Excessive use of tigecycline, a glycylcycline antibiotic, could potentially lead to reduced effectiveness of successive therapies. This phenomenon is known as antibiotic resistance [1][2]. According to a study, tigecycline is associated with a high risk of developing resistance, which could limit its future utility and impact the success of subsequent treatments [2].

Moreover, the overuse of tigecycline may contribute to the emergence of resistance mechanisms in bacteria, further complicating the treatment of infections [3]. This could result in increased morbidity and mortality rates, prolonged hospital stays, and higher healthcare costs [3].

In summary, excessive tigecycline use could have significant effects on successive therapies due to the increased risk of antibiotic resistance. This could lead to reduced treatment options, higher healthcare costs, and worse patient outcomes [1][2][3].

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/TIGECYCLINE
[2] https://pubmed.ncbi.nlm.nih.gov/24564226/
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6391853/