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This appendix provides a summary of basic pharmacokinetic information pertaining to small-molecule drugs that are in common clinical use and are delivered to the systemic circulation by parenteral or nonparenteral administration. Because of space limitations, this list cannot be exhaustive. Drugs designed exclusively for topical administration and not significantly absorbed into the bloodstream (e.g., ophthalmic and some dermal applications) are not included. A few other selection criteria have influenced the makeup of the list, but, in general, the authors have tried to include one or more representative drugs in each of the therapeutic areas in this text, based on distinct mechanism(s) of action. In some instances, drugs may be excluded because pharmacokinetics are not relevant to their therapeutic dosing regimen design. An obvious case is when drug efficacy is not apparently correlated with drug concentration in a reversible fashion (e.g., some cytotoxic anticancer drugs). In some instances, sufficient pharmacokinetic data are not available.
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Often, the issue comes down to deciding which of the many drugs within a class should be selected. This is particularly problematic when the choices are largely therapeutically equivalent. Two criteria that have proven useful are prevalence of use and uniqueness of mechanism of action. For the present edition, we have consulted the top 200 selling drugs in 2020 for usage data. Drugs that fall into that list and meet the criteria above are generally selected. We have also consulted all new FDA drug approvals between 2016 and 2020. As mentioned above, a less used drug may be included if it has a different mechanism of action than the frequently used drugs, some additional actions that offer a unique therapeutic advantage, or a more acceptable side effect profile. Pharmacokinetic data for many older drugs not included in this appendix can be found in earlier editions of this book.
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With rare exceptions (e.g., interferons), recombinant therapeutic proteins have been excluded from this compilation. In many cases, the therapeutic protein interacts with specific tissue or cellular targets with exquisite affinity; as a result, clinical efficacy seldom correlates with circulating drug concentration and pharmacokinetics are not considered critical in guiding dosing. For example, for a number of therapeutic antibodies, the antibody is administered at a fixed dose and at prolonged intervals that allow for its near-complete clearance (e.g., infliximab). There is also the constraint of space in the book; hence, the appendix focuses on small-molecule drugs.
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A major objective of this appendix is to present pharmacokinetic data in a format that informs the clinician of the essential characteristics of drug disposition that form the basis of drug-dosage regimen design. Table AI-1 contains quantitative information about the absorption, distribution, and elimination of drugs; the effects of some disease states, age, pregnancy, and sex on these processes, where significant; and the correlation of efficacy and toxicity with drug concentrations in blood/plasma. The general principles that underlie the design of appropriate maintenance dose and ...