Modular Drug Delivery System for Minimizing Trauma During and After Insertion of a Cochlear Lead

Abstract

A system for delivering a therapeutic agent to biological tissue includes a surgically implantable lead to be inserted into the biological tissue. The surgically implantable lead includes a preformed cavity. A modular capsule is configured to be retained within the preformed cavity. The modular capsule includes a first therapeutic agent and a second therapeutic agent, wherein the first therapeutic agent elutes rapidly into the biological tissue and the second therapeutic agent elutes more slowly into the biological tissue.

1 . A system for delivering a therapeutic agent to biological tissue comprising:
 a surgically implantable lead configured to be inserted into the biological tissue, the surgically implantable lead comprising a preformed cavity; and   a modular capsule configured to be retained within the preformed cavity, the modular capsule comprising a first therapeutic agent and a second therapeutic agent, wherein the first therapeutic agent is configured to rapidly elute into the biological tissue and the second therapeutic agent is configured to more slowly elute into the biological tissue.   
     
     
         2 . The system of  claim 1 , wherein the first therapeutic agent has a higher solubility in aqueous solutions than the second therapeutic agent. 
     
     
         3 . The system of  claim 1 , wherein the first therapeutic agent comprises dexamethosone (DEX) salt and the second therapeutic agent comprises dexamethosone base (DXMb). 
     
     
         4 . The system of  claim 3 , wherein the DEX salt elutes into a surrounding aqueous solution at higher concentrations than the DXMb. 
     
     
         5 . The system of  claim 1 , further comprising a permeable membrane interposed between the biological tissue and therapeutic agents, wherein the first therapeutic agent in a first portion of the capsule has greater access to the membrane and elutes through the membrane in greater proportion than the second therapeutic agent placed in a second portion of the capsule with lesser access to the membrane. 
     
     
         6 . The system of  claim 5 , wherein the permeable membrane comprises least one of porous polytetrafluoroethylene, a silicone membrane, fluorinated ethylene propylene, or cellulose acetate. 
     
     
         7 . The system of  claim 1 , wherein at least one of the first therapeutic agent and the second therapeutic agent comprise microspheres. 
     
     
         8 . The system of  claim 1 , wherein the first therapeutic agent comprises powered dexamethosone (DEX) salt having a first particle size and the second therapeutic agent comprises dexamethosone base (DXMb) having a second different particle size. 
     
     
         9 . The system of  claim 8 , wherein the modular capsule further comprises a permeable membrane encapsulating the powered DEX salt and DXMb. 
     
     
         10 . The system of  claim 1 , wherein the modular capsule comprises a polymer matrix and mixed DXMb and DEX salt particulates. 
     
     
         11 . The system of  claim 1 , wherein the preformed cavity is covered by porous metal layer comprising a number of porous elution paths. 
     
     
         12 . A system for delivering a therapeutic agent to biological tissue comprising:
 a surgically implantable lead configured to be inserted into the biological tissue, the surgically implantable lead comprising a preformed cavity; and   a modular capsule configured to be retained within the preformed cavity, the modular capsule comprising a drug release profile when inserted in biological tissue, the drug release profile comprising a high initial concentration of a first therapeutic agent and a long term lower concentration of a second therapeutic agent.   
     
     
         13 . A modular capsule for delivering a therapeutic agent to biological tissue, the modular capsule comprising:
 a membrane;   a first portion comprising a first therapeutic agent; and   a second portion comprising a second therapeutic agent;   wherein the first portion has more direct access to the membrane than the second capsule such that the first therapeutic agent elutes through the membrane in greater proportion than the second therapeutic agent.   
     
     
         14 . The capsule of  claim 13 , wherein the first therapeutic agent comprises dexamethosone (DEX) salt and the second therapeutic agent comprises dexamethosone base (DXMb). 
     
     
         15 . The capsule of  claim 13 , wherein elution of the first therapeutic agent comprises a first particle size and the second therapeutic agent comprises a second particle size. 
     
     
         16 . The capsule of  claim 13 , wherein the modular capsule comprises a solid tablet comprising DXMb and DEX salt. 
     
     
         17 . The capsule of  claim 13 , wherein the capsule releases approximately 0.3 to 0.6 micrograms per day of DXMb into cochlear tissues. 
     
     
         18 . The capsule of  claim 13 , wherein the membrane comprises polyvinyl alcohol (PVA) and walls of the capsule comprise silicone.