Your body downregulates beta-2 adrenergic receptors in response to persistent clenbuterol usage, hence renders clenbuterol less effective over time. This is why you have to cycle it and increase your dose to keep it working.
Ketotifen is an anti-allergic drug which upregulates beta-2 receptors and counteracts the downregulative nature of beta-2 receptors. Though, you still can't keep using clenbuterol forever even if you take ketotifen. Downregulating beta-2 receptors in response to "unnatural" increase in metabolic rate is not the only weapon in your body's arsenal.
And I can't see any reason to keep taking clenbuterol infinitely.
Also, there are some studies which implies clenbuterol is more effective at burning fat when combined with T3. Check this one out, hypothroidic rats medicated with clenbuterol show no difference in body composition before and after:
https://www.ncbi.nlm.nih.gov/pubmed/1765845
And quoting "There was no evidence for a
consistent effect of clenbuterol on lipolysis in vivo, measured by plasma glycerol level." from this:
https://www.ncbi.nlm.nih.gov/pubmed/1876572
And you're not going to be happy with long-term use of clenbuterol after all:
https://www.ncbi.nlm.nih.gov/pubmed/23844963
You do not need to add drug after drug to mask/decrease side effects of another, especially if you're not prepping for a contest.
I am not pointing finger at someone, or you, in this case. It is just my two cents on this topic.