Bioavailability of tolazamide from tablets: comparison of in vitro and in vivo results

Interference Assessment of Various Endogenous and Exogenous Substances on the Performance of the Eversense Long-Term Implantable Continuous Glucose Monitoring System

BACKGROUND

A variety of prescriptions and over-the-counter medications interfere with transcutaneous continuous glucose monitoring (CGM) sensors. This study characterized the interference profile of the Eversense^® CGM System (Senseonics, Inc., Germantown, MD), which has a different mechanism of glucose detection than other CGM systems.

MATERIALS AND METHODS

Sensor bias (sensor glucose concentration measurement - plasma glucose concentration measured by a reference test) was measured in vitro against 41 different substances at supratherapeutic/supraphysiologic plasma concentrations. Testing was performed using a paired-sample method adapted from the Clinical and Laboratory Standards Institute guidance document EP7-A2. Any substance producing sensor bias that exceeded the International Organization for Standardization (ISO) document 15197:2013 limits was then tested using an in vitro dose-response method to determine whether the concentration producing a significant sensor bias was within physiologic/therapeutic concentration ranges.

RESULTS

Eight of 41 substances produced a sensor bias that exceeded ISO 15197:2013 limits when tested in vitro at supratherapeutic/supraphysiologic plasma concentrations. Only two of these substances (tetracycline and mannitol) exceeded bias limits within therapeutic concentration ranges. Notably, neither acetaminophen nor ascorbic acid, which are substances reported to interfere with other CGM systems, produced sensor bias that exceeded ISO limits when used at physiologic concentrations.

CONCLUSIONS

Although tetracycline and mannitol interfered with the Eversense sensor, substances frequently reported to interfere with enzymatic, electrochemical-based transcutaneous CGM systems, such as acetaminophen and ascorbic acid, did not affect Eversense readings.

Performance of a new meter designed for assisted monitoring of blood glucose and point-of-care testing

BACKGROUND

Blood glucose (BG) meters used for assisted monitoring of blood glucose (AMBG) require different attributes compared with meters designed for home use. These include safety considerations (i.e., minimized risk of blood-borne pathogen transmission), capability for testing multiple blood sample types, and enhanced performance specifications. The OneTouch® Verio™Pro+ BG meter is designed to incorporate all of these attributes.

METHODS

Meter accuracy was assessed in clinical studies with arterial, venous, and capillary blood samples with a hematocrit range of 22.9-59.8%. The effect of interferents, including anticoagulants, on accuracy was evaluated. The meter disinfection protocol was validated, and instructions for use and user acceptance of the system were assessed.

RESULTS

A total of 97% (549/566) of BG measures from all blood sample types and 95.5% (191/200) of arterial blood samples were within ±12 mg/dl or 12.5% of reference measurements. The system was unaffected by 4 anticoagulants and 57 of 59 endogenous and exogenous compounds; it was affected by 2 compounds: pralidoxime iodide and xylose. Bleach wipes were sufficient to disinfect the meter. Users felt that the meter's quality control (QC) prompts would help them to comply with regulatory requirements.

CONCLUSION

The meter provided accurate measurements of different blood samples over a wide hematocrit range and was not affected by 57 physiologic and therapeutic compounds. The QC prompts and specific infection-mitigating design further aid to make this meter system practical for AMBG in care facilities.

Elimination of metformin-croscarmellose sodium interaction by competition

During analytical method development and validation, a strong charge interaction between metformin and croscarmellose sodium was observed when the aqueous solution containing metformin was spiked with croscarmellose sodium. The charge interaction resulted in the retention of metformin in croscarmellose sodium and caused a serious drug recovery problem. The percent recovery of metformin in the solution was much lower than its theoretical values, especially in the low metformin concentration range. To overcome the metformin-croscarmellose interaction, arginine was selected as a competitor for the binding sites on croscarmellose sodium. Because of the competition and stronger interaction between arginine and croscarmellose sodium than metformin and croscarmellose sodium, a complete recovery of metformin in presence of arginine in both low and high concentration ranges was achieved. The effect of arginine on the recovery of metformin and the competition mechanism are discussed in this paper.

Improved oral bioavailability of artemisinin through inclusion complexation with beta- and gamma-cyclodextrins

The bioavailability of beta- and gamma-cyclodextrin artemisinin complexes was evaluated in comparison with a normal commercially available preparation, Artemisinin 250. Twelve healthy male volunteers participated in the study conducted according to a three-way crossover design. The bioavailability was compared using the parameters, total area under the plasma level-time curve (AUC(0-infinity)), peak plasma concentration (C(max)), and time to reach peak plasma concentration (T(max)). A statistically significant difference was observed between the values of the complexes and Artemisinin 250 for the three parameters. However, no statistically significant difference was observed between the values of the beta- and gamma-cyclodextrin complexes. Moreover, the 90% confidence interval for the ratio of the AUC(0-infinity) values of the beta-cyclodextrin complex over those of Artemisinin 250 was estimated to be between 1.51-2.04, while that of C(max) was between 1.73-2.93. For the gamma-cyclodextrin complex, the respective intervals were 1.30-1.76 and 1.43-2.43. These findings indicated that the beta- and gamma-cyclodextrin complexes had a much higher rate and extent of bioavailability compared to Artemisinin 250. In addition, the absorption of artemisinin was observed to be poor and negligible when the preparations started to arrive in the colon. This could be attributed to poor dissolution of artemisinin in the semi-solid faecal matter in the lower part of the gastrointestinal tract.

