Bioavailability of drug

Solubility in aqueous and organic Crystalline and polymorphic forms solvents Solvation and hydration 

Bisacodyl is a laxative that is indicated in short-term treatment of constipation evacuation of colon for rectal and bowel evaluation preparation for delivery or surgery. Bisacodyl is the only diphenyhnethane derivative available in the United States. It is marketed as an enteric-coated preparation (Dulcolax, Correctol, others) and as a suppository for rectal administration. The usual oral daily dose of bisacodyl is 10 to 15 mg for adults and 5 to 10 mg for children 6 to 12 years old. The drug requires hydrolysis by endogenous esterases in the bowel for activation, and so the laxative effects after an oral dose usually are not produced in less than 6 hours taken at bedtime, it will produce its effect the next morning. Suppositories work much more rapidly. 

Bismuth is an antidiarrheal agent that produces antisecre-tory and antimicrobial effects it may have an antiinflammatory effect. It is indicated in the treatment of indigestion without causing constipation, nausea, abdominal cramps and for control of diarrhea, including traveler s diarrhea. 

Bismuth compounds have been used to treat a variety of gastrointestinal diseases and symptoms for centuries, although their mechanism of action remains poorly understood. Pepto-Bismol (bismuth subsalicylate is an over-the-counter preparation estimated to be used by 60% of American households. It is a crystal complex consisting of trivalent bismuth and salicylate suspended in a mixture of magnesium aluminum silicate clay, hi the low pH of the stomach, the bismuth subsalicylate reacts with hydrochloric acid to form bismuth oxychloride and salicylic acid. While 99% of the bismuth passes unaltered and unabsorbed into the feces, the salicylate is absorbed in the stomach and small intestine. Thus, caution should be used in patients taking salicylates for other indications. 

Each of the ingredients is individually active in vitro against most strains of H. pylori. 

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Co-administration of ofloxacin and chitosan in eyedrops increased the bioavailabUity of the antibiotic [290]. Trimethyl chitosan was more effective because of its solubility (plain chitosan precipitates at the pH of the tear fluid). On the other hand, N-carboxymethyl chitosan did not enhance the corneal permeability nevertheless it mediated zero-order ofloxacin absorption, leading to a time-constant effective antibiotic concentration [291]. Also W,0-carboxymethyl chitosan is suitable as an excipient in ophthalmic formulations to improve the retention and the bioavailability of drugs such as pilocarpine, timolol maleate, neomycin sulfate, and ephedrine. Most of the drugs are sensitive to pH, and the composition should have an acidic pH, to enhance stability of the drug. The delivery should be made through an anion exchange resin that adjusts the pH at around 7 [292]. Chitosan solutions do not lend themselves to thermal sterilization. A chitosan suspension, however. 

Veber DF, Johnson SR, Cheng H-Y, Smith BR, Ward KW, Kopple KD. Molecular properties that influence the oral bioavailability of drug candidates. J Med Chem 2002 45 2615-23. 

Veber, D., Johnson, S., Cheng, H., Smith, B., Ward, K., Kopple, K. D. Molecular properties that infiuence the oral bioavailability of drug candidates. /. Med. Chem. 2002, 45, 2615-2623. 

The bioavailability of drugs from tablets can be markedly influenced by the rate and efficiency of the initial disintegration and dissolution process. Unfortunately, one is faced with a compromise situation — a structure that has both a durable structure prior to administration and the ability to readily break down when placed in the in vivo environment. One of the major factors affecting both these properties is the structure of the tablet, in particular its density (or porosity) and the pore structure. Study of the significance of such measurements and interpretation of the results is a relatively recent field of interest. 

Mandagere, A. K., T. N. Thompson, and K. K. Hwang. Graphical model for estimating oral bioavailability of drugs in humans and other species from their Caco-2 permeability and in vitro liver enzyme metabolic stability rates, J. Med. Chem. 2002, 45, 304-311... 

Mechanisms of dissolution kinetics of crystals have been intensively studied in the pharmaceutical domain, because the rate of dissolution affects the bioavailability of drug crystals. Many efforts have been made to describe the crystal dissolution behavior. A variety of empirical or semi-empirical models have been used to describe drug dissolution or release from formulations [1-6]. Noyes and Whitney published the first quantitative study of the dissolution process in 1897 [7]. They found that the dissolution process is diffusion controlled and involves no chemical reaction. The Noyes-Whitney equation simply states that the dissolution rate is directly proportional to the difference between the solubility and the solution concentration ... 

Chiou, W. L., Buehler, P. W., Comparison of oral absorption and bioavailability of drugs between monkey and human, Pharm. Res. 

Definition of Absorption and Bioavailability of Drugs following Oral Administration... 

Chiou WL and Buehler PW (2002) Comparison of Oral Absorption and Bioavailability of Drugs Between Monkey and Human. Pharm Res 19 pp 868-874. 

Tronde A, Norden B, Marchner H, Wendel AK, Lennernas H, Bengtsson UH (2003) Pulmonary absorption rate and bioavailability of drugs in vivo in rats structure-absorption relationships and physicochemical profiling of inhaled drugs. JPharmSci 92 1216-1233. 

Molecular properties that influence the oral bioavailability of drug candidates. 

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