Subcutaneous vs Intravenous Pembrolizumab: What Changed

For the first several years of pembrolizumab's availability, receiving it meant attending a hospital oncology unit for an intravenous infusion - typically 30 minutes, every three weeks. The development and regulatory approval of a subcutaneous (SC) formulation marked a significant shift in how the drug can be delivered - without compromising on clinical outcomes.

The KEYNOTE-D18 trial

KEYNOTE-D18 was the pivotal clinical trial establishing the equivalence of the subcutaneous pembrolizumab formulation. The trial enrolled adult patients with NSCLC and measured pharmacokinetic parameters - specifically the area under the concentration-time curve (AUC) and peak drug concentration (Cmax) - in patients receiving either the IV or SC formulation.

The primary endpoint was bioequivalence, defined as drug exposure within an accepted 80-125% margin between the two formulations. The SC formulation met this endpoint. Safety and efficacy outcomes were also comparable. On the basis of these data, the SC formulation received regulatory approval as an equivalent alternative to IV administration.

What bioequivalence means in practice

Bioequivalence does not mean pharmacologically identical. Small differences in the rate of absorption and the concentration-time profile are expected between routes of administration - this is normal and anticipated. What bioequivalence establishes is that these differences fall within limits shown not to result in clinically meaningful differences in efficacy or safety.

In practical terms: the same drug reaches the same target (T cells expressing PD-1) in the same effective amounts. The mechanism of action, the anti-tumour effect, and the side effect profile are the same. The only difference is how the drug gets into the body.

The practical difference

IV pembrolizumab requires a prepared infusion bag, IV access (a cannula or port), 30 minutes of administration time, and post-infusion observation - all of which require hospital infrastructure. The SC formulation is a ready-to-use device: a syringe with the drug pre-loaded. It is injected under the skin in approximately 3-5 minutes, without IV access, an infusion pump, or an oncology day unit.

This difference in infrastructure is what makes home administration viable. A qualified oncology nurse can administer the SC injection safely in a home setting, supported by pre- and post-injection monitoring and remote clinical oversight.

The treatment schedule

The SC formulation of pembrolizumab is available at both the 200mg (every 3 weeks) and 400mg (every 6 weeks) dose schedules. The 400mg every-6-weeks schedule - introduced more recently - means some patients only require a home visit once every six weeks, substantially reducing the logistical burden of treatment compared to the original IV schedule.