Pharmaceutical companies insist they pay the right amount of tax but have provided few details of the dollars involved ahead of a public hearing on tax avoidance on Wednesday.

Representatives of nine companies, including household names Pfizer and GlaxoSmithKline, will appear before a senate economics committee in Sydney.

Pfizer Australia says it has an effective tax rate on underlying profit that is "consistently above Australia's corporate tax rate of 30 per cent".

"Pfizer Australia's practices have been subject to rigorous review and have not resulted in any disputes with the [Australian Tax Office] or adjustments to the tax filings," managing director David Gallagher said in a written submission to the committee ahead of his appearance on Wednesday.

For more details, go to: http://www.afr.com/news/politics/national/pfizer-glaxosmithkline-astrazeneca-to-face-grilling-on-tax-20150629-gi0gcb