Bioavailability of benzodiazepines following rectal administration of diazepam in dogs

ACVIM Consensus Statement on the management of status epilepticus and cluster seizures in dogs and cats

BACKGROUND

Seizure emergencies (ie, status epilepticus [SE] and cluster seizures [CS]), are common challenging disorders with complex pathophysiology, rapidly progressive drug-resistant and self-sustaining character, and high morbidity and mortality. Current treatment approaches are characterized by considerable variations, but official guidelines are lacking.

OBJECTIVES

To establish evidence-based guidelines and an agreement among board-certified specialists for the appropriate management of SE and CS in dogs and cats.

ANIMALS

None.

MATERIALS AND METHODS

A panel of 5 specialists was formed to assess and summarize evidence in the peer-reviewed literature with the aim to establish consensus clinical recommendations. Evidence from veterinary pharmacokinetic studies, basic research, and human medicine also was used to support the panel's recommendations, especially for the interventions where veterinary clinical evidence was lacking.

RESULTS

The majority of the evidence was on the first-line management (ie, benzodiazepines and their various administration routes) in both species. Overall, there was less evidence available on the management of emergency seizure disorders in cats in contrast to dogs. Most recommendations made by the panel were supported by a combination of a moderate level of veterinary clinical evidence and pharmacokinetic data as well as studies in humans and basic research studies.

CONCLUSIONS AND CLINICAL RELEVANCE

Successful management of seizure emergencies should include an early, rapid, and stage-based treatment approach consisting of interventions with moderate to preferably high ACVIM recommendations; management of complications and underlying causes related to seizure emergencies should accompany antiseizure medications.

Update on Anticonvulsant Therapy in the Emergent Small Animal Patient

Seizures are common in veterinary patients and control is critical to the overall patient health. The benzodiazepine class of drugs (diazepam, midazolam, and lorazepam) often are the drug class of choice; however, levetiracetam and propofol also have been gaining favor as anticonvulsant drugs for acute seizure management. After cessation of seizures, practitioners then can discuss long-term seizure control on a case-by-case basis with clients.

Pharmacokinetic evaluation of novel midazolam gel formulations following buccal administration to healthy dogs

OBJECTIVE To determine the physiochemical properties and pharmacokinetics of 3 midazolam gel formulations following buccal administration to dogs. ANIMALS 5 healthy adult hounds. PROCEDURES In phase 1 of a 2-phase study, 2 gel formulations were developed that contained 1% midazolam in a poloxamer 407 (P1) or hydroxypropyl methylcellulose (H1) base and underwent rheological and in vitro release analyses. Each formulation was buccally administered to 5 dogs such that 0.3 mg of midazolam/kg was delivered. Each dog also received midazolam hydrochloride (0.3 mg/kg, IV). There was a 3-day interval between treatments. Blood samples were collected immediately before and at predetermined times for 8 hours after drug administration for determination of plasma midazolam concentration and pharmacokinetic analysis. During phase 2, a gel containing 2% midazolam in a hydroxypropyl methylcellulose base (H2) was developed on the basis of phase 1 results. That gel was buccally administered such that midazolam doses of 0.3 and 0.6 mg/kg were delivered. Each dog also received midazolam (0.3 mg/kg, IV). All posttreatment procedures were the same as those for phase 1. RESULTS The H1 and H2 formulations had lower viscosity, greater bioavailability, and peak plasma midazolam concentrations that were approximately 2-fold as high, compared with those for the P1 formulation. The mean peak plasma midazolam concentration for the H2 formulation was 187.0 and 106.3 ng/mL when the midazolam dose administered was 0.6 and 0.3 mg/kg, respectively. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that buccal administration of gel formulations might be a viable alternative for midazolam administration to dogs.

Intranasal Midazolam versus Rectal Diazepam for the Management of Canine Status Epilepticus: A Multicenter Randomized Parallel-Group Clinical Trial

Background

Intranasal administration of benzodiazepines has shown superiority over rectal administration for terminating emergency epileptic seizures in human trials. No such clinical trials have been performed in dogs.

