Sublingual administration, bioavailability

Disposition in the Body. Rapidly and almost completely absorbed after oral or sublingual administration bioavailability almost 100%. Metabolised by enzymatic denitration and by glucuronide conjugation. About 80% of a dose is excreted in the urine in 24 hours. 

The sublingual administration of methyltestosterone was examined by Alkalay et al. The sublingual tablet produced a 50%i higher relative bio availability when compared with the oral tablet or oral solution. The increased bioavailability was attributed to the avoidance of first-pass hepatic metabolism due to absorption from the sublingual vasculature and lymphatics. 

The bioavailability of xylazine after intramuscular (i.m.) injection is 40-48% (Garcia-Villar et al 1981). The 2 agonists are effective when administered by i.v. or i.m. injection. Sublingual administration of romifidine (120 xg/kg) has been shown to be ineffective in producing a sedative effect (Freeman England 1999). Detomidine is approximately 68% protein bound in equine blood (Singh et al 1987). 

Bioavailability of most dmgs is greater with rectal (suppository) administration than with sublingual administration... 

Absorption/Distributton - Gl and sublingual absorption of ergotamine is incomplete and erratic following oral administration, peak blood levels are reached in about 2 hours. Following intranasal administration, however, the mean bioavailability of dihydroergotamine mesylate is 32% relative to the injectable administration. 

Because of the prominent first-pass effects and their tendency to inhibit MAO in the gut (resulting in tyramine pressor effects), alternative routes of administration are being developed. For example, selegiline is available in both transdermal and sublingual forms that bypass both gut and liver. These routes decrease the risk of food interactions and provide substantially increased bioavailability. 

After IV injection, the drug is delivered immediately and totally into the blood (100% bioavailability). In contrast, a drug administered via any other route (intramuscular, subcutaneous, intestinal, rectal, buccal, sublingual, nasal, pulmonary and vaginal) will have to circumvent various physical and chemical barriers (discussed below), so that the bioavailability will be lower in comparison to that obtained after iv administration. For example, to achieve 100% bioavailability via the oral route requires the drug to ... 

Although not routinely given by the buccal or sublingual routes, several research studies have shown that absorption of morphine from the mouth gives rise to effective analgesia and that these routes may provide suitable alternatives to parenteral administration. " Clinical studies have suggested that the bioavailability of morphine is 40-50% greater after buccal than intramuscular administration as plasma morphine... 

Ketobemidone is a narcotic analgesic that has been used clinically in Scandinavia and other European countries. The mean bioavailability in humans has been reported to be approximately 35% following oral administration, but this can be substantially improved when administered by the sublingual or buccal route. To date, in vitro work has focussed on the use of the ketobemidone prodrugs (largely esters), and published results suggest that, as with morphine sulfate, buccal mucosa permeation is greatly improved.[4 °l... 

Seo, H., Uekama, K. Enhanced bioavailability of digoxin by -cyclo-dextrin complexation evaluation for sublingual and oral administrations in human. Yakugaku. Zasshi 1989, 109, 778—782. 

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