Bilastin

Bilastine is a representative of the H1 antihistamine drug class.

There are four known histamine receptors (H1 to H4), and allergy symptoms of the nose, eyes, and skin are mediated largely via H1 receptors.

First-generation H1 antihistamines, such as clemastine, dimetindene, and diphenhydramine, have a central depressant effect in addition to their antiallergic effect, which is absent in second-generation agents, for example (levo)cetirizine, (des)loratadine, or bilastine. Although the second-generation substances can also cross the blood-brain barrier, they are actively eliminated from the CNS by the transport protein P-glycoprotein (P-gp). Bilastine also does not have an antimuscarinic effect, which is exhibited by diphenhydramine, for example, among the older substances.

After oral intake, bilastine is rapidly absorbed; the maximum plasma concentration is reached after about 1.3 hours. Bilastine is not metabolized and is excreted unchanged in the urine (approximately one-third) and feces (approximately two-thirds). Neither renal nor hepatic insufficiency requires dose adjustment. In healthy humans, the mean elimination half-life is 14.5 hours.

Seasonal or year-round allergic rhinoconjunctivitis and urticaria are the indications for Bilastin. In the case of seasonal symptoms, the duration of use should be limited to the period of exposure. For year-round allergy, continuous treatment is possible. Bilastine has been available over-the-counter in pharmacies since 2022 in a dosage of 20 mg.

For precautionary reasons, Bilastin should not be taken during pregnancy; there is no clear recommendation for use during breastfeeding. A possible alternative is loratadine, for which Embryotox, the pharmacovigilance and advisory center for embryonic toxicology at the Charité hospital in Berlin, gives an unqualified green light in all phases of pregnancy and during breastfeeding.

The recommended dosage for adults and adolescents aged twelve years and older is 20 mg (one tablet) once daily. Not yet available, but probably soon in sight following a positive vote by the expert committee on prescription, is also a lower dosage of 10 mg per tablet, which will then also be intended for children between six and eleven years of age with a body weight of at least 20 kg. Since food or fruit juices - especially grapefruit juice - reduce the oral bioavailability of bilastine by 30 percent, the patient should not eat anything or drink any juice two hours before and one hour after taking the tablet.

Fatigue and somnolence are the most important potential side effects of H1 antihistamines, but they are much less pronounced with second-generation agents than with their predecessors. For bilastine, the frequency of somnolence and fatigue is reported in the SmPC as 3.06 percent and 0.83 percent, respectively, although 2.86 percent of patients on placebo would have reported somnolence and 1.32 percent fatigue, respectively.

Occasional side effects: Herpes infections; Increase in appetite, anxiety, insomnia, ringing in the ears, dizziness, cardiac arrhythmias (right bundle branch block, sinus arrhythmia), ECG changes, dizziness, difficulty breathing, nasal discomfort, dry nasal mucosa, upper abdominal pain, abdominal pain, Nausea, stomach discomfort, diarrhea, dry mouth, indigestion, gastritis, pruritus, fatigue, improvement of pre-existing conditions, weakness, laboratory changes (gamma-GT, ALAT, ASAT, creatinine or triglycerides elevated), weight gain.

According to the technical information, there are no clinically relevant interactions apart from the aforementioned interaction with food, not even with alcohol or other centrally depressant agents such as the benzodiazepine lorazepam.

If bilastine is taken together with other foods, the absorption of the active ingredient into the body is reduced by one-third and the effect weakens significantly. The same is true when taken with grapefruit juice and could be true for other fruit juices. Thus, taking the active ingredient should always be done one hour before or two hours after other food and drink.

In patients with moderate or severe renal impairment, concomitant administration of bilastine and agents that interfere with its breakdown may increase the risk of side effects from bilastine. These agents include the antifungal drug ketoconazole, the macrolide antibioticErythromycin, ciclosporin (used to treat rejection after organ transplantation), ritonavir (HIV therapeutic), or diltiazem (antihypertensive). The combination with these drugs will therefore be avoided by the physician in kidney patients if possible.

In healthy individuals, on the other hand, ritonavir and rifampicin (a tuberculosis drug) can weaken the effect of bilastine.

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