Hepatic first-pass effect and controlled drug delivery following rectal administration

Colon targeted delivery of niclosamide from β-cyclodextrin inclusion complex incorporated electrospun Eudragit® L100 nanofibers

Electrospun nanofibers incorporated with inclusion complex (IC) of niclosamide (NIC) and hydroxypropyl-beta-cyclodextrin (HPβCD) (NIC-HPβCD-IC) was produced from pH-responsive polymer (Eudragit® L100, EUD), which disintegrates at pH values higher than 6, (EUD-NIC-HPβCD-IC-NF) for targeted delivery of NIC to the colon. Pristine EUD nanofibers (EUD-NF), only NIC loaded (EUD-NIC-NF) and physical mixture of NIC and HPβCD loaded EUD nanofibers (EUD-NIC-HPβCD-NF) were also produced as reference. SEM images revealed the bead-free and uniform morphology of nanofibers. XRD, TGA, and DSC were also performed for both NIC-HPβCD-IC and electrospun nanofibers and it was seen that there are some NIC molecules, which cannot make IC. Dissolution studies were carried out for 240 min at pH 1.2 and pH 7 simulating stomach and colon, respectively. EUD-NIC-NF released almost 53 % of NIC in 120 min, whereas EUD-NIC-HPβCD-NF (15 %) and EUD-NIC-HPβCD-IC-NF (8 %) released at most 15 % of NIC in 120 min. Then, remained NIC in the nanofibers released into the colon for the next 120 min. The slight difference in the release of NIC into stomach from EUD-NIC-HPβCD-NF and EUD-NIC-HPβCD-IC-NF might be due to the uncomplexed NIC molecules in EUD-NIC-HPβCD-IC-NF. More importantly, EUD-NIC-HPβCD-IC-NF was quite effective for preventing the release of NIC in the stomach in contrast to EUD-NIC-NF, which has already released more than half amount of NIC in 120 min. In conclusion, this study might open new areas for developing targeted delivery systems by the combination of nanofibers and CD-ICs for hydrophobic drugs such as NIC.

Methylcellulose and polyacrylate binary hydrogels used as rectal suppository to prevent type I diabetes

The purpose of this study was to fabricate a novel binary hydrogel, and the insulin-loaded hydrogel was used as rectal suppository to prevent type I diabetes. The binary hydrogel was synthesized via solution polymerization. Its structure was studied by Fourier transform infrared spectroscopy (FTIR) and Raman spectra. The swelling behaviors of binary hydrogels were revealed in pH 1.2, 6.8 and 7.4 buffers, respectively. Their inner morphologies were observed with a scanning electron microscope (SEM). Insulin (INS) was selected as a model drug and encapsulated into the binary hydrogels. INS release study was carried out in pH 7.4 buffer. The hypoglycemic effects of INS-loaded hydrogels were studied by rectal administration. FTIR and Raman spectra confirmed the obtaining of binary hydrogels. The hydrogel showed a high swelling ratio in pH 7.4 (rectum environment). SEM photographs illustrated that many micro-pores in the inner of binary hydrogels, which could accommodate abundant guest molecule (e.g. INS). INS release profile suggested that INS-loaded hydrogels could diffuse INS at a sustained manner. Animal studies proved that INS-loaded binary hydrogel had an obvious hypoglycemic effect. Therefore, it could be speculated that the binary hydrogel had a potential application on treating type I diabetes by rectal administration.

The effects of morphine and methylnaltrexone on gastrointestinal pain in healthy male participants

BACKGROUND

Opioid antagonists are increasingly used to abolish the gastrointestinal side effects of opioids. However, they can potentially interfere with local analgesia exerted via opioid receptors in the gut. Thus, in the current study we aimed to explore the effect of rectal morphine before and after blocking opioid receptors outside the central nervous system with methylnaltrexone (MNTX).

METHODS

In this randomized, placebo controlled, cross-over study 15 healthy male participants received the following drugs at three separate sessions: (i) placebo, (ii) 30 mg morphine administered per rectum, or (iii) 12 mg MNTX given subcutaneously before 30 mg rectal morphine. At baseline and after drug administration peripheral and central effects of the drugs were assessed by experimental pain to the skin, muscle, rectum and pupillometry.

KEY RESULTS

Compared to placebo there was no local effect of morphine on mechanical rectal distension. In contrast, an increase in tolerated volume was seen following MNTX/morphine administration (p < 0.001), starting 7 min after dosing. Both morphine and MNTX/morphine had a central effect manifested as an increase in mechanical muscle pressure thresholds (both p < 0.001) and a decrease in pupil diameter (both p < 0.001). These effects occurred 30 min after dosing.

CONCLUSIONS & INFERENCES

No peripheral analgesic effect of morphine was found. Methodological shortcomings may have contributed to the lack of peripheral analgesia and thus, a peripheral morphine effect on rectal pain cannot be excluded. On the other hand, the combination of MNTX and morphine exerted a local effect on rectal distensions and seems to improve analgesia.

