This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pharmacology, Subject name: Pharmacology
[{'content': 'Which of the following best describes the drug phenomenon at pKa=pH? \nSelect and explain. \nA. Drug exists as 50% ionized and 50% unionized, B. Drug exists as 25% ionized and 75% unionized, C. Drug exists as 75% ionized and 25% unionized, D. Drug is completely (100%) Ionized', 'role': 'user'}, {'content': 'Answer: A \nExplanation: pka is numerically equal to the pH at which a drug is 50% ionized. The pKa of a drug is the hydrogen ion concentration (pH) at which 50% of the drug exists in its ionized hydrophilic form (i.e., in equilibrium with its un-ionized lipophilic form) pKa is a different term than pH pH is simply a measure of the concentration in a given solution pKa is defined as the pH were a drug exists as 50% ionized and 50% unionized If pKa-pH = 0, then 50% of drug is ionized and 50% is unionized Ref: KDT 7th edition Pgno: 11,12', 'role': 'assistant'}]