Water‐soluble β‐Cyclodextrins in Paediatric Oral Solutions of Spironolactone: Preclinical Evaluation of Spironolactone Bioavailability from Solutions of β‐Cyclodextrin Derivatives in Rats

Abstract Water‐soluble derivatives of β‐cyclodextrin have been considered for solubilization of spironolactone in the formulation of a safe liquid preparation for premature infants. The oral absorption of spironolactone was studied in rats to evaluate the need to adjust spironolactone dosage in prospective clinical studies. Spironolactone was administered in solutions of sulphobutyl ether β‐cyclodextrin (SBE7) or dimethyl‐β‐cyclodextrin (DM‐β‐CyD) and also as spironolactone‐containing powder papers (reference preparation). Spironolactone in SBE7 solution was administered intravenously to assess the extent of intestinal absorption from the different formulations. Spironolactone and the metabolites 7α‐thiospirolactone, 7α‐thiomethylspirolactone and canrenone were determined in rat serum after intravenous administration of spironolactone. Half‐lives for spironolactone, 7α‐thiomethylspirolactone and canrenone were 0.72 ± 0.17, 1.5 ± 0.3 and 2.2 ± 0.3 h, respectively. Although, according to C max values, 7α‐thiomethyl‐spirolactone was the major serum metabolite in rats, higher AUC (area under the serum concentration‐time curve) values were obtained for canrenone. After oral administration of spironolactone the bioavailabilities evaluated from the AUC values of 7α‐thiomethylspirolactone were 27.5 ± 9.3%, 81.3 ± 28.8% and 82.8 ± 28.6% for powder papers, DM‐β‐CyD and SBE7 solutions, respectively. The oral absorption of spironolactone by rats was better after administration of spironolactone in SBE7 and DM‐β‐CyD solutions than after administration as powder papers. Both cyclodextrin formulations enhanced spironolactone bioavailability to a similar extent despite some deacetylation of spironolactone in the presence of SBE7. A reduction of spironolactone dosage would be recommended during clinical studies with premature infants. These results indicate that SBE7 could be a safe and suitable excipient for the solubilization of spironolactone in paediatric formulations.