Cetirizine dosing

Values are the means from six separate experiments. SE was less than 10% of the mean. Dose of test compounds, chlorpheniramine maleate and cetirizine are 10 mg/kg for antihistaminic activity, and 5 mg/kg for sedative-hypnotic activity... 

As sedation is one of the major side effects associated with antihistamines, the test compounds were also evaluated for their sedative potentials. This was determined by measuring the reduction in locomotor activity using an ac-tophotometer [6,7]. The test compounds and the reference standards (chlorpheniramine maleate and cetirizine) were administrated orally at a dose of 5 mg/kg in 1% CMC. 

Renal/Hepatic function impairment Use a lower initial dose of loratadine, desloratadine, and cetirizine in patients with renal or hepatic impairment. 

No advantage over loratadine or cetirizine lower doses associated with less sedation and efficacy... 

The second generation H -receptor antagonist cetirizine is a reacemate consisting of equal quantities of 2 enantiomers, levocetirizine [(R)-enantiomer] and dextrocetirizine [(S)-enantiomer]. In vitro and human pharmacodynamic studies have provided evidence that levocetirizine is the more active enantiomer, accounting for most or all clinical antihistaminic activity of racemic cetirizine this activity of levocetirizine is seen at half the dose of cetirizine. 

In term of pharmacokinetics, cetirizine (4) is rapidly absorbed, reaching a peak plasma concentration of 257 pg/L within 1 h of administration at a dose of 10 mg in healthy volunteers. The AUC is 2.87 mg/L with this dose. 

In healthy volunteers promethazine caused impaired cognitive function and psychomotor performance (64). The test battery consisted of critical flicker fusion, choice reaction time, compensatory tracking task, and assessment of subjective sedation. Cetirizine and loratadine at all doses tested were not significantly different from placebo in any of the tests used. 

In a double-blind, crossover study levocetirizine 5 mg once daily for 4 days was compared with cetirizine 10 mg, loratadine 10 mg, promethazine 30 mg, and placebo in terms of nervous system inhibitory effects in 20 healthy volunteers (456). With the exception of promethazine none of the drugs had disruptive or sedative effects on objective measurements in a comprehensive battery of psychomotor and cognitive tests. These studies suggest that levocetirizine has minimal sedative effects in healthy individuals when given in its recommended dose. 

Severe urticaria and anaphylaxis associated with pyridostigmine (an unspecified dose) occurred in a 54-year-old woman with myasthenia gravis (9). Urticaria started almost immediately after introduction of the drug but was partially controlled by the antihistamine cetirizine. However, pyridostigmine was stopped after 2 months and the urticaria resolved completely. Rechallenge with oral pyridostigmine led to an anaphylactic reaction that was treated with subcutaneous adrenaline. There were no sequelae. 

In a comparison of cetirizine and loratadine, cetirizine 10 mg had acute sedative effects and impaired driving performance (65), whereas loratadine had no sedating potential furthermore, there was an additive effect of alcohol and cetirizine but not alcohol and loratadine. However, in a study using a driving simulator cetirizine 10 mg did not affect driving ability (66). In other studies cetirizine 20 mg caused significant sedation, while in one study there was a dose-dependent sedative effect with 10 mg and 20 mg but not 5 mg (67). Pooling the available data (SEDA-16, 163) shows that cetirizine is little more sedative than loratadine and terfenadine. 

Dose-proportional C ux values arc achieved within I hour of oral administration of cetirizine. Food slows the rate of cetirizine absorption but docs not affect the overall extent. Consistent with the polar nature of this carboxylic acid drag less than 10% of peak plasma levels have been measured in the brain. Cetirizine is not extensively metabolized, aiul more than 70% of a lO-mg oral dose is excreted in the urine (>80% as unchanged drug) and 10% is recovered in the feces. The drug is highly protein bound (93%) and has a terminal half-life of 8.3 hours. The clearance of cetirizine i< reduced in elderly subjc cts and in renally and hcpalicnlh impaired patients. "... 

Acrivastine has a rapid onset of action and a short half-life, necessitating more frequent dosing than cetirizine or loratadine, but it may be useful to give rapid relief. 

The second-generation ( nonsedating ) Hj antagonists e.g., loratadine, cetirizine, and fexofenadine) are largely excluded from the brain when given in therapeutic doses because they do not cross the blood-brain barrier. An interesting and useful property of certain Hj antagonists is the capacity to counter motion sickness see Chapters 7 and 37). This effect was first observed with dimenhydrinate and subsequently with diphenhydramine (the active moiety of dimenhydrinate), various piperazine derivatives, and promethazine. 

A. blocker antihistamines are structurally related to histamine and antagonize the effects of histamine on H., receptor sites. They possess anticholinergic effects (except the nonsedating agents astemizole, azelastine, cetirizine, desloratadine, fexofenadine, loratadine, and terfenadine). They may also stimulate or depress the CNS, and some agents (eg, diphenhydramine) have local anesthetic and membrane-depressant effects in large doses. 

The non-sedating antihistamines seem to cause little or no drowsiness in most patients and the risks if taken alone or with alcohol appear to be minimal or absent. However, the incidence of sedation varies with the non-sedating antihistamine (e.g. sedation appears to be lower with fexofenadine and loratadine than with acrivastine or cetirizine) and with the individual (e.g. women may be more affected than men). Therefore, patients should be advised to be alert to the possibility of drowsiness if they have not taken the drug before. Any drowsiness would be apparent after the first few doses. The patient information leaflets for acrivastine and cetirizine suggest avoidance of alcohol or excessive amounts of alcohol, and caution is advised with levocetirizine. ... 

A single 240-mg dose of intravenous theophylline was given to 6 healthy subjects after they had taken cetirizine 10 mg twice daily for 3.5 days. There was no change in theophylline pharmacokinetics, but the half-life of cetirizine was decreased by 19%. This change in cetirizine pharmacokinetics was not considered to be clinically relevant. ... 

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