Pharmacokinetics and muscle histopathology of intramuscular valproate

Neuroprotection by delayed triple therapy following sarin nerve agent insult in the rat

The development of refractory status epilepticus (SE) induced by sarin intoxication presents a therapeutic challenge. In our current research we evaluate the efficacy of a delayed combined triple treatment in ending the abnormal epileptiform seizure activity (ESA) and the ensuing of long-term neuronal insult. SE was induced in male Sprague-Dawley rats by exposure to 1.2LD50 sarin insufficiently treated by atropine and TMB4 (TA) 1 min later. Triple treatment of ketamine, midazolam and valproic acid was administered 30 min or 1 h post exposure and was compared to a delayed single treatment with midazolam alone. Toxicity and electrocorticogram activity were monitored during the first week and behavioral evaluation performed 3 weeks post exposure followed by brain biochemical and immunohistopathological analyses. The addition of both single and triple treatments reduced mortality and enhanced weight recovery compared to the TA-only treated group. The triple treatment also significantly minimized the duration of the ESA, reduced the sarin-induced increase in the neuroinflammatory marker PGE2, the brain damage marker TSPO, decreased the gliosis, astrocytosis and neuronal damage compared to the TA+ midazolam or only TA treated groups. Finally, the triple treatment eliminated the sarin exposed increased open field activity, as well as impairing recognition memory as seen in the other experimental groups. The delayed triple treatment may serve as an efficient therapy, which prevents brain insult propagation following sarin-induced refractory SE, even if treatment is postponed for up to 1 h.

Intravenous and Intramuscular Formulations of Antiseizure Drugs in the Treatment of Epilepsy

Intravenous and intramuscular antiseizure drugs (ASDs) are essential in the treatment of clinical seizure emergencies as well as in replacement therapy when oral administration is not possible. The parenteral formulations provide rapid delivery and complete (intravenous) or nearly complete (intramuscular) bioavailability. Controlled administration of the ASD is feasible with intravenous but not intramuscular formulations. This article reviews the literature and discusses the chemistry, pharmacology, pharmacokinetics, and clinical use of currently available intravenous and intramuscular ASD formulations as well as the development of new formulations and agents. Intravenous or intramuscular formulations of lorazepam, diazepam, midazolam, and clonazepam are typically used as the initial treatment agents in seizure emergencies. Recent studies also support the use of intramuscular midazolam as easier than the intravenous delivery of lorazepam in the pre-hospital setting. However, benzodiazepines may be associated with hypotension and respiratory depression. Although loading with intravenous phenytoin was an early approach to treatment, it is associated with cardiac arrhythmias, hypotension, and tissue injury at the injection site. This has made it less favored than fosphenytoin, a water-soluble, phosphorylated phenytoin molecule. Other drugs being used for acute seizure emergencies are intravenous formulations of valproic acid, levetiracetam, and lacosamide. However, the comparative effectiveness of these for status epilepticus (SE) has not been evaluated adequately. Consequently, guidelines for the medical management of SE continue to recommend lorazepam followed by fosphenytoin, or phenytoin if fosphenytoin is not available. Intravenous solutions for carbamazepine, lamotrigine, and topiramate have been developed but remain investigational. The current ASDs were not developed for use in emergency situations, but were adapted from ASDs approved for chronic oral use. New approaches for bringing drugs from experimental models to treatment of human SE are needed.

Intramuscular and rectal therapies of acute seizures

The intramuscular (IM) and rectal routes are alternative routes of delivery for antiepileptic drugs (AEDs) when the intravenous route is not practical or possible. For treatment of acute seizures, the AED used should have a short time to maximum concentration (Tmax). Some AEDs have preparations that may be given intramuscularly. These include the benzodiazepines (diazepam, lorazepam, and midazolam) and others (fosphenytoin, levetiracetam). Although phenytoin and valproate have parenteral preparations, these should not be given intramuscularly. A recent study of prehospital treatment of status epilepticus evaluated a midazolam (MDZ) autoinjector delivering IM drug compared to IV lorazepam (LZP). Seizures were absent on arrival to the emergency department in 73.4% of the IM MDZ compared to a 63.4% response in LZP-treated subjects (p < 0.001 for superiority). Almost all AEDs have been evaluated for rectal administration as solutions, gels, and suppositories. In a placebo-controlled study, diazepam (DZP) was administered at home by caregivers in doses that ranged from 0.2 to 0.5 mg/kg. Diazepam was superior to placebo in reduced seizure frequency in children (p < 0.001) and in adults (p = 0.02) and time to recurrent seizures after an initial treatment (p < 0.001). Thus, at this time, only MZD given intramuscularly and DZP given rectally appear to have the properties required for rapid enough absorption to be useful when intravenous routes are not possible. Some drugs cannot be administered rectally owing to factors such as poor absorption or poor solubility in aqueous solutions. The relative rectal bioavailability of gabapentin, oxcarbazepine, and phenytoin is so low that the current formulations are not considered to be suitable for administration by this route. When administered as a solution, diazepam is rapidly absorbed rectally, reaching the Tmax within 5-20 min in children. By contrast, rectal administration of lorazepam is relatively slow, with a Tmax of 1-2h. The dependence of gabapentin on an active transport system, and the much-reduced surface area of the rectum compared with the small intestine, may be responsible for its lack of absorption from the rectum. This article is part of a Special Issue entitled "Status Epilepticus".

