Pharmacokinetics can be described as "what your body does to the drug", or a description of what changes occur to the drug molecule after taking the medication (via any route - intravenous, oral, rectal, vaginal, topical, etc.). This includes absorption, distribution, metabolism, and excretion.
Pharmacodynamics can be described as "what the drug does to your body", or the therapeutic or toxicologic effects of a medication. Generally, the pharmacodynamics of a medication are simply referred to as the pharmacologic effect of the medication.
Both pharmacokinetics and pharmacodynamics are important when looking at the overall pharmacology of a medication. Both processes are studied and determined in phase I and II clinical trials.
Pharmacokinetics gives details about the path followed by the drug from absorption moment to excretion moment.
Clinical pharmacokinetics principles ensure an effective drug therapy and decreased toxicity on pacients.
Pharmacodynamics describes not only the path followed by the drug from absorption moment to excretion moment but the pharmacological effects.
Pharmacodynamics gives information about drug potency using the 50% effective concentration scale (EC_50) and it gives information about the tolerance to a drug with exposure and increased drug metabolism.