From the Guidelines
Cimetidine can generally be safely prescribed with hydroxyzine for pruritus, as they have different mechanisms of action and can work complementarily to relieve itching. The British Association of Dermatologists' guidelines for the investigation and management of generalized pruritus in adults without an underlying dermatosis, 2018, suggest considering H1 and H2 antagonists in combination, such as fexofenadine and cimetidine, for the relief of itch 1. Additionally, sedative antihistamines like hydroxyzine are recommended in the short-term or palliative setting for pruritus 1.
When using this combination, it is essential to monitor for increased sedation, as both medications can cause drowsiness, particularly hydroxyzine. The typical adult dose of hydroxyzine for pruritus is 25-50 mg 3-4 times daily, while cimetidine is usually prescribed at 400 mg twice daily or 800 mg at bedtime. Elderly patients may need lower doses of both medications due to increased sensitivity to side effects. While this combination doesn't have significant drug interactions, cimetidine can inhibit certain liver enzymes and potentially increase levels of other medications the patient might be taking, so a medication review is advisable 1.
Some key points to consider when prescribing this combination include:
- Monitoring for increased sedation and adjusting doses as needed
- Informing patients about the potential for drowsiness and advising them to avoid driving or operating machinery until they know how the medication affects them
- Conducting regular medication reviews to minimize potential drug interactions
- Considering alternative treatment options, such as nonsedative antihistamines or other therapies, if the combination of cimetidine and hydroxyzine is not effective or is not well-tolerated.
From the Research
Safety of Cimetidine with Hydroxyzine for Pruritus
- There is limited direct evidence on the safety of prescribing cimetidine with hydroxyzine for pruritus 2, 3, 4, 5, 6.
- However, it is known that hydroxyzine is an older antihistamine with sedative and anticholinergic effects, while cimetidine is an H2 antagonist that can increase the risk of toxicity of other drugs, especially in elderly patients 4.
- A study suggests that the combination of an antihistamine and an H2 antagonist, such as chlorpheniramine and cimetidine, may be effective for symptomatic dermatographism, a type of urticaria 3.
- Cetirizine, a metabolite of hydroxyzine, has been shown to be effective in treating chronic idiopathic urticaria with fewer sedative effects than hydroxyzine 5.
- The anticholinergic activities of various antihistamines, including hydroxyzine, have been compared in functional models, but the results do not directly address the safety of combining cimetidine with hydroxyzine 6.