Amlodipine and Nifedipine
Amlodipine and nifedipine are calcium channel blockers that are used to treat hypertension. Oxidation reactions by gut microorganisms biotransform these agents into inactive metabolites, which are then excreted in the feces.[4] Although many patients will achieve a therapeutic effect from these medications despite the bacterial inactivation of a portion of the dose, recent clinical studies have identified some common situations that may impact the overall therapeutic approaches for these drugs.
In one study, Yoo and colleagues investigated the coadministration of amlodipine and ampicillin to determine how antibiotic therapy impacts the gut microbiome and amlodipine pharmacokinetics. When antibiotics were given with amlodipine, the gut microbiome's biotransformation effect was suppressed and the systemic bioavailability of amlodipine was increased.[4] The rate and extent of amlodipine absorption were significantly increased during coadministration with ampicillin, as the gut microbiome was impaired and less likely to deactivate the drug. This effect held true when other antibiotic classes, such as tetracyclines, macrolides, and cephalosporins, were used.[4] Although the magnitude and clinical impact of this interaction are difficult to determine, it may be important to monitor patients to ensure that no supratherapeutic effects, such as hypotension, occur, given the increased bioavailability of amlodipine when administered concurrently with certain antibiotics.
Zhang and colleagues examined possible effects of altitude on hypoxia and gut-microbe diversity and activity.[3] Knowing that gut microflora inactivate nifedipine, the researchers simulated a high-altitude, low-oxygen environment and monitored the number of microorganisms present as well as their bioactivity. The hypoxic environment resulted in a reduction in the number of Enterobacteriaceae, the gram-negative rod that is a normal component of the gut's microbiome and one of the organisms responsible for this metabolic deactivation.[3] The researchers hypothesized that the presence of fewer of these organisms could mean higher nifedipine bioavailability, which might have significant effects for travelers who transition rapidly from low-altitude to highaltitude environments.[3]
US Pharmacist. 2023;48(2):18-22. © 2023 Jobson Publishing
