50-60%.
Diltiazem is a significant hepatic microsomal enzyme inhibitor (especially of CYP3A4) and, therefore, will affect the pharmacokinetics and consequently possibly the efficacy and tolerance of some substances used in veterinary medicine (see Interactions).