Herb-Drug Interactions: Pelargonium

2011

Pelargonium sidoides DC. and Pelargonium reniforme Curt. (Geraniaceae)

Synonym(s) and related species

Geranium, South African geranium.

Pharmacopoeias

Pelargonium Root (British Ph 2009, European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4).

Constituents

The active constituents of pelargonium root are not conclusively known, although they are thought to be proanthocyan-idin oligomers based on epigallo- and gallocatechin. A unique series of O-galloyl-C-glucosylflavones, and novel ellagitannins with a (1)C(4) glucopyranose core (trivially named pelargoniins), have been found in Pelargonium reniforme. There are also oxygenated benzopyranones such as 6,7,8-trihydroxycoumarin and 8-hydroxy-5,6,7-trimethoxycoumarin, predominantly as sulphated derivatives. The natural coumarins found in Pelargonium sidoides do not possess the structure required for anticoagulant activity.

Use and indications

Pelargonium is used in the treatment of acute bronchitis, tonsillitis and upper respiratory tract infections.

Pharmacokinetics

No relevant pharmacokinetic data found.

Interactions overview

Pelargonium does not appear to affect either the pharmacokinetics or the anticoagulant response to warfarin.

Pelargonium + Food

No interactions found.

Pelargonium + Herbal medicines

No interactions found.

Pelargonium + Warfarin and related drugs

The interaction between pelargonium and warfarin is based on experimental evidence only.

Clinical evidence

No interactions found.

Experimental evidence

In a study in rats, pelargonium 500mg/kg (alcoholic extract of Pelargonium sidoides root, Umckaloabo) given for 14 days had no significant effect on the pharmacokinetics of a single 0.2-mg/kg dose of warfarin given on day 15. In a separate study, the coagulation parameters (thromboplastin time, partial thromboplastin time and thrombin time) of rats remained unchanged when they were given pelargonium up to 500mg/kg daily for 2 weeks. Furthermore, coagulation parameters in response to warfarin 0.05 mg/kg did not differ when pelargonium 500 mg/kg was also given.

Mechanism

It has been suggested that the natural coumarins present in pelargonium may affect the anticoagulant response to warfarin.

Importance and management

Evidence is limited to this one study in rats, but the coumarin constituents of pelargonium have not been found to possess anticoagulant activity (consider also coumarins). The manufacturers of a UK product containing Pelargonium sidoides (Kaloba) state that it may theoretically have an effect on coagulation and therefore interact with anticoagulants. However, the natural coumarins found in Pelargonium sidoides do not possess the structure required for anticoagulant activity, and the evidence above supports the conclusion that an interaction is unlikely. Therefore, the dose of warfarin does not need adjusting if Pelargonium sidoides extracts are also given.