Objective

To evaluate the clinical efficacy of intranasal midazolam (IN‐MDZ), via a mucosal atomization device, as a first‐line management option for canine status epilepticus and compare it to rectal administration of diazepam (R‐DZP) for controlling status epilepticus before intravenous access is available.

Animals

Client‐owned dogs with idiopathic or structural epilepsy manifesting status epilepticus within a hospital environment were used. Dogs were randomly allocated to treatment with IN‐MDZ (n = 20) or R‐DZP (n = 15).

Methods

Randomized parallel‐group clinical trial. Seizure cessation time and adverse effects were recorded. For each dog, treatment was considered successful if the seizure ceased within 5 minutes and did not recur within 10 minutes after administration. The 95% confidence interval was used to detect the true population of dogs that were successfully treated. The Fisher's 2‐tailed exact test was used to compare the 2 groups, and the results were considered statistically significant if P < .05.

Results

IN‐MDZ and R‐DZP terminated status epilepticus in 70% (14/20) and 20% (3/15) of cases, respectively (P = .0059). All dogs showed sedation and ataxia.

Conclusions and Clinical Importance

IN‐MDZ is a quick, safe and effective first‐line medication for controlling status epilepticus in dogs and appears superior to R‐DZP. IN‐MDZ might be a valuable treatment option when intravenous access is not available and for treatment of status epilepticus in dogs at home.

Evaluation of plasma diazepam and nordiazepam concentrations following administration of diazepam intravenously or via suppository per rectum in dogs

OBJECTIVE

To evaluate the pharmacokinetics of diazepam administered per rectum via compounded (ie, not commercially available) suppositories and determine whether a dose of 2 mg/kg in this formulation would result in plasma concentrations shown to be effective for control of status epilepticus or cluster seizures (ie, 150 to 300 ng/mL) in dogs within a clinically useful interval (10 to 15 minutes).

ANIMALS

6 healthy mixed-breed dogs.

PROCEDURES

Dogs were randomly assigned to 2 groups of 3 dogs each in a crossover-design study. Diazepam (2 mg/kg) was administered IV or via suppository per rectum, and blood samples were collected at predetermined time points. Following a 6- or 7-day washout period, each group received the alternate treatment. Plasma concentrations of diazepam and nordiazepam were analyzed via reversed phase high-performance liquid chromatography.

RESULTS

Plasma concentrations of diazepam and nordiazepam exceeded the targeted range ≤ 3 minutes after IV administration in all dogs. After suppository administration, targeted concentrations of diazepam were not detected in any dogs, and targeted concentrations of nordiazepam were detected after 90 minutes (n = 2 dogs) or 120 minutes (3) or were not achieved (1).

CONCLUSIONS AND CLINICAL RELEVANCE

On the basis of these results, administration of 2 mg of diazepam/kg via the compounded suppositories used in the present study cannot be recommended for emergency treatment of seizures in dogs.

The pharmacokinetics of midazolam after intravenous, intramuscular, and rectal administration in healthy dogs

Intravenous benzodiazepines are utilized as first-line drugs to treat prolonged epileptic seizures in dogs and alternative routes of administration are required when venous access is limited. This study compared the pharmacokinetics of midazolam after intravenous (IV), intramuscular (IM), and rectal (PR) administration. Six healthy dogs were administered 0.2 mg/kg midazolam IV, IM, or PR in a randomized, 3-way crossover design with a 3-day washout between study periods. Blood samples were collected at baseline and at predetermined intervals until 480 min after administration. Plasma midazolam concentrations were measured by high-pressure liquid chromatography with UV detection. Rectal administration resulted in erratic systemic availability with undetectable to low plasma concentrations. Arithmetic mean values ± SD for midazolam peak plasma concentrations were 0.86 ± 0.36 μg/mL (C0) and 0.20 ± 0.06 μg/mL (Cmax), following IV and IM administration, respectively. Time to peak concentration (Tmax ) after IM administration was 7.8 ± 2.4 min with a bioavailability of 50 ± 16%. Findings suggest that IM midazolam might be useful in treating seizures in dogs when venous access is unavailable, but higher doses may be needed to account for intermediate bioavailability. Rectal administration is likely of limited efficacy for treating seizures in dogs.

