Phenobarbital adverse effects

The most common adverse reaction associated with phenobarbital is sedation, which can range from mild sleepiness or drowsiness to somnolence. These dru > may also cause nausea, vomiting, constipation, bradycardia, hypoventilation, skin rash, headache fever, and diarrhea Agitation, rather than sedation, may occur in some patients. Some of these adverse effects may be reduced or eliminated as therapy continues. Occasionally, a slight dosage reduction, without reducing the ability of the drug to control the seizures, will reduce or eliminate some of these adverse reactions. 

One chronic adverse effect that is of concern is osteoporosis.32,33 Carbamazepine, phenytoin, phenobarbital, oxcarbazepine, and valproate have all been shown to decrease bone mineral density, even after only 6 months of treatment. Data on the relationship between other AEDs and osteoporosis are not currently available. Multiple studies have shown the risk of osteoporosis due to chronic AED use to be similar to the risk with chronic use of corticosteroids. Patients taking carbamazepine, phenytoin, phenobarbital, or valproate for longer than 6 months should take supplemental calcium and vitamin D. Additionally routine monitoring for osteoporosis should be performed every 2 years, and patients should be instructed on ways to protect themselves from fractures. 

Monitor for acute and chronic adverse effects of AEDs. Acute adverse effects are best detected by a thorough neurologic examination at clinic visits. Instruct patients to report sedation, ataxia, rash, or other problems immediately. Monitor for chronic adverse effects including a loss of bone mineral density, which should be measured every 2 years in patients taking phenytoin, phenobarbital, carbamazepine, and valproate. 

Buspirone (BuSpar) [Anxiolytic] WARNING Closely monitor for worsening depression or emergence of suicidality Uses Short-term relief of anxiety Action Antianxiety antagonizes CNS serotonin receptors Dose Initial 7.5 mg PO bid T by 5 mg q2-3d to effect usual 20-30 mg/d max 60 mg/d Contra w/ MAOI Caution [B, /-] Avoid w/ severe hepatic/renal insuff Disp Tabs SE Drowsiness, dizziness, HA, N, EPS, serotonin synd, hostility, depression Notes No abuse potential or physical/psychologic d endence Interactions T Effects W/ erythromycin, clarithromycin, itraconazole, ketoconazole, diltiazem, verapamil, grapefruit juice effects W/ carbamazepine, rifampin, phenytoin, dexamethasone, phenobarbital, fluoxetine EMS T Sedation w/ concurrent EtOH use grapefruit juice may T risk of adverse effects OD May cause dizziness, miosis, N/V symptomatic and supportive... 

Primidone is an other second line barbiturate used orally to control tonic-clonic and partial seizures. It is a pro-drug as it is metabolized to phenobarbital and phenylethylmalonamide (PEMA), however both the parent compound as well as the metabolites have anti seizure activity. Its use is more difficult to monitor and adverse effects occur even more frequently than with phenobarbital. 

All barbiturates (except phenobarbital) except when used to control seizures Are highly addictive and cause more adverse effects than most sedative or hypnotic drugs in elderly patients. High... 

Some physicians prefer either metharbital or mephobarbital—especially the latter—to phenobarbital because of supposed decreased adverse effects. Only anecdotal data are available to support such comparisons. 

The dose-related adverse effects of primidone are similar to those of its metabolite, phenobarbital, except that drowsiness occurs early in treatment and may be prominent if the initial dose is too large. Gradual increments are indicated when starting the drug in either children or adults. 

Adverse effects Sedation, ataxia, nystagmus, vertigo, and acute psychotic reactions may occur with chronic use. Nausea and vomiting are seen as well as a morbilliform rash in sensitive individuals. Agitation and confusion occur at high doses. Rebound seizures can occur on discontinuance of phenobarbital. 

Correct choice = D. Primidone does not cause hepatotoxicity. The adverse effects seen with this drug are the same as those seen with phenobarbital. 

Clozapine has been used to treat benign essential tremor refractory to the usual drugs (propranolol, primidone, alprazolam, phenobarbital, and botulinum toxin) in a randomized, double-blind, crossover study in 15 patients with essential tremor (58). Responders with more than 50% improvement after a single dose of clozapine 12.5 mg, compared with placebo, subsequently received 39-50 mg unblinded for a mean of 16 months. Tremor was effectively reduced by a single dose of clozapine in 13 of 15 patients sedation was the only adverse effect reported. 

In a multicenter, randomized, double-blind comparison of diazepam (0.15 mg/kg followed by phenytoin 18 mg/kg), lorazepam (0.1 mg/kg), phenobarbital (15 mg/kg), and phenytoin (18 mg/kg) in 518 patients with generalized convulsive status epilepticus, lorazepam was more effective than phenytoin and at least as effective as phenobarbital or diazepam plus phenytoin (1). Drug-related adverse effects did not differ significantly among the treatments and included hypoventilation (up to 17%), hypotension (up to 59%), and cardiac rhythm disturbances (up to 9%). 

There was an unexpectedly high frequency of adverse effects in a pediatric intensive care unit with the combination of high-dose phenobarbital and beta-lactam antibiotics, mainly cefotaxime (353). The reactions, which mostly affected the skin and blood, were only rarely reproduced by a single component, suggesting an interaction. However, these findings have not been confirmed, and their impact is unclear. 

Of 26 patients with complex partial seizures refractory to phenytoin, carbamazepine, phenobarbital, or primidone, mesuximide produced a 50% or greater reduction in seizure frequency in eight after 8 weeks, and five of those continued to benefit after 3-34 months (1). Drowsiness, gastrointestinal disturbances, hiccups, irritability, and headache were the common adverse effects. 

The adverse effects of methylphenobarbital are similar to those of phenobarbital, to which methylphenobarbital is metabolized. 

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