The effect of soybean oil refuse powder used as vehicle on the absorption of oxolinic acid in chickens under fasting and nonfasting conditions and the correlation with in vitro dissolution

The effect of soybean oil refuse powder (SOR) when used as a vehicle on the absorption of oxolinic acid (OXA) powder in chicken, the dissolution profile of OXA and the correlation between in vivo and in vitro study were examined. To examine in vivo bioavailability, chickens fed or fasted were studied using a 2 x 2 crossover design. The OXA was administered OXA or OXA-SOR (1 : 9) mixture 20 mg OXA/kg. In vitro dissolution rates for OXA and OXA-SOR were measured using the paddle (PD) and the rotatory dialysis cell dissolution (PTSW) methods. Maximum plasma concentration (Cmax) and area under the curve (AUC) were significantly increased by the addition of SOR to OXA. Differences between OXA and OXA-SOR were more remarkable under fasted as compared with fed condition. In vitro dissolution rates of OXA-SOR pH 1.2, 6.5 and 7.2 as determined by the PD and the PTSW methods were increased in the presence of SOR vehicle. Differences between OXA and OXA-SOR in vitro dissolution rates were greater than in vivo bioavailability. Correlation between in vitro release (%) and in vivo absorption (%) showed good linearity (gamma=0.8805-0.9999).

Drug-excipient interactions and their affect on absorption

Excipient(s) are traditionally thought of as inert but they can have a tremendous impact on the ultimate pharmacological availability of a drug substance when added to a formulation. The magnitude of this effect will depend on the characteristics of the drug and on the quantity and properties of the excipients. The aim of this article is to identify the various physicochemical and physiological processes that can be altered by drug-excipient interactions and to explore mechanisms by which they might occur. The regulatory implications of drug-excipient interactions will also be discussed.

Novel approach to the analysis of in vitro-in vivo relationships

The objective of this study was to quantify the dependence of degree of in vitro-in vivo correlation on the relative rates of dissolution and intestinal permeation and on the fraction of dose absorbed. The following equation was derived assuming first-order dissolution and permeation after oral drug administration: Fa = fa-1(1 - alpha(alpha - 1)-1 (1 - Fd) + (alpha - 1)-1(1 - Fd)alpha), where Fa is the fraction of the total amount of drug absorbed at time t, fa the fraction of the dose absorbed at t = infinitive, alpha is the ratio of the first-order permeation rate constant to the first-order dissolution rate constant, and Fd is the fraction of dose dissolved in vitro at time t. This equation was examined in order to pursue a theoretical treatment of in vitro-in vivo correlation. The degree of in vitro-in vivo correlation between Fa and Fd was measured by r2. alpha was varied between 1000 and 0.001. fa was varied between 0.1 and 1.0. Points employed in the linear regression were geometrically balanced about the derived equation. r2 values decreased as alpha decreased for all values of fa. r2 values were virtually independent of fa for all values of alpha, except for 0.01 < alpha < 1.0. The slope of the regression was modulated by both alpha and fa; larger alpha and smaller fa each increased slope. Application of the equation to a piroxicam data set demonstrated the equation's utility relative to the USP Level A correlation approach. It is concluded that the degree of in vitro-in vivo correlation depends on the relative rates of dissolution and intestinal permeation and on the fraction of dose absorbed and that the derived model merits further study.

The relationship between the pharmacokinetics and pharmacodynamic effects of oral hypoglycaemic drugs

Oral hypoglycaemic drugs have widely differing pharmacokinetic properties. Possible pharmacodynamic benefits include greater efficacy and fewer adverse effects. In general, it has not been possible to demonstrate unequivocal differences in clinical efficacy between the sulphonylureas during long term use, although there are clear differences in potency. These differences have been emphasised to the extent that the term 'second-generation' has been used for the most potent sulphonylureas, but there is little to suggest that potency is of any therapeutic significance. Trials to study differences in efficacy have rarely been of acceptable design. They have often used fixed doses of drugs, begging the question of whether true potency ratios have been established for chronic treatment. They have rarely involved substantial numbers of patients in double-blind crossover studies with a suitable washout period. Trials which show that there is a clear relationship between drug concentrations in blood and drug effects (whether therapeutic effects or adverse effects such as severe hypoglycaemia) are generally lacking. Qualitative and semiquantitative analysis of adverse effects supports the concept that drugs with a long half-life (e.g. chlorpropamide), renally excreted active metabolites (e.g. acetohexamide) or unusual properties (e.g. glibenclamide, which accumulates progressively in islet tissue) are more likely to cause prolonged hypoglycaemia, which may be fatal. The major adverse effect of treatment with biguanides is lactic acidosis, and this probably occurs more commonly in patients treated with phenformin than those treated with metformin because of pharmacogenetic variation in phenformin metabolism. The available evidence therefore favours the use of drugs with a short elimination half-life which are extensively metabolised and which have no active metabolites.

Influence of tablet dissolution on furosemide bioavailability: a bioequivalence study

In order to evaluate the in vitro dissolution and in vivo bioavailability relationship for furosemide, a bioequivalence study was carried out. Furosemide (40 mg) was administered orally to 12 normal volunteers in a 6 x 6 crossover design using six products (five tablets and one solution) obtained from three pharmaceutical companies. Plasma and urine concentrations of furosemide were quantitated by high-performance liquid chromatography (HPLC). Plasma furosemide profiles were analyzed by non-compartmental methods. Compared to the oral solution, all of the formulations exhibited lower peak furosemide concentrations, longer mean residence times, and, in some cases, diminished bioavailability (range, 66-96%). Similar results were obtained when the reference product (a rapidly dissolving tablet) was used as the standard. All of the products failed the 75/75 rule when compared to either reference standard, apparently because of large intersubject variability. The total amount of furosemide excreted in urine could be associated with the percentage drug dissolved (in vitro) at 30 min. The pH 5.6 dissolution medium (compared to pH 4.6) appears to be an appropriate test medium for assuring batch uniformity and bioequivalence of furosemide products.