Flip–flop kinetics, or flip–flop pharmacokinetics, describes an atypical situation in pharmacokinetics where a drug's rate of absorption or the rate at which it enters the bloodstream is slower than its elimination rate. That is, when the ka (absorption constant) is slower than ke (elimination constant). The term "flip–flop" indicates that the downward slope more closely represents ka rather than ke. Flip–flop kinetics can create difficulties in the determination and interpretation of pharmacokinetic parameters if not recognized.