Population pharmacokinetics of morphine and morphine-6-glucuronide following rectal administration--a dose escalation study

INTRODUCTION

To safely and effectively administer morphine as liquid formulation via the rectal route, a thorough understanding of the pharmacokinetics is warranted. The aims were: (1) to develop a population pharmacokinetic model of liquid rectal morphine and morphine-6-glucoronide (M6G), (2) to simulate clinically relevant rectal doses of morphine and (3) to assess the tolerability and safety.

MATERIAL AND METHODS

This open label, dose escalation, four-sequence study was conducted in 10 healthy males. Three escalating doses of morphine hydrochloride (10mg, 15 mg and 20 mg) were administered 20 cm from the anal verge. A 2mg morphine hydrochloride dose was administered intravenously as reference. Blood samples were drawn at baseline and at nine time points post dosing. Serum was obtained by centrifugation and assayed for contents of morphine and M6G with a validated high performance liquid chromatographic method. Modelling was performed using NONMEM 7.2 and the first order conditional estimation method with interaction.

RESULTS

A two compartment distribution model with one absorption transit compartment for rectal administration and systemic clearance from the central compartment best described data. Systemic PK parameters were allometric scaled with body weight. The mean morphine absorption transit time was 0.6h, clearance 78 L/h [relative standard error (RSE) 12%] and absolute bioavailability 24% (RSE 11%). To obtain clinically relevant serum concentrations, simulations revealed that a single morphine hydrochloride dose of 35 mg will provide sufficient peak serum concentration levels and a 46 mg dose four times daily is suggested to maintain clinically relevant steady-state concentrations. Body weight was suggested to be an important covariate for morphine exposure. No severe side effects were observed.

CONCLUSION

A population pharmacokinetic model of liquid rectal morphine and M6G was developed. The model can be used to simulate rectal doses to maintain analgesic activity in the clinic. The studied doses were safe and well tolerated.

Diclofenac pharmacokinetic meta-analysis and dose recommendations for surgical pain in children aged 1-12 years

BACKGROUND

Diclofenac is an effective, opiate-sparing analgesic for acute pain in children, which is commonly used in pediatric surgical units. Recently, a Cochrane review concluded the major knowledge gap in diclofenac use is dosing information. A pharmacokinetic meta-analysis has been undertaken with the aim of recommending a dose for children aged 1-12 years.

METHODS

Studies containing diclofenac pharmacokinetic data were identified during a Cochrane systematic review, and authors were asked to provide raw data. A pooled population analysis was undertaken in NONMEM to define the pharmacokinetics of intravenous, oral, and rectal diclofenac in children. Simulations were performed to recommend a dose yielding an equivalent area under diclofenac concentration-time curve (AUC) to a 50-mg dispersible tablet in adults.

RESULTS

Data from 111 children aged 1-14 years consisting of 375 samples following intravenous, oral suspension, and suppositories were used. Adult dispersible tablet and suspension data were added to provide a reference AUC and support the absorption modeling, respectively. A three-compartment model described disposition, a dual-absorption compartment model was used for suspension and dispersible tablet data, and single-absorption compartment model for suppositories. The estimate of clearance was 16.5 l·h(-1) ·70 kg(-1) and bioavailabilities were 0.36, 0.63, and 0.35 for suspension, suppository, and dispersible tablets, respectively.

CONCLUSIONS

Single doses of 0.3 mg·kg(-1) for intravenous, 0.5 mg·kg(-1) for suppositories, and 1 mg·kg(-1) for oral diclofenac in children aged 1-12 years are recommended as they yield a similar AUC to 50 mg in adults.

Pathways of paracetamol absorption from layered excipient suppositories: artificial intelligence approach

When studying paracetamol availability after rectal administration, the differences between slower and faster release suppositories were discovered. Approach with modelling and simulation of compartment-based models was used to explore the differences. A study of paracetamol from layered excipient suppositories shows that many different mechanisms are involved in the drug pharmacokinetics. There is also a large number of articles, each dealing with only one or with a few of the mechanisms. However, there is little information available on how the mechanisms interact in the organism and thus govern the pharmacokinetics of the drug, which means that systemic view in the expert knowledge is missing. In the case of paracetamol rectal availability the use of partially fuzzyfied model allowed systemic combination of all described mechanisms found in the literature and measured data. In spite of non-identifiability, the model showed that patterns that explained differences in bioavailabilities of the two formulations of suppositories could be found. Results of modelling and simulation show that "in vivo" there is practically no difference in cumulative release profiles between the two formulations. However, due to higher content of mono-di-glycerides in a slower release formulation, the extent of absorption is augmented both by absorption-enhancing effect of mono-di-glycerides and the liver bypass mechanism via diminished viscosity.