Bioavailability dosage forms

Drug absorption is highly variable in neonates and infants [21,22]. Older children appear to have absorption patterns similar to adults unless chronic illness or surgical procedures alter absorption. Differences in bile excretion, bowel length, and surface area probably contribute to the reduced bioavailability of cyclosporine seen in pediatric liver transplant patients [22a]. Impaired absorption has also been observed in severely malnourished children [22b]. A rapid GI transit time may contribute to the malabsorption of carbamazepine tablets, which has been reported in a child [23]. Selection of a more readily available bioavailable dosage form, such as chewable tablets or liquids, should be promoted for pediatric patients. 

ADME Biopharmaceutics Bioavailability Dosage forms Pharmacokinetics Routes of administration Advanced drug delivery Slow release... 

The fraction of the orally administered dose that is bioavailable to the systemic circulation (Fsystemjc) is dependent upon the fraction of the dose that is released from the dosage form (/released), multiplied by the fraction that is absorbed into the portal circulation on its way to the liver (/absorbed this is the fraction that escapes gut metabolism), multiplied by the fraction of the dose that escapes the hepatic first-pass effect (/hepatic)- Since this is a multiplicative process if, for... 

Equation (41) is useful for comparing the bioavailabilities of two dosage forms of the same drug administered to the same group of subjects. If it is... 

Whenever a drug is administered by an extra-vascular route, there is a danger that part of the dose may not reach the blood (i.e., absorption may not be complete). When the intravenous route is used, the drug is placed directly in the blood therefore an IV injection is, by definition, 100% absorbed. The absolute bioavailability of an extravascular dosage form is defined relative to an IV injection. If IV data are not available, the relative bioavailability may be defined relative to a standard dosage form. For example, the bioavailability of a tablet may be defined relative to an oral solution of the drug. 

If dosage form 2 [Eq. (42)] is an intravenous dosage form, the absolute bioavailability of the extravascular dosage form (dosage form 1) is given by ... 

Absolute bioavailability AUCextravascuiar (extravascular dosage form) AUCiv... 

Assuming that the AUC for a 100 mg IV dose given to the same group of volunteers was 86.7h.pg/mL, the absolute bioavailability of the extravascular dosage form is... 

For this calculation, it is unnecessary to assume that Vd and/or kei are the same for the two studies. It is only necessary that fe be the same in both studies. This is usually a valid assumption unless the drug undergoes a significant amount of first-pass metabolism in the gut wall or liver following oral administration or a significant amount of decomposition at an intra muscular (IM) injection site. When this occurs, the availability of the extravascular dosage form may appear to be low, but the fault will not lie with the formulation. The bioavailability will be a true reflection of the therapeutic efficacy of the drug product, and reformulation may not increase bioavailability. 

WJ Westlake. The design and analysis of comparative blood-level trails In J Swarbrick, ed. Current Concepts in the Pharmaceutical Sciences Dosage Form Design and Bioavailability. Philadelphia, PA Lea Febiger, 1973. 

The effect of particle size reduction on the bioavailability of nitrofurantoin was shown in Fig. 4. The microcrystalline form (< 10 pm) is more rapidly and completely absorbed from the tablet dosage form than is the macrocrystalline form (74-177 pm) from the capsule dosage form. This is not a completely satisfactory illustration of the effect of particle size on the rate and extent of availability, since other manufacturing variables have not been held constant. Nevertheless, it does suggest some correlation between particle size, dissolution rate, and rate of availability. 

M. Rowland, Effect of some physiologic factors on bioavailability of oral dosage forms, in Dosage Form Design and Bioavailability (J. Swarbrick, Ed.), Lea Febiger, Philadelphia, 1973, pp. 181-222. 

Topical preparations, like all other dosage forms, must be formulated, manufactured, and packaged in a manner that assures that they meet general standards of bioavailability, physical (physical system) stability, chemical (ingredient) stability, freedom from contamination, and elegance. Like all other pharmaceuticals, these factors must remain essentially invariant over the stated shelf life of the product and they must be reproducible from batch to batch. 

