Suspensions, bioavailability

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. 

Cefuroxime axetil 30 mg/kg per day in 2 doses (max 1 g/day with suspension adult 250 mg twice daily) Nausea, vomiting, diarrhea, rash, diaper rash Suspension gritty and bitter tasting, not interchangeable with tablets (less bioavailable)... 

A Selen, PG Welling. Bioavailability of hydrochlorothiazide from tablets and suspensions. J Pharm 18. Sci 73 359-365, 1984. 

Suspension. If the drug is not sufficiently soluble, it can be formulated as a suspension. A suspension may also be desired to improve stability, bioavailability, or efficacy. The major topical ophthalmic suspensions are the steroid anti-inflammatory agents prednisolone acetate, dexamethasone, fluorometholone, and rimex-olone. Water-soluble salts of prednisolone phosphate and dexamethasone phosphate are available however, they have a lower steroid potency and are poorly absorbed. 

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. 

A number of oral solution or suspension products are included in the EPARs. Apart from the usual points of consideration for active ingredients and excipients, particular mention is made of possible precipitation of active ingredient when a solution is in use, the inclusion of excipients having a major impact on bioavailability, the need for flavoring to mask the taste of the active ingredient, relative potency compared with other routes of administration, preservation issues, dosing devices and the precision and accuracy of the dose delivered, and bioequivalence where formulations have been modified during the development process. 

S. Abdel-Rahman, D. Blowey, R. Kauffmann, and G. Kearns, Comparative bioavailability of loracarbef chewable tablet vs. oral suspension in children, Pediatr. Infect. Dis. J., 17(12), 1171 (1998). 

Sjovall J, Sjoqvist R, Huitfeldt B, Nyqvist H. Correlation between the bioavailability of microencapsulated bacampicillin hydrochloride in suspension and in vitro microcapsule dissolution. J Pharm Sci 1984 73 141—145. 

The oral bioavailability of hypericum may be altered and improved by a combination of its constituents. A hypericum extract containing naphthodianthrones is inactive in a water suspension, but very effective when another constituent, procyanidin, is present. Procyanidin had the effect of increasing the water solubility of naphthodianthrones, and thus increasing their pharmacokinetic availability (Butterweck et ai. 1997). Further, the facilitative effect of procyanidin exhibited an inverted U curve. 

Hazardous substances may be protected from microbial attack by physical or chemical envelopes. These protective barriers must be destroyed mechanically or chemically to produce fine particles or waste suspensions to increase the surface area for microbial attachment and subsequent biodegradation. Another way to increase the bioavailability of hydrophobic substances is washing of waste or soil by water or a solution of surface-active substances (surfactants). The disadvantage of this technology is the production of secondary hazardous... 

Absorption - The pharmacokinetic properties of voriconazole are similar following administration by the IV and oral routes. The oral bioavailability of voriconazole is estimated to be 96% (CV 13%). Bioequivalence was established between the 200 mg tablet and the 40 mg/mL oral suspension... 

Sales of Ca supplements alone were 875 million in the United States in 2002, and comprised 60% of all mineral supplement sales (Anonymous, 2004). In 2004, sales of Ca supplements increased by 9.3% (Uhland et ah, 2004), possibly to some extent in response to the Surgeon General s report on bone health that was issued that year. More recently in 2006, it was projected that dietary supplement sales in the United States would approach 5 billion (Anonymous, 2006). While Ca derived from a balanced diet is preferable, Ca supplements are a popular noncaloric alternative for increasing daily Ca intake. There are a vast number of oral Ca supplements available in the market place in the form of capsules, tablets, chewable tablets, effervescent tablets, liquids, powders, suspensions, wafers, and granules. However, not all Ca salts are equally soluble or bioavailable and the dose of Ca on the label of a supplement may not necessarily be reflective of the relative amount of available Ca once consumed. Furthermore, the same Ca salt may be more or less bioavailable depending on the production process and materials used to manufacture the supplement. 

---