Concerns about the health of drug companies after a warning from a whistleblower at the US Food and Drug Administration (FDA) have hit shares.
The FDA's Dr David Graham warned that certain drugs from AstraZeneca, Roche and GlaxoSmithKline (GSK) needed further regulatory attention.
AstraZeneca responded during the afternoon on Friday by insisting the FDA had said it had no safety concerns.
AstraZeneca shares fell 9.6% on Friday, while GSK shares slipped 4.2%.
Dr Graham's warning came as he was speaking to the US Senate on Thursday on Merck's banned drug Vioxx.
During his talk he cast doubt on the FDA's competence.
Dr Graham's list of drugs requiring further scrutiny from the Food and Drug Administration included
AstraZeneca's Crestor, GlaxoSmithKline's Serevent and Roche's Accutane.
In response, AstraZeneca said during Friday afternoon: "We have been assured today at senior levels in the FDA that there is no concern in relation to Crestor's safety".
Glaxo says its quest is to "enable people to do more, feel better and live longer"
Merrill Lynch, the US investment bank, noted that neither asthma drug, Serevent, nor acne drug, Accutane, accounted for a big share of their makers' profits.
But it expects cholesterol-cutting Crestor to make up 12% of AstraZeneca's sales by 2008.
A forthcoming article in the US American Medical Association Review is expected to cover the drug's kidney side-effects.
Safe and effective
Unethical behaviour by drug companies has been in the spotlight after New York attorney general Eliot Spitzer fined GSK for allegedly suppressing negative clinical trial data on Seroxat.
In a statement issued on Thursday GSK said it stands behind Serevent, saying it is "safe and effective".
It added that: "any issues concerning mortality...have been fully considered by the FDA, resulting in a black box warning that was included in the medicine's label" in August 2003.