Interactions, drug antagonist

It is to be expected that a drug with an agonist action at a particular receptor type will interact with antagonists at that receptor. For example, the bron-chodilator action of a selective beta-2-adrenoceptor agonist such as salbutamol will be antagonised by non-selective beta-adrenoceptor antagonsists. 

Interactions. Drugs that lower gastric acidity, e.g. antacids, histamine H2 receptor antagonists, impair the absorption of ketoconazole from the gastrointestinal tract. Like all imidazoles, ketoconazole binds strongly to several cytochrome P450 isoenzymes and thus inhibits the metabolism (and increases effects of) oral anticoagulants, phenytoin and cyclosporin, and increases the risk of cardiac arrhythmias with terfenadine. A disulfiram-like reaction occurs with alcohol. Concurrent use of rifampicin, by enzyme induction of CYP 3A, markedly reduces the plasma concentration of ketoconazole. 

Drug interactions Cimetidine is a CYP450 inhibitor and can inhibit the metabolism of phenytoin, warfarin, and theophylline. Famotidine, nizatidine, and ranitidine are unlikely to cause clinically significant drug interactions. All antagonists have the potential to interact with other drugs that require gastric acid for absorption (e.g., ketoconazole, itraconazole). 

Catecholamines exert their effects through specific receptors on the target cell surface. However, the effects elicited depend on the type or subtype of receptor with which they interact. There are three types of catecholamine receptor dopamine, a-adrenergic, and )S-adrenergic. Each of these consists of at least two or more subtypes, which differ with respect to ligand affinity, tissue distribution, postreceptor events, and drug antagonists (Table 32-3). 

Drug-Drug and Drug-Food Interactions. Drugs commonly used in the CKD population that may decrease absorption of oral iron include calcium preparations and antacids. Oral iron may also decrease the absorption of quinolone antibiotics. Medications that increase gastric pH such as H2-antagonists and proton pump inhibitors may also decrease iron absorption since iron absorption in the duodenum is maximized at an acidic pH. 

The ergolines have provided a number of drugs that show interaction with neurotransmitters. Depending on the substitution pattern, they may be dopamine agonists or antagonists, a-adrenergic blockers, or Inhibitors of the release of prolactin. A recent member of the series, pergolide... 

Discuss the uses, general drug action, general adverse reactions, contraindications, precautions, and interactions of the narcotic antagonists. 

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