Pharmaceutical principles are the underlying physicochemical principles that allow a drug to be incorporated into a pharmaceutical dosage form (e.g., solid, solution, capsule). These principles apply whether the drug is extemporaneously compounded by the pharmacist or manufactured for commercial distribution as a drug product.
A. The finished dosage form contains the active drug ingredient in association with nondrug (usually inert) ingredients (excipients) that make up the vehicle, or formulation matrix.
B. The drug delivery system concept, which has evolved since the 1960s, is a more holistic concept. It embraces not only the drug (or prodrug) and its formulation matrix, but also the dynamic interactions among the drug, its formulation matrix, its container, and the physiologic milieux of the patient. These dynamic interactions are the subject of biopharmaceutics.
The application of pharmaceutical principles to drug dosage forms is illustrated when drug dosage forms are categorized according to their physical state, degree of heterogeneity, and chemical composition. The usual relevant states of matter are gases, liquids, and solids.
The stability of the active component of a drug is a major criterion in the rational design and evaluation of drug dosage forms. Problems with stability can determine whether a given formulation is accepted or rejected.
- Extensive chemical degradation of the active ingredient can cause substantial loss of active ingredient from the dosage form.
- Chemical degradation can produce a toxic product that has undesirable side effects.
- Instability of the drug product can cause decreased bioavailability. As a result, the therapeutic efficacy of the dosage form may be substantially reduced.