oa South African Family Practice - Drug interactions of antihypertensive agents : SA Hypertension Society Supplement

Volume 54, Issue 2
  • ISSN : 2078-6190
  • E-ISSN: 2078-6204



The pharmacodynamic interactions of beta blockers can be predicted. Beta blockers depress the sinoatrial (SA) and atrioventricular (AV) nodes when combined with other negative inotropic agents (Table I). Those drugs that are metabolised by the liver, metoprolol, carvedilol, labetalol and propranolol, are prone to hepatic interactions. Of this group, metoprolol and carvedilol are more frequently used. Metoprolol is metabolised by the hepatic CYP2D6 system, that is inhibited by paroxetine, a widely used antidepressant and selective serotonin reuptake inhibitor. The hepatic system is also inhibited by propoxyphene, an opioid pain-relief agent, available in South Africa as Distalgesic®, although it was recently withdrawn in the USA. Carvedilol is metabolised by the same system, with the same possible interactions.

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