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→Pharmacokinetic Considerations
==Pharmacokinetic Considerations==
==Pharmacokinetic Considerations==
They are organic acids, hydrophilic and will ionise at physiological pH. They generally have poor oral bioavailability as they unstable in acid environments. They have a limited volume of distribution (0.2-0.3l/kg), this means the drug is mainly confined to plasma and interstitial space. As the are lipophilic they can't enter cells and won't cross the blood brain barrier, unless it is damaged. They have short half-lives of about 0.5 - 1.2 hours. They are readily excreted by the kidneys, via tubular secretion in the proximal convoluted tubule. This results in high concentrations of the drug in urine.
Exceptions are:
* Cefalexin which is stable in acid and so suitable for oral dosing.
* Ceforperazone is excreted in bile rather than in urine.
==Side Effects and Contraindications==
==Side Effects and Contraindications==