Term	Definition
Oral liquid formulation	A pediatric oral liquid formulation available on the drug market, provided by the pharmaceutical company
Formulation manipulation	Change in (oral) drug formulation (e.g., crushing of tablets, opening of capsules, dissolving content in a vehicle) that is needed in clinical practice but is not described in the drug label
BCS class	System to categorize drugs according to their permeability and solubility [95] BCS class I: high solubility, high permeability BCS class II: low solubility, high permeability BCS class III: high solubility, low permeability BCS class IV: low solubility, low permeability
Solubility	The minimum solubility of the drug across a pH range from 1 to 8 and at a temperature of 37 ± 0.5 °C. High-solubility drugs are those with a ratio of dose to solubility volume that is less than or equal to 250 mL [95]
Permeability	The effective human jejunal wall permeability of a drug. High-permeability drugs are generally those with an extent of absorption greater than or equal to 90% and are not associated with any documented instability in the gastrointestinal tract [95]
Bioavailability	The extent and rate at which an active pharmaceutical ingredient (API) is absorbed in the systemic circulation and available at the site of drug action [95]. This is dependent upon the AUC, Cmax and Tmax of a medicinal product
Bioequivalence	The term bioequivalence was introduced to ensure safety and efficacy and comparable in vivo performance of two medicinal products containing the same active substance. Bioequivalence between two medicinal products is assumed when the bioavailability (determined by a plasma concentration curve from which AUC, Cmax and Tmax can be calculated) is between 80% and 125% of the reference medicinal product. This is investigated in a bioequivalence or bioavailability study that meet the requirements of the study design described in the EMA or FDA bioequivalence guidelines and, as a main goal, investigates bioequivalence between two medicinal products containing the same active substance [9,10]
Similar PK parameters	Similar PK parameters (i.e., AUC and Cmax) of the manipulated oral dosage form that are within 80–125% of the solid oral dosage form. This is typically shown in a PK study that as a main outcome calculated PK parameters and investigated treatment outcomes (such as toxicity and response) of an solid oral dosage form and as a secondary outcome included PK parameter calculations of manipulated oral dosage forms but do not meet the requirements of EMA or FDA bioequivalence guidelines [9,10]
BCS = Biopharmaceutics Classification System; AUC = area under the curve; Cmax = maximum plasma concentration; EMA = European Medical Agency; FDA = U.S. Food and Drug Administration; PK = pharmacokinetics.