Giving drugs per rectum for systemic effect

Crossing the Blood-Brain Barrier: A Review on Drug Delivery Strategies for Treatment of the Central Nervous System Diseases

Many drugs have been designed to treat diseases of the central nervous system (CNS), especially neurodegenerative diseases. However, the presence of tight junctions at the blood-brain barrier has often compromised the efficiency of drug delivery to target sites in the brain. The principles of drug delivery systems across the blood-brain barrier are dependent on substrate-specific (i.e. protein transport and transcytosis) and non-specific (i.e. transcellular and paracellular) transport pathways, which are crucial factors in attempts to design efficient drug delivery strategies. This review describes how the blood-brain barrier presents the main challenge in delivering drugs to treat brain diseases and discusses the advantages and disadvantages of ongoing neurotherapeutic delivery strategies in overcoming this limitation. In addition, we discuss the application of colloidal carrier systems, particularly nanoparticles, as potential tools for therapy for the CNS diseases.

Pharmacokinetics of low-dose and high-dose buprenorphine in cats after rectal administration of different formulations

OBJECTIVES

A prospective experimental study was performed in nine young healthy cats to investigate a pharmacokinetic profile and the clinical relevance of rectally administered buprenorphine. Rectal pH value was measured in all nine cats.

METHODS

Blood was collected 15, 30, 60, 90, 120, 240 and 480 mins and 24 h after the rectal administration of a suppository and a gel at doses between 0.02 mg/kg and 0.1 mg/kg buprenorphine to determine the plasma concentration of buprenorphine. Rectal pH was measured with pH paper.

RESULTS

Upon pharmacokinetic non-compartment analysis of high-dose buprenorphine (0.1 mg/kg), average maximal plasma concentration was found to be 1.13 ng/ml, time to maximal plasma concentration was 45 mins and area under the plasma concentration-time curve was 94.19 ng*min/ml, representing low but potential bioavailability. Mean residual time was 152.2 mins and the half-life was 92.6 mins. A wide range of plasma concentrations within the cohort was measured and two of the cats had to be excluded from statistical analysis owing to incomplete uptake. Vital parameters of all cats were considered to be normal but three of the cats showed mydriasis up to 8 h after application. After the administration of a low-dose suppository or a rectal gel (0.02 mg/kg) within pilot studies, no buprenorphine was detected in cat plasma. Rectal pH in all cats was between 7.7 and 8.

CONCLUSIONS AND RELEVANCE

The rectal application of buprenorphine at a dose of 0.1 mg/kg revealed a potential but weak uptake in cats. Regarding effective concentrations in previous pharmacokinetic investigations, rectal administration is currently not recommended for good provision of opioid analgesia in cats. Pharmacological investigations of formulation and galenics in order to improve the rectal bioavailability of buprenorphine remain to be clarified before further dose-finding and pharmacokinetic/pharmacodynamic studies are performed.

A systematic review of the pharmacokinetics of antiepileptic drugs in neonates with refractory seizures

BACKGROUND

Neonatal seizures are associated with neurological sequelae and an increased risk of epilepsy later in life. Phenobarbital and phenytoin remain the antiepileptic drugs (AEDs) most commonly used to treat neonatal seizures, despite their suboptimal effectiveness and safety. As a result, other AEDs, such as levetiracetam and topiramate, are often used in neonates with refractory seizures, despite limited data and off-label use.

OBJECTIVES

To systematically review published pharmacokinetic data for second-line AEDs used in neonates with seizures and to provide dosing recommendations for these agents in the neonatal population.

METHODS

A literature search was conducted in PubMed (1949-May 2012), Medline (1950-May 2012), and Embase (1980-May 2012). Each study was ranked according to the quality of evidence it provided, based on the classification system developed by the US Preventive Services Task Force. Information extracted from each study included study design, number of subjects, gestational and postnatal age, AED dosage regimen, pharmacokinetic parameters, pharmacokinetic model, AED serum concentrations, and sampling times.

RESULTS

Nineteen relevant pharmacokinetic studies involving a total of 8 different drugs were identified. No prospective, randomized, controlled studies (level I evidence) or nonrandomized controlled studies (level II-I evidence) were identified; 2 studies were prospective, nonrandomized, uncontrolled (cohort) studies (level II-2 evidence), 11 studies obtained evidence from multiple time series (level II-3 evidence), and 6 studies were case reports or descriptive studies (level III evidence).

CONCLUSIONS

There are limited pharmacokinetic data for the use of carbamazepine, levetiracetam, lidocaine, paraldehyde, topiramate, valproic acid, and vigabatrin for neonates with seizures refractory to treatment with first-line antiepileptic agents. Further research is needed to elucidate target AED serum concentrations (if any) required to optimize effectiveness and minimize dose-related adverse effects in neonates.

