Which of the following is a side effect of methylxanthines?

• A. Hypotonia
• B. Sedation
• C. Tachycardia
• D. Hypertension

Answer: (C)

Methylxanthines stimulate the heart and central nervous system, so cardiovascular effects are a key concern when using them. Theophylline, a classic methylxanthine, works by antagonizing adenosine receptors and inhibiting phosphodiesterase, which increases intracellular cAMP and boosts sympathetic activity. This combination commonly leads to an increased heart rate, i.e., tachycardia. Among the given options, tachycardia best reflects this stimulant effect on the cardiovascular system. Hypotonia and sedation are not typical for methylxanthines—in fact these drugs tend to promote alertness rather than sedation. While hypertension can occur with sympathetic activation, tachycardia is the most characteristic and consistently reported side effect.