Prevention of form-deprivation myopia with pirenzepine: a study of drug delivery and distribution

The present study investigated the drug distribution and elimination profil es in ocular tissues of pirenzepine, a selective M-1 muscarinic antagonist known to inhibit myopia. Results demonstrate that (1) Intravitreal injectio ns of the M1 selective antagonist pirenzepine were more effective at preven ting form-deprivation myopia than subconjunctival injections. (2) Maximum d rug levels were reached within 1 hr for both retina and sclera following in travitreal (28 and 11 nanomole) and subconjunctival (0.25 and 1 nanomole) i njection. Intravitreal injection proved a more effective route of drug deli very to all ocular tissues compared to subconjunctival injection. (3) Elimi nation times of pirenzepine from ocular tissues were much shorter than thos e reported for blood plasma. (4) Histological examination revealed no evide nce of gross toxic effects at doses effective in inhibiting induced axial m yopia. In conclusion, pirenzepine was effective at reducing form-deprivatio n myopia in a dose-dependent manner with no evidence of disruption to the r etina. However, results were not conclusive as to where pirenzepine may hav e its site of action in preventing form-deprivation myopia. (C) 1999 The Co llege of Optometrists. Published by Elsevier Science Ltd. All rights reserv ed.