Kinetics of buccal absorption of propafenone single oral loading dose in healthy humans

Understanding the oral mucosal absorption and resulting clinical pharmacokinetics of asenapine

Absorption of drugs from the oral cavity into the mucosal tissues is typically a fast event. Dissolved drugs partition into the mucosal membranes and within minutes will reach equilibrium with drug in solution in the oral cavity. However, this does not always equate to rapid drug appearance in the systemic circulation. This has been attributed to slow partitioning out of the mucosal tissues and into the systemic circulation. Based on information from literature, physicochemical properties of asenapine, and clinical data, we conclude that for sublingually administered asenapine, the exposure is primarily a function of rapid partitioning into the mucosal membranes. This is followed by slow partitioning out of the mucosal tissues and into the systemic circulation, leading to a T (max) value of about 1 h. The bioavailability of asenapine at doses below the saturation solubility in the mouth does not change and is controlled primarily by mass transport equilibrium. At doses above the saturation solubility, the bioavailability becomes more dependent not only on the distribution equilibrium but also on contact time in the mouth because additional variables (e.g. dissolution rate of the drug) need to be accounted for. These explanations are consistent with oral cavity absorption models from the literature and can be used to accurately describe the clinical data for asenapine.

Extemporaneous suspension of propafenone: attending lack of pediatric formulations in Mexico

BACKGROUND

Physicians have frequently encountered difficulties when prescribing drugs not available in doses suitable for pediatric age groups. Furthermore, children have difficulty swallowing tablets. This study aimed to determine the stability of an oral propafenone suspension made from commercial tablets with a syrup vehicle and to establish its reliable use with children.

METHODS

An extemporaneous suspension of propafenone 1.5 mg/ml was prepared with commercial tablets. Its physicochemical and microbiologic stability was established by constant monitoring during 90 days at room temperature (15 +/- 5 degrees C) and at refrigeration (3-5 degrees C). Plasma levels of propafenona were measured in two children with supraventricular tachycardia at steady state.

RESULTS

The suspension was stable, maintaining its original physicochemical and microbiologic properties. Moreover, no apparent changes in color or odor were observed. Plasma levels of propafenone in patients demonstrated therapeutic concentrations after they had taken the suspension, with no unwanted outcome.

CONCLUSIONS

The conservation of both physicochemical and microbiologic stability of the suspension represents an option for the administration of propafenone to children.

Ambroxol Lozenge Bioavailability

OBJECTIVE

To examine whether or not the early dissolution/absorption in the oral cavity of lozenge administration contributes to superior bioavailability of ambroxol compared with the commercially available tablet.

METHODS

24-hour plasma level pharmacokinetic profiles of 20 healthy volunteers receiving oral administration of identical single doses (30mg) of lozenges and a commercially available tablet with a 1-week washout period were collected. The data were analysed by a non-compartmental model with a statistical moment and mean transit time concept. The mean transit times obtained after lozenge and tablet administration were compared.

RESULTS

The variance in absorption phase was significantly higher than that in the distribution/elimination phase in the pharmacokinetic profiles of the lozenge, suggesting additional absorption processes. The mean transit time of the tablet was significantly greater than that of the lozenge, by 7.69 hours with a 90% confidence interval (CI) of 3.11, 12.27. Early drug dissolution/absorption in the oral cavity and gastrointestinal absorption was successfully modelled to the pharmacokinetic profiles after lozenge administration. The additional availability of the drug to systemic circulation was mainly due to complete dissolution in the oral cavity prior to absorption as well as to oral mucosal transport. Between the two processes, dissolution was proposed to be a limiting step, since oral mucosal absorption was at a very high rate. The estimated average dissolution rate constant (90% CI) in first-order fashion was 0.13h(-1) (0.08, 0.32).

CONCLUSION

Absorption rates between lozenge and tablet could be differentiated with the aid of the mean transit time concept. However, estimation of oral mucosal absorption was not possible because the blood sampling intervals were not sufficiently frequent.

Oral mucosal drug delivery: clinical pharmacokinetics and therapeutic applications

Oral mucosal drug delivery is an alternative method of systemic drug delivery that offers several advantages over both injectable and enteral methods. Because the oral mucosa is highly vascularised, drugs that are absorbed through the oral mucosa directly enter the systemic circulation, bypassing the gastrointestinal tract and first-pass metabolism in the liver. For some drugs, this results in rapid onset of action via a more comfortable and convenient delivery route than the intravenous route. Not all drugs, however, can be administered through the oral mucosa because of the characteristics of the oral mucosa and the physicochemical properties of the drug. Several cardiovascular drugs administered transmucosally have been studied extensively. Nitroglycerin is one of the most common drugs delivered through the oral mucosa. Research on other cardiovascular drugs, such as captopril, verapamil and propafenone, has proven promising. Oral transmucosal delivery of analgesics has received considerable attention. Oral transmucosal fentanyl is designed to deliver rapid analgesia for breakthrough pain, providing patients with a noninvasive, easy to use and nonintimidating option. For analgesics that are used to treat mild to moderate pain, rapid onset has relatively little benefit and oral mucosal delivery is a poor option. Oral mucosal delivery of sedatives such as midazolam, triazolam and etomidate has shown favourable results with clinical advantages over other routes of administration. Oral mucosal delivery of the antinausea drugs scopolamine and prochlorperazine has received some attention, as has oral mucosal delivery of drugs for erectile dysfunction. Oral transmucosal formulations of testosterone and estrogen have been developed. In clinical studies, sublingual testosterone has been shown to result in increases in lean muscle mass and muscle strength, improvement in positive mood parameters, and increases in genital responsiveness in women. Short-term administration of estrogen to menopausal women with cardiovascular disease has been shown to produce coronary and peripheral vasodilation, reduction of vascular resistance and improvement in endothelial function. Studies of sublingual administration of estrogen are needed to clarify the most beneficial regimen. Although many drugs have been evaluated for oral transmucosal delivery, few are commercially available. The clinical need for oral transmucosal delivery of a drug must be high enough to offset the high costs associated with developing this type of product. Drugs considered for oral transmucosal delivery are limited to existing products, and until there is a change in the selection and development process for new drugs, candidates for oral transmucosal delivery will be limited.