Sodium valproate as a cause of recurrent transudative pleural effusion: a case report

INTRODUCTION

There are few reported cases of neutrophilic pleural effusions associated with valproic acid therapy. Most of them are of eosinophilic exudates with or without blood eosinophilia.

CASE PRESENTATION

This case study describes a 70-year-old man with recurrent episodes of eosinophilic transudative pleural effusions associated with sodium valproate treatment. The recurrence of effusion after re-administration of the drug is strongly suggestive of an association between them. To the best of our knowledge, this is the first reported case with a pleural effusion with these characteristics caused by sodium valproate.

CONCLUSION

This is the first report in the literature, with a full understanding of the etiology but with an unknown drug mechanism. This case report is of interest to different medical specialists (such as pulmonologists, neurologists, cardiologists) and pharmacologists.

Comparative disposition of pharmacologic markers for cytochrome P-450 mediated metabolism, glomerular filtration rate, and extracellular and total body fluid volume of Greyhound and Beagle dogs

The purpose of the study was to compare the disposition of pharmacologic markers for cytochrome P-450 (CYP) metabolism, glomerular filtration rate (GFR), and extracellular (ECFV) and total body fluid volumes (TBFV) of Greyhounds and Beagles. Six healthy Greyhound and six healthy Beagle dogs were studied. Antipyrine, a marker for CYP metabolism and TBFV, and inulin, a marker for the GFR and ECFV, were administered i.v. Samples were collected at predetermined times and plasma was analyzed by validated high-pressure liquid chromatography (HPLC) methods. There were no differences in the disposition or pharmacokinetic parameters for inulin between the dog breeds. However, the clearance of antipyrine (mean = 8.33 mL/min/kg) in Greyhounds was significantly slower than Beagles (13.42 mL/min/kg, P = 0.004). The volume of distribution of antipyrine was significantly larger in Greyhounds (0.789 L/kg) than in Beagles (0.644 L/kg, P = 0.01). The half-life of antipyrine was significantly longer in Greyhounds (1.09 h) compared with Beagles (0.55 h, P = 0.002). The in vitro plasma protein binding of antipyrine was significantly less in Greyhounds (28%) compared with Beagles (40.3%, P = 0.008). Greyhounds exhibited significantly slower CYP metabolism, higher TBFV, and lower in vitro protein binding of antipyrine compared with Beagles. No differences in GFR or ECFV were found.

Fosphenytoin: clinical pharmacokinetics and comparative advantages in the acute treatment of seizures

Fosphenytoin is a phosphate ester prodrug developed as an alternative to intravenous phenytoin for acute treatment of seizures. Advantages include more convenient and rapid intravenous administration, availability for intramuscular injection, and low potential for adverse local reactions at injection sites. Drawbacks include the occurrence of transient paraesthesias and pruritus at rapid infusion rates, and cost. Fosphenytoin is highly bound (93-98%) to plasma proteins. Saturable binding at higher plasma concentrations accounts for an increase in its distribution volume and clearance with increasing dose and infusion rate. Fosphenytoin is entirely eliminated through metabolism to phenytoin by blood and tissue phosphatases. The bioavailability of the derived phenytoin relative to intravenous phenytoin is approximately 100% following intravenous or intramuscular administration. The half-life for conversion of fosphenytoin to phenytoin ranges from 7-15 minutes. Faster intravenous infusion rates and competitive displacement of derived phenytoin from plasma protein binding sites by fosphenytoin compensate for the expected conversion-related delay in appearance of phenytoin in the plasma. Unbound phenytoin plasma concentrations achieved with intravenous fosphenytoin loading doses of 100-150 or 50-100mg phenytoin sodium equivalents/min are comparable, and achieved at similar times, to those with equimolar doses of intravenous phenytoin at 50 (maximum recommended rate) or 20-40 mg/min, respectively. The rapid achievement of effective concentrations permits the use of fosphenytoin in emergency situations, such as status epilepticus. Following intramuscular administration, therapeutic phenytoin plasma concentrations are observed within 30 minutes and maximum plasma concentrations occur at approximately 30 minutes for fosphenytoin and at 2-4 hours for derived phenytoin. Plasma concentration profiles for fosphenytoin and total and unbound phenytoin in infants and children closely approximate those in adults following intravenous or intramuscular fosphenytoin at comparable doses and infusion rates. Earlier and higher unbound phenytoin plasma concentrations, and thus an increase in systemic adverse effects, may occur following intravenous fosphenytoin loading doses in patients with a decreased ability to bind fosphenytoin and phenytoin (renal or hepatic disease, hypoalbuminaemia, the elderly). Close monitoring and reduction in the infusion rate by 25-50% are recommended when intravenous loading doses of fosphenytoin are administered in these patients. The potential exists for clinically significant interactions when fosphenytoin is coadministered with other highly protein bound drugs. The pharmacokinetic properties of fosphenytoin permit the drug to serve as a well tolerated and effective alternative to parenteral phenytoin in the emergency and non-emergency management of acute seizures in children and adults.