There is no data available on undesirable effects of this combination. However, side effects have been reported with individual molecules.
Montelukast: Common side effects include dyspepsia, abdominal pain, rash, dizziness, headache, fatigue, fever, trauma, cough, nasal congestion, influenza.
The following adverse reactions have been reported in post-marketing use:
Blood and lymphatic system disorders: increased bleeding tendency.
Immune system disorders: hypersensitivity reactions including anaphylaxis, hepatic eosinophilic infiltration.
Psychiatric disorders: dream abnormalities including nightmares, hallucinations, insomnia, irritability, anxiety, restlessness, agitation including aggressive behaviour, tremor, depression, suicidal thinking and behaviour (suicidality) in very rare cases.
Nervous system disorders: dizziness, drowsiness, paraesthesia/hypoesthesia, seizure.
Respiratory, thoracic and mediastinal disorders: epistaxis.
Cardiac disorders: palpitations.
Gastrointestinal disorders: diarrhea, dry mouth, dyspepsia, nausea, vomiting.
Hepatobiliary disorders: elevated levels of serum transaminases (ALT, AST), rare cases of cholestatic hepatitis, hepatocellular liver-injury, and mixed-pattern liver injury have been reported in patients treated with Montelukast. Most of these occurred in combination with other confounding factors, such as use of other medications, or when montelukast was administered to patients who had underlying potential for liver disease, such as alcohol use or other forms of hepatitis.
Skin and subcutaneous tissue disorders: angioedema, bruising, urticaria, pruritus, rash, erythema nodosum.
Musculoskeletal and connective tissue disorders: arthralgia, myalgia including muscle cramps.
General disorders and administration site conditions: asthenia/fatigue, malaise, edema. Very rare cases of Churg-Strauss Syndrome (CSS) have been reported during montelukast treatment in asthmatic patients. In rare cases, patients with asthma on therapy with Montelukast may present with systemic eosinophilia, sometimes presenting with clinical features of vasculitis consistent with Churg-Strauss syndrome. A causal association between Montelukast and these underlying conditions has not been established.
Levocetirizine dihydrochloride: Use of Levocetirizine has been associated with somnolence, fatigue, nasopharyngitis, dry mouth, and pharyngitis in subjects 12 years of age and older. Further uncommon incidences of adverse reactions like asthenia or abdominal pain were observed. In addition to the adverse reactions reported during clinical studies and listed previously, very rare cases of the following adverse drug reactions have been reported in post-marketing experience.
Immune system disorders: hypersensitivity including anaphylaxis.
Psychiatric disorders: aggression, agitation.
Nervous system disorders: convulsion.
Eye disorders: visual disturbances.
Cardiac disorders: palpitations.
Respiratory, thoracic, and mediastinal disorders: dyspnea.
Gastrointestinal disorders: nausea.
Hepatobiliary disorders: hepatitis.
Skin and subcutaneous tissue disorders: angioneurotic edema, fixed drug eruption, pruritus, rash, urticaria.
Bone disorders: myalgia.
Investigations: weight increased, abnormal liver function tests.
Seek medical attention immediately at the first sign of any adverse drug reaction.