MD Donovan, DR Flanagan. Bioavailability of disperse dosage form. In HA Lieberman, MM Rieger, GS Banker, eds. Pharmaceutical Dosage Forms Disperse Systems, Vol. 1. 2nd ed. New York Marcel Dekker, 1996, pp 315-376. 

Colorants do not contribute to therapeutic activity, nor do they improve product bioavailability or stability. Indeed, they increase the cost and complication of the manufacturing process. Their main role is to facilitate identification and to enhance the esthetic appearance of the product. In common with all material to be ingested by humans, solid dosage forms are severely restricted in the coloring agents that are allowable. This situation is complicated by the lack in international agreement on an approved list of colorants suitable for ingestion. 

Waiver of in vivo bioavailability and bioequivalence studies for immediate release solid oral dosage forms based on a biopharmaceutics classification system. Center for Drug Evaluation and Research, Food and Drug Administration, issued 8/2000, posted 8/31/2000. http //www.fda.gov/cder/guidance/ index, htm... 

Those aspects critical to the in vivo bioavailability of the product and routine control tests proposed to ensure that the product has consistent bioavailability from batch to batch. Where a product has low in vivo absorption, the evidence should be discussed and a conclusion reached as to whether this is due to intrinsic properties of the active ingredient(s) or whether it is related to the properties of the dosage form concerned. In the case of products intended to have a nonsystemic effect, the potential for systemic absorption may need to be considered. This may involve specific studies to determine the levels of the active ingredient(s) in the blood, plasma, urine, or feces and a discussion of the clinical significance of those results. 

The physical characteristics should be considered (in combination as appropriate) in relation to the proposed dosage form and route of administration. Factors to be considered extend to solubility characteristics, crystal form and properties, moisture or solvent content, particle size and size distribution (which may affect bioavailability, content uniformity, suspension properties, stability, and preclinical or clinical acceptability), polymorphism, etc. 

The information requirements for products such as prolonged-release oral dosage forms will depend on whether or not it has been possible, during the development of the product, to establish an in vivo-in vitro correlation between clinical data and dissolution studies. In vivo-in vitro correlations should be attempted using product at different stages of development, but bioavailability and pharmacokinetics data from pivotal clinical studies using at least pilot-scale production materials and possibly routine production material are particularly important. Where it is not possible to establish an in vivo-in vitro correlation, additional data will be required to compare the bioavailability of product developed at laboratory scale, pilot scale, and production scale. In the absence of an in vivo-in vitro correlation, the dissolution test will be a quality control tool rather than a surrogate marker for in vivo performance of the product. 

Product bioavailability is mentioned, especially where it is low. Where there are differences between the formulations tested for bioavailability during the development process and the formulation to be marketed, there is considerable discussion of the data provided on the bioequivalence of the different products and/or formulations. This is particularly so where, for example, early clinical studies were undertaken with capsules but the marketed dosage form is to be a tablet. Bioequivalence data and pharmacokinetic data (e.g., in crossover studies) and comparative dissolution studies are usually reported. This is particularly significant where the different strengths of the final products are not achieved by using different quantities of the same granulate formulation. Process optimization may also be addressed in such cases. 

Comparative bioavailability data are discussed where a number of different dosage forms/routes of administration have been used during the development process, e.g., tablets, capsules, oral solutions, granules, and injections. 

The critical void in pediatric drug therapy now lies in effective drug-delivery systems. Some inroads have been made in the manufacturing of pediatric dosing systems, particularly OTC preparations. There needs to be a redirection of the focus in nonparenteral drug formulations towards pediatric dosage forms with proven stability and bioavailability that can be easily and accurately administered to infants and children. 

FDA Guidance for Industry Waiver of in vivo Bioavailability and Bioequivalence Studies for Immediate Release Solid Oral Dosage Forms Containing Certain Active Moieties/ Active Ingredients Based on a Biopharmaceutics Classification System, CDER-GUID 2062dft.wpd Draft, Jan. 1999. 

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