Here, by way of comparison, is the euthanasia recommendation of the Royal Dutch Society for the Advancement of Pharmacy, a translation of which is available here.

Based on the information and considerations in Chapter 3, the KNMP's Euthanasics Task Force has amended its original recommendations as follows:

Parenteral administration
Intravenous administration is the most reliable and rapid way to accomplish euthanasia and therefore can be safely recommended.
A coma is first induced by intravenous administration of 20 mg/kg thiopental sodium (Nesdonal) in a small volume (10 ml physiological saline). Then a triple intravenous dose of a non-depolarizing neuromuscular muscle relaxant is given, such as 20 mg pancuronium dibromide (Pavulon) or 20 mg vecuronium bromide (Norcuron).

The present California protocol provides for 6.5 g or 6500 mg. That is more than triple the KNMP's recommended coma-inducing dose even for a 100 kg (220 lb) inmate.

The PLoS article in the news today cites the KNMP as authority for the proposition that pentothal alone is not recommended, but it curiously fails to mention what that organization does recommend.

The Washington Post article by Rob Stein notes at the end:

In an editorial accompanying the paper, the editors of the journal said they were not publishing the study in the hopes of prompting improvements to the protocol. Instead, they are hoping it will fuel a campaign to abolish executions.

Nothing is worse for science than being driven by a political agenda.