Itraconazole is given in an encapsulated formula which depends on an acidic pH to dissolve. PPIs like omeprazole increase the stomach's pH, thus decreasing the amount of itraconazole absorbed. Poor absorption does not allow itraconazole to reach its therapeutic plasma concentration. A solution for this would be to give the itraconazole via oral solution or IV.
This patient still has histoplasmosis. Omeprazole (a PPI) changes the pH of the stomach and can prevent the absorption of certain drugs that require acidic breakdown to be absorbed. Omeprazole is also a P450 inhibitor, increasing the effect and concentration of other drugs.
Azoles (including itraconazole) and omeprazole are both P450 inhibitors. (p450 interactions FA2018 P247, azoles FA2018 p199.
submitted by โcassdawg(1780)
Omeprazole is a proton pump inhibitor which affects the bioavailability of itraconazole presumably by interfering with absorption as it decreases gastric pH.
https://www.ncbi.nlm.nih.gov/pubmed/9626921
https://www.ebmconsult.com/articles/ppi-proton-pump-inhibitors-decrease-absorption-itraconazole