Bioavailability of a novel midazolam gel after intranasal administration in dogs

OBJECTIVE

To compare the pharmacokinetics of a novel bioadhesive gel formulation of midazolam after intranasal (IN) administration with that of midazolam solution after IN, IV, and rectal administration to dogs.

ANIMALS

10 (5 males and 5 females) healthy adult Beagles.

PROCEDURES

Dogs were assigned to 4 treatment groups for a crossover study design. Initially, midazolam solution (5 mg/mL) was administered (0.2 mg/kg) IV to group 1, rectally to group 2, and IN to group 3; a 0.4% hydroxypropyl methylcellulose midazolam gel formulation (50 mg/mL) was administered (0.2 mg/kg, IN) to group 4. Each dog received all 4 treatments; there was a 7-day washout period between subsequent treatments. Blood samples were collected before and after midazolam administration. Plasma concentration of midazolam was determined by use of high-performance liquid chromatography.

RESULTS

The peak plasma concentration after IN administration of the gel formulation was significantly higher than that after IN and rectal administration of the solution. Mean ± SD time to peak concentration was 11.70 ± 2.63 minutes (gel IN), 17.50 ± 2.64 minutes (solution IN), and 39 ± 14.49 minutes (solution rectally). Mean bioavailability of midazolam was 70.4% (gel IN), 52.0% (solution IN), and 49.0% (solution rectally). Bioavailability after IN administration of the gel formulation was significantly higher than that after IN and rectal administration of the solution.

CONCLUSIONS AND CLINICAL RELEVANCE

IN administration of midazolam gel was superior to both IN and rectal administration of midazolam solution with respect to peak plasma concentration and bioavailability.

Comparison of plasma benzodiazepine concentrations following intranasal and intravenous administration of diazepam to dogs

OBJECTIVE

To determine whether plasma concentrations of benzodiazepines (BDZ) in dogs following intranasal (IN) administration of diazepam are comparable to concentrations following IV administration.

ANIMALS

6 (4 male, 2 female) healthy adult Greyhounds.

PROCEDURE

Dogs were randomly assigned to 2 groups of 3 dogs in a crossover design. Diazepam (0.5 mg/kg of body weight) was administered intravenously to dogs in group 1 and intranasally to dogs in group 2. Blood was collected from the jugular vein of each dog into tubes containing lithium heparin before and 3, 6, 9, 12, 15, 20, 30, 60, 120, 240, and 480 minutes following diazepam administration. After a 4-day washout period, dogs in group 1 received diazepam intranasally, dogs in group 2 received diazepam intravenously, and blood was again collected. Plasma concentration of BDZ was determined by use of a fluorescence polarization immunoassay.

RESULTS

Mean (+/- SD) peak plasma concentration of BDZ following IV administration (1,316 +/- 216 microg/L) was greater than that following IN administration (448 +/- 41 microg/L). Time to peak concentration was < or = 3 minutes following IV administration and 4.5 +/- 1.5 minutes following IN administration. Mean bioavailability of BDZ following IN administration was 80 +/- 9%.

CONCLUSIONS AND CLINICAL RELEVANCE

Diazepam is rapidly and efficiently absorbed following IN administration of the parenteral formulation. Plasma concentrations match or exceed the suggested therapeutic concentration (300 microg/L). Intranasal administration of diazepam may be useful for treatment of seizures in dogs by owners or when intravenous access is not readily available.

Pharmacokinetics, pharmacodynamics, and analgesic effects of morphine after rectal, intramuscular, and intravenous administration in dogs

OBJECTIVE

To compare systemic bioavailability and duration for therapeutic plasma concentrations and cardiovascular, respiratory, and analgesic effects of morphine administered per rectum, compared with IV and IM administration in dogs.

ANIMALS

6 healthy Beagles.