In vitro and in vivo characteristics of a thermogelling and bioadhesive delivery system intended for rectal administration of quinine in children

The aim of this work was to improve the rectal bioavailability of quinine hydrochloride by designing thermosensitive and mucoadhesive gels intended for rectal delivery. The rheological and mucoadhesive properties of poloxamer 407 solutions have been modulated by addition of hydroxypropylmethycellulose (HPMC) and propanediol-1,2. In vitro release and rectal absorption of quinine have been highlighted by a dialysis dissolution testing method and by the determination of bioavailability of the different formulations in rabbits. Increasing the proportions of HPMC and poloxamer in the formulations resulted in a prolonged release of quinine. Indeed, compared to the DT 50% of a rectal solution and a simple HPMC gel (27 and 65 min, respectively) the DT 50% of thermosensitive ternary systems was increased and ranged between 80 and 138 min, depending on the system composition. The release rate depended strongly on the elasticity of the gels after thermogelation. The absolute rectal bioavailability of quinine determined in rabbits was significantly improved with these thermosensitive and adhesive systems. It increased from 62% for the rectal solution to 98% for a ternary system 16/0.5/30 (poloxamer (16%)/HPMC (0.5%)/propanediol-1,2 (30%)). As a result of combined bioadhesion and prolonged release of quinine in vivo, higher average values of MRT and t(max) (9.1+/-0.2h and 30 min, respectively) were obtained compared to the rectal solution (6.9+/-0.9h and 15 min, respectively). Moreover, these formulations presented a very good rectal tolerance. Modulation by HPMC of the viscoelastic and mucoadhesive properties of poloxamer 407 thermogelling solutions allowed a prolonged release of quinine hydrochloride and an improvement of bioavailability in rabbit.

Efficacy and safety of intranasal lorazepam versus intramuscular paraldehyde for protracted convulsions in children: an open randomised trial

BACKGROUND

In sub-Saharan Africa, rectal diazepam or intramuscular paraldehyde are commonly used as first-line anticonvulsant agents in the emergency treatment of seizures in children. These treatments can be expensive and sometimes toxic. We aimed to assess a drug and delivery system that is potentially more effective, safer, and easier to administer than those presently in use.

METHODS

We did an open randomised trial in a paediatric emergency department of a tertiary hospital in Malawi. 160 children aged over 2 months with seizures persisting for more than 5 min were randomly assigned to receive either intranasal lorazepam (100 microg/kg, n=80) or intramuscular paraldehyde (0.2 mL/kg, n=80). The primary outcome measure was whether the presenting seizure stopped with one dose of assigned anticonvulsant agent within 10 min of administration. The primary analysis was by intention-to-treat. This study is registered with ClinicalTrials.gov, number NCT00116064.

FINDINGS

Intranasal lorazepam stopped convulsions within 10 min in 60 (75%) episodes treated (absolute risk 0.75, 95% CI 0.64-0.84), and intramuscular paraldehyde in 49 (61.3%; absolute risk 0.61, 95% CI 0.49-0.72). No clinically important cardiorespiratory events were seen in either group (95% binomial exact CI 0-4.5%), and all children finished the trial.

INTERPRETATION

Intranasal lorazepam is effective, safe, and provides a less invasive alternative to intramuscular paraldehyde in children with protracted convulsions. The ease of use of this drug makes it an attractive and preferable prehospital treatment option.

Alternative routes of drug administration--advantages and disadvantages (subject review). American Academy of Pediatrics. Committee on Drugs

During the past 20 years, advances in drug formulations and innovative routes of administration have been made. Our understanding of drug transport across tissues has increased. These changes have often resulted in improved patient adherence to the therapeutic regimen and pharmacologic response. The administration of drugs by transdermal or transmucosal routes offers the advantage of being relatively painless.12 Also, the potential for greater flexibility in a variety of clinical situations exists, often precluding the need to establish intravenous access, which is a particular benefit for children.

This statement focuses on the advantages and disadvantages of alternative routes of drug administration. Issues of particular importance in the care of pediatric patients, especially factors that could lead to drug-related toxicity or adverse responses, are emphasized.

Clinical pharmacokinetics in infants and children. A reappraisal

A significant increase in the knowledge base in paediatric clinical pharmacology has occurred over the past 2 decades and has largely been the result of important scientific and sociological advancements pertaining to paediatric therapeutics. Although the data on drug disposition in infants and children have increased considerably over the past few years, pharmacokinetic-pharmacodynamic interactions, particularly the effect of development on pharmacodynamics, remain poorly understood. The impact of developmental physiology on drug absorption, distribution, metabolism and elimination in infants and children is reviewed and contrasted to the determinants of clinical pharmacokinetics in neonates. The most notable differences in drug disposition between infants and children when compared with neonates and young adults centre around alterations in body water and serum protein composition and the affinity/capacity for hepatic biotransformation of xenobiotics. As opposed to examining the effect of age on the disposition of specific compounds, the differences in developmental pharmacology are highlighted by the review of important and/or emerging pharmacokinetic-pharmacodynamic controversies in infants and children. These include the issues of altered drug distribution and metabolism in cystic fibrosis, pharmacokinetic determinants of successful antimicrobial therapy in bacterial meningitis and the pharmacokinetic determinants of immunosuppression treatment with cyclosporin. The pharmacological differences which are characteristic of development in both infants and children are also reviewed by examination of considerations for clinical pharmacokinetic evaluations such as specific routes and techniques for both drug administration and determination of sampling strategies. Clinical pharmacokinetics will continue to function as a bridge between the generation of new information and the practical application of this knowledge. Consequently, pharmacokinetics provides a pharmacological tool for use in research and clinical care. The clinical application of this tool is examined by a review of the pertinent assumptions and limitations, as well as useful mathematical techniques for use in paediatric patients. Additionally, 'non-traditional' uses of clinical pharmacokinetics (forensic application and use to evaluate organ function) in infants and children are discussed as are considerations for research use of clinical pharmacokinetic data.