Altered diltiazem metabolism in the neonatal rabbit following intra-uterine chronic exposure to diltiazem

Investigation of diltiazem metabolism in fish using a hybrid quadrupole/orbital trap mass spectrometer

RATIONALE

Diltiazem, a calcium channel blocker drug, is widespread in the environment because of its incomplete elimination during water treatment. It can cause negative effects on aquatic organisms; thus, a rapid and sensitive liquid chromatography/mass spectrometry (LC/MS) method to detect its presence was developed. Our approach is based on accurate mass measurements using a hybrid quadrupole-orbital trap mass spectrometer that was used to measure diltiazem and its metabolites in fish tissue.

METHODS

Blood plasma, muscle, liver, and kidney tissues of rainbow trout (Oncorhynchus mykiss), exposed for 42 days to 30 μg L(-1) diltiazem, were used for the method development. No metabolite standards were required to identify the diltiazem biotransformation products in the fish tissue.

RESULTS

Overall, 17 phase I diltiazem metabolites (including isomeric forms) were detected and tentatively identified using the MassFrontier spectral interpretation software. A semi-quantitative approach was used for organ-dependent comparison of the metabolite concentrations.

CONCLUSIONS

These data increase our understanding about diltiazem and its metabolites in aquatic organisms, such as fish. These encompass desmethylation, desacetylation and hydroxylation as well as their combinations. This study represents the first report of the complex diltiazem phase I metabolic pathways in fish.

Penetration of diltiazem into breast milk and its pharmacokinetics in the lactating rabbit

1. The aim was to investigate the milk transfer and pharmacokinetics of diltiazem (DTZ) in the lactating rabbit following DTZ intravenous (i.v.) administration. In addition, DTZ metabolism in mammary tissue and milk was also studied. 2. The pharmacokinetic parameters that largely determine drug disposition (AUC, VD, CL) showed no significant differences between the non-lactating and lactating rabbit. 3. When DTZ was administered to the lactating rabbit, the observed DTZ milk-to-blood AUC ratio (M/B) closely correlated with the calculated ratio, as predicted by a diffusional model, suggesting that DTZ passes into milk via non-ionic diffusion and that other factors which may affect the milk transfer seem to have limited relevance. 4. After a single intravenous dose of DTZ to the lactating rabbit, deacetyldiltiazem (M1) and demethyldiltiazem (MA) were observed in blood, but only M1 could be detected in milk. 5. In conclusion, DTZ seems to diffuse freely into milk after its i.v. administration to the lactating rabbit and should not be given to nursing mammals because of the potential risk for their young. This risk may be even higher because of the presence of M1 (a pharmacologically active metabolite) in milk after administration of the parent drug.