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In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation. [ 1 ] By definition, when a medication is administered intravenously , its bioavailability is 100%.
Absolute bioavailability refers to the bioavailability of a drug when administered via an extravascular dosage form (i.e. oral tablet, suppository, subcutaneous, etc.) compared with the bioavailability of the same drug administered intravenously (IV). This is done by comparing the AUC of the non-intravenous dosage form with the AUC for the drug ...
Absorption by some other routes, such as intravenous therapy, intramuscular injection, enteral nutrition, is even more straightforward and there is less variability in absorption and bioavailability is often near 100%. Intravascular administration does not involve absorption, and there is no loss of drug. [4]
The bioavailability of testosterone when administered as a subcutaneous pellet implant is virtually 100%. [86] Levels of testosterone vary considerably between individuals, but are fairly constant within individuals. [41] The absorption half-life of subdermal testosterone implants is 2.5 months. [8]
Although the bioavailability of oral progesterone is increased if it is taken with food, its overall bioavailability is still low, even if measured using IA. [18] It has been suggested that the improvement in progesterone levels when oral progesterone is taken with food may be due to enhanced lymphatic absorption, allowing oral progesterone to ...
At a practical level, a drug's bioavailability can be defined as the proportion of the drug that reaches the systemic circulation. From this perspective the intravenous administration of a drug provides the greatest possible bioavailability, and this method is considered to yield a bioavailability of 1 (or 100%). Bioavailability of other ...
For an intravenously administered drug, the bioavailability F will equal 1, since the drug is directly introduced to the bloodstream. If the patient requires an oral dose, bioavailability will be less than 1 (depending upon absorption, first pass metabolism etc.), requiring a larger loading dose.
The absorption of vaginal estradiol is slightly greater in women with vaginal atrophy. [72] Vaginal estradiol has high bioavailability and greatly increased potency compared to oral estradiol, with about 10- to 20-fold the comparative potency of oral estradiol. [10]