Slide 12 of 76
Notes:
- Drug interactions may be classified as being either pharmacokinetic or pharmacodynamic in nature. With pharmacokinetic interactions, absorption, distribution, metabolism, or elimination may be affected, resulting in an alteration of the amount and/or concentration of one or both agents in the body. Sometimes this is desirable, if the pharmacokinetic profile of a drug is improved. On the other hand, certain interactions may be undesirable when the disposition of an agent with a narrow therapeutic index is affected.
- With pharmacodynamic interactions, additive, synergistic, or antagonistic drug combinations may affect parameters of pharmacologic response, including efficacy and toxicity.
- Pharmacodynamic drug-drug interactions may be beneficial, when agents with complementary mechanisms of action (e.g., reverse transciptase inhibitors plus protease inhibitors or NNRTIs) are administered to enhance clinical efficacy.
- In contrast, certain combinations may be undesirable if antagonism or additive toxicity occurs. For example, lamivudine and zalcitabine have been shown to negatively interact in vitro, likely via competition for intracellular phosphorylation, and thus should not be coadministered. Similar concern exists regarding the combination of zidovudine and stavudine.
