Large penetration of intermittent photovoltaic generation (PV) would pose formidable challenges for utilities, to provide inertial and primary frequency response (PFR). PV generation would reduce the generation share of synchronous generators and hence reduce generator inertia & PFR. This necessitates an additional response from interruptible loads, to make frequency stable following contingency like generation outage. In this regard, this paper proposes a novel interruptible load (IL) constrained PFR scheduling framework with the objective of operation cost minimization. Case studies are carried out on IEEE RTS 24 bus and the performance of the proposed approach is analyzed in terms of PFR, IL and operation cost with variation in PV penetration. Results obtained shows that IL response supports the system frequency at conditions like low demand and minimum inertia following largest generation outage. Proposed model could be potentially enhanced to incorporate response from other load types and technologies like energy storage and electric vehicles.