I commend the authors of the study “Effect of dacryocystorhinostomy on systemic adverse effects of topical timolol maleate” for a well conducted study.
However I wish to point out some of the confounding variables in the study which affect the conclusion.
The age, sex and body weight of the sample under study is not mentioned. The bioavailability of any drug will be affected by the age, sex and body weight of the individual. The results would have been more reliable if the study was done on a sample of similar age group, sex and body weight.
The patients were not fasting before the test and not kept fasting for two hours thereafter. The presence of food in the stomach will alter the pharmacodynamics of the drug even if the topical drug is not metabolized until the second pass.
The mean IOP in the control situation was 14.8 mm Hg. This was recorded in the eye on the unoperated side. The mean IOP in the eye on the operated side is not mentioned and need not necessarily be the same. The comparison of the results of situation A and B are hence not valid.
The repeat test after DCR surgery was conducted at 6 weeks after surgery when there is a possibility of inflammation of the nasal mucosa which may increase the absorption of the drug.
The serum peak levels of Timolol after a drop of topical Timolol maleate is achieved 15 min after instillation of the drug at which time no record of IOP, BP or pulse was made.
Finally the study would have been better supported if accompanied by an assay of serum levels of Timolol maleate.
In conclusion, it may be said that following DCR surgery there is a strong possibility of altered pharmacokinetics of the drug rather than the pharmacodynamics.
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3. Ohno Y, Iga T, Yamada Y, Nagahara M, Araie M, Takayanagj R. Pharmacokinetic and pharmacodynamic analysis of systemic effect of topically applied timolol maleate ophthalmic gelling vehicle (Rysmon® TG) Curr Eye Res. 2005;30:319–28