What a difference 10 years can make. Today, with the ever-growing list of antiretroviral medications, the possibility of adverse drug interactions is confusing to patients, physicians and pharmacists alike. Witness the recent reports of medication dispensation errors, wherein pharmacists have mixed up Viramune with Viracept or Retrovir with ritonavir, as examples of how simple mistakes can lead to harmful interactions. Pharmacokinetic interactions are those that describe how a drug is processed by the body, influencing absorption, metabolism, distribution and excretion. An example of an adverse pharmacokinetic reaction would be taking ddI with food, which would decrease absorption of the drug.
Pharmacodynamic interactions involve drug activity and toxicity.
To make it easier to understand the difference between the two categories, think of pharmacokinetics as what the body does to the drug while pharamcodynamics describe what the drug does to the body. A combination of AZT and ganciclovir are both potential bone marrow suppressors and could increase the risk of such suppression. Another example is the peripheral neuropathy many people have experienced with either ddI or ddC, which has led to the recommendation that the two drugs not be taken together in order to prevent a significant increase in toxicity. Besides potential pharmacist dispensation errors, mistakes leading to drug-drug interactions can occur because the patient is getting prescription medications from more than one medical provider. Many people with HIV see a primary care physician and several specialists.