PROCEDURE

In a randomized study, each dog received the following: morphine IV (0.5 mg/kg of body weight), morphine per rectum (1, 2, and 5 mg/kg as a suppository and 2 mg/kg as a solution), and a control treatment. Intramuscular administration of morphine (1 mg/kg) was evaluated separately. Heart and respiratory rates, systolic, diastolic, and mean blood pressures, adverse effects, and plasma morphine concentrations were measured. Analgesia was defined as an increase in response threshold, compared with baseline values, to applications of noxious mechanical (pressure) and thermal (heat) stimuli. Data were evaluated, using Friedman repeated-measures ANOVA on ranks and Student-Newman-Keuls post-hoc t-tests.

RESULTS

Significant differences were not found in cardiovascular, respiratory, or analgesia values between control and morphine groups. Overall systemic bioavailability of morphine administered per rectum was 19.6%. Plasma morphine concentration after administration of the highest dose (5 mg/kg) as a suppository was significantly higher than concentrations 60 and 360 minutes after IV and IM administration, respectively. A single route of administration did not consistently fulfill our criteria for providing analgesia.

CONCLUSIONS AND CLINICAL RELEVANCE

Rectal administration of morphine did not increase bioavailability above that reported for oral administration of morphine in dogs. Low bioavailability and plasma concentrations limit the clinical usefulness of morphine administered per rectum in dogs.

Chronic phenobarbital therapy reduces plasma benzodiazepine concentrations after intravenous and rectal administration of diazepam in the dog

Disposition of diazepam (DZ) 2 mg/kg after single bolus intravenous (i.v.) and rectal (p.r.) administration before and after 30 day oral phenobarbital therapy was investigated in normal dogs. Adverse cardiovascular and neurologic effects for each drug, dosage and route of administration were evaluated. Plasma benzodiazepine concentrations were determined by fluorescence polarization immunoassay. This assay measured DZ and its active metabolites, oxazepam and nordiazepam to provide a total benzodiazepine concentration. Mean peak plasma concentrations after i.v. administration were 5963 and 5565 ng/mL, before and after phenobarbital treatment, respectively. After p.r. administration, mean peak concentrations were 629 ng/mL and 274 ng/mL and were reached within 30 min before and after phenobarbital treatment, respectively. The target concentration for potential seizure control (i.e. 150 ng/mL) was attained in five dogs in the post phenobarbital p.r. group with a median time to attainment of target concentration of 8 min. The administration of phenobarbital resulted in significantly lower areas under the plasma concentration vs. time curves (AUC) for both i.v. and p.r. administration. Similarly, there was a reduction in maximal plasma concentration, bioavailability (F), mean residence time, and time to target and peak concentrations in the postphenobarbital p.r. group, as compared to the prephenobarbital p.r. group. Adverse cardiovascular and neurologic effects were short-lived and were considered of minor clinical significance. Overall, chronic phenobarbital therapy in the dog reduces total benzodiazepine concentration after i.v. and p.r. administration presumably due to increased hepatic clearance of DZ and its metabolites oxazepam and nordiazepam. Despite this finding, administration of DZ rectally at 2 mg/kg may be a clinically useful alternative to i.v. administration to treat emergency seizures when i.v. therapy is not possible in dogs on chronic phenobarbital therapy.

Anticonvulsant therapy in small animals

Successful control of seizures with anticonvulsant drugs reflects a balance in achieving seizure control while minimizing undesirable drug side effects. Variability in the disposition of anticonvulsants and interaction among them are important confounders of successful therapy. This article will provide a review of selected anticonvulsants, focusing on drugs most likely to control seizures in small animals. The proper use of anticonvulsants will be discussed, with emphasis on differences in individual drug disposition, detection of these differences, and rational approaches to responding to these differences by dose modification. The primary target of discussion will be treatment of generalized, tonic clonic seizures, the most common type afflicting small animals. Opinions regarding anticonvulsive therapy vary among clinicians. Most of the comments and recommendations offered in this discussion reflect observations made from our therapeutic drug monitoring service and completed and ongoing clinical trials that focus on the use of anticonvulsants used either alone or in combination with